Aptamers and their biological applications. Sensors (Basel). 2012;12:612-631. [PMID: 22368488 PMCID: PMC3279232 DOI: 10.3390/s120100612]

Selection of a new aptamer targeting amoxicillin for utilization in a label-free electrochemical biosensor

Pharmaceutical pollution has received considerable attention because of the harmful effects of pharmaceutical compounds on human health, even in trace amounts. Amoxicillin is one of the frequently used antibiotics that was included in the list of emerging water pollutants. Therefore, a highly selective and rapid technique for amoxicillin detection is required. In this work, a new aptamer was selected for amoxicillin and utilized for the development of a label-free electrochemical aptasensor. Aptamer selection was performed using the systematic evolution of ligands by exponential enrichment. The selected aptamer showed good specificity against other antibiotics, including the structurally related antibiotics: ampicillin and ciprofloxacin. Among the selected aptamers, Amx3 exhibited the lowest dissociation constant value of 112.9 nM. An aptasensor was developed by immobilization of thiolated Amx3 aptamer onto gold screen-printed electrodes via self-assembly, which was characterized using cyclic voltammetry and electrochemical impedance spectroscopy. The detection was realized by monitoring the change in the differential pulse voltammetry peak current in the ferro/ferricyanide redox couple upon binding of the aptasensor to amoxicillin. The aptasensor showed very good sensitivity with an ultralow limit of detection of 0.097 nM. When the aptasensor was tested using actual spiked milk samples, excellent recovery percentages were observed. The label-free electrochemical aptasensor developed herein is a promising tool for the selective and sensitive detection of amoxicillin in environmental samples.

Computational Frontiers in Aptamer-Based Nanomedicine for Precision Therapeutics: A Comprehensive Review

In the rapidly evolving landscape of nanomedicine, aptamers have emerged as powerful molecular tools, demonstrating immense potential in targeted therapeutics, diagnostics, and drug delivery systems. This paper explores the computational features of aptamers in nanomedicine, highlighting their advantages over antibodies, including selectivity, low immunogenicity, and a simple production process. A comprehensive overview of the aptamer development process, specifically the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process, sheds light on the intricate methodologies behind aptamer selection. The historical evolution of aptamers and their diverse applications in nanomedicine are discussed, emphasizing their pivotal role in targeted drug delivery, precision medicine and therapeutics. Furthermore, we explore the integration of artificial intelligence (AI), machine learning (ML), Internet of Things (IoT), Internet of Medical Things (IoMT), and nanotechnology in aptameric development, illustrating how these cutting-edge technologies are revolutionizing the selection and optimization of aptamers for tailored biomedical applications. This paper also discusses challenges in computational methods for advancing aptamers, including reliable prediction models, extensive data analysis, and multiomics data incorporation. It also addresses ethical concerns and restrictions related to AI and IoT use in aptamer research. The paper examines progress in computer simulations for nanomedicine. By elucidating the importance of aptamers, understanding their superiority over antibodies, and exploring the historical context and challenges, this review serves as a valuable resource for researchers and practitioners aiming to harness the full potential of aptamers in the rapidly evolving field of nanomedicine.

Aptamer-Drug conjugates for a targeted and synergistic anticancer Response: Exploiting T30923-5-fluoro-2'-deoxyuridine (INT-FdU) derivatives

One of the most appealing approaches for cancer treatment is targeted therapy, which is based on the use of drugs able to target cancer cells without affecting normal ones. This strategy lets to overcome the major limitation of conventional chemotherapy, namely the lack of specificity of anticancer drugs, which often leads to severe side effects, decreasing the therapy effectiveness. Delivery of cell-killing substances to tumor cells is one-way targeted drug therapy can work. Generally, monoclonal antibodies are combined with chemotherapeutic drugs, allowing cellular uptake through the binding to their targets on the surface of cancer cells. Aptamer-drug conjugates represent a promising alternative solution to antibodies to minimize off-target effects, considering the remarkable selective binding capabilities of aptamers. In this study, to enhance the therapeutic efficacy of the antineoplastic agent 5-fluoro-2'-deoxyuridine (FdU) in various cancer cells, we focused on the development of a novel conjugate using the antiproliferative aptamer T30923 (INT) as a drug vehicle. Three derivatives composed of T30923 conjugated with a different number of FdU units were synthesized, and their structural and biological properties were thoroughly characterized, highlighting their potential for targeted and synergistic anticancer responses.

Development and optimization of a DNA aptamer to delay β-bungarotoxin-induced lethality in a rodent model

Current treatment of snakebite relies on immunoglobulin-rich antivenoms. However, production of these antivenoms is complicated and costly. Aptamers - single-stranded DNAs or RNAs with specific folding structures that bind to specific target molecules - represent excellent alternatives or complements to antibody-based therapeutics. However, no studies have systematically assessed the feasibility of using aptamers to mitigate venom-induced toxicity in vivo. β-bungarotoxin is the predominant protein responsible for the toxicity of the venom of Bungarus multicinctus, a prominent venomous snake inhabiting Taiwan. In this study, we reported the screening and optimization of a DNA aptamer against β-bungarotoxin and tested its utility in a mouse model. After 14 rounds of directed evolution of ligands by exponential enrichment, an aptamer, called BB3, displaying remarkable binding affinity and specificity for β-bungarotoxin was obtained. Following structural prediction and point-modification experiments, BB3 underwent truncation and was modified with 2'-O-methylation and a 3'-inverted dT. This optimized aptamer showed sustained, high-affinity binding for β-bungarotoxin and exhibited remarkable nuclease resistance in plasma. Importantly, administration of this optimized aptamer extended the survival time of mice treated with a lethal dose of β-bungarotoxin. Collectively, our data provide a compelling illustration of the potential of aptamers as promising candidates for development of recombinant antivenom therapies.

Role of Natural Binding Proteins in Therapy and Diagnostics

This review systematically investigates the critical role of natural binding proteins (NBPs), encompassing DNA-, RNA-, carbohydrate-, fatty acid-, and chitin-binding proteins, in the realms of oncology and diagnostics. In an era where cancer continues to pose significant challenges to healthcare systems worldwide, the innovative exploration of NBPs offers a promising frontier for advancing both the diagnostic accuracy and therapeutic efficacy of cancer management strategies. This manuscript provides an in-depth examination of the unique mechanisms by which NBPs interact with specific molecular targets, highlighting their potential to revolutionize cancer diagnostics and therapy. Furthermore, it discusses the burgeoning research on aptamers, demonstrating their utility as 'nucleic acid antibodies' for targeted therapy and precision diagnostics. Despite the promising applications of NBPs and aptamers in enhancing early cancer detection and developing personalized treatment protocols, this review identifies a critical knowledge gap: the need for comprehensive studies to understand the diverse functionalities and therapeutic potentials of NBPs across different cancer types and diagnostic scenarios. By bridging this gap, this manuscript underscores the importance of NBPs and aptamers in paving the way for next-generation diagnostics and targeted cancer treatments.

The molecular interaction of six single-stranded DNA aptamers to cardiac troponin I revealed by docking and molecular dynamics simulation

Cardiac troponin I (cTnI) is a cardiac biomarker for diagnosing ischemic heart disease and acute myocardial infarction. Current biochemical assays use antibodies (Abs) due to their high specificity and sensitivity. However, there are some limitations, such as the high-cost production of Abs due to complex instruments, reagents, and steps; the variability of Abs quality from batch to batch; the low stability at high temperatures; and the difficulty of chemical modification. Aptamer overcomes the limitations of antibodies, such as relatively lower cost, high reproducibility, high stability, and ease of being chemically modified. Aptamers are three-dimensional architectures of single-stranded RNA or DNA that bind to targets such as proteins. Six aptamers (Tro1-Tro6) with higher binding affinity than an antibody have been identified, but the molecular interaction has not been studied. In this study, six DNA aptamers were modeled and docked to cTnI protein. Molecular docking revealed that the interaction between all aptamer and cTnI happened in the similar cTnI region. The interaction between aptamer and cTnI involved hydrophobic interaction, hydrogen bonds, π-cation interactions, π-stack interactions, and salt-bridge formation. The calculated binding energy of all complexes was negative, which means that the complex formation was thermodynamically favorable. The electrostatic energy term was the main driving force of the interaction between all aptamer and cTnI. This study could be used to predict the behavior of further modified aptamer to improve aptamer performance.

Aptamer biosensor design for the detection of endocrine-disrupting chemicals small organic molecules using novel bioinformatics methods

Endocrine-disrupting chemicals (EDCs) are substances that can disrupt the normal functioning of hormones.Using aptamers, which are biological recognition elements, biosensors can quickly and accurately detect EDCs in environmental samples. However, the elucidation of aptamer structures by conventional methods is highly challenging due to their complexity. This has led to the development of three-dimensional aptamer structures based on different models and techniques. To do this, we developed a way to predict the 3D structures of the SS DNA needed for this sequence by starting with an aptamer sequence that has biosensor properties specific to bisphenol-A (BPA), one of the chemicals found in water samples that can interfere with hormones. In addition, we will elucidate the intermolecular mechanisms and binding affinity between aptamers and endocrine disruptors using bioinformatics techniques such as molecular docking, molecular dynamics simulation, and binding energies. The outcomes of our study are to compare modeling programs and force fields to see how reliable they are and how well they agree with results found in the existing literature, to understand the intermolecular mechanisms and affinity of aptamer-based biosensors, and to find a new way to make aptamers that takes less time and costs less.

Gold Nanoparticle-Decorated Catalytic Micromotor-Based Aptassay for Rapid Electrochemical Label-Free Amyloid-β42 Oligomer Determination in Clinical Samples from Alzheimer's Patients

Micromotor (MM) technology offers a valuable and smart on-the-move biosensing microscale approach in clinical settings where sample availability is scarce in the case of Alzheimer's disease (AD). Soluble amyloid-β protein oligomers (AβO) (mainly AβO42) that circulate in biological fluids have been recognized as a molecular biomarker and therapeutic target of AD due to their high toxicity, and they are correlated much more strongly with AD compared to the insoluble Aβ monomers. A graphene oxide (GO)-gold nanoparticles (AuNPs)/nickel (Ni)/platinum nanoparticles (PtNPs) micromotors (MMGO-AuNPs)-based electrochemical label-free aptassay is proposed for sensitive, accurate, and rapid determination of AβO42 in complex clinical samples such as brain tissue, cerebrospinal fluid (CSF), and plasma from AD patients. An approach that implies the in situ formation of AuNPs on the GO external layer of tubular MM in only one step during MM electrosynthesis was performed (MMGO-AuNPs). The AβO42 specific thiolated-aptamer (AptAβO42) was immobilized in the MMGO-AuNPs via Au-S interaction, allowing for the selective recognition of the AβO42 (MMGO-AuNPs-AptAβO42-AβO42). AuNPs were smartly used not only to covalently bind a specific thiolated-aptamer for the design of a label-free electrochemical aptassay but also to improve the final MM propulsion performance due to their catalytic activity (approximately 2.0× speed). This on-the-move bioplatform provided a fast (5 min), selective, precise (RSD < 8%), and accurate quantification of AβO42 (recoveries 94-102%) with excellent sensitivity (LOD = 0.10 pg mL-1) and wide linear range (0.5-500 pg mL-1) in ultralow volumes of the clinical sample of AD patients (5 μL), without any dilution. Remarkably, our MM-based bioplatform demonstrated the competitiveness for the determination of AβO42 in the target samples against the dot blot analysis, which requires more than 14 h to provide qualitative results only. It is also important to highlight its applicability to the potential analysis of liquid biopsies as plasma and CSF samples, improving the reliability of the diagnosis given the heterogeneity and temporal complexity of neurodegenerative diseases. The excellent results obtained demonstrate the analytical potency of our approach as a future tool for clinical/POCT (Point-of-care testing) routine scenarios.

Ushering in the era of regenerative surgery

Tissue loss, irrespective of etiology, often requires extensive reconstruction. In many instances, the need exceeds what current treatments and technologies modern medicine can offer. Tissue engineering has made immense strides within the past few decades due to advances in biologics, biomaterials, and manufacturing. The convergence of these three domains has created limitless potential for future surgical care. Unfortunately, there still exists a disconnect on how to best implant these 'replacement parts' and care for the patient. It is therefore vital to develop paradigms for the integration of advanced surgical and tissue engineering technologies. This paper explores the convergence between tissue engineering and reconstructive surgery. We will describe the clinical problem of tissue loss, discuss currently available solutions, address limitations, and propose processes for integrating surgery and tissue engineering, thereby ushering in the era of regenerative surgery.

A new DNA aptamer which binds to SARS-CoV-2 spike protein and reduces pro-inflammatory response

COVID-19 caused by SARS-CoV-2 spread rapidly around the world, endangering the health of people globally. The SARS-CoV-2 spike protein initiates entry into target cells by binding to human angiotensin-converting enzyme 2 (ACE2). In this study, we developed DNA aptamers that specifically bind to the SARS-CoV-2 spike protein, thereby inhibiting its binding to ACE2. DNA aptamers are small nucleic acid fragments with random structures that selectively bind to various target molecules. We identified nine aptamers targeting the SARS-CoV-2 spike protein using the systematic evolution of ligands by exponential enrichment (SELEX) method and selected three optimal aptamers by comparing their binding affinities. Additionally, we confirmed that the DNA aptamers suppressed pro-inflammatory cytokines induced by the SARS-CoV-2 spike protein in ACE2-overexpressing HEK293 cells. Overall, the DNA aptamer developed in this study has the potential to bind to the SARS-CoV-2 spike protein and inhibit or block its interaction with ACE2. Thus, our DNA aptamers can be used as new biological tools for the prevention and diagnosis of SARS-CoV-2 infection.

A Novel DNA Aptamer Probe Recognizing Castration Resistant Prostate Cancer in vitro and in vivo Based on Cell-SELEX

Background

Early recognition of castration-resistant state is of significance for timely adjustment of treatment regimens and improvement of prognosis.

Purpose

This study aims to screen new aptamers CRda8 and CRda21 which recognize castration resistant prostate cancer (CRPC) cells with high affinity and specificity by SELEX technology.

Methods

The enrichment of specific aptamer candidates was monitored by flow cytometric analysis. The affinity and specificity of aptamer candidates were evaluated by flow cytometry and immunofluorescence assay. MR imaging of CRda21-conjugated polyethylene glycol (PEG)-Fe3O4 nanoparticles to CRPC was further explored in vivo.

Results

Both aptamers showed high specificity to target cells with dissociation constants in the nanomolar range, and did not recognize other tested cells. The staining of clinical tissue sections with fluorescent dye labeled aptamers showed that sections from CRPC exhibited stronger fluorescence while sections from benign prostatic hyperplasia and androgen dependent prostate cancer did not exhibit notable fluorescence. In vivo MRI demonstrated that CRda21-conjugated PEG-Fe3O4 had good affinity to CRPC and produced strong T2WI signal intensity reduction distinguished from peritumoral tissue.

Conclusion

The high affinity and specificity of CRda8 and CRda21 make the aptamer hold potential for early recognition of castration-resistant state and diagnosis of CRPC at the cellular level.

Computational aptamer design for spike glycoprotein (S) (SARS CoV-2) detection with an electrochemical aptasensor

A new bioinformatic platform (APTERION) was used to design in a short time and with high specificity an aptamer for the detection of the spike protein, a structural protein of SARS-CoV-2 virus, responsible for the COVID-19 pandemic. The aptamer concentration on the carbon electrode surface was optimized using static contact angle and fluorescence method, while specificity was tested using differential pulse voltammetry (DPV) associated to carbon screen-printed electrodes. The data obtained demonstrated the good features of the aptamer which could be used to create a rapid method for the detection of SARS-CoV-2 virus. In fact, it is specific for spike also when tested against bovine serum albumin and lysozyme, competitor proteins if saliva is used as sample to test for the virus presence. Spectrofluorometric characterization allowed to measure the amount of aptamer present on the carbon electrode surface, while DPV measurements proved the affinity of the aptamer towards the spike protein and gave quantitative results. The acquired data allowed to conclude that the APTERION bioinformatic platform is a good method for aptamer design for rapidity and specificity. KEY POINTS: • Spike protein detection using an electrochemical biosensor • Aptamer characterization by contact angle and fluorescent measurements on electrode surface • Computational design of specific aptamers to speed up the aptameric sequence time.

Engineering high affinity antigen-binders: Beyond conventional antibodies

For decades, antibodies have remained the archetypal binding proteins that can be rapidly produced with high affinity and specificity against virtually any target. A conventional antibody is still considered the prototype of a binding molecule. It is therefore not surprising that antibodies are routinely used in basic scientific and biomedical research, analytical workflows, molecular diagnostics etc. and represent the fastest growing sector in the field of biotechnology. However, several limitations associated with conventional antibodies, including stringent requirement of animal immunizations, mammalian cells for expression, issues on stability and aggregation, bulkier size and the overall time and cost of production has propelled evolution of concepts along alternative antigen binders. Rapidly evolving protein engineering approaches and high throughput screening platforms have further complemented the development of myriads of classes of non-conventional protein binders including antibody derived as well as non-antibody based molecular scaffolds. These non-canonical binders are finding use across disciplines of which diagnostics and therapeutics are the most noteworthy.

Selection of DNA aptamers for the aptamer-assisted magnetic capture of the purified xylanase from Aspergillus niger

Xylanases are a group of enzymes that catalyze the hydrolysis of xylan. Xylanases have wide industrial applications, and they can produced by various organisms. In this study, we aimed to develop aptamers for the capture of xylanase produced by a wild-type Aspergillus niger strain. Xylanase was produced by Aspergillus niger in a 5-liter stirred-tank bioreactor and then purified by column chromatography. Magnetic bead-based SELEX (Systematic Evolution of Ligands by Exponential Enrichment) was performed to select DNA aptamers specific to the purified xylanase. After nine rounds of selection, next-generation sequencing (NGS) analysis was performed. Four aptamers, namely AXYL-1, AXYL-2, AXYL-3, and AXYL-4, were identified for further characterization. The binding properties of the selected aptamers were characterized by fluorescence quenching (FQ) analysis and an enzyme-linked aptamer assay (ELAA). The Kd values were found to be in the low μM range. Then, each aptamer was immobilized on streptavidin-coated magnetic particles, and the recovery ratio of xylanase was determined. Although AXYL-1 wasn't effective, AXYL-2, AXYL-3, and AXYL-4 were proven to capture the xylanase. The maximum recovery rate of xylanase was found to be approximately 54 %.

A potent multifunctional ZIF-8 nanoplatform developed for colorectal cancer therapy by triple-delivery of chemo/radio/targeted therapy agents

BACKGROUND

Multimodal cancer therapy has garnered significant interest due to its ability to target tumor cells from various perspectives. The advancement of novel nano-delivery platforms represents a promising approach for improving treatment effectiveness while minimizing detrimental effects on healthy tissues.

METHODS

This study aimed to develop a multifunctional nano-delivery system capable of simultaneously delivering an anti-cancer drug, a radiosensitizer agent, and a targeting moiety (three-in-one) for the triple combination therapy of colorectal cancer (CRC). This unique nano-platform, called Apt-PEG-DOX/ZIF-8@GQD, encapsulated both doxorubicin (DOX) and graphene quantum dots (GQDs) within the zeolitic imidazolate framework-8 (ZIF-8). To enhance the safety and anti-cancer potential of the platform, heterobifunctional polyethylene glycol (PEG) and an epithelial cell adhesion molecule (EpCAM) aptamer were conjugated with the system, resulting in the formation of targeted Apt-PEG-DOX/ZIF-8@GQD NPs. The physical and chemical characteristics of Apt-PEG-DOX/ZIF-8@GQD were thoroughly examined, and its therapeutic efficacy was evaluated in combination with radiotherapy (RT) against both EpCAM-positive HT-29 and EpCAM-negative CHO cells. Furthermore, the potential of Apt-PEG-DOX/ZIF-8@GQD as a tumor-specific, radio-enhancing, non-toxic, and controllable delivery system for in vivo cancer treatment was explored using immunocompromised C57BL/6 mice bearing human HT-29 tumors.

RESULTS

The large surface area of ZIF-8 (1013 m2 g-1) enabled successful loading of DOX with an encapsulation efficiency of approximately ∼90%. The synthesis of Apt-PEG-DOX/ZIF-8@GQD resulted in uniform particles with an average diameter of 100 nm. This targeted platform exhibited rapid decomposition under acidic conditions, facilitating an on-demand release of DOX after endosomal escape. In vitro experiments revealed that the biocompatible nano-platform induced selective toxicity in HT-29 cells by enhancing X-ray absorption. Moreover, in vivo experiments demonstrated that the therapeutic efficacy of Apt-PEG-ZIF-8/DOX@GQD against HT-29 tumors was enhanced through the synergistic effects of chemotherapy, radiotherapy, and targeted therapy, with minimal side effects.

CONCLUSION

The combination of Apt-PEG-DOX/ZIF-8@GQD with RT as a multimodal therapy approach demonstrated promising potential for the targeted treatment of CRC and enhancing therapeutic effectiveness. The co-delivery of DOX and GQD using this nano-platform holds great promise for improving the outcome of CRC treatment.

Aptamers: A Cutting-Edge Approach for Gram-Negative Bacterial Pathogen Identification

Early and accurate diagnoses of pathogenic microorganisms is essential to correctly identify diseases, treating infections, and tracking disease outbreaks associated with microbial infections, to develop precautionary measures that allow a fast and effective response in epidemics and pandemics, thus improving public health. Aptamers are a class of synthetic nucleic acid molecules with the potential to be used for medical purposes, since they can be directed towards any target molecule. Currently, the use of aptamers has increased because they are a useful tool in the detection of specific targets. We present a brief review of the use of aptamers to detect and identify bacteria or even some toxins with clinical importance. This work describes the advances in the technology of aptamers, with the purpose of providing knowledge to develop new aptamers for diagnoses and treatment of different diseases caused by infectious microorganisms.

Aptamer-Based Switching System for Communication of Non-Interacting Proteins

Biological macromolecules, such as DNA, RNA, and proteins in living organisms, form an intricate network that plays a key role in many biological processes. Many attempts have been made to build new networks by connecting non-communicable proteins with network mediators, especially using antibodies. In this study, we devised an aptamer-based switching system that enables communication between non-interacting proteins. As a proof of concept, two proteins, Cas13a and T7 RNA polymerase (T7 RNAP), were rationally connected using an aptamer that specifically binds to T7 RNAP. The proposed switching system can be modulated in both signal-on and signal-off manners and its responsiveness to the target activator can be controlled by adjusting the reaction time. This study paves the way for the expansion of biological networks by mediating interactions between proteins using aptamers.

Biomimetic Bacterial Capsule for Enhanced Aptamer Display and Cell Recognition

Great effort has been made to encapsulate or coat living mammalian cells for a variety of applications ranging from diabetes treatment to three-dimensional printing. However, no study has reported the synthesis of a biomimetic bacterial capsule to display high-affinity aptamers on the cell surface for enhanced cell recognition. Therefore, we synthesized an ultrathin alginate-polylysine coating to display aptamers on the surface of living cells with natural killer (NK) cells as a model. The results show that this coating-mediated aptamer display is more stable than direct cholesterol insertion into the lipid bilayer. The half-life of the aptamer on the cell surface can be increased from less than 1.5 to over 20 h. NK cells coated with the biomimetic bacterial capsule exhibit a high efficiency in recognizing and killing target cells. Therefore, this work has demonstrated a promising cell coating method for the display of aptamers for enhanced cell recognition.

Wearing the Lab: Advances and Challenges in Skin-Interfaced Systems for Continuous Biochemical Sensing

Continuous, on-demand, and, most importantly, contextual data regarding individual biomarker concentrations exemplify the holy grail for personalized health and performance monitoring. This is well-illustrated for continuous glucose monitoring, which has drastically improved outcomes and quality of life for diabetic patients over the past 2 decades. Recent advances in wearable biosensing technologies (biorecognition elements, transduction mechanisms, materials, and integration schemes) have begun to make monitoring of other clinically relevant analytes a reality via minimally invasive skin-interfaced devices. However, several challenges concerning sensitivity, specificity, calibration, sensor longevity, and overall device lifetime must be addressed before these systems can be made commercially viable. In this chapter, a logical framework for developing a wearable skin-interfaced device for a desired application is proposed with careful consideration of the feasibility of monitoring certain analytes in sweat and interstitial fluid and the current development of the tools available to do so. Specifically, we focus on recent advancements in the engineering of biorecognition elements, the development of more robust signal transduction mechanisms, and novel integration schemes that allow for continuous quantitative analysis. Furthermore, we highlight the most compelling and promising prospects in the field of wearable biosensing and the challenges that remain in translating these technologies into useful products for disease management and for optimizing human performance.

Chimeric Protein Switch Biosensors

Rapid detection of protein and small-molecule analytes is a valuable technique across multiple disciplines, but most in vitro testing of biological or environmental samples requires long, laborious processes and trained personnel in laboratory settings, leading to long wait times for results and high expenses. Fusion of recognition with reporter elements has been introduced to detection methods such as enzyme-linked immunoassays (ELISA), with enzyme-conjugated secondary antibodies removing one of the many incubation and wash steps. Chimeric protein switch biosensors go further and provide a platform for homogenous mix-and-read assays where long wash and incubation steps are eradicated from the process. Chimeric protein switch biosensors consist of an enzyme switch (the reporter) coupled to a recognition element, where binding of the analyte results in switching the activity of the reporter enzyme on or off. Several chimeric protein switch biosensors have successfully been developed for analytes ranging from small molecule drugs to large protein biomarkers. There are two main formats of chimeric protein switch biosensor developed, one-component and multi-component, and these formats exhibit unique advantages and disadvantages. Genetically fusing a recognition protein to the enzyme switch has many advantages in the production and performance of the biosensor. A range of immune and synthetic binding proteins have been developed as alternatives to antibodies, including antibody mimetics or antibody fragments. These are mainly small, easily manipulated proteins and can be genetically fused to a reporter for recombinant expression or manipulated to allow chemical fusion. Here, aspects of chimeric protein switch biosensors will be reviewed with a comparison of different classes of recognition elements and switching mechanisms.

Selection of Aptamers for Use as Molecular Probes in AFM Detection of Proteins

Currently, there is great interest in the development of highly sensitive bioanalytical systems for diagnosing diseases at an early stage, when pathological biomarkers are present in biological fluids at low concentrations and there are no clinical manifestations. A promising direction is the use of molecular detectors-highly sensitive devices that detect signals from single biomacromolecules. A typical detector in this class is the atomic force microscope (AFM). The high sensitivity of an AFM-based bioanalysis system is determined by the size of the sensing element of an atomic force microscope-the cantilever-the radius of the curvature of which is comparable to that of a biomolecule. Biospecific molecular probe-target interactions are used to ensure detection system specificity. Antibodies, aptamers, synthetic antibodies, and peptides can be used as molecular probes. This study has demonstrated the possibility of using aptamers as molecular probes for AFM-based detection of the ovarian cancer biomarker CA125. Antigen detection in a nanomolar solution was carried out using AFM chips with immobilized aptamers, commercially available or synthesized based on sequences from open sources. Both aptamer types can be used for antigen detection, but the availability of sequence information enables additional modeling of the aptamer structure with allowance for modifications necessary for immobilization of the aptamer on an AFM chip surface. Information on the structure and oligomeric composition of aptamers in the solution was acquired by combining small-angle X-ray scattering and molecular modeling. Modeling enabled pre-selection, before the experimental stage, of aptamers for use as surface-immobilized molecular probes.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Field effect transistor based wearable biosensors for healthcare monitoring

The rapid advancement of wearable biosensors has revolutionized healthcare monitoring by screening in a non-invasive and continuous manner. Among various sensing techniques, field-effect transistor (FET)-based wearable biosensors attract increasing attention due to their advantages such as label-free detection, fast response, easy operation, and capability of integration. This review explores the innovative developments and applications of FET-based wearable biosensors for healthcare monitoring. Beginning with an introduction to the significance of wearable biosensors, the paper gives an overview of structural and operational principles of FETs, providing insights into their diverse classifications. Next, the paper discusses the fabrication methods, semiconductor surface modification techniques and gate surface functionalization strategies. This background lays the foundation for exploring specific FET-based biosensor designs, including enzyme, antibody and nanobody, aptamer, as well as ion-sensitive membrane sensors. Subsequently, the paper investigates the incorporation of FET-based biosensors in monitoring biomarkers present in physiological fluids such as sweat, tears, saliva, and skin interstitial fluid (ISF). Finally, we address challenges, technical issues, and opportunities related to FET-based biosensor applications. This comprehensive review underscores the transformative potential of FET-based wearable biosensors in healthcare monitoring. By offering a multidimensional perspective on device design, fabrication, functionalization and applications, this paper aims to serve as a valuable resource for researchers in the field of biosensing technology and personalized healthcare.

Fast detection of Staphylococcus aureus using thiol-functionalized WS2 quantum dots and Bi2O2Se nanosheets hybrid through a fluorescence recovery mechanism

Ultrafast and sensitive detection of Staphylococcus aureus (S. aureus), a harmful Gram-positive human pathogenic bacterium, by two-dimensional layered materials continues to be a challenge. Herein, we have studied the sensing of S. aureus using a tungsten disulfide (WS2) quantum dot (QD) and bismuth oxyselenide (Bi2O2Se) nanosheet (NS) hybrid through their unique optical functionalities. The WS2 QDs of a mean diameter of 2.5 nm were synthesized by liquid exfoliation. Due to the quantum confinement and functional groups, the WS2 QDs exhibit high fluorescence (FL) yield under UV excitation. The addition of Bi2O2Se NSs resulted in the adsorption of WS2 QDs on their surface, resulting in quenching of the FL emission due to nonfluorescent complex formation between the WS2 QDs and Bi2O2Se NSs. A specific sequencing single-standard DNA (ssDNA) aptamer, which identifies and explicitly binds with S. aureus, was attached to the defect sites of the WS2 QDs for selective detection. The thiol-modified ssDNA aptamers attach covalently to the WS2 QD defect sites, which was confirmed by Raman and X-ray photoelectron spectroscopy (XPS). The interaction of S. aureus with the aptamer functionalized WS2 QDs weakens the van der Waals interaction between the WS2 QDs and Bi2O2Se NSs, which results in the detachment of the WS2 QDs from the Bi2O2Se NS surface and restores the FL intensity of the WS2 QDs, thus allowing the efficient detection of S. aureus. Similar measurements with non-targeted bacteria show that the system is quite selective towards S. aureus. Our FL-based biosensor has a linear response in the range of 103-107 CFU mL-1 (colony formation unit mL-1) with a detection limit of 580 CFU mL-1. We have observed a fast response time of 15 minutes for sensing, which is superior to the previous reports. The proposed system was tested in human urine and can detect S. aureus in human urine samples selectively, proving its potential in real-life applications. The reported approach is versatile enough for sensing other biomolecules and metal ions by choosing suitable receptors.

Development of a label-free impedimetric aptasensor for the detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is responsible for various nosocomial infections, which is known as a clinically crucial opportunistic pathogen. Therefore, rapid detection of this pathogen is critical to prevent the spread of infection and appropriate treatment. Biological detection probes, such as aptamers and synthetic receptors can be used as diagnostic layers to detect bacteria. In this work, an electrochemical aptasensor was developed for the ultrasensitive detection of A. baumannii by electrochemical impedance spectroscopy (EIS). The aptamer was immobilized on the surface of a CSPE modified with the nanocomposite Fe3O4@SiO2@Glyoxal (Gly) for selective and label-free detection of A. baumannii. The charge transfers resistance (Rct) between redox couple [Fe(CN)63-/4-] and the surface of aptasensor in the Nyquist plot of EIS study was used as electroanalytical signal for detection and determination of A. baumannii. The obtained results showed that the constructed aptasensor could specifically detect A. baumannii in the concentration range from 1.0 × 103-1.0 × 108 Colony-forming unit (CFU)/mL and with a detection limit of 150 CFU/mL (S/N = 3). In addition to its sensitivity, the biosensor exhibits high selectivity over some other pathogens. Therefore, a simple, inexpensive, rapid, label-free, selective, and sensitive electrochemical aptasensor was developed to detect A. baumannii.

A systematic review of emerging technologies to enhance the treatment of ovarian cancer

The efficacy and safety of chemotherapy are two major challenges when it comes to treating ovarian cancer. The associated undesirable side effects of chemotherapy agents jeopardize the clinical intent and the efficiency of the therapy. Multiple studies have been published describing new developments and novel strategies utilizing the latest therapeutic and drug delivery technologies to address the efficacy and safety of chemotherapeutics in ovarian cancers. We have identified five novel technologies that are available and, if used, have the potential to mitigate the above-mentioned challenges. Nanocarriers in different forms (Nano-gel, Aptamer, peptide medicated formulations, Antibody-drug conjugation, surface charge, and nanovesicle technologies) are developed and available to be employed to target the cancerous tissue. These strategies are promising to improve clinical efficacy and reduce side effects. We have systematically searched and analyzed published data, as well as the authors intent for the described technology on each publication. We narrowed to 81 key articles and extracted their data to be discussed in this review. In summary, the selected articles investigated the pharmacokinetic properties of drugs combined with nanocarriers and found significant improvement in efficacy and safety by reducing the IC50 values and drug doses. These key papers described promising novel technologies in anti-cancer therapeutic approaches to enable sustained drug release and achieve prolonged drug performance near the tumor site or target tissue.

The Use of Wearable Technology in Providing Assistive Solutions for Mental Well-Being

The main goal of this manuscript is to provide an extensive literature review and analysis of certain biomarkers, which are frequently used to identify stress, anxiety, and other emotions, leading to potential solutions for the monitoring of mental wellness using wearable technologies. It is possible to see the impacts of several biomarkers in detecting stress levels and their effectiveness with an investigation into the literature on this subject. Biofeedback training has demonstrated some psychological effects, such as a reduction in anxiety and self-control enhancement. This survey demonstrates backed up by evidence that wearable devices are assistive in providing health and mental wellness solutions. Because physical activity tracing would reduce the stress stressors, which affect the subject's body, therefore, it would also affect the mental activity and would lead to a reduction in cognitive mental load.

A capacitive laser-induced graphene based aptasensor for SARS-CoV-2 detection in human saliva

SARS-CoV-2 virus induced CoVID-19 pandemic has accelerated the development of diagnostic tools. Devices integrated with electrochemical biosensors may be an interesting alternative to respond to the high demand for testing, particularly in contexts where access to standard detection technologies is lacking. Aptamers as recognition elements are useful due to their stability, specificity, and sensitivity to binding target molecules. We have developed a non-invasive electrochemical aptamer-based biosensor targeting SARS-CoV-2 in human saliva. The aptamer is expected to detect the Spike protein of SARS-CoV-2 wildtype and its variants. Laser-induced graphene (LIG) electrodes coated with platinum nanoparticles were biofunctionalized with a biotin-tagged aptamer. Electrochemical Impedance Spectroscopy (EIS) for BA.1 sensing was conducted in sodium chloride/sodium bicarbonate solution supplemented with pooled saliva. To estimate sensing performance, the aptasensor was tested with contrived samples of UV-attenuated virions from 10 to 10,000 copies/ml. Selectivity was assessed by exposing the aptasensor to non-targeted viruses (hCoV-OC43, Influenza A, and RSV-A). EIS data outputs were further used to select a suitable response variable and cutoff frequency. Capacitance increases in response to the gradual loading of the attenuated BA.1. The aptasensor was sensitive and specific for BA.1 at a lower viral load (10-100 copies/ml) and was capable of discriminating between negative and positive contrived samples (with strain specificity against other viruses: OC43, Influenza A, and RSV-A). The aptasensor detected SARS-CoV-2 with an estimated LOD of 1790 copies/ml in contrived samples. In human clinical samples, the aptasensor presents an accuracy of 72%, with 75% of positive percent of agreement and 67% of negative percent of agreement. Our results show that the aptasensor is a promising candidate to detect SARS-CoV-2 during early stages of infection when virion concentrations are low, which may be useful for preventing the asymptomatic spread of CoVID-19.

Single vs sandwich aptamers: Towards the detection of human epidermal growth factor receptor 2 using composites of phthalocyanine and nanoparticles

The superiority of the sandwich over a single aptamer based aptasensor assay for the detection of the human epidermal growth factor receptor 2 (HER2) is demonstrated for the first time. Cobalt tris-3,5 dimethoxy-phenoxy pyridine (5) oxy (2)- carboxylic acid phthalocyanine (CoMPhPyCPc) and sulphur/nitrogen doped graphene quantum dots (SNGQDs) and cerium oxide nanoparticles (CeO₂NPs) nanocomposite (SNGQDs@CeO₂NPs) were used for electrode modification of glassy carbon electrode (GCE) both individually and combined to form the substrates: GCE/SNGQDs@CeO₂NPs, GCE/CoMPhPyCPc and GCE/SNGQDs@CeO₂NPs/CoMPhPyCPc. The designed substrates were used as immobilization platforms for the amino functionalized HB5 aptamer for the development of both single and sandwich aptasensor assays. A novel bioconjugate, made of the HB5 aptamer and nanocomposite (HB5-SNGQDs@CeO₂NPs) was fabricated, and characterized using ultra-violet/visible, Fourier transform infrared, and Raman spectroscopies as well as scanning electron microscopy. HB5-SNGQDs@CeO₂NPs was applied as a secondary aptamer in the design of novel sandwich assays towards the electrochemical detection of HER2. The performance of the designed aptasensors were evaluated using electrochemical impedance spectroscopy. The sandwich assay gave low limit of detection of 0.00088 pg/mL, high sensitivity of 773925 Ω pg^-1mL, showed stability, and good precision in real samples towards HER2 detection.

Emerging Progress of RNA-Based Antitumor Therapeutics

RNA-based therapeutics (e.g., mRNAs, siRNAs, microRNAs, ASOs, and saRNAs) have considerable potential for tumor treatment. The development and optimization of RNA modifications and delivery systems enable the stable and efficient delivery of RNA cargos in vivo to elicit an antitumor response. Targeted RNA-based therapeutics with multiple specificities and high efficacies are now available. In this review, we discuss progress in RNA-based antitumor therapeutics, including mRNAs, siRNAs, miRNAs, ASOs, saRNAs, RNA aptamers, and CRISPR-based gene editing. We focus on the immunogenicity, stability, translation efficiency, and delivery of RNA drugs, and summarize their optimization and the development of delivery systems. In addition, we describe the mechanisms by which RNA-based therapeutics induce antitumor responses. Furthermore, we review the merits and limitations of RNA cargos and their therapeutic potential for cancers.

Electrochemical Detection of Different Foodborne Bacteria for Point-of-Care Applications

Bacterial infections resulting from foodborne pathogenic bacteria cause millions of infections that greatly threaten human health and are one of the leading causes of mortality around the world. To counter this, the early, rapid, and accurate detection of bacterial infections is very important to address serious health issue concerns. We, therefore, present an electrochemical biosensor based on aptamers that selectively bind with the DNA of specific bacteria for the accurate and rapid detection of various foodborne bacteria for the selective determination of bacterial infection types. Different aptamers were synthesized and immobilized on Au electrodes for selective bindings of different types of bacterial DNA (Escherichia coli, Salmonella enterica, and Staphylococcus aureus) for the accurate detection and quantification of bacterial concentrations from 10¹ to 10⁷ CFU/mL without using any labeling methods. Under optimized conditions, the sensor showed a good response to the various concentrations of bacteria, and a robust calibration curve was obtained. The sensor could detect the bacterial concentration at meager quantities and possessed an LOD of 4.2 × 10¹, 6.1 × 10¹, and 4.4 × 10¹ CFU/mL for S. Typhimurium, E. Coli, and S. aureus, respectively, with a linear range from 10⁰ to 10⁴ CFU/mL for the total bacteria probe and 10⁰ to 10³ CFU/mL for individual probes, respectively. The proposed biosensor is simple and rapid and has shown a good response to bacterial DNA detections and thus can be applied in clinical applications and food safety monitoring.

Improving aptamer performance: key factors and strategies

Aptamers are functional single-stranded oligonucleotide fragments isolated from randomized libraries by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), exhibiting excellent affinity and specificity toward targets. Compared with traditional antibody reagents, aptamers display many desirable properties, such as low variation and high flexibility, and they are suitable for artificial and large-scale synthesis. These advantages make aptamers have a broad application potential ranging from biosensors, bioimaging to therapeutics and other areas of application. However, the overall performance of aptamer pre-selected by SELEX screening is far from being satisfactory. To improve aptamer performance and applicability, various post-SELEX optimization methods have been developed in the last decade. In this review, we first discuss the key factors that influence the performance or properties of aptamers, and then we summarize the key strategies of post-SELEX optimization which have been successfully used to improve aptamer performance, such as truncation, extension, mutagenesis and modification, splitting, and multivalent integration. This review shall provide a comprehensive summary and discussion of post-SELEX optimization methods developed in recent years. Moreover, by discussing the mechanism of each approach, we highlight the importance of choosing the proper method to perform post-SELEX optimization.

Aptamer-functionalized field-effect transistor biosensors for disease diagnosis and environmental monitoring

Nano-biosensors that are composed of recognition molecules and nanomaterials have been extensively utilized in disease diagnosis, health management, and environmental monitoring. As a type of nano-biosensors, molecular specificity field-effect transistor (FET) biosensors with signal amplification capability exhibit prominent advantages including fast response speed, ease of miniaturization, and integration, promising their high sensitivity for molecules detection and identification. With intrinsic characteristics of high stability and structural tunability, aptamer has become one of the most commonly applied biological recognition units in the FET sensing fields. This review summarizes the recent progress of FET biosensors based on aptamer functionalized nanomaterials in medical diagnosis and environmental monitoring. The structure, sensing principles, preparation methods, and functionalization strategies of aptamer modified FET biosensors were comprehensively summarized. The relationship between structure and sensing performance of FET biosensors was reviewed. Furthermore, the challenges and future perspectives of FET biosensors were also discussed, so as to provide support for the future development of efficient healthcare management and environmental monitoring devices.

Screening and identification of a DNA aptamer to construct the label-free fluorescent aptasensor for ultrasensitive and selective detection of clothianidin residue in agricultural products

Clothianidin pesticide not only pollutes the ecological environment, but also poses a potential threat to human health. Thus, it is of great importance to develop efficient and accurate methods to recognize and detect clothianidin residues in agricultural products. Aptamer has the advantages of easy modification, high affinity and good stability, which is particularly suitable as a recognition biomolecule for pesticide detection. However, the aptamer against clothianidin has not been reported. Herein, the aptamer (named CLO-1) had good selectivity and strong affinity (K_d = 40.66 ± 3.47 nM) to clothianidin pesticide, which was screened for the first time by Capture-SELEX strategy. The binding effect of CLO-1 aptamer to clothianidin was further studied by circular dichroism (CD) spectroscopy and molecular docking technique. Finally, the CLO-1 aptamer was used as the recognition molecule to construct a label-free fluorescent aptasensor using GeneGreen dye as sensing signal for the highly sensitive detection of clothianidin pesticide. The constructed fluorescent aptasensor had the limit of detection (LOD) as low as 5.527 μg L^-1 for clothianidin, and displayed good selectivity against other competitive pesticides. The aptasensor was applied to detect the clothianidin spiked in tomatoes, pears and cabbages, and the recovery rate was good in the range of 81.99%-106.64%. This study provides a good application prospect for the recognition and detection of clothianidin.

Aptamer-Based Point-of-Care Devices: Emerging Technologies and Integration of Computational Methods

Recent innovations in point-of-care (POC) diagnostic technologies have paved a critical road for the improved application of biomedicine through the deployment of accurate and affordable programs into resource-scarce settings. The utilization of antibodies as a bio-recognition element in POC devices is currently limited due to obstacles associated with cost and production, impeding its widespread adoption. One promising alternative, on the other hand, is aptamer integration, i.e., short sequences of single-stranded DNA and RNA structures. The advantageous properties of these molecules are as follows: small molecular size, amenability to chemical modification, low- or nonimmunogenic characteristics, and their reproducibility within a short generation time. The utilization of these aforementioned features is critical in developing sensitive and portable POC systems. Furthermore, the deficiencies related to past experimental efforts to improve biosensor schematics, including the design of biorecognition elements, can be tackled with the integration of computational tools. These complementary tools enable the prediction of the reliability and functionality of the molecular structure of aptamers. In this review, we have overviewed the usage of aptamers in the development of novel and portable POC devices, in addition to highlighting the insights that simulations and other computational methods can provide into the use of aptamer modeling for POC integration.

Fighting Methicillin-Resistant Staphylococcus aureus with Targeted Nanoparticles

Antimicrobial resistance (AMR) is considered one of the greatest threats to global health. Methicillin-resistant Staphylococcus aureus (MRSA) remains at the core of this threat, accounting for about 90% of S. aureus infections widespread in the community and hospital settings. In recent years, the use of nanoparticles (NPs) has emerged as a promising strategy to treat MRSA infections. NPs can act directly as antibacterial agents via antibiotic-independent activity and/or serve as drug delivery systems (DDSs), releasing loaded antibiotics. Nonetheless, directing NPs to the infection site is fundamental for effective MRSA treatment so that highly concentrated therapeutic agents are delivered to the infection site while directly reducing the toxicity to healthy human cells. This leads to decreased AMR emergence and less disturbance of the individual's healthy microbiota. Hence, this review compiles and discusses the scientific evidence related to targeted NPs developed for MRSA treatment.

Customization of aptamer to develop CRISPR/Cas12a-derived ultrasensitive biosensor

The CRISPR/Cas systems have provided wide biosensing applications. Particularly, the aptamer-involved CRISPR/Cas sensor system powerfully expanded to non-nucleic-acid targets. However, tailoring the sequence of the aptamer to explore the relationship between affinity and the activation of CRISPR/Cas12a trans-cleavage activity has not been reported yet. Herein, we developed a series of new aptamers toward the spike protein 1(S1) of SARS-CoV-2. Surface plasmon resonance measurements showed that the affinity of these aptamers to S1 was at the nM level. Subsequently, a "SET" effect (Sequence Essential Trans-cleavage activity) is discovered for the activation of CRISPR/Cas12a trans-cleavage activity. That is, an aptamer, as the activator, sequence needs to be tailored to activate CRISPR/Cas12a efficiently. A balance should be reached between affinity and activation ability. On the one hand, high affinity ensures target recognition performance, and on the other hand, activation can achieve adequate amplification and output of recognition signals. The optimized sequence (with 27 nucleotides, for short 27-nt) not only recognizes the target with a high affinity and specificity but also can trigger the CRISPR/Cas12a trans-cleavage activity efficiently, showing an excellent detection performance in electrochemical biosensors. The detection limit for SARS-CoV-2 S1 can be low at 1.5 pg mL^-1. The new CRISPR/Cas12a-derived aptasensor also displays a remarkable ability to detect Beta, Delta, and Omicron variants but is selective toward other kinds of proteins. Above all, it is robust for point-of-care testing (POCT) in complex biological fluids, such as saliva, urine, and serum, and provides a universal and scalable detecting platform. Our results provide new insights into aptamer development and a different strategy for COVID-19 antigen detection and biosensor development.

Aptamers Targeting Membrane Proteins for Sensor and Diagnostic Applications

Many biological processes (physiological or pathological) are relevant to membrane proteins (MPs), which account for almost 30% of the total of human proteins. As such, MPs can serve as predictive molecular biomarkers for disease diagnosis and prognosis. Indeed, cell surface MPs are an important class of attractive targets of the currently prescribed therapeutic drugs and diagnostic molecules used in disease detection. The oligonucleotides known as aptamers can be selected against a particular target with high affinity and selectivity by iterative rounds of in vitro library evolution, known as Systematic Evolution of Ligands by EXponential Enrichment (SELEX). As an alternative to antibodies, aptamers offer unique features like thermal stability, low-cost, reuse, ease of chemical modification, and compatibility with various detection techniques. Particularly, immobilized-aptamer sensing platforms have been under investigation for diagnostics and have demonstrated significant value compared to other analytical techniques. These "aptasensors" can be classified into several types based on their working principle, which are commonly electrochemical, optical, or mass-sensitive. In this review, we review the studies on aptamer-based MP-sensing technologies for diagnostic applications and have included new methodological variations undertaken in recent years.

Week-Long Operation of Electrochemical Aptamer Sensors: New Insights into Self-Assembled Monolayer Degradation Mechanisms and Solutions for Stability in Serum at Body Temperature

Conventional wisdom suggests that widely utilized self-assembled alkylthiolate monolayers on gold are too unstable to last more than several days when exposed to complex fluids such as raw serum at body temperature. Demonstrated here is that these monolayers can not only last at least 1 week under such harsh conditions but that significant applied value can be captured for continuous electrochemical aptamer biosensors. Electrochemical aptamer biosensors provide an ideal tool to investigate monolayer degradation, as aptamer sensors require a tightly packed monolayer to preserve sensor signal vs background current and readily reveal fouling by albumin and other solutes when operating in biofluids. Week-long operation in serum at 37 °C is achieved by (1) increasing van der Waals interactions between adjacent monolayer molecules to increase the activation energy required for desorption, (2) optimizing electrochemical measurement to decrease both alkylthiolate oxidation and electric-field-induced desorption, and (3) mitigating fouling using protective zwitterionic membranes and zwitterion-based blocking layers with antifouling properties. This work further proposes origins and mechanisms of monolayer degradation in a logical stepwise manner that was previously unobservable over multiday time scales. Several of the observed results are surprising, revealing that short-term improvements to sensor longevity (i.e., hours) actually increase sensor degradation in the longer term (i.e., days). The results and underlying insights on mechanisms not only push forward fundamental understanding of stability for self-assembled monolayers but also demonstrate an important milestone for continuous electrochemical aptamer biosensors.

Biomedical applications of aptamer-modified chitosan nanomaterials: An updated review

Among polysaccharides of environmental and economic interest, chitosan (CS) is receiving much attention, particularly in the food and biotechnology industries to encapsulate active food ingredients and immobilize enzymes. CS nanoparticles (CS NPs) combine the intrinsic beneficial properties of both natural polymers and nanoscale particles such as quantum size effect, biocompatibility, biodegradability, and ease of modification, and have great potential for bioimaging, drug delivery, and biosensing applications. Aptamers are single-stranded oligonucleotides that can fold into predetermined structures and bind to the corresponding biomolecules. They are mainly used as targeting ligands in biosensors, disease diagnostic kits and treatment strategies. They can deliver contrast agents and drugs into cancer cells and tissues, control microorganism growth and precisely target pathogens. Aptamer-conjugated CS NPs can significantly improve the efficacy of conventional therapies, minimize their side effects on normal tissues, and overcome the enhanced permeability retention (EPR) effect. Further, aptamer-conjugated carbohydrate-based nanobiopolymers have shown excellent antibacterial and antiviral properties and can be used to develop novel biosensors for the efficient detection of antibiotics, toxins, and other biomolecules. This updated review aims to provide a comprehensive overview of the bioapplications of aptamer-conjugated CS NPs used as innovative diagnostic and therapeutic platforms, their limitations, and potential future directions.

Recent Advances in Recognition Receptors for Electrochemical Biosensing of Mycotoxins-A Review

Mycotoxins are naturally occurring toxic secondary metabolites produced by fungi in cereals and foodstuffs during the stages of cultivation and storage. Electrochemical biosensing has emerged as a rapid, efficient, and economical approach for the detection and quantification of mycotoxins in different sample media. An electrochemical biosensor consists of two main units, a recognition receptor and a signal transducer. Natural or artificial antibodies, aptamers, molecularly imprinted polymers (MIP), peptides, and DNAzymes have been extensively employed as selective recognition receptors for the electrochemical biosensing of mycotoxins. This article affords a detailed discussion of the recent advances and future prospects of various types of recognition receptors exploited in the electrochemical biosensing of mycotoxins.

Laser-induced graphene-based electrochemical biosensors for environmental applications: a perspective

Biosensors are miniaturized devices that provide the advantage of in situ and point-of-care monitoring of analytes of interest. Electrochemical biosensors use the mechanism of oxidation-reduction reactions and measurement of corresponding electron transfer as changes in current, voltage, or other parameters using different electrochemical techniques. The use of electrochemically active materials is critical for the effective functioning of electrochemical biosensors. Laser-induced graphene (LIG) has garnered increasing interest in biosensor development and improvement due to its high electrical conductivity, specific surface area, and simple and scalable fabrication process. The effort of this perspective is to understand the existing classes of analytes and the mechanisms of their detection using LIG-based biosensors. The manuscript has highlighted the potential use of LIG, its modifications, and its use with various receptors for sensing various environmental pollutants. Although the conventional graphene-based sensors effectively detect trace levels for many analytes in different applications, the chemical and energy-intensive fabrication and time-consuming processes make it imperative to explore a low-cost and scalable option such as LIG for biosensors production. The focus of these potential biosensors has been kept on detection analytes of environmental significance such as heavy metals ions, organic and inorganic compounds, fertilizers, pesticides, pathogens, and antibiotics. The use of LIG directly as an electrode, its modifications with nanomaterials and polymers, and its combination with bioreceptors such as aptamers and polymers has been summarized. The strengths, weaknesses, opportunities, and threats analysis has also been done to understand the viability of incorporating LIG-based electrochemical biosensors for environmental applications.

Acoustofluidic separation of proteins from platelets in human blood plasma using aptamer-functionalized microparticles

Microfluidic liquid biopsy has emerged as a promising clinical assay for early diagnosis. Herein, we propose acoustofluidic separation of biomarker proteins from platelets in plasma using aptamer-functionalized microparticles. As model proteins, C-reactive protein and thrombin were spiked in human platelet-rich plasma. The target proteins were selectively conjugated with their corresponding aptamer-functionalized microparticles of different sizes, and the particle complexes served as a mobile carrier for the conjugated proteins. The proposed acoustofluidic device was composed of an interdigital transducer (IDT) patterned on a piezoelectric substrate and a disposable polydimethylsiloxane (PDMS) microfluidic chip. The PDMS chip was placed in a tilted arrangement with the IDT to utilize both vertical and horizontal components of surface acoustic wave-induced acoustic radiation force (ARF) for multiplexed assay at high-throughput. The two different-sized particles experienced the ARF at different magnitudes and were separated from platelets in plasma. The IDT on the piezoelectric substrate could be reusable, while the microfluidic chip can be replaceable for repeated assays. The sample processing throughput with the separation efficiency >95% has been improved such that the volumetric flow rate and flow velocity were 1.6 ml/h and 37 mm/s, respectively. For the prevention of platelet activation and protein adsorption to the microchannel, polyethylene oxide solution was introduced as sheath flows and coating on to the walls. We conducted scanning electron microscopy, x-ray photoemission spectroscopy , and sodium dodecyl sulfate- analysis before and after the separation to confirm the protein capture and separation. We expect that the proposed approach will provide new prospects for particle-based liquid biopsy using blood.

A simple aptamer/gold nanoparticle aggregation-based colorimetric assay for oxidized low-density lipoprotein determination

Oxidized low-density lipoprotein (oxLDL) is the leading cause of atherosclerosis and cardiovascular diseases. Here, we created a simple colorimetric assay for sensitive and specific determination of oxLDL using a selective aptamer coupled with salt-induced gold nanoparticle (AuNP) aggregation. The aptamer was chosen by Systematic Evolution of Ligands by Exponential Enrichment to obtain a novel selective sequence towards oxLDL (as 5'-CCATCACGGGGCAGGCGGACAAGGGGTAAGGGCCACATCA-3'). Mixing a 5 μM aptamer solution with an aliquot of a sample containing oxLDL followed by adding AuNP solution (OD = 1) and 80 mmol L^-1 NaCl achieved rapid results within 19 min: linear response to oxLDL from 0.002 to 0.5 μmol L^-1 with high selectivity, a recovery accuracy of 100-111% at the 95% confidence interval, and within-run and between-run precision of 1-6% and 1-5% coefficient variations, respectively. Artificial serum diluted at least 1:8 with distilled water, analyzed by the aptamer-based colorimetric assay, showed excellent correlation with conventional thiobarbituric acid reactive substances (TBARS) (R² = 0.9792) as a rapid colorimetric method without the need for sample preparation other than dilution.

Selection and Identification of an ssDNA Aptamer for Fibroblast Activation Protein

As a type II transmembrane serine protease, fibroblast activation protein (FAP) is specifically expressed on the surface of fibroblasts associated with a variety of epithelial-derived malignancies such as pancreatic cancer, breast cancer, and colon cancer. It participates in the processes of tumorigenesis, progression, and immunosuppression. FAP constitutes an important target for tumor treatment; however, the current studies on FAP are mainly related to structural characteristics, enzymatic properties, and biological functions, and aptamers of FAP have not been investigated. In this work, by using recombinant human FAP as the target, five candidate aptamers, which are AptFAP-A1, AptFAP-A2, AptFAP-A3, AptFAP-A4, and AptFAP-A5, were selected by capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX), and their secondary structures were predicted to be mainly stem-loop. Moreover, the CE-laser-induced fluorescence (LIF) method was used to determine the equilibrium dissociation constant K_D values between the FAP protein and candidate aptamers, and the K_D value was in the low molar range. Finally, Cy5-labeled aptamers were co-incubated with human pancreatic cancer-associated fibroblasts highly expressing FAP protein, and confocal microscopy imaging showed that aptamer AptFAP-A4 had the highest affinities with the cells. The FAP aptamers screened in this study provide a promising direction for the development of rapid tumor diagnosis and targeted therapy.

Recent advances in targeted antibacterial therapy basing on nanomaterials

Bacterial infection has become one of the leading causes of death worldwide, particularly in low-income countries. Despite the fact that antibiotics have provided successful management in bacterial infections, the long-term overconsumption and abuse of antibiotics has contributed to the emergence of multidrug resistant bacteria. To address this challenge, nanomaterials with intrinsic antibacterial properties or that serve as drug carriers have been substantially developed as an alternative to fight against bacterial infection. Systematically and deeply understanding the antibacterial mechanisms of nanomaterials is extremely important for designing new therapeutics. Recently, nanomaterials-mediated targeted bacteria depletion in either a passive or active manner is one of the most promising approaches for antibacterial treatment by increasing local concentration around bacterial cells to enhance inhibitory activity and reduce side effects. Passive targeting approach is widely explored by searching nanomaterial-based alternatives to antibiotics, while active targeting strategy relies on biomimetic or biomolecular surface feature that can selectively recognize targeted bacteria. In this review article, we summarize the recent developments in the field of targeted antibacterial therapy based on nanomaterials, which will promote more innovative thinking focusing on the treatment of multidrug-resistant bacteria.

A novel aptamer beacon for rapid screening of recombinant cells and in vivo monitoring of recombinant proteins

Recombinant protein drugs, which are typically produced by mammalian host cells, have been approved for the treatment of a range of diseases. Accordingly, systems for selecting recombinant cell lines with efficient protein expression and for testing the content of recombinant proteins in vivo are crucial to the large-scale production and application of protein-based therapeutic drugs. In this study, we designed three aptamer beacons to detect His-tag, a common label of recombinant proteins. We found that all three beacons could specifically and quantitatively measure the His-tagged recombinant proteins with a short reaction time. Among these three beacons, the 6H5-MU beacon had the highest sensitivity for His polypeptides with a detection limit of 250 ng/mL and the shortest detection time within 1 min. Furthermore, we established a rapid and highly effective recombinant cell line construction system, which could obtain monoclonal cell lines with high yields of target proteins within 21 days, by combining 6H5-MU with pSB, a novel plasmid composed of a Sleeping Beauty transposase and a transposon. Finally, 6H5-MU also discriminately tested the serum concentration of His-tagged recombinant proteins in vivo, with consistent results compared to enzyme-linked immunosorbent assay (ELISA). We thus established a rapid and high-throughput method for generating recombinant cell lines and in vivo monitoring of recombinant protein levels, thereby providing a new platform for the development and preparation of recombinant protein drugs. KEY POINTS: • The 6H5-MU aptamer beacon rapidly and accurately binds to His-tagged recombinant proteins. • A system for rapid and high-throughput generation of recombinant cell lines is established using 6H5-MU and pSB. • 6H5-MU allows in vivo monitoring of recombinant protein levels.

Switchable DNA Photocatalysts for Radical Polymerization Controlled by Chemical Stimuli

Polymerization catalysts that activate in response to specific chemical triggers offer spatial and temporal control over polymer synthesis, facilitating the development of responsive materials and custom polymer coatings. However, existing catalysts switch their activity through mechanisms that are not generalizable to chemically diverse stimuli. To approach the level of control exhibited in biological polymer synthesis, switchable polymerization catalysts need to be configurable for activation in response to diverse chemical stimuli. Here, we combine synthetic photocatalysts with conformation-switching DNA aptamers to create polymerization catalysts that respond to diverse chemical stimuli. We use the secondary structure of DNA to bring a photocatalyst and quencher dye into proximity, turning off photocatalysis. The DNA structure can be precisely designed to change conformation in response to a molecular trigger, moving the photocatalyst far from the quencher and activating photocatalysis. We show these photocatalysts can initiate free-radical polymerization to form bulk hydrogels in response to complementary DNA, a metal ion (Zn2+), or small molecules (glucose and hydrocortisone). We demonstrate the biocompatibility of these switchable photocatalysts by triggering their activation on the surface of yeast cells. Finally, we perform reversible-deactivation radical polymerization through photoinduced electron/energy transfer reversible addition-fragmentation chain-transfer in a dual-stimulus manner, in which catalytic activity is regulated reversibly by photoirradiation and the conformational state of the DNA catalyst. These results demonstrate that DNA conformational changes triggered by chemically diverse stimuli can regulate the activity of radical polymerization photocatalysts. This platform offers new capabilities in spatially and temporally controlled polymer synthesis, with potential applications in diagnostics, sensing, and environmentally responsive materials.

Bifunctional G-Quadruplex Aptamer Targeting Nucleolin and Topoisomerase 1: Antiproliferative Activity and Synergistic Effect of Conjugated Drugs

As a counterpart to antibody-drug conjugates (ADCs), aptamer-drug conjugates (ApDCs) have been considered a promising strategy for targeted therapy due to the various benefits of aptamers. However, an aptamer merely serves as a targeting ligand in ApDCs, whereas the antibody enables the unexpected therapeutic efficacy of ADCs through antibody-dependent cellular cytotoxicity (ADCC). In this study, we developed a tumor-specific aptamer with an effector function and used it to confirm the feasibility of more potent ApDCs. First, we designed a nucleolin (NCL)-binding G-quadruplex (GQ) library based on the ability of NCL to bind to telomeric sequences. We then identified a bifunctional GQ aptamer (BGA) inhibiting the catalytic activity of topoisomerase 1 (TOP1) by forming an irreversible cleavage complex. Our BGA specifically targeted NCL-positive MCF-7 cells, exhibiting antiproliferative activity, and this suggested that tumor-specific therapeutic aptamers can be developed by using a biased library to screen aptamer candidates for functional targets. Finally, we utilized DM1, which has a synergistic interaction with TOP1 inhibitors, as a conjugated drug. BGA-DM1 exerted an anticancer effect 20-fold stronger than free DM1 and even 10-fold stronger than AS1411 (NCL aptamer)-DM1, highlighting our approach to develop synergistic ApDCs. Therefore, we anticipate that our library might be utilized for the identification of aptamers with effector functions. Furthermore, by employing such aptamers and appropriate drugs, synergistic ApDCs can be developed for targeted cancer therapy in a manner distinct from how ADCs exhibit additional therapeutic efficacy.