Selection of DNA aptamers against penicillin G using Capture-SELEX for the development of an impedimetric sensor

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.

A review on magnetic beads-based SELEX technologies: Applications from small to large target molecules

This review summarizes the stepwise strategy and key points for magnetic beads (MBs)-based aptamer selection which is suitable for isolating aptamers against small and large molecules via systematic evolution of ligands by exponential enrichment (SELEX). Particularities, if any, are discussed according to the target size. Examples targeting small molecules (<1000 Da) such as xenobiotics, toxins, pesticides, herbicides, illegal additives, hormones, and large targets such as proteins (biomarkers, pathogens) are discussed and presented in tabular formats. Of special interest are the latest advances in more efficient alternatives, which are based on novel instrumentation, materials or microelectronics, such as fluorescence MBs-SELEX or microfluidic chip system-assisted MBs-SELEX. Limitations and perspectives of MBs-SELEX are also reviewed. Taken together, this review aims to provide practical insights into MBs-SELEX technologies and their ability to screen multiple potential aptamers against targets from small to large molecules.

Aptamer Technologies in Neuroscience, Neuro-Diagnostics and Neuro-Medicine Development

Aptamers developed using in vitro Systematic Evolution of Ligands by Exponential Enrichment (SELEX) technology are single-stranded nucleic acids 10-100 nucleotides in length. Their targets, often with specificity and high affinity, range from ions and small molecules to proteins and other biological molecules as well as larger systems, including cells, tissues, and animals. Aptamers often rival conventional antibodies with improved performance, due to aptamers' unique biophysical and biochemical properties, including small size, synthetic accessibility, facile modification, low production cost, and low immunogenicity. Therefore, there is sustained interest in engineering and adapting aptamers for many applications, including diagnostics and therapeutics. Recently, aptamers have shown promise as early diagnostic biomarkers and in precision medicine for neurodegenerative and neurological diseases. Here, we critically review neuro-targeting aptamers and their potential applications in neuroscience research, neuro-diagnostics, and neuro-medicine. We also discuss challenges that must be overcome, including delivery across the blood-brain barrier, increased affinity, and improved in vivo stability and in vivo pharmacokinetic properties.

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.

A novel strategy for therapeutic drug monitoring: application of biosensors to quantify antimicrobials in biological matrices

Over the past few years, therapeutic drug monitoring (TDM) has gained practical significance in antimicrobial precision therapy. Yet two categories of mainstream TDM techniques (chromatographic analysis and immunoassays) that are widely adopted nowadays retain certain inherent limitations. The use of biosensors, an innovative strategy for rapid evaluation of antimicrobial concentrations in biological samples, enables the implementation of point-of-care testing (POCT) and continuous monitoring, which may circumvent the constraints of conventional TDM and provide strong technological support for individualized antimicrobial treatment. This comprehensive review summarizes the investigations that have harnessed biosensors to detect antimicrobial drugs in biological matrices, provides insights into the performance and characteristics of each sensing form, and explores the feasibility of translating them into clinical practice. Furthermore, the future trends and obstacles to achieving POCT and continuous monitoring are discussed. More efforts are necessary to address the four key 'appropriateness' challenges to deploy biosensors in clinical practice, paving the way for personalized antimicrobial stewardship.

Aptamer-modified metal organic frameworks for measurement of food contaminants: a review

The measurement of food contaminants faces a great challenge owing to the increasing demand for safe food, increasing consumption of fast food, and rapidly changing patterns of human consumption. As different types of contaminants in food products can pose different levels of threat to human health, it is desirable to develop specific and rapid methods for their identification and quantification. During the past few years, metal-organic framework (MOF)-based materials have been extensively explored in the development of food safety sensors. MOFs are porous crystalline materials with tunable composition, dynamic porosity, and facile surface functionalization. The construction of high-performance biosensors for a range of applications (e.g., food safety, environmental monitoring, and biochemical diagnostics) can thus be promoted through the synergistic combination of MOFs with aptamers. Accordingly, this review article delineates recent innovations achieved for the aptamer-functionalized MOFs toward the detection of food contaminants. First, we describe the basic concepts involved in the detection of food contaminants in terms of the advantages and disadvantages of the commonly used analytical methods (e.g., DNA-based methods (PCR/real-time PCR/multiplex PCR/digital PCR) and protein-based methods (enzyme-linked immunosorbent assay/immunochromatography assay/immunosensor/mass spectrometry). Afterward, the progress in aptamer-functionalized MOF biosensors is discussed with respect to the sensing mechanisms (e.g., the role of MOFs as signal probes and carriers for loading signal probes) along with their performance evaluation (e.g., in terms of sensitivity). We finally discuss challenges and opportunities associated with the development of aptamer-functionalized MOFs for the measurement of food contaminants.

Tools and techniques for the discovery of therapeutic aptamers: recent advances

INTRODUCTION

The pursuit of novel therapeutic agents for serious diseases such as cancer has been a global endeavor. Aptamers characteristic of high affinity, programmability, low immunogenicity, and rapid permeability hold great promise for the treatment of diseases. Yet obtaining the approval for therapeutic aptamers remains challenging. Consequently, researchers are increasingly devoted to exploring innovative strategies and technologies to advance the development of these therapeutic aptamers.

AREAS COVERED

The authors provide a comprehensive summary of the recent progress of the SELEX (Systematic Evolution of Ligands by EXponential enrichment) technique, and how the integration of modern tools has facilitated the identification of therapeutic aptamers. Additionally, the engineering of aptamers to enhance their functional attributes, such as inhibiting and targeting, is discussed, demonstrating the potential to broaden their scope of utility.

EXPERT OPINION

The grand potential of aptamers and the insufficient development of relevant drugs have spurred countless efforts for stimulating their discovery and application in the therapeutic field. While SELEX techniques have undergone significant developments with the aid of advanced analysis instruments and ingeniously updated aptameric engineering strategies, several challenges still impede their clinical translation. A key challenge lies in the insufficient understanding of binding conformation and susceptibility to degradation under physiological conditions. Despite the hurdles, our opinion is optimistic. With continued progress in overcoming these obstacles, the widespread utilization of aptamers for clinical therapy is envisioned to become a reality soon.

Aptamer Sensors for the Detection of Antibiotic Residues- A Mini-Review

Food security is a global issue, since it is closely related to human health. Antibiotics play a significant role in animal husbandry owing to their desirable broad-spectrum antibacterial activity. However, irrational use of antibiotics has caused serious environmental pollution and food safety problems; thus, the on-site detection of antibiotics is in high demand in environmental analysis and food safety assessment. Aptamer-based sensors are simple to use, accurate, inexpensive, selective, and are suitable for detecting antibiotics for environmental and food safety analysis. This review summarizes the recent advances in aptamer-based electrochemical, fluorescent, and colorimetric sensors for antibiotics detection. The review focuses on the detection principles of different aptamer sensors and recent achievements in developing electrochemical, fluorescent, and colorimetric aptamer sensors. The advantages and disadvantages of different sensors, current challenges, and future trends of aptamer-based sensors are also discussed.

Aptamer-Assisted Proximity Ligation Assay for Sensitive Detection of Infectious Bronchitis Coronavirus

Infectious bronchitis virus (IBV) is a coronavirus responsible for major health problems in the poultry industry. New virus strains continue to appear, causing large economic losses. To develop a rapid and accurate new quantitative assay for diagnosis of the virus without DNA extraction, we selected highly specific single-stranded DNA (ssDNA) aptamers with a high affinity to IBV, using the systematic evolution of ligands by exponential enrichment (SELEX) technology for aptamer screening, followed by high-throughput sequencing technology. Two of these aptamers, AptIBV5 and AptIBV2, were used to establish homogenous and solid-phase proximity ligation assays (PLAs). The developed assays were evaluated for their sensitivity and specificity using collected field samples and then compared to the newly developed sandwich enzyme-linked aptamer assay (ELAA) and reverse transcription-quantitative PCR (qRT-PCR), as the gold-standard method. The solid-phase PLA showed a lower limit of detection and a broader dynamic range than the two other assays. The developed technique may serve as an alternative assay for the diagnosis of IBV, with the potential to be extended to the detection of other important animal or human viruses. IMPORTANCE Infectious bronchitis virus (IBV) causes high morbidity and mortality and large economic losses in the poultry industry. The virus has the ability to genetically mutate into new IBV strains, causing devastating disease and outbreaks. To better monitor the emergence of this virus, the development of a rapid and highly sensitive diagnostic method should be implemented. For this, we generated aptamers with high affinity and specificity to the IBV in an ssDNA library. Using two high-affinity aptamers, we developed a sandwich ELAA and a very sensitive aptamer-based proximity ligation assay (PLA). The new assay showed high sensitivity and specificity and was used to detect IBV in farm samples. The PLA was compared to the newly developed sandwich ELAA and qRT-PCR, as the gold-standard technique.

Selection of spore-specific aptamers for Geobacillus stearothermophilus, a food spoilage bacterium

Due to their ability to form extremely heat resistant spores, anaerobic bacteria are responsible for frequent food spoilage. The development of rapid and specific methods for the detection and quantification of spore contamination is therefore of major interest. In this paper, we describe for the first time the selection of aptamers specific to spores of Geobacillus stearothermophilus (Gbs), which induce flat sour spoilage in vegetable cans. Eighteen Spore-SELEX cycles were performed including 4 counter-selections with 12 bacteria commonly found in cannery. To optimise candidate amplification, PCR in emulsion was performed, and high-throughput sequencing analysis was applied to follow candidate evolution. Sequencing of aptamers from cycle 18 revealed 43 overrepresented sequences whose copy number exceeds 0.15% of the total obtained sequences. Within this group, the A01 aptamer presented a much higher enrichment with a relative abundance of 17.71%. Affinity and specificity for Gbs spores of the 10 most abundant candidates at cycle 18 were confirmed by PCR assay based on aptamer-spore complex formation and filtration step. Obtaining these aptamers is the starting point for the future development of biosensors dedicated to the detection of Gbs spores.

Capture-SELEX: Selection Strategy, Aptamer Identification, and Biosensing Application

Small-molecule contaminants, such as antibiotics, pesticides, and plasticizers, have emerged as one of the substances most detrimental to human health and the environment. Therefore, it is crucial to develop low-cost, user-friendly, and portable biosensors capable of rapidly detecting these contaminants. Antibodies have traditionally been used as biorecognition elements. However, aptamers have recently been applied as biorecognition elements in aptamer-based biosensors, also known as aptasensors. The systematic evolution of ligands by exponential enrichment (SELEX) is an in vitro technique used to generate aptamers that bind their targets with high affinity and specificity. Over the past decade, a modified SELEX method known as Capture-SELEX has been widely used to generate DNA or RNA aptamers that bind small molecules. In this review, we summarize the recent strategies used for Capture-SELEX, describe the methods commonly used for detecting and characterizing small-molecule-aptamer interactions, and discuss the development of aptamer-based biosensors for various applications. We also discuss the challenges of the Capture-SELEX platform and biosensor development and the possibilities for their future application.

Advances in Aptamers-Based Applications in Breast Cancer: Drug Delivery, Therapeutics, and Diagnostics

Aptamers are synthetic single-stranded oligonucleotides (such as RNA and DNA) evolved in vitro using Systematic Evolution of Ligands through Exponential enrichment (SELEX) techniques. Aptamers are evolved to have high affinity and specificity to targets; hence, they have a great potential for use in therapeutics as delivery agents and/or in treatment strategies. Aptamers can be chemically synthesized and modified in a cost-effective manner and are easy to hybridize to a variety of nano-particles and other agents which has paved a way for targeted therapy and diagnostics applications such as in breast tumors. In this review, we systematically explain different aptamer adoption approaches to therapeutic or diagnostic uses when addressing breast tumors. We summarize the current therapeutic techniques to address breast tumors including aptamer-base approaches. We discuss the next aptamer-based therapeutic and diagnostic approaches targeting breast tumors. Finally, we provide a perspective on the future of aptamer-based sensors for breast therapeutics and diagnostics. In this section, the therapeutic applications of aptamers will be discussed for the targeting therapy of breast cancer.

Ultrasensitive immunosensing of Penicillin G in food samples using reduced graphene oxide (rGO) decorated electrode surface

The impact of uncontrolled antibiotic use in animals has subsequently led to emergence of antibiotic-resistant bacteria among humans due to consumption of animal by-products. Hence, to investigate antibiotic contamination in animal origin food products, we have developed a reduced graphene oxide (rGO) based immunosensor using fabricated electrode conjugated with anti-Penicillin antibody (rGO/Pen-Ab) for sensitive detection of Penicillin G. To execute this, Penicillin was first conjugated with Bovine Serum Albumin (BSA) which was confirmed via chromatographic, spectroscopic and electrophoretic-based techniques against both the in-house developed Penicillin conjugate (Pen-BSA) as well as the commercial Penicillin conjugate (Com-Pen-BSA). Further, we fabricated electrode based on one step synthesized rGO and immobilized with antibodies generated against Pen-BSA (Pen-Ab), and Com-Pen-BSA (Com-Pen-Ab), separately for detection of Penicillin. Each synthesis and conjugation step was confirmed by different spectroscopic methods. For efficient working of the electrode, various parameters were optimized using Voltammetry. The limit of detection for Penicillin G against Pen-Ab and Com-Pen-Ab was determined as 0.724 pM and 0.668 pM respectively and both displayed negligible cross reactivity against other β-lactam antibiotics (Cefalexin and Ampicillin). Furthermore, antibiotics were also detected in spiked milk, egg and meat samples and the electrode was evaluated for repeatability and storage stability. In conclusion, in-house developed Pen-Ab showed better sensitivity as compared to Com-Pen-Ab. The fabricated rGO/Pen-Ab biosensor shows future potential for rapid detection of penicillin and other β-lactam antibiotics for safe consumption of animal by-products in humans.

Future perspectives on aptamer for application in food authentication

Food fraudulence and food contamination are major concerns, particularly among consumers with specific dietary, cultural, lifestyle, and religious requirements. Current food authentication methods have several drawbacks and limitations, necessitating the development of a simpler, more sensitive, and rapid detection approach for food screening analysis, such as an aptamer-based biosensor system. Although the use of aptamer is growing in various fields, aptamer applications for food authentication are still lacking. In this review, we discuss the limitations of existing food authentication technologies and describe the applications of aptamer in food analyses. We also project several potential targets or marker molecules to be targeted in the SELEX process. Finally, this review highlights the drawbacks of current aptamer technologies and outlines the potential route of aptamer selection and applications for successful food authentication. This review provides an overview of the use of aptamer in food research and its potential application as a molecular reporter for rapid detection in food authentication process. Developing databases to store all biochemical profiles of food and applying machine learning algorithms against the biochemical profiles are urged to accelerate the identification of more reliable biomarker molecules as aptamer targets for food authentication.

Split aptamer acquisition mechanisms and current application in antibiotics detection: a short review

Antibiotic contamination is becoming a prominent global issue. Therefore, sensitive, specific and simple technology is desirable the demand for antibiotics detection. Biosensors based on split aptamer has gradually attracted extensive attention for antibiotic detection due to its higher sensitivity, lower cost, false positive/negative avoidance and flexibility in sensor design. Although many of the reported split aptamers are antibiotics aptamers, the acquisition and mechanism of splitting is still unknow. In this review, six reported split aptamers in antibiotics are outlined, including Enrofloxacin, Kanamycin, Tetracycline, Tobramycin, Neomycin, Streptomycin, which have contributed to promote interest, awareness and thoughts into this emerging research field. The study introduced the pros and cons of split aptamers, summarized the assembly principle of split aptamer and discussed the intermolecular binding of antibiotic-aptamer complexes. In addition, the recent application of split aptamers in antibiotic detection are introduced. Split aptamers have a promising future in the design and development of biosensors for antibiotic detection in food and other field. The development of the antibiotic split aptamer meets many challenges including mechanism discovery, stability improvement and new biosensor development. It is believed that split aptamer could be a powerful molecular probe and plays an important role in aptamer biosensor.

A Novel SELEX Based on Immobilizing Libraries Enables Screening of Saxitoxin Aptamers for BLI Aptasensor Applications

Saxitoxin (STX) is one of the potent marine biotoxins that has high rate of lethality. However, there are no effective treatments at present, and the existing detection methods need to be further explored because of ethical problems or technical limitations. In this work, oligonucleotide aptamers toward STX were screened based on immobilizing libraries on Immobilized Metal-Chelate (IMC), such as Ni-NTA Sepharose, and the IMC-SELEX was conducted by the G-quadruplex library and the random library, respectively. Aptamer 45e (from the G-quadruplex library) and aptamer 75a were obtained after optimization, and aptamer 45e turned out to have a higher affinity toward STX. Furthermore, it was found that the hydrogen bonding and the van der Waals forces (VDW) played major roles in the high efficiency and specificity between STX and 45e by means of molecular docking and dynamics simulation. Based on this, aptamer 45e-1 with the Kd value of 19 nM was obtained by further optimization, which was then used to construct a simple, label-free and real-time optical BLI aptasensor for the detection of STX. This aptasensor showed good reproducibility and stability. In summary, with the advantages of screening aptamers of high efficiency and specificity toward the targets, the proposed IMC-SELEX provides a promising screening strategy for discovering aptamers, which could be used as the potential molecular recognition elements in the fields of biomedicine, food safety and environmental monitoring.

Development of a new dual electrochemical immunosensor for a rapid and sensitive detection of enrofloxacin in meat samples

A novel dual electrochemical immunosensor was fabricated for the rapid and sensitive detection of enrofloxacin (EF) antibiotic in meat. Anti-quinolone antibody was immobilized onto screen-printed dual carbon electrodes via carbodiimide coupling. A new electrochemical probe was synthesized by conjugating difloxacin and aminoferrocene, whose oxidation was measured at + 0.2 V vs. Ag/AgCl by differential pulse voltammetry. The detection principle was based on the competitive binding of this conjugate and free EF on immobilized antibodies. The proposed immunosensor allowed detection of EF at concentrations ranging from 0.005 µg.mL^-1 to 0.01 µg.mL^-1 with a detection limit of 0.003 µg.mL^-1. The immunosensor was stable for at least 1 month at 4 °C and displayed a good specificity for other fluoroquinolones. The new dual electrode design offered an improved accuracy as one electrode was used as negative control. The efficiency of the sensor and the adequacy of the extraction process were finally validated by detecting EF in different meat samples.

Selection of Aptamer for N-Methyl Mesoporphyrin IX to Develop Porphyrin Metalation DNAzyme

Mesoporphyrin IX (MPIX) contains a planar macrocycle center that can interact with various divalent metal ions through the exposed binding sites, leading to the metalation of MPIX. The DNA aptamers for porphyrin molecules usually display different catalytic functions (termed deoxyribozymes or DNAzymes), which can accelerate such chemical reactions. Inspired by this, an affinity chromatography selection approach was designed for identifying a porphyrin metalation DNAzyme. In our experiment, N-methyl mesoporphyrin IX (NMM), an analog of MPIX, is used as the target molecule, owing to its stable and high fluorescence enhancement after combining with specific oligonucleotides. Our results showed that the selected aptamer Nm1 is capable of binding to NMM with a low micromolar dissociation constant (0.75 ± 0.08 μM) and displays a catalytic activity for MPIX metalation with 3.3-fold rate enhancement. The protocol for isolation of such a porphyrin metalation DNAzyme is described in detail here.

Hybrid Antibody-Aptamer Assay for Detection of Tetrodotoxin in Pufferfish

The marine toxin tetrodotoxin (TTX) poses a great risk to public health safety due to its severe paralytic effects after ingestion. Seafood poisoning caused by the consumption of contaminated marine species like pufferfish due to its expansion to nonendemic areas has increased the need for fast and reliable detection of the toxin to effectively implement prevention strategies. Liquid chromatography-mass spectrometry is considered the most accurate method, although competitive immunoassays have also been reported. In this work, we sought to develop an aptamer-based assay for the rapid, sensitive, and cost-effective detection of TTX in pufferfish. Using capture-SELEX combined with next-generation sequencing, aptamers were identified, and their binding properties were evaluated. Finally, a highly sensitive and user-friendly hybrid antibody–aptamer sandwich assay was developed with superior performance compared to several assays reported in the literature and commercial immunoassay kits. The assay was successfully applied to the quantification of TTX in pufferfish extracts, and the results obtained correlated very well with a competitive magnetic bead-based immunoassay performed in parallel for comparison. This is one of the very few works reported in the literature of such hybrid assays for small-molecule analytes whose compatibility with field samples is also demonstrated.

Development of gold nanoparticles-aptamer nanocomposite for multiplexed analysis of antibiotics and design of molecular logic gates

The widespread use of antibiotics caused severe problems of antibiotic residues in foodstuffs and water, posing a serious threat to public health and thus urging the development of sensitive, selective, and rapid detection methods for antibiotics. In this study, a fluorescence resonance energy transfer (FRET)-based system is developed for the multiplexed analysis of chloramphenicol (CAP) and streptomycin (Strep) with detection limits of 2.51 and 8.69μg l^-1, respectively. The FRET-based system consists of Cy3-tagged anti-CAP aptamer-conjugated gold nanoparticles (AuNPs) (referred to as AuNPs-AptCAP) and Cy5-tagged anti-Strep aptamer-conjugated AuNPs (referred to as AuNPs-AptStrep). In addition, AuNPs-AptCAP and AuNPs-AptStrep have been demonstrated to serve as signal transducers for implementing a series of logic operations such as YES, NOT, INH, OR, (2-4)-Decoder and even more complicated multi-level logic gates (OR-INH). Based on the outputs of logic operations, it could be figured out whether targeted analytes were present or not, thus enabling multiplex sensing and evaluation of pollution status. This proof of concept study might provide a new route for the enhanced sensing performance to distinguish different pollution status as well as the design of molecular mimics of logic elements to demonstrate better applicability.

Oligonucleotide aptamers: Recent advances in their screening, molecular conformation and therapeutic applications

Aptamers are single stranded oligonucleotides with specific recognition and binding ability to target molecules, which can be obtained by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Aptamers have the advantages of low molecular weight, low immunogenicity, easy modification and high stability. They play promising role in promoting food safety, monitoring the environment and basic research, especially in clinical diagnosis and therapeutic drugs. To date, great achievements regarding the selection, modifications and application of aptamers have been made. However, since it is still a challenge to obtain aptamers with high affinity in a more effective way, few aptamer-based products have already successfully entered into clinical use. This review aims to provide a thorough overview of the latest advances in this rapidly developing field, focusing on aptamer screening methods for different targets, the structure of the interaction between aptamers and target substances, and the challenges and potential of current therapeutic aptamers.

Systematic Evolution of Ligands by Exponential Enrichment Technologies and Aptamer-Based Applications: Recent Progress and Challenges in Precision Medicine of Infectious Diseases

Infectious diseases are considered as a pressing challenge to global public health. Accurate and rapid diagnostics tools for early recognition of the pathogen, as well as individualized precision therapy are essential for controlling the spread of infectious diseases. Aptamers, which were screened by systematic evolution of ligands by exponential enrichment (SELEX), can bind to targets with high affinity and specificity so that have exciting potential in both diagnosis and treatment of infectious diseases. In this review, we provide a comprehensive overview of the latest development of SELEX technology and focus on the applications of aptamer-based technologies in infectious diseases, such as targeted drug-delivery, treatments and biosensors for diagnosing. The challenges and the future development in this field of clinical application will also be discussed.

Advances and Challenges in Small-Molecule DNA Aptamer Isolation, Characterization, and Sensor Development

Aptamers are short oligonucleotides isolated in vitro from randomized libraries that can bind to specific molecules with high affinity, and offer a number of advantages relative to antibodies as biorecognition elements in biosensors. However, it remains difficult and labor-intensive to develop aptamer-based sensors for small-molecule detection. Here, we review the challenges and advances in the isolation and characterization of small-molecule-binding DNA aptamers and their use in sensors. First, we discuss in vitro methodologies for the isolation of aptamers, and provide guidance on selecting the appropriate strategy for generating aptamers with optimal binding properties for a given application. We next examine techniques for characterizing aptamer-target binding and structure. Afterwards, we discuss various small-molecule sensing platforms based on original or engineered aptamers, and their detection applications. Finally, we conclude with a general workflow to develop aptamer-based small-molecule sensors for real-world applications.

Penicillin biosensor based on rhombus-shaped porous carbon/hematoxylin/penicillinase

In this experiment, we designed an electrochemical sensor using penicillinase (Pen X)-rhombus porous carbon (RPC) as the detection element and hematoxylin as the indicator to detect low concentrations of penicillin sodium (Pen G). A differential pulse voltammetry (DPV) method was used to detect Pen G in the concentration range of 10^-8 -10^-5 mg·mL^-1 under optimal experimental conditions. The results showed that the peak current value and the logarithm of Pen G concentration showed a good linear relationship (R² = 0.9915), and the LOD was 2.68 × 10^-7 mg·mL^-1 (S/N = 3). The actual milk samples were detected by the addition method and compared with the high-performance liquid phase method; no significant difference was found in the detection results. The working electrode prepared by cross-linking method not only extends the service life of the sensor, but also improves the sensitivity and reproducibility of the sensor. It can also be used to detect the Pen G residue in the actual milk samples repeatedly. PRACTICAL APPLICATION: In this study, an electrochemical sensor for the rapid detection of penicillin sodium in milk was prepared, which has good sensitivity and fast detection speed.

The Role of Aryldiazonium Chemistry in Designing Electrochemical Aptasensors for the Detection of Food Contaminants

Food safety monitoring assays based on synthetic recognition structures such as aptamers are receiving considerable attention due to their remarkable advantages in terms of their ability to bind to a wide range of target analytes, strong binding affinity, facile manufacturing, and cost-effectiveness. Although aptasensors for food monitoring are still in the development stage, the use of an electrochemical detection route, combined with the wide range of materials available as transducers and the proper immobilization strategy of the aptamer at the transducer surface, can lead to powerful analytical tools. In such a context, employing aryldiazonium salts for the surface derivatization of transducer electrodes serves as a simple, versatile and robust strategy to fine-tune the interface properties and to facilitate the convenient anchoring and stability of the aptamer. By summarizing the most important results disclosed in the last years, this article provides a comprehensive review that emphasizes the contribution of aryldiazonium chemistry in developing electrochemical aptasensors for food safety monitoring.

DNA aptamer selection and detection of marine biotoxin 20 Methyl Spirolide G

This study reports the selection of DNA aptamer for the detection of 20 Methyl Spirolide G (SPXG). After 10 rounds of selection, theenriched pool of aptamers specific to SPXGwas cloned, sequenced and clustered into seven families based onsimilarity. Three sequences SPX1, SPX2 and SPX7, each belonging to different clades were further evaluated for their binding affinity. Surface plasmonresonancestudies determined the highest affinity K_Dof 0.0345x10^-8 M for aptamer SPX7. A label-free microscale thermophoresis-based aptasensing using SPX7 with highest affinity, indicated a linear detection range from 1.9 to 125000 pg/mL (LOD = 0.39 pg/mL; LOQ = 1.17 pg/mL). Spiking studies in simulated contaminated samples of mussel and scallop indicated recoveries in the range of 86 to 108%. Results of this study indicate the successful development of an aptamer for detection of SPXG at picogram levels. It also opens up avenues to develop other sensing platforms for detection of SPXG using the reported aptamer.

Contribution of Nanomaterials to the Development of Electrochemical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The detection of antimicrobial residues in food products of animal origin is of utmost importance. Indeed antimicrobial residues could be present in animal derived food products because of animal treatments for curative purposes or from illegal use. The usual screening methods to detect antimicrobial residues in food are microbiological, immunological or physico-chemical methods. The development of biosensors to propose sensitive, cheap and quick alternatives to classical methods is constantly increasing. Aptasensors are one of the major trends proposed in the literature, in parallel with the development of immunosensors based on antibodies. The characteristics of electrochemical sensors (i.e., low cost, miniaturization, and portable instrumentation) make them very good candidates to develop screening methods for antimicrobial residues in food products. This review will focus on the recent advances in the development of electrochemical aptasensors for the detection of antimicrobial residues in food products. The contribution of nanomaterials to improve the performance characteristics of electrochemical aptasensors (e.g., Sensitivity, easiness, stability) in the last ten years, as well as signal amplification techniques will be highlighted.

Capture-SELEX for aptamer selection: A short review

The emerging aptamer, developed through the systematic evolution of ligands by exponential enrichment (SELEX) process, has revolutionized and facilitated the discoveries in basic research. Among all SELEX technology, Capture-SELEX is a variant of the in vitro selection process, which is suitable for isolating aptamers against small molecules. Capture-SELEX library was developed to enable the immobilization of the oligonucleotides instead of the target molecules during the aptamer selection process. The review provides an update on the recent-advances in this new screening method with particular emphasis on key points of capture protocol and its applications. The limitations and the prospects of the Capture-SELEX are also discussed. We hope that present review will inspire more researchers to understand the selection problems from the perspective of Capture-SELEX. Moreover, it will open new pave to improve the efficiency and success of screening to meet the growing demand for aptasensor discovery in small molecules.

Ensuring seafood safe to spoon: a brief review of biosensors for marine biotoxin monitoring

With harmful algal blooms, marine food poisoning caused by marine biotoxins frequently occurs and is life-threatening if severe. However, the conventional detection methods of marine toxins have a few limitations: low sensitivity and high-cost. Therefore, it is necessary to establish a fast and sensitive on-site detection method for real seafood sample. Biosensors based on aptamers, antibodies, and cells have been applied in marine toxins monitoring. This review presents the classification and toxic effects of marine toxins, and recent biosensor for marine toxin detection. In addition, we have compared the superiority and limitation of these biosensors. Finally, challenges and opportunities of biosensors in food safety detection were discussed. Considering the excellent results achieved by the aptasensor in the field of detection, it seems ready to be put into practical applications.

Pinacho D. Personalized Medicine for Antibiotics: The Role of Nanobiosensors in Therapeutic Drug Monitoring

Due to the high bacterial resistance to antibiotics (AB), it has become necessary to adjust the dose aimed at personalized medicine by means of therapeutic drug monitoring (TDM). TDM is a fundamental tool for measuring the concentration of drugs that have a limited or highly toxic dose in different body fluids, such as blood, plasma, serum, and urine, among others. Using different techniques that allow for the pharmacokinetic (PK) and pharmacodynamic (PD) analysis of the drug, TDM can reduce the risks inherent in treatment. Among these techniques, nanotechnology focused on biosensors, which are relevant due to their versatility, sensitivity, specificity, and low cost. They provide results in real time, using an element for biological recognition coupled to a signal transducer. This review describes recent advances in the quantification of AB using biosensors with a focus on TDM as a fundamental aspect of personalized medicine.

Magnetic mesoporous carbon material based electrochemical sensor for rapid detection of penicillin sodium in milk

In recent years, to increase growth rate and prevent infectious diseases, an excessive use of antibiotics in livestock breeding processes has resulted in the presence of antibiotic residues in animal foods. In this experiment, a new kind of electrochemical sensor is prepared based on magnetic mesoporous hollow carbon microspheres (MHM) as a penicillinase (Pen X) adsorption carrier to rapidly detect penicillin sodium (Pen G), named Pen X/MHM/MGCE. The MHM-adsorbed penicillinase can be separated from the solution by magnetic attraction and fixed on a magnetic glassy carbon electrode by physical adsorption, which is easy to operate and avoids the interference of a crosslinking agent at the active site of the enzyme. A differential pulse voltammetry (DPV) method is used to immerse the working electrode in test samples containing different concentrations of penicillin sodium solution with 0.5 mg/mL oxidized hematoxylin. According to the quantitative relationship between the current value and the concentration of penicillin sodium, the concentration of penicillin sodium in the tested samples can be determined. The detection range of the sensor is 10^-8 to 10^-2 mg/mL, the linear relationship is good (R² = 0.9983), and the detection limit (LOD) is 2.655 × 10^-7 mg/mL (S/N = 3). The detection of penicillin sodium in milk using a standard addition method shows good recovery. Furthermore, the proposed method has the advantages of a wide detection range, good enzyme immobilization capacity, good precision and stability, convenient cleaning, and recycling of solid materials. Thus, it can successfully achieve rapid detection in milk samples. PRACTICAL APPLICATION: The sensor provides a low detection limit and high recovery rate of electrode material; therefore, the sensor can realize the rapid and quantitative detection of penicillin sodium in milk.

The Growing Interest in Development of Innovative Optical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The presence of antimicrobial residues in food-producing animals can lead to harmful effects on the consumer (e.g., allergies, antimicrobial resistance, toxicological effects) and cause issues in food transformation (i.e., cheese, yogurts production). Therefore, to control antimicrobial residues in food products of animal origin, screening methods are of utmost importance. Microbiological and immunological methods (e.g., ELISA, dipsticks) are conventional screening methods. Biosensors are an innovative solution for the development of more performant screening methods. Among the different kinds of biosensing elements (e.g., antibodies, aptamers, molecularly imprinted polymers (MIP), enzymes), aptamers for targeting antimicrobial residues are in continuous development since 2000. Therefore, this review has highlighted recent advances in the development of aptasensors, which present multiple advantages over immunosensors. Most of the aptasensors described in the literature for the detection of antimicrobial residues in animal-derived food products are either optical or electrochemical sensors. In this review, I have focused on optical aptasensors and showed how nanotechnologies (nanomaterials, micro/nanofluidics, and signal amplification techniques) largely contribute to the improvement of their performance (sensitivity, specificity, miniaturization, portability). Finally, I have explored different techniques to develop multiplex screening methods. Multiplex screening methods are necessary for the wide spectrum detection of antimicrobials authorized for animal treatment (i.e., having maximum residue limits).

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.

Optical Biosensors for Therapeutic Drug Monitoring

Therapeutic drug monitoring (TDM) is a fundamental tool when administering drugs that have a limited dosage or high toxicity, which could endanger the lives of patients. To carry out this monitoring, one can use different biological fluids, including blood, plasma, serum, and urine, among others. The help of specialized methodologies for TDM will allow for the pharmacodynamic and pharmacokinetic analysis of drugs and help adjust the dose before or during their administration. Techniques that are more versatile and label free for the rapid quantification of drugs employ biosensors, devices that consist of one element for biological recognition coupled to a signal transducer. Among biosensors are those of the optical biosensor type, which have been used for the quantification of different molecules of clinical interest, such as antibiotics, anticonvulsants, anti-cancer drugs, and heart failure. This review presents an overview of TDM at the global level considering various aspects and clinical applications. In addition, we review the contributions of optical biosensors to TDM.