Protein Detection with Aptamer Biosensors

AS1411aptamer conjugated liposomes for targeted delivery of arsenic trioxide in mouse xenograft model of melanoma cancer

Development of AS1411aptamer-conjugated liposomes for targeted delivery of arsenic trioxide is the primary goal of this study. AS1411aptamer was used as ligand to target nucleolin, which is highly expressed on the surface of melanoma cancer cells. The targeted liposomes were constructed by the thin film method, and arsenic trioxide was loaded as cobalt (II) hydrogen arsenite (CHA) to increase the loading efficiency and stability of the liposomes. The liposomal structure was characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and field emission scanning electron microscopy (FESEM). In addition, particle sizes and zeta potential of the CHA-loaded liposomes (CHAL) and aptamer-functionalized CHA-loaded liposomes (AP-CHAL) were determined. In vitro cytotoxicity of CHAL and AP-CHAL were evaluated using MTT assay in murine melanoma (B16) and mouse embryonic fibroblast (MEF) cell lines. The encapsulation efficiency of CHAL and AP-CHAL was reported as 60.2 ± 6.5% and 58.7 ± 4.2%, respectively. In vivo antitumor activity of CHAL and AP-CHAL in the B16 tumor-xenograft mouse model was dramatically observed. All mice of both groups survived until the end of treatment and showed body weight gain. The tumor protrusion completely disappeared in 50% of the mice in these groups. Furthermore, histopathology studies demonstrated that CHAL and AP-CHAL did not induce significant toxicity in healthy mice tissues. However, unlike the CHAL group, which showed an initial increase in tumor volume, a specific antitumor effect was observed in the AP-CHAL group from the beginning of treatment. The results showed that AP-CHAL can be used as an effective drug delivery system with high potential in the treatment of solid tumors.

Paper-Based Analytical Devices for Cancer Liquid Biopsy

Liquid biopsies have caused a significant revolution in cancer diagnosis, and the use of point of care (PoC) platforms has the potential to bring liquid biopsy-based cancer detection closer to patients. These platforms provide rapid and on-site analysis by reducing the time between sample collection and results output. The aim of this tutorial content is to provide readers an in-depth understanding regarding the choice of the ideal sensing platform suitable for specific cancer-related biomarkers.

Sensing Levofloxacin with an RNA Aptamer as a Bioreceptor

To combat the growing threat of antibiotic resistance, environmental testing for antibiotic contamination is gaining an increasing role. This study aims to develop an easy-to-use assay for the detection of the fluoroquinolone antibiotic levofloxacin. Levofloxacin is used in human and veterinary medicine and has been detected in wastewater and river water. An RNA aptamer against levofloxacin was selected using RNA Capture-SELEX. The 73 nt long aptamer folds into three stems with a central three-way junction. It binds levofloxacin with a Kd of 6 µM and discriminates the closely related compound ciprofloxacin. Furthermore, the selection process was analyzed using a next-generation sequencing approach to better understand the sequence evolution throughout the selection. The aptamer was used as a bioreceptor for the development of a lateral flow assay. The biosensor exploited the innate characteristic of RNA Capture-SELEX to select aptamers that displace a complementary DNA oligonucleotide upon ligand binding. The lateral flow assay achieved a limit of visual detection of 100 µM. While the sensitivity of this assay constrains its immediate use in environmental testing, the present study can serve as a template for the selection of RNA aptamer-based biosensors.

Wearable and Implantable Cortisol-Sensing Electronics for Stress Monitoring

Cortisol is a steroid hormone that is released from the body in response to stress. Although a moderate level of cortisol secretion can help the body maintain homeostasis, excessive secretion can cause various diseases, such as depression and anxiety. Conventional methods for cortisol measurement undergo procedures that limit continuous monitoring, typically collecting samples of bodily fluids, followed by separate analysis in a laboratory setting that takes several hours. Thus, recent studies demonstrate wearable, miniaturized sensors integrated with electronic modules that enable wireless real-time analysis. Here, the primary focus is on wearable and implantable electronic devices that continuously measure cortisol concentration. Diverse types of cortisol-sensing techniques, such as antibody-, DNA-aptamer-, and molecularly imprinted polymer-based sensors, as well as wearable and implantable devices that aim to continuously monitor cortisol in a minimally invasive fashion are discussed. In addition to the cortisol monitors that directly measure stress levels, other schemes that indirectly measure stress, such as electrophysiological signals and sweat are also summarized. Finally, the challenges and future directions in stress monitoring and management electronics are reviewed.

Development of an Electrochemical, Aptamer-Based Sensor for Dynamic Detection of Neuropeptide Y

The ability to monitor dynamic changes in neuropeptide Y (NPY) levels in complex environments can have an impact on many fields, including neuroscience and immunology. Here, we describe the development of an electrochemical, aptamer-based (E-AB) sensor for the dynamic (reversible) measurement of physiologically relevant (nanomolar) concentrations of neuropeptide Y. The E-AB sensors are fabricated using a previously described 80 nucleotide aptamer1 reported to specifically bind NPY with a binding affinity Kd = 0.3 ± 0.2 uM. We investigated two redox tag placement locations on the aptamer sequence (terminal vs internal) and various sensor fabrication and interrogation parameters to tune the performance of the resulting sensor. The best-performing sensor architecture displayed a physiologically relevant dynamic range (nM) and low limit of detection and is selective among competitors and similar molecules. The development of this sensor accomplishes two breakthroughs: first, the development of a nonmicrofluidic aptamer-based electrochemical sensor that can detect NPY on a physiologically relevant (seconds to minutes) time scale and across a relevant concentration range; second, the expansion of the range of molecules for which an electrochemical, aptamer-based sensor can be used.

Aptamer-Protein Interactions: From Regulation to Biomolecular Detection

Serving as the basis of cell life, interactions between nucleic acids and proteins play essential roles in fundamental cellular processes. Aptamers are unique single-stranded oligonucleotides generated by in vitro evolution methods, possessing the ability to interact with proteins specifically. Altering the structure of aptamers will largely modulate their interactions with proteins and further affect related cellular behaviors. Recently, with the in-depth research of aptamer-protein interactions, the analytical assays based on their interactions have been widely developed and become a powerful tool for biomolecular detection. There are some insightful reviews on aptamers applied in protein detection, while few systematic discussions are from the perspective of regulating aptamer-protein interactions. Herein, we comprehensively introduce the methods for regulating aptamer-protein interactions and elaborate on the detection techniques for analyzing aptamer-protein interactions. Additionally, this review provides a broad summary of analytical assays based on the regulation of aptamer-protein interactions for detecting biomolecules. Finally, we present our perspectives regarding the opportunities and challenges of analytical assays for biological analysis, aiming to provide guidance for disease mechanism research and drug discovery.

Quantitative measurement of CA 15-3 cancer biomarker using an electrochemical aptasensor based on the electrodeposition of Au thin film on cauliflower-like rGO-MoS2 nanocomposite

The present research was conducted to design and construct an electrochemical aptasensor for evaluating carbohydrate antigen 15-3 (CA15-3) as a biomarker for breast cancer. The aptasensor has been fabricated by a gold thin film (AuTF) electrodeposited on a cauliflower-like reduced graphene oxide-molybdenum sulfide nanocomposite (rGO-MoS2). The modified electrode's surface was used to immobilize the thiolated aptamer, which was subsequently treated with CA 15-3 antigen. The aptasensor fabrication process was assessed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This research also applied EIS to the quantitative measurement of CA 15-3 antigen by the proposed aptasensor. The interfacial charge transfer resistance (Rct) alteration before and after incubation of CA 15-3 by the immobilized aptamer was considered a signal for the quantitative measurement of CA 15-3. A linear concentration ranging from 5.0 to 200.0 U mL-1 with a detection limit of 3.0 × 10-1 U mL-1 was obtained for CA 15-3 using the EIS method. This designed aptasensor indicates satisfactory repeatability and stability, good selectivity, and high sensitivity. Moreover, clinical samples were assayed by the prepared aptasensor and compared with the ELISA method, yielding acceptable results. The recovery and relative standard deviation (RSD) of CA 15-3 in human serum samples were in the range 95.0 to 107.0% and 3.5 to 7.5%, respectively.

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.

Modern Electrochemical Biosensing Based on Nucleic Acids and Carbon Nanomaterials

To meet the requirements of novel therapies, effective treatments should be supported by diagnostic tools characterized by appropriate analytical and working parameters. These are, in particular, fast and reliable responses that are proportional to analyte concentration, with low detection limits, high selectivity, cost-efficient construction, and portability, allowing for the development of point-of-care devices. Biosensors using nucleic acids as receptors has turned out to be an effective approach for meeting the abovementioned requirements. Careful design of the receptor layers will allow them to obtain DNA biosensors that are dedicated to almost any analyte, including ions, low and high molecular weight compounds, nucleic acids, proteins, and even whole cells. The impulse for the application of carbon nanomaterials in electrochemical DNA biosensors is rooted in the possibility to further influence their analytical parameters and adjust them to the chosen analysis. Such nanomaterials enable the lowering of the detection limit, the extension of the biosensor linear response, or the increase in selectivity. This is possible thanks to their high conductivity, large surface-to-area ratio, ease of chemical modification, and introduction of other nanomaterials, such as nanoparticles, into the carbon structures. This review discusses the recent advances on the design and application of carbon nanomaterials in electrochemical DNA biosensors that are dedicated especially to modern medical diagnostics.

2D-Materials-Based Wearable Biosensor Systems

As an evolutionary success in life science, wearable biosensor systems, which can monitor human health information and quantify vital signs in real time, have been actively studied. Research in wearable biosensor systems is mainly focused on the design of sensors with various flexible materials. Among them, 2D materials with excellent mechanical, optical, and electrical properties provide the expected characteristics to address the challenges of developing microminiaturized wearable biosensor systems. This review summarizes the recent research progresses in 2D-materials-based wearable biosensors including e-skin, contact lens sensors, and others. Then, we highlight the challenges of flexible power supply technologies for smart systems. The latest advances in biosensor systems involving wearable wristbands, diabetic patches, and smart contact lenses are also discussed. This review will enable a better understanding of the design principle of 2D biosensors, offering insights into innovative technologies for future biosensor systems toward their practical applications.

Emergence of infectious diseases and role of advanced nanomaterials in point-of-care diagnostics: a review

Infectious outbreaks are the foremost global public health concern, challenging the current healthcare system, which claims millions of lives annually. The most crucial way to control an infectious outbreak is by early detection through point-of-care (POC) diagnostics. POC diagnostics are highly advantageous owing to the prompt diagnosis, which is economical, simple and highly efficient with remote access capabilities. In particular, utilization of nanomaterials to architect POC devices has enabled highly integrated and portable (compact) devices with enhanced efficiency. As such, this review will detail the factors influencing the emergence of infectious diseases and methods for fast and accurate detection, thus elucidating the underlying factors of these infections. Furthermore, it comprehensively highlights the importance of different nanomaterials in POCs to detect nucleic acid, whole pathogens, proteins and antibody detection systems. Finally, we summarize findings reported on nanomaterials based on advanced POCs such as lab-on-chip, lab-on-disc-devices, point-of-action and hospital-on-chip. To this end, we discuss the challenges, potential solutions, prospects of integrating internet-of-things, artificial intelligence, 5G communications and data clouding to achieve intelligent POCs.

Biosensors Integration in Blood-Brain Barrier-on-a-Chip: Emerging Platform for Monitoring Neurodegenerative Diseases

Over the most recent decades, the development of new biological platforms to study disease progression and drug efficacy has been of great interest due to the high increase in the rate of neurodegenerative diseases (NDDs). Therefore, blood–brain barrier (BBB) as an organ-on-a-chip (OoC) platform to mimic brain-barrier performance could offer a deeper understanding of NDDs as well as a very valuable tool for drug permeability testing for new treatments. A very attractive improvement of BBB-oC technology is the integration of detection systems to provide continuous monitoring of biomarkers in real time and a fully automated analysis of drug permeably, rendering more efficient platforms for commercialization. In this Perspective, an overview of the main BBB-oC configurations is introduced and a critical vision of the BBB-oC platforms integrating electronic read out systems is detailed, indicating the strengths and weaknesses of current devices, proposing the great potential for biosensors integration in BBB-oC. In this direction, we name potential biomarkers to monitor the evolution of NDDs related to the BBB and/or drug cytotoxicity using biosensor technology in BBB-oC.

The use of high-affinity polyhistidine binders as masking probes for the selection of an NDM-1 specific aptamer

The emergence of carbapenemase-producing multi-drug resistant Enterobacteriaceae poses a dramatic, world-wide health risk. Limited treatment options and a lack of easy-to-use methods for the detection of infections with multi-drug resistant bacteria leave the health-care system with a fast-growing challenge. Aptamers are single stranded DNA or RNA molecules that bind to their targets with high affinity and specificity and can therefore serve as outstanding detection probes. However, an effective aptamer selection process is often hampered by non-specific binding. When selections are carried out against recombinant proteins, purification tags (e.g. polyhistidine) serve as attractive side targets, which may impede protein target binding. In this study, aptamer selection was carried out against N-terminally hexa-histidine tagged New Delhi metallo-ß-lactamase 1. After 14 selection rounds binding to polyhistidine was detected rather than to New Delhi metallo-ß-lactamase 1. Hence, the selection strategy was changed. As one aptamer candidate showed remarkable binding affinity to polyhistidine, it was used as a masking probe and selection was restarted from selection round 10. Finally, after three consecutive selection rounds, an aptamer with specific binding properties to New Delhi metallo-ß-lactamase 1 was identified. This aptamer may serve as a much-needed detection probe for New Delhi metallo-ß-lactamase 1 expressing Enterobacteriaceae.

Development of a textile based protein sensor for monitoring the healing progress of a wound

This article focuses on the design and fabrication of flexible textile-based protein sensors to be embedded in wound dressings. Chronic wounds require continuous monitoring to prevent further complications and to determine the best course of treatment in the case of infection. As proteins are essential for the progression of wound healing, they can be used as an indicator of wound status. Through measuring protein concentrations, the sensor can assess and monitor the wound condition continuously as a function of time. The protein sensor consists of electrodes that are directly screen printed using both silver and carbon composite inks on polyester nonwoven fabric which was deliberately selected as this is one of the common backing fabric types currently used in wound dressings. These sensors were experimentally evaluated and compared to each other by using albumin protein solution of pH 7. A comprehensive set of cyclic voltammetry measurements was used to determine the optimal sensor design the measurement of protein in solution. As a result, the best sensor design is comprised of silver conductive tracks but a carbon layer as the working and counter electrodes at the interface zone. This design prevents the formation of silver dioxide and protects the sensor from rapid decay, which allows for the recording of consecutive measurements using the same sensor. The chosen printed protein sensor was able to detect bovine serum albumin at concentrations ranging from 30 to 0.3 mg/mL with a sensitivity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.0026 \mu $$\end{document}0.0026μA/M. Further testing was performed to assess the sensor’s ability to identify BSA from other interferential substances usually present in wound fluids and the results show that it can be distinguishable.

Development of novel aptasensor for ultra-sensitive detection of myoglobin via electrochemical signal amplification of methylene blue using poly (styrene)-block-poly (acrylic acid) amphiphilic copolymer

Amplification of electrochemical signal in order to betterment of limit of detection in determination of biomarkers has an important role in early detection of some dangerous diseases such as cancers. For this purpose, in this research, two types of poly (styrene)-block-poly (acrylic acid) amphiphilic copolymer (PS₆₁-b-PAA₅₉₆ and PS₅₉₆-b-PAA₆₁) were synthesized by controlled radical polymerization method via reversible addition-fragmentation chain transfer polymerization (RAFT) technique. Chemical structure of block copolymers was confirmed by FT-IR spectroscopy and their surface morphology was assessed by scanning electron microscopy (SEM). Self-assembly of these block copolymers into polymeric vesicles (polymersomes), loading and release efficiency of methylene blue as an electroactive indicator were investigated in DMF and THF solvents. On the basis of our findings PS₆₁-b-PAA₅₉₆ has better capability for loading and release of MB than PS₅₉₆-b-PAA₆₁. Then the obtained methylene blue-loaded polymersome successfully used for development of an aptasensor toward determination of trace amounts of myoglobin. The proposed aptasensor showed a wide linear range from 1.0 aM to 1.0 μM with an ultra-low detection limit of 0.73 aM. Applying this amplification strategy, determination of myoglobin in real samples was successfully performed.

Gold nanoparticle-assisted SELEX as a visual monitoring platform for the development of small molecule-binding DNA aptasensors

To resolve time-consuming and imperceptible monitoring problems in the traditional systematic evolution of ligands by exponential enrichment (SELEX), we report gold nanoparticle-assisted SELEX (GNP-SELEX) as a visual, proofreading, and self-monitoring platform and its application to small molecule-binding single-stranded DNA (ssDNA) aptasensors. Through the colorimetric changes between rounds, GNP-SELEX enabled the rapid determination of target-specific aptamer library enrichment with neither target modification nor extra monitoring process. We identified ssDNA aptamers with high selectivity and binding affinity by targeting two small molecules (brassinolide; BL and bisphenol A; BPA) as a model. The rational design of selected aptamers by 3D molecular simulation increased their ability to detect BL or BPA in real samples as bioreceptors. These results suggest that GNP-SELEX is useful as a self-monitoring platform to discover ssDNA aptamers as well as to develop aptasensors for diverse targets in a rapid and simple way.

Aptamer-Based Detection of Circulating Targets for Precision Medicine

The past decade has witnessed ongoing progress in precision medicine to improve human health. As an emerging diagnostic technique, liquid biopsy can provide real-time, comprehensive, dynamic physiological and pathological information in a noninvasive manner, opening a new window for precision medicine. Liquid biopsy depends on the sensitive and reliable detection of circulating targets (e.g., cells, extracellular vesicles, proteins, microRNAs) from body fluids, the performance of which is largely governed by recognition ligands. Aptamers are single-stranded functional oligonucleotides, capable of folding into unique tertiary structures to bind to their targets with superior specificity and affinity. Their mature evolution procedure, facile modification, and affinity regulation, as well as versatile structural design and engineering, make aptamers ideal recognition ligands for liquid biopsy. In this review, we present a broad overview of aptamer-based liquid biopsy techniques for precision medicine. We begin with recent advances in aptamer selection, followed by a summary of state-of-the-art strategies for multivalent aptamer assembly and aptamer interface modification. We will further describe aptamer-based micro-/nanoisolation platforms, aptamer-enabled release methods, and aptamer-assisted signal amplification and detection strategies. Finally, we present our perspectives regarding the opportunities and challenges of aptamer-based liquid biopsy for precision medicine.

DNA Nanostructures in the Fight Against Infectious Diseases

Throughout history, humanity has been threatened by countless epidemic and pandemic outbreaks of infectious diseases, from the Justinianic Plague to the Spanish flu to COVID-19. While numerous antimicrobial and antiviral drugs have been developed over the last 200 years to face these threats, the globalized and highly connected world of the 21st century demands for an ever-increasing efficiency in the detection and treatment of infectious diseases. Consequently, the rapidly evolving field of nanomedicine has taken up the challenge and developed a plethora of strategies to fight infectious diseases with the help of various nanomaterials such as noble metal nanoparticles, liposomes, nanogels, and virus capsids. DNA nanotechnology represents a comparatively recent addition to the nanomedicine arsenal, which, over the past decade, has made great progress in the area of cancer diagnostics and therapy. However, the past few years have seen also an increasing number of DNA nanotechnology-related studies that particularly focus on the detection and inhibition of microbial and viral pathogens. Herein, a brief overview of this rather young research field is provided, successful concepts as well as potential challenges are identified, and promising directions for future research are highlighted.

Fabrication and evaluation of aptamer-conjugated paclitaxel-loaded magnetic nanoparticles for targeted therapy on breast cancer cells

Targeted drug delivery vehicles make it possible to deliver anti-cancer drugs to the cells or tissues of interest. Aptamers are peptide or oligonucleotide molecules that can serve as targeting elements of drug carriers. In the current study, we evaluated the capacity of an aptamer-based drug carrier to deliver Paclitaxel (PTX) to cancer cells. After being synthesized, SPIONs@PTX-SYL3C aptamer was characterized using different methods, including differential light scattering (DLS), infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Encapsulation efficiency (EE) and loading efficiency (LE) were also evaluated. The carrier was applied on 4T1, MCF 7, and MCF-10A breast cell lines to evaluate its drug delivery potency and specificity. EE and LE were calculated to be 77.6% and 7.76%, respectively. MTT results revealed that aptameric SPIONs@PTX was more toxic than non-aptameric SPIONs@PTX. Flowcytometry analysis and DAPI staining confirmed that SPIONs@PTX-Aptamer had higher cell internalization rate when compared to non-targeted SPIONs@PTX. Our results indicate that aptamer-conjugated SPIONs@PTX has a good capacity in recognizing its target cells and inhibiting their growth and division.

Label-free attomolar protein detection using a MEMS optical interferometric surface-stress immunosensor with a freestanding PMMA/parylene-C nanosheet

We demonstrated an optical interferometer-based surface-stress immunosensor using freestanding polymethyl methacrylate (PMMA)/parylene-C nanosheet with high sensitivity for detection of biomolecules. PMMA/parylene-C nanosheets were transferred onto a silicon substrate with microcavities to fabricate freestanding submicron-thick membrane with a sealed cavity structure. The adhesive force between the transferred parylene-C and binder parylene-C layer was measured to be 1.06-2.4 N/10 mm by tape test. Evading Debye shielding, these nanomechanical sensors allow detection of the adsorption on the membrane surface through changes in surface stress transduced by the electric charge. We optimized the density of receptors and mode of immobilization for high sensitivity. To evaluate the selectivity of the sensor, membrane deflections induced by various proteins were measured and the spectral shifts showed high selectivity only for the target antigen. The minimum limit of detection (LOD) of the sensor for human serum albumin antigen was 0.1-1 fg/mL (1.5-15 aM), which was 20,000 times lower than that of the conventional micro-cantilever sensor.

Emerging biosensors in detection of natural products

Natural products (NPs) are a valuable source in the food, pharmaceutical, agricultural, environmental, and many other industrial sectors. Their beneficial properties along with their potential toxicities make the detection, determination or quantification of NPs essential for their application. The advanced instrumental methods require time-consuming sample preparation and analysis. In contrast, biosensors allow rapid detection of NPs, especially in complex media, and are the preferred choice of detection when speed and high throughput are intended. Here, we review diverse biosensors reported for the detection of NPs. The emerging approaches for improving the efficiency of biosensors, such as microfluidics, nanotechnology, and magnetic beads, are also discussed. The simultaneous use of two detection techniques is suggested as a robust strategy for precise detection of a specific NP with structural complexity in complicated matrices. The parallel detection of a variety of NPs structures or biological activities in a mixture of extract in a single detection phase is among the anticipated future advancements in this field which can be achieved using multisystem biosensors applying multiple flow cells, sensing elements, and detection mechanisms on miniaturized folded chips.

Dual-recognition molecularly imprinted aptasensor based on gold nanoparticles decorated carboxylated carbon nanotubes for highly selective and sensitive determination of histamine in different matrices

In this study, an electrochemical aptamer based sensor (aptasensor) was proposed for specific recognition of histamine (HIS). The electrochemical aptasensor based on fabrication of glassy carbon electrode (GCE) with molecular imprinted polymer (MIP) and DNA aptamers on gold nanoparticles (AuNPs) and carboxylated carbon nanotubes (cCNTs) (MIP-apta/AuNPs/cCNTs/GCE). The aptasensor exhibits high selectivity towards HIS detection as it has two recognition elements which are MIP cavities and aptamer interaction. Upon exposure of MIP-apt/AuNPs/cCNTs/GCE to HIS, the current of redox probe was decreased that depends on the template (HIS) concentration. The effects of aptamer concentration, incubation time, pH and AuNPs electro-deposition time were optimized. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were used to analyze HIS in complicated matrices. Favorable performance of MIP-apt/AuNPs/cCNTs/GCE was achieved with linearity ranges of 0.46-35 nmol L^-1 and 0.35-35 nmol L^-1 with limits of detection (LODs, S/N = 3) of 0.15 nmol L^-1 and 0.11 nmol L^-1 using DPV and EIS, respectively. The fabricated aptasensor displayed high selectivity, desirable reproducibility and stability. The MIP-apt/AuNPs/cCNTs/GCE was used to detect HIS in human plasma and canned tuna samples with good recoveries % and RSDs %.

Aptamers vs. antibodies as capture probes in optical porous silicon biosensors

Over the past decade aptamers have emerged as a promising class of bioreceptors for biosensing applications with significant advantages over conventional antibodies. However, experimental studies comparing aptasensors and immunosensors, under equivalent conditions, are limited and the results are inconclusive, in terms of benefits and limitations of each bioreceptor type. In the present work, the performance of aptamer and antibody bioreceptors for the detection of a his-tagged protein, used as a model target, is compared. The bioreceptors are immobilized onto a nanostructured porous silicon (PSi) thin film, used as the optical transducer, and the target protein is detected in a real-time and label-free format by reflective interferometric Fourier transform spectroscopy. For the antibodies, random-oriented immobilization onto the PSi nanostructure results in a poor biosensing performance. Contrary, Fc-oriented immobilization of the antibodies shows a similar biosensing performance to that exhibited by the aptamer-based biosensor, in terms of binding rate, dynamic detection range, limit of detection and selectivity. The aptasensor outperforms in terms of its reusability and storability, while the immunosensor could not be regenerated for subsequent experiments.

In vitro selection of DNA aptamers and their integration in a competitive voltammetric biosensor for azlocillin determination in waste water

The uncontrolled usage of veterinary antibiotics has led to their widespread pollution in waterways and milk products. Potential impact of antibiotic residues on the environment and human health such as increased antibiotic resistance of microorganisms and triggering allergic reactions in humans have been reported. In this work, we developed a highly selective and sensitive voltammetric aptasensor for on-step, sensitive and low cost detection of azlocillin antibiotic, one of the broad spectrum β-lactam antibiotics. The successful selection of DNA aptamers against azlocillin was accomplished using systemic evolution of ligands by exponential enrichment (SELEX) method. Fluorescence-binding assays showed dissociation constant of 55 nM for one of the selected aptamers (Az9). This aptamer was used to construct a competitive voltammetric aptasensor for azlocillin. A limit of detection of 1.2 pg/mL as well as remarkable selectivity against potential interfering agents, including amoxicillin, were achieved. This signal-off competitive sensor takes 30-50 min to complete the quantification of the target antibiotic. The sensor was challenged by detecting the target directly in complex environments such as tap and waste water where good recovery percentages were achieved.

Gluten Detection Methods and Their Critical Role in Assuring Safe Diets for Celiac Patients

Celiac disease, wheat sensitivity, and allergy represent three different reactions, which may occur in genetically predisposed individuals on the ingestion of wheat and derived products with various manifestations. Improvements in the disease diagnostics and understanding of disease etiology unveiled that these disorders are widespread around the globe affecting about 7% of the population. The only known treatment so far is a life-long gluten-free diet, which is almost impossible to follow because of the contamination of allegedly "gluten-free" products. Accidental contamination of inherently gluten-free products could take place at any level from field to shelf because of the ubiquity of these proteins/grains. Gluten contamination of allegedly "gluten-free" products is a constant threat to celiac patients and a major health concern. Several detection procedures have been proposed to determine the level of contamination in products for celiac patients. The present article aims to review the advantages and disadvantages of different gluten detection methods, with emphasis on the recent technology that allows identification of the immunogenic-gluten peptides without the use of antibodies. The possibility to detect gluten contamination by different approaches with similar or better detection efficiency in different raw and processed foods will guarantee the safety of the foods for celiac patients.

Therapeutic potential of ectopic olfactory and taste receptors

Olfactory and taste receptors are expressed primarily in the nasal olfactory epithelium and gustatory taste bud cells, where they transmit real-time sensory signals to the brain. However, they are also expressed in multiple extra-nasal and extra-oral tissues, being implicated in diverse biological processes including sperm chemotaxis, muscle regeneration, bronchoconstriction and bronchodilatation, inflammation, appetite regulation and energy metabolism. Elucidation of the physiological roles of these ectopic receptors is revealing potential therapeutic and diagnostic applications in conditions including wounds, hair loss, asthma, obesity and cancers. This Review outlines current understanding of the diverse functions of ectopic olfactory and taste receptors and assesses their potential to be therapeutically exploited.

Noble Metal Nanoparticles-Based Colorimetric Biosensor for Visual Quantification: A Mini Review

Nobel metal can be used to form a category of nanoparticles, termed noble metal nanoparticles (NMNPs), which are inert (resistant to oxidation/corrosion) and have unique physical and optical properties. NMNPs, particularly gold and silver nanoparticles (AuNPs and AgNPs), are highly accurate and sensitive visual biosensors for the analytical detection of a wide range of inorganic and organic compounds. The interaction between noble metal nanoparticles (NMNPs) and inorganic/organic molecules produces colorimetric shifts that enable the accurate and sensitive detection of toxins, heavy metal ions, nucleic acids, lipids, proteins, antibodies, and other molecules. Hydrogen bonding, electrostatic interactions, and steric effects of inorganic/organic molecules with NMNPs surface can react or displacing capping agents, inducing crosslinking and non-crosslinking, broadening, or shifting local surface plasmon resonance absorption. NMNPs-based biosensors have been widely applied to a series of simple, rapid, and low-cost diagnostic products using colorimetric readout or simple visual assessment. In this mini review, we introduce the concepts and properties of NMNPs with chemical reduction synthesis, tunable optical property, and surface modification technique that benefit the development of NMNPs-based colorimetric biosensors, especially for the visual quantification. The “aggregation strategy” based detection principle of NMNPs colorimetric biosensors with the mechanism of crosslinking and non-crosslinking have been discussed, particularly, the critical coagulation concentration-based salt titration methodology have been exhibited by derived equations to explain non-crosslinking strategy be applied to NMNPs based visual quantification. Among the broad categories of NMNPs based biosensor detection analyses, we typically focused on four types of molecules (melamine, single/double strand DNA, mercury ions, and proteins) with discussion from the standpoint of the interaction between NMNPs surface with molecules, and DNA engineered NMNPs-based biosensor applications. Taken together, NMNPs-based colorimetric biosensors have the potential to serve as a simple yet reliable technique to enable visual quantification.

Simultaneous detection of multiple NT-proBNP clinical samples utilizing an aptamer-based sandwich assay on an integrated microfluidic system

Although cardiovascular diseases such as heart failure (HF) affect 30 million people globally, the early detection of HF has, until recently, been difficult and prone to misdiagnoses. Monitoring the circulatory levels of a relatively new biomarker, the N-terminal prohormone of a B-type natriuretic peptide, could be used for early risk evaluation of HF. Therefore, we developed a pneumatically-driven, automatic integrated microfluidic platform equipped with micromixers, micropumps, and microvalves for the simultaneous detection of NT-proBNP in up to six clinical samples within 25 min by using a novel aptamer-based sandwich assay, and the limit of detection was only 1.53 pg mL-1; given that the chip is 64% more compact than those developed in our prior works and requires only 5 μL of sample input, it may serve as a promising tool for early diagnosis of HF.

d-/l-Isothymidine incorporation in the core sequence of aptamer BC15 enhanced its binding affinity to the hnRNP A1 protein

The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) was reported to participate in the development of a variety of tumors. BC15 is a DNA aptamer targeting hnRNP A1. Firstly, through sequence truncation, we identified 31-mer sequence BC15-31 as the core sequence of BC15 with a strong binding affinity and high selectivity to the hnRNP A1 protein. Isothymidine (isoT) modification was then applied for the structural optimization of BC15-31, systematic modification and biological evaluation were carried out. Incorporation of isoT in the 1,3 sites at the 5'-end of BC15-31 can significantly enhance the protein affinity. Chemical modifications close to the 3'-end can greatly improve the stability of the aptamer. Furthermore, BC15-31 modified with isoT at both the 5'-end and 3'-end displayed an additive effect with enhanced bioactivity and stability at the same time. Our study strategy on BC15 provides a useful guideline for chemical modification and optimization of the aptamer for further clinical application.

Synthetic antibody: Prospects in aquaculture biosecurity

The emerging technology of aptamers that is also known as synthetic antibodies is rivalling antibodies research in the recent years. The unique yet important features of aptamers are advancing antibodies in diverse applications, which include disease diagnosis, prophylactic and therapeutic. The versatility of aptamer has further extended its application to function as gene expression modulator, known as synthetic riboswitches. This report reviewed and discussed the applications of aptamers technology in the biosecurity of aquaculture, the promising developments in biosensor detection for disease diagnosis as well as prophylactic and therapeutic measurements. The application of aptamers technology in immunophenotyping study of aquatic animal is highlighted. Lastly, the future perspective of aptamers in the management of aquatic animal health is discussed, special emphasis on the potential application of aptamers as synthetic riboswitches to enhance host immunity, as well as the growth performance.

Assessing the Quality of in Silico Produced Biomolecules: The Discovery of a New Conformer

The computational procedures for predicting the 3D structure of aptamers interacting with different biological molecules have gained increasing attention in recent years. The information acquired through these methods represents a crucial input for research, especially when relevant crystallographic data are not available. A number of software programs able to perform macromolecular docking are currently accessible, leading to the prediction of the quaternary structure of complexes formed by two or more interacting biological macromolecules. Nevertheless, the scoring protocols employed for ranking the candidate structures do not always produce satisfactory results, making difficult the identification of structures that are most likely to occur in nature. In this paper, we propose a novel procedure to improve the predictive performances of computational scoring protocols, using a maximum likelihood estimate based on topological and electrical properties of interacting biomolecules. The reliability of the new computational approach, enabling the ranking of aptamer-protein configurations produced by an open source docking program, has been assessed by its successful application to a set of antiangiopoietin aptamers, for which experimental data highlighting the sequence-dependent affinity toward the target protein are available. The procedure led to the identification of two main types of aptamer conformers involved in angiopoietin binding. Interestingly, one of these reproduces the arrangement of angiopoietin with its natural target, tyrosine kinase, while the other one is completely unexpected. The possible scenarios related to these results have been discussed. The methodology here described can be used to refine the outcomes of different computational procedures and can be applied to a wide range of biological molecules, thus representing a new tool for guiding the design of bioinspired sensors with enhanced selectivity.

Sensitive and specific detection of proteins based on target-responsive DNA polymerase activity

We herein describe a novel method for the detection of target protein based on the target-responsive DNA polymerase activity. In the sensor, two different types of DNA aptamers with the respective functions: one binds to the target protein and the other binds to DNA polymerase, are rationally engineered and combined to form the detection probe that regulates DNA polymerase activity in response to the target protein. In the presence of target protein, the detection probe becomes destabilized and stops the inhibition of DNA polymerase activity. Consequently, the active DNA polymerase initiates the primer extension reaction on the target-specific DNA aptamer, which recycles the target protein to promote another activation cycle of DNA polymerase. In addition, DNA polymerase also catalyzes the primer extension reaction on the primer/template complex in conjugation with TaqMan probe, leading to the significantly enhanced fluorescence intensities. With this novel strategy, we detected a model target protein, lysozyme with a limit of detection as low as 0.80 nM. In addition, the practical applicability of this system was successfully demonstrated by determining lysozyme in human serum.

Characterization and Inkjet Printing of an RNA Aptamer for Paper-Based Biosensing of Ciprofloxacin

The excessive use of antibiotics in food-producing animals causes a steady rise of multiple antibiotic resistance in foodborne bacteria. Next to sulfonamides, the most common antibiotics groups are fluoroquinolones, aminoglycosides, and ß-lactams. Therefore, there is a need for a quick, efficient, and low-cost detection procedure for antibiotics. In this study, we propose an inkjet-printed aptamer-based biosensor developed for the detection of the fluoroquinolone ciprofloxacin. Due to their extraordinary high affinity and specificity, aptamers are already widely used in various applications. Here we present a ciprofloxacin-binding RNA aptamer developed by systematic evolution of ligands by exponential enrichment (SELEX). We characterized the secondary structure of the aptamer and determined the KD to 36 nM that allow detection of antibiotic contamination in a relevant range. We demonstrate that RNA aptamers can be inkjet-printed, dried, and resolved while keeping their functionality consistently intact. With this proof of concept, we are paving the way for a potential range of additional aptamer-based, printable biosensors.

Disposable Voltammetric Immunosensors Integrated with Microfluidic Platforms for Biomedical, Agricultural and Food Analyses: A Review

Disposable immunosensors are analytical devices used for the quantification of a broad variety of analytes in different areas such as clinical, environmental, agricultural and food quality management. They detect the analytes by means of the strong interactions between antibodies and antigens, which provide concentration-dependent signals. For the herein highlighted voltammetric immunosensors, the analytical measurements are due to changes in the electrical signals on the surface of the transducers. The possibility of using disposable and miniaturized immunoassays is a very interesting alternative for voltammetric analyses, mainly, when associated with screen-printing technologies (screen-printed electrodes, SPEs), and microfluidic platforms. The aim of this paper is to discuss a carefully selected literature about different examples of SPEs-based immunosensors associated with microfluidic technologies for diseases, food, agricultural and environmental analysis. Technological aspects of the development of the voltammetric immunoassays such as the signal amplification, construction of paper-based microfluidic platforms and the utilization of microfluidic devices for point-of-care testing will be presented as well.

Aptamer Functionalized DNA Hydrogel for Wise-Stage Controlled Protein Release

With the simple functionalization method and good biocompatibility, an aptamer-integrated DNA hydrogel is used as the protein delivery system with an adjustable release rate and time by using complementary sequences (CSs) as the biomolecular trigger. The aptamer-functionalized DNA hydrogel was prepared via a one-pot self-assembly process from two kinds of DNA building blocks (X-shaped and L-shaped DNA units) and a single-stranded aptamer. The gelling process was achieved under physiological conditions within one minute. In the absence of the triggering CSs, the aptamer grafted in the hydrogel exhibited a stable state for protein-specific capture. While hybridizing with the triggering CSs, the aptamer is turned into a double-stranded structure, resulting in the fast dissociation of protein with a wise-stage controlled release program. Further, the DNA hydrogel with excellent cytocompatibility has been successfully applied to human serum, forming a complex matrix. The whole process of protein capture and release were biocompatible and could not refer to any adverse factor of the protein or cells. Thus, the aptamer-functionalized DNA hydrogel will be a good candidate for controlled protein delivery.

Development of DNA aptamer-based sensor for electrochemical detection of C-reactive protein

C-reactive protein (CRP) is a crucial biomarker of cardiovascular diseases and for its detection both optical and electrochemical techniques were applied. This study concerns the application of DNA aptamer as recognition layer for CRP detection. For that purpose aptamer immobilization method on gold surface was selected and the content of receptor layer was optimized to ensure an efficient binding to target protein. The quality of the monolayer was verified by the application of chronocoulometry and atomic force microscopy. Using thiolated aptamers provided the formation of layers of highest density and stability. The square-wave voltammetry experiments performed in the presence of methylene blue redox indicator revealed a linear response of aptasensor towards CRP in the range from 1 to 100 pM. Moreover, a DNA aptamer - based sensor showed good selectivity towards C-reactive protein in comparison to interfering proteins including BSA and IgE. Finally, the analysis of CRP in serum sample was conducted using the developed aptasensor.

Screening and multiple detection of cancer exosomes using an SERS-based method

As a kind of most important cancer biomarker, exosomes are getting more frequently investigated in cancer diagnosis. In this study, we proposed an SERS-based method for the screening and simultaneous multiple detection of exosomes using magnetic substrates and SERS probes. Specifically, the capturing substrates are achieved using gold shell magnetic nanobeads modified by aptamers, which can capture most kinds of exosomes by recognizing the generic surface protein CD63. Moreover, the SERS probes are made of gold nanoparticles decorated with a Raman reporter and a specific aptamer for targeting exosomes. Further, for the simultaneous detection of multiple kinds of exosomes, three kinds of SERS probes were designed using different SERS reporters. While detecting specific kinds of exosomes, the capturing substrates were mixed with these three kinds of SERS probes. When the target exosome is present, an apta-immunocomplex can be formed among the target exosomes, the substrate, and the corresponding kind of SERS probes, and the other non-specific SERS probes remain in the suspension. Hence, an SERS signal with a decreased intensity will be detected in the supernatant, indicating the presence of the target exosomes. Finally, this detection method has also been successfully employed for the detection of exosomes in real blood samples; this proves that the proposed SERS-based method is a promising tool for clinical cancer screening based on exosomes.

Exonuclease-assisted multicolor aptasensor for visual detection of ochratoxin A based on G-quadruplex-hemin DNAzyme-mediated etching of gold nanorod

An exonuclease-assisted multicolor aptasensor was developed for the visual detection of ochratoxin A (OTA). It is based on the etching of gold nanorods (AuNRs) mediated by a G-quadruplex-hemin DNAzyme. A DNA sequence (AG4-OTA) was designed that comprises a hemin aptamer and an OTA aptamer. OTA binds to AG4-OTA to form an antiparallel G-quadruplex, which halts its digestion by exonuclease I (Exo I) from the 3'-end of AG4-OTA. Thus, the retained hemin aptamer can bind to hemin to form a G-quadruplex-hemin DNAzyme. This DNAzyme has peroxidase-like activity that catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ to produce its diimine derivative (TMB²⁺) in acidic solution. TMB²⁺ can etch the AuNRs by oxidizing Au(0) into Au(I). This results in the generation of rainbow-like colors and provides a multicolor platform for the visual detection of OTA. The assay is based on the use of a single isolated aptamer and possesses obvious advantages such as multi-color visual inspection, relatively high sensitivity and accuracy. It can be used to detect as little as 30 nM concentrations of OTA by visual observation and even 10 nM concentrations by spectrophotometry. The method was successfully applied to the determination of OTA in spiked beer where it gave recoveries of 101-108%, with a relative standard deviation (RSD, n = 5) of <5%. Graphical abstract Schematic of an exonuclease-assisted multicolor bioassay based on the G-quadruplex-hemin DNAzyme-mediated etching of gold nanorods (AuNRs). It enables visual detection of ochratoxin A (OTA) with a detection limit of 30 nM.

Aptamer-Patterned Hydrogel Films for Spatiotemporally Programmable Capture and Release of Multiple Proteins

Various hydrogels have been used for protein delivery in the treatment of human diseases. Nevertheless, it is always difficult to control the capture and release of multiple proteins in different regions and periods. This research successfully proves that multiple proteins can be captured and released from the aptamer-patterned hydrogel films with an adjustable release rate at a prospective time and in specific regions utilizing the complementary DNA strand of aptamers via photoclick chemistry and DNA hybridization. The hydrogel film is successfully applied to complex matrixes such as human serum and has excellent cytocompatibility. Thus, the aptamer-patterned hydrogel film will be a good candidate for controlled delivery of multiple proteins.