Specific detection of avian influenza H5N2 whole virus particles on lateral flow strips using a pair of sandwich-type aptamers

Process, advances, and perspectives of graphene oxide-SELEX for the development of aptamer molecular probes: A comprehensive review

BACKGROUND

Aptamers are screened via the systematic evolution of ligands by exponential enrichment (SELEX) and are widely used in molecular diagnostics and targeted therapies. The development of efficient and convenient SELEX technology has facilitated rapid access to high-performance aptamers, thereby advancing the aptamer industry. Graphene oxide (GO) serves as an immobilization matrix for libraries in GO-SELEX, making it suitable for screening aptamers against diverse targets.

RESULTS

This review summarizes the detailed steps involved in GO-SELEX, including monitoring methods, various sublibrary acquisition methods, and practical applications from its inception to the present day. In addition, the potential of GO-SELEX in the development of broad-spectrum aptamers is explored, and its current limitations for future development are emphasized. This review effectively promotes the application of the GO-SELEX technique by providing valuable insights and assisting researchers interested in conducting related studies.

SIGNIFICANCE AND NOVELTY

To date, no review on the topic of GO-SELEX has been published, making it challenging for researchers to initiate studies in this area. We believe that this review will broaden the SELEX options available to researchers, ensuring that they can meet the growing demand for molecular probes in the scientific domain.

Current strategies for monitoring and controlling bacterial biofilm formation on medical surfaces

Biofilms, intricate microbial communities that attach to surfaces, especially medical devices, form an exopolysaccharide matrix, which enables bacteria to resist environmental pressures and conventional antimicrobial agents, leading to the emergence of multi-drug resistance. Biofilm-related infections associated with medical devices are a significant public health threat, compromising device performance. Therefore, developing effective methods for supervising and managing biofilm growth is imperative. This in-depth review presents a systematic overview of strategies for monitoring and controlling bacterial biofilms. We first outline the biofilm creation process and its regulatory mechanisms. The discussion then progresses to advancements in biosensors for biofilm detection and diverse treatment strategies. Lastly, this review examines the obstacles and new perspectives associated with this domain to facilitate the advancement of innovative monitoring and control solutions. These advancements are vital in combating the spread of multi drug-resistant bacteria and mitigating public health risks associated with infections from biofilm formation on medical instruments.

Viral aptamer screening and aptamer-based biosensors for virus detection: A review

Virus-induced infectious diseases have a detrimental effect on public health and exert significant influence on the global economy. Therefore, the rapid and accurate detection of viruses is crucial for effectively preventing and diagnosing infections. Aptamer-based detection technologies have attracted researchers' attention as promising solutions. Aptamers, small single-stranded DNA or RNA screened via systematic evolution of ligands by exponential enrichment (SELEX), possess a high affinity towards their target molecules. Numerous aptamers targeting viral marker proteins or virions have been developed and widely employed in aptamer-based biosensors (aptasensor) for virus detection. This review introduces SELEX schemes for screening aptamers and discusses distinctive SELEX strategies designed explicitly for viral targets. Furthermore, recent advances in aptamer-based biosensing methods for detecting common viruses using different virus-specific aptamers are summarized. Finally, limitations and prospects associated with developing of aptamer-based biosensors are discussed.

Structure of plasmonic multi spectral Apta sensor and analyzing of bulk and surface sensitivity

In this work, a multispectral aptasensor structure, including a sub-layer and two side walls, was presented. The cells are positioned at the down and top of the structure, with the down cells oriented perpendicular to the walls and the top cells aligned parallel to the walls. The validity of the findings was verified by the utilization of a numerical simulation technique known as 3D Finite Difference Time Domain (FDTD). The biosensor under consideration exhibits sensitivities of 1093.7 nm/RIU, 754 nm/RIU, and 707.43 nm/RIU in mode III, mode II, and mode I, respectively. In the majority of instances, the quantity of analyte available is insufficient to coat the surface of the sensor thoroughly. Consequently, in this study, the evaluation of surface sensitivity was undertaken alongside bulk sensitivity. The surface sensitivity of the suggested structure for mode II in the sensor layer, with thicknesses of 10, 20, 30, and 70 nm, is measured to be 25, 78, 344, and 717.636 nm/RIU, respectively. Our design incorporates a unique arrangement of sub-layer and side walls, with cells positioned to maximize interaction with the target analyte. This innovative configuration, combined with Ag for its superior plasmonic properties, enables the detection of E. coli O157 with remarkable sensitivity.

Emerging Biomimetic Sensor Technologies for the Detection of Pathogenic Bacteria: A Commercial Viability Study

Ensuring a rapid and accurate identification of harmful bacteria is crucial in various fields including environmental monitoring, food safety, and clinical diagnostics. Conventional detection methods often suffer from limitations such as long analysis time, complexity, and the need for qualified personnel. Therefore, a lot of research effort is devoted to developing technologies with the potential to revolutionize the detection of pathogenic bacteria by offering rapid, sensitive, and user-friendly platforms for point-of-care analysis. In this light, biosensors have gained significant commercial attention in recent years due to their simplicity, portability, and rapid analysis capabilities. The purpose of this review is to identify a trend by analyzing which biosensor technologies have become commercially successful in the field of bacteria detection. Moreover, we highlight the characteristics that a biosensor must possess to finally arrive in the market and therefore in the hands of the end-user, and we present critical examples of the market applications of various technologies. The aim is to investigate the reason why certain technologies have achieved commercial success and extrapolate these trends to the future economic viability of a new subfield in the world of biosensing: the development of biomimetic sensor platforms. Therefore, an overview of recent advances in the field of biomimetic bacteria detection will be presented, after which the challenges that need to be addressed in the coming years to improve market penetration will be critically evaluated. We will zoom into the current shortcomings of biomimetic sensors based on imprinting technology and aptamers and try to come up with a recommendation for further development based on the trends observed from previous commercial success stories in biosensing.

Surface-Activated Ti3C2Tx Adsorption of Acetylene Black Coupled with Polyaniline as a Signal Tag for the Detection of the ESAT-6 Antigen of Mycobacterium tuberculosis

Early secretory antigenic target-6 (ESAT-6) is regarded as the most immunogenic protein produced by Mycobacterium tuberculosis, whose detection is of great clinical significance for tuberculosis diagnosis. However, the detection of the ESAT-6 antigen has been hampered by the expensive cost and complex experimental procedures, resulting in low sensitivity. Herein, we developed a titanium carbide (Ti3C2Tx)-based aptasensor for ESAT-6 detection utilizing a triple-signal amplification strategy. First, acetylene black (AB) was immobilized on Ti3C2Tx through a cross-linking reaction to form the Ti3C2Tx-AB-PAn nanocomposite. Meanwhile, AB served as a conductive bridge, and Ti3C2Tx can synergistically promote the electron transfer of PAn. Ti3C2Tx-AB-PAn exhibited outstanding conductivity, high electrochemical signals, and abundant sites for the loading of ESAT-6 binding aptamer II (EBA II) to form a novel signal tag. Second, N-CNTs were adsorbed on NiMn layered double hydride (NiMn LDH) nanoflowers to obtain NiMn LDH/N-CNTs, exhibiting excellent conductivity and preeminent stability to be used as electrode modification materials. Third, the biotinylated EBA (EBA I) was immobilized onto a streptavidin-coated sensing interface, forming an amplification platform for further signal enhancement. More importantly, as a result of the synergistic effect of the triple-signal amplification platform, the aptasensor exhibited a wide detection linear range from 10 fg mL-1 to 100 ng mL-1 and a detection limit of 4.07 fg mL-1 for ESAT-6. We envision that our aptasensor provides a way for the detection of ESAT-6 to assist in the diagnosis of tuberculosis.

Recent progress of SELEX methods for screening nucleic acid aptamers

Nucleic acid aptamers are oligonucleotide sequences screened by an in vitro methodology called Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Known as "chemical antibodies", aptamers can achieve specific recognition towards the targets through conformational changes with high affinity, and possess multiple attractive features including, but not limited to, easy and inexpensive to prepare by chemical synthesis, relatively stable and low batch-to-batch variability, easy modification and signal amplification, and low immunogenicity. Now, aptamers are attracting researchers' attentions from more than 25 disciplines, and have showed great potential for application and economic benefits in disease diagnosis, environmental detection, food security, drug delivery and discovery. Although some aptamers exist naturally as the ligand-binding elements of riboswitches, SELEX is a recognized method for aptamers screening. After thirty-two years of development, a series of SELEX methods have been investigated and developed, as well as have shown unique advantages to improve sequence performances or to explore screening mechanisms. This review would mainly focus on the novel or improved SELEX methods that are available in the past five years. Firstly, we present a clear overview of the aptamer's history, features, and SELEX development. Then, we highlight the specific examples to emphasize the recent progress of SELEX methods in terms of carrier materials, technical improvements, real sample-improved screening, post-SELEX and other methods, as well as their respects of screening strategies, implementation features, screening parameters. Finally, we discuss the remaining challenges that have the potential to hinder the success of SELEX and aptamers in practical applications, and provide the suggestions and future directions for developing more convenient, efficient, and stable SELEX methods in the future.

Plasmonic aptasensor with antifouling dual-functional surface layer for lysozyme detection in food

Antifouling coatings are critically necessary for optical biosensors for various analytical application sectors, from medical diagnostics to foodborne pathogen detection. They help avoid non-specific protein/cell attachment on the active biosensor surface and catch the analytes directly in the complex media. Advances in antifouling plasmonic surfaces have been mainly focused on detecting clinical biomarkers in real biofluids, whereas developing antifouling coatings for direct analysis of analytes in complex media has been scarcely investigated for food quality control and safety. Herein, we propose a new low-fouling poly-l-lysine (PLL)-based surface layer for directly detecting an allergen protein, lysozyme, in the food matrix using surface plasmon resonance. The PLL-based polymer contains densely immobilized anionic oligopeptide side chains to create an electric charge-balanced layer able to repel the non-specific adsorption of undesired molecules on the biosensor surface. It also includes sparsely attached aptamer probes for capturing lysozyme directly in food sources with no pre-analytical sample treatment. We optimized the surface layer fabrication condition and tested the dual-functional surface to evaluate its ability to detect the target protein selectively. The developed analytical approach allowed for achieving a limit of detection of 0.04 μg mL-1 (2.95 nM) and a limit of quantification of 0.13 μg mL-1 (8.95 nM). Lysozyme was successfully quantified in milk samples using the plasmonic dual-functional aptasensor without sample pre-treatment or target isolation, illustrating the device's utility.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Sensitive and rapid detection of influenza A virus for disease surveillance using dual-probe electrochemical biosensor

Influenza A virus (IAV) can cause influenza, a highly infectious zoonotic respiratory disease, and early detection is essential to prevent and control its rapid spread in the population. Given the limitations of traditional detection methods in clinical laboratories, we report a large surface TPB-DVA COFs (TPB: 1,3,5-Tris(4-aminophenyl) benzene, DVA: 1,4-Benzenedicarboxaldehyd, COFs: Covalent organic frameworks) nanomaterial modified electrochemical DNA biosensor, which has dual-probe specific recognition and signal amplification. The biosensor enables quantitative detection of influenza A viruses' complementary DNA (cDNA) from 10 fM to 1 × 10³ nM (LOD = 5.42 fM) with good specificity and high selectivity. The reliability of the biosensor and portable device was verified by comparing the virus concentrations in animal tissues with those measured by digital droplet PCR (ddPCR) (P > 0.05). Moreover, the potential for influenza surveillance in this work was demonstrated by detecting the tissue samples from mice at different stages of infection. In summary, the good performance of this electrochemical DNA biosensor we proposed suggested it has the potential to be a rapid detection device for the influenza A virus, which could assist doctors or other professionals in obtaining rapid and accurate results for outbreak investigation and disease diagnosis.

Rational Design of Trident Aptamer Scaffold for Rapid and Accurate Monitoring of 25-Hydroxyvitamin D3 Metabolism in Living Cells

The level of 25-hydroxyvitamin D₃ [25(OH)VD3] in human blood is considered as the best indicator of vitamin D status, and its deficiency or excess can lead to various health problems. Current methods for monitoring 25(OH)VD3 metabolism in living cells have limitations in terms of sensitivity and specificity and are often expensive and time-consuming. To address these issues, an innovative trident scaffold-assisted aptasensor (TSA) system has been developed for the online quantitative monitoring of 25(OH)VD3 in complex biological environments. Through the computer-aided design, the TSA system includes an aptamer molecule recognition layer that is uniformly oriented, maximizing binding site availability, and enhancing sensitivity. The TSA system achieved the direct, highly sensitive, and selective detection of 25(OH)VD3 over a wide concentration range (17.4-12,800 nM), with a limit of detection of 17.4 nM. Moreover, we evaluated the efficacy of the system in monitoring the biotransformation of 25(OH)VD3 in human liver cancer cells (HepG2) and normal liver cells (L-02), demonstrating its potential as a platform for drug-drug interaction studies and candidate drug screening.

Discrimination of the H1N1 and H5N2 Variants of Influenza A Virus Using an Isomeric Sialic Acid-Conjugated Graphene Field-Effect Transistor

There has been a continuous effort to fabricate a fast, sensitive, and inexpensive system for influenza virus detection to meet the demand for effective screening in point-of-care testing. Herein, we report a sialic acid (SA)-conjugated graphene field-effect transistor (SA-GFET) sensor designed using α2,3-linked sialic acid (3'-SA) and α2,6-linked sialic acid (6'-SA) for the detection and discrimination of the hemagglutinin (HA) protein of the H5N2 and H1N1 viruses. 3'-SA and 6'-SA specific for H5 and H1 influenza were used in the SA-GFET to capture the HA protein of the influenza virus. The net charge of the captured viral sample led to a change in the electrical current of the SA-GFET platform, which could be correlated to the concentration of the viral sample. This SA-GFET platform exhibited a highly sensitive response in the range of 10¹-10⁶ pfu mL^-1, with a limit of detection (LOD) of 10¹ pfu mL^-1 in buffer solution and a response time of approximately 10 s. The selectivity of the SA-GFET platform for the H1N1 and H5N2 influenza viruses was verified by testing analogous respiratory viruses, i.e., influenza B and the spike protein of SARS-CoV-2 and MERS-CoV, on the SA-GFET. Overall, the results demonstrate that the developed dual-channel SA-GFET platform can potentially serve as a highly efficient and sensitive sensing platform for the rapid detection of infectious diseases.

Biosensors for healthcare: current and future perspectives

Biosensors are utilized in several different fields, including medicine, food, and the environment; in this review, we examine recent developments in biosensors for healthcare. These involve three distinct types of biosensor: biosensors for in vitro diagnosis with blood, saliva, or urine samples; continuous monitoring biosensors (CMBs); and wearable biosensors. Biosensors for in vitro diagnosis have seen a significant expansion recently, with newly reported clustered regularly interspaced short palindromic repeats (CRISPR)/Cas methodologies and improvements to many established integrated biosensor devices, including lateral flow assays (LFAs) and microfluidic/electrochemical paper-based analytical devices (μPADs/ePADs). We conclude with a discussion of two novel groups of biosensors that have drawn great attention recently, continuous monitoring and wearable biosensors, as well as with perspectives on the commercialization and future of biosensors.

Aptamer-based Emerging Tools for Viral Biomarker Detection: A Focus on SARS-CoV-2

Viral infections can cause fatal illnesses to humans as well as animals. Early detection of viruses is therefore crucial to provide effective treatment to patients. Recently, the Covid-19 pandemic has undoubtedly given an alarming call to develop rapid and sensitive detection platforms. The viral diagnostic tools need to be fast, affordable, and easy to operate with high sensitivity and specificity equivalent or superior to the currently used diagnostic methods. The present detection methods include direct detection of viral antigens or measuring the response of antibodies to viral infections. However, the sensitivity and quantification of the virus are still a significant challenge. Detection tools employing synthetic binding molecules like aptamers may provide several advantages over the conventional methods that use antibodies in the assay format. Aptamers are highly stable and tailorable molecules and are therefore ideal for detection and chemical sensing applications. This review article discusses various advances made in aptamer-based viral detection platforms, including electrochemical, optical, and colorimetric methods to detect viruses, specifically SARS-Cov-2. Considering the several advantages, aptamers could be game-changing in designing high-throughput biosensors for viruses and other biomedical applications in the future.

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.

Aptamer-based biosensors for virus protein detection

Virus threatens life health seriously. The accurate early diagnosis of the virus is vital for clinical control and treatment of virus infection. Aptamers are small single-stranded oligonucleotides (DNAs or RNAs). In this review, we summarized aptasensors for virus detection in recent years according to the classification of the viral target protein, and illustrated common detection mechanisms in the aptasensors (colorimetry, fluorescence assay, surface plasmon resonance (SPR), surface-enhanced raman spectroscopy (SERS), electrochemical detection, and field-effect transistor (FET)). Furthermore, aptamers against different target proteins of viruses were summarized. The relationships between the different biomarkers of the viruses and the detection methods, and their performances were revealed. In addition, the challenges and future directions of aptasensors were discussed. This review will provide valuable references for constructing on-site aptasensors for detecting viruses, especially the SARS-CoV-2.

Aptamers: A prospective tool for infectious diseases diagnosis

It is well known that people's health is seriously threatened by various pathogens (such as Mycobacterium tuberculosis, Treponema pallidum, Novel coronavirus, HIV, Mucor, etc.), which leads to heavy socioeconomic burdens. Therefore, early and accurate pathogen diagnosis is essential for timely and effective therapies. Up to now, diagnosing human contagious diseases at molecule and nano levels is remarkably difficult owing to insufficient valid probes when it comes to determining the biological markers of pathogens. Aptamers are a set of high‐specificity and high‐sensitivity plastic oligonucleotides screened in vitro via the selective expansion of ligands by exponential enrichment (SELEX). With the advent of aptamer‐based technologies, their merits have aroused mounting academic interest. In recent years, as new detection and treatment tools, nucleic acid aptamers have been extensively utilized in the field of biomedicine, such as pathogen detection, new drug development, clinical diagnosis, nanotechnology, etc. However, the traditional SELEX method is cumbersome and has a long screening cycle, and it takes several months to screen out aptamers with high specificity. With the persistent development of SELEX‐based aptamer screening technologies, the application scenarios of aptamers have become more and more extensive. The present research briefly reviews the research progress of nucleic acid aptamers in the field of biomedicine, especially in the diagnosis of contagious diseases.

A New Method for Abrin Detection Based on the Interaction between Target Molecules and Fluorescently Labeled Aptamers on Magnetic Microspheres

A quantitative structure-activity relationship (QSAR) model for the structure and affinity of abrin aptamers was established. A higher affinity abrin aptamer based on the established QSAR model was screened by site-directed mutagenesis. The fluorescence quenching effect between magnetic microspheres and fluorescent molecules was studied for the first time. A new method for abrin detection based on the interaction between target molecules and fluorescently labeled aptamers on magnetic microspheres was developed, with the detection limit of 5 ng mL^-1. This method can overcome the influence of complex environmental interferents in abrin detection and can meet the analysis requirements for simulated samples such as water, soil, and food.

An overview of advancement in aptasensors for influenza detection

INTRODUCTION

The platforms for early identification of infectious diseases such as influenza has seen a surge in recent years as delayed diagnosis of such infections can lead to dreadful effects causing large numbers of deaths. The time taken in detection of an infectious disease may vary from a few days to a few weeks depending upon the choice of the techniques. So, there is an urgent need for advanced methodologies for early diagnosis of the influenza.

AREAS COVERED

The emergence of "Aptasensor" synergistically with biosensors for diagnosis has opened a new era for sensitive, selective and early detection approaches. This review described various conventional as well as advanced methods based on artificial immunogenic nucleotide sequences complementing a part of the virus, i.e., aptamers based aptasensors for influenza diagnosis and the challenges faced in their commercialization.

EXPERT OPINION

Although numerous traditional methods are available for influenza detection but mostly associated with low sensitivity, specificity, high cost, trained personnel, and animals required for virus culture/ antibody raising as the major drawbacks. Aptamers can be manufactured invitro as 'chemical antibodies' at commercial level, no animal required. Following these advantages, aptamers can pave the way for an efficient diagnostic technique as compared to other existing conventional methods..

Recent developments of aptamer-based lateral flow assays for point-of-care (POC) diagnostics

In the field of lateral flow assay (LFA), the application of aptamer as a bioreceptor has been implemented to overcome the limitations of antibodies, such as tedious in vivo processes, short shelf-life, and functionalization issues. To address these limitations aptamer-based LFA (ALFA) is preferred to antibody-based LFA that produces higher sensitivity and specificity. In principle, aptamers have a strong affinity towards their targets like small, large, and non-immunogenic molecules because of their high affinity, sensitivity, low dissociation constant, cost-effectiveness, and flexible nature. Thus, ALFA can be considered an efficient biosensor model for its superior portability, rapid detection with quick turnaround time, and usability by a non-technical person at any location with simple visual output. This review concisely overviews ALFA, its principles, formats, aptamer selection process, and biomedical applications. In addition, the critical components to design, develop, test, and amplify signals to create ALFA are discussed in brief. In addition, the aspects of conceptualization of ALFA product transforming from bench-side laboratory design and fabrication to commercial market are addressed in detail.

One-step high-throughput detection of low-abundance biomarker BDNF using a biolayer interferometry-based 3D aptasensor

Although biosensors for signal monitoring have been extensively developed, their application in one-step high-throughput detection of low-abundance disease biomarkers remains challenging. This study presents a 3D aptasensor based on a biolayer interferometry (BLI) technique, followed by the sensitive and rapid detection of the specific biomarker brain-derived neurotrophic factor (BDNF) for early screening of glaucoma, an irreversible disease that causes blindness. The developed 3D aptasensor enabled one-step batch conversion of the low-abundance biomarker BDNF binding into optical interference signal, which was mainly attributed to the following factors: (1) A dimeric aptamer with extremely high targeting affinity was constructed as a biorecognition molecule, (2) highly sensitive 3D matrix sensors were integrated as signal transduction elements, and (3) the BLI Octet system with automated, high-throughput, and real-time online monitoring capabilities was used for reporting. The 3D aptasensor exhibited a broad detection window from 0.41 to 250 ng/mL BDNF, with a limit of detection of 0.2 ng/mL. Furthermore, detection of BDNF in glaucoma patient serum using the aptasensor showed good agreement with ELISA findings as well as the clinical diagnosis of the patient, demonstrating the feasibility of the system as a screening tool for glaucoma. This one-step high-throughput screening approach provides a valuable solution for the early diagnosis of glaucoma and may reduce the risk of blindness in visually impaired people.

Point-of-Care Diagnostics for Farm Animal Diseases: From Biosensors to Integrated Lab-on-Chip Devices

Zoonoses and animal diseases threaten human health and livestock biosecurity and productivity. Currently, laboratory confirmation of animal disease outbreaks requires centralized laboratories and trained personnel; it is expensive and time-consuming, and it often does not coincide with the onset or progress of diseases. Point-of-care (POC) diagnostics are rapid, simple, and cost-effective devices and tests, that can be directly applied on field for the detection of animal pathogens. The development of POC diagnostics for use in human medicine has displayed remarkable progress. Nevertheless, animal POC testing has not yet unfolded its full potential. POC devices and tests for animal diseases face many challenges, such as insufficient validation, simplicity, and portability. Emerging technologies and advanced materials are expected to overcome some of these challenges and could popularize animal POC testing. This review aims to: (i) present the main concepts and formats of POC devices and tests, such as lateral flow assays and lab-on-chip devices; (ii) summarize the mode of operation and recent advances in biosensor and POC devices for the detection of farm animal diseases; (iii) present some of the regulatory aspects of POC commercialization in the EU, USA, and Japan; and (iv) summarize the challenges and future perspectives of animal POC testing.

Applications of Surface Plasmon Resonance and Biolayer Interferometry for Virus–Ligand Binding

Surface plasmon resonance and biolayer interferometry are two common real-time and label-free assays that quantify binding events by providing kinetic parameters. There is increased interest in using these techniques to characterize whole virus-ligand interactions, as the methods allow for more accurate characterization than that of a viral subunit-ligand interaction. This review aims to summarize and evaluate the uses of these technologies specifically in virus–ligand and virus-like particle–ligand binding cases to guide the field towards studies that apply these robust methods for whole virus-based studies.

A Universal DNA Aptamer that Recognizes Spike Proteins of Diverse SARS‐CoV‐2 Variants of Concern

We report on a unique DNA aptamer, denoted MSA52, that displays universally high affinity for the spike proteins of wildtype SARS‐CoV‐2 as well as the Alpha, Beta, Gamma, Epsilon, Kappa, Delta and Omicron variants. Using an aptamer pool produced from round 13 of selection against the S1 domain of the wildtype spike protein, we carried out one‐round SELEX experiments using five different trimeric spike proteins from variants, followed by high‐throughput sequencing and sequence alignment analysis of aptamers that formed complexes with all proteins. A previously unidentified aptamer, MSA52, showed K_d values ranging from 2 to 10 nM for all variant spike proteins, and also bound similarly to variants not present in the reselection experiments. This aptamer also recognized pseudotyped lentiviruses (PL) expressing eight different spike proteins of SARS‐CoV‐2 with K_d values between 20 and 50 pM, and was integrated into a simple colorimetric assay for detection of multiple PL variants. This discovery provides evidence that aptamers can be generated with high affinity to multiple variants of a single protein, including emerging variants, making it well‐suited for molecular recognition of rapidly evolving targets such as those found in SARS‐CoV‐2.

A new cognate aptamer pair-based sandwich-type electrochemical biosensor for sensitive detection of Staphylococcus aureus

A pair of aptamers for Staphylococcus aureus (S. aureus) is immensely needed for developing sandwich-type signal-on electrochemical aptasensors. In this study, we have successfully developed a cognate pair of aptamers that bind to S. aureus simultaneously, among many aptamer candidates screened out after a total of ten rounds of bacterial cell-based systemic evolution of ligands by exponential enrichment (SELEX). The obtained aptamer candidates have been estimated by using flow cytometry and confocal microscope, to evaluate their binding affinity and specificity to the target cells. The screening for sandwich-type binding of cognate pair of aptamers with S. aureus was conducted by enzyme-based colorimetric assay and confirmed by circular dichroism (CD), two-color fluorescence imaging analysis, additionally. The cognate pair of two aptamers, named SA37 and SA81, showed very good affinity and specificity to S. aureus with their dissociation constants (Kd) of 16.5 ± 3.4 nM and 14.47 ± 8.18 nM, respectively. These newly discovered cognate pair of aptamers have been very successfully implemented to develop a sandwich-type signal-on electrochemical biosensor with the limit of detection (LOD) of 39 CFUs and 414 CFUs in buffer and spiked tap water samples, respectively. This study showed that this cognate pair of aptamers-based detection of S. aureus enables simple, rapid, and robust biosensors for food safety management.

GlycoGrip: Cell Surface-Inspired Universal Sensor for Betacoronaviruses

Inspired by the role of cell-surface glycoproteins as coreceptors for pathogens, we report the development of GlycoGrip: a glycopolymer-based lateral flow assay for detecting SARS-CoV-2 and its variants. GlycoGrip utilizes glycopolymers for primary capture and antispike antibodies labeled with gold nanoparticles for signal-generating detection. A lock-step integration between experiment and computation has enabled efficient optimization of GlycoGrip test strips which can selectively, sensitively, and rapidly detect SARS-CoV-2 and its variants in biofluids. Employing the power of the glycocalyx in a diagnostic assay has distinct advantages over conventional immunoassays as glycopolymers can bind to antigens in a multivalent capacity and are highly adaptable for mutated strains. As new variants of SARS-CoV-2 are identified, GlycoGrip will serve as a highly reconfigurable biosensor for their detection. Additionally, via extensive ensemble-based docking simulations which incorporate protein and glycan motion, we have elucidated important clues as to how heparan sulfate and other glycocalyx components may bind the spike glycoprotein during SARS-CoV-2 host-cell infection. GlycoGrip is a promising and generalizable alternative to costly, labor-intensive RT-PCR, and we envision it will be broadly useful, including for rural or low-income populations that are historically undertested and under-reported in infection statistics.

Aptamer-Based Lateral Flow Assays: Current Trends in Clinical Diagnostic Rapid Tests

The lateral flow assay (LFA) is an extensively used paper-based platform for the rapid and on-site detection of different analytes. The method is user-friendly with no need for sophisticated operation and only includes adding sample. Generally, antibodies are employed as the biorecognition elements in the LFA. However, antibodies possess several disadvantages including poor stability, high batch-to-batch variation, long development time, high price and need for ethical approval and cold chain. Because of these limitations, aptamers screened by an in vitro process can be a good alternative to antibodies as biorecognition molecules in the LFA. In recent years, aptamer-based LFAs have been investigated for the detection of different analytes in point-of-care diagnostics. In this review, we summarize the applications of aptamer technology in LFAs in clinical diagnostic rapid tests for the detection of biomarkers, microbial analytes, hormones and antibiotics. Performance, advantages and drawbacks of the developed assays are also discussed.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Advanced Point-of-Care Testing Technologies for Human Acute Respiratory Virus Detection

The ever-growing global threats to human life caused by the human acute respiratory virus (RV) infections have cost billions of lives, created a significant economic burden, and shaped society for centuries. The timely response to emerging RVs could save human lives and reduce the medical care burden. The development of RV detection technologies is essential for potentially preventing RV pandemic and epidemics. However, commonly used detection technologies lack sensitivity, specificity, and speed, thus often failing to provide the rapid turnaround times. To address this problem, new technologies are devised to address the performance inadequacies of the traditional methods. These emerging technologies offer improvements in convenience, speed, flexibility, and portability of point-of-care test (POCT). Herein, recent developments in POCT are comprehensively reviewed for eight typical acute respiratory viruses. This review discusses the challenges and opportunities of various recognition and detection strategies and discusses these according to their detection principles, including nucleic acid amplification, optical POCT, electrochemistry, lateral flow assays, microfluidics, enzyme-linked immunosorbent assays, and microarrays. The importance of limits of detection, throughput, portability, and specificity when testing clinical samples in resource-limited settings is emphasized. Finally, the evaluation of commercial POCT kits for both essential RV diagnosis and clinical-oriented practices is included.

Lateral Flow Strip Assay for Detection of Mycoplasma hyorhinis Based on a Pair of Sandwich-Type Aptamers

Mycoplasma hyorhinis is a normal flora in swine respiratory tract and also often found in multiple human tumor tissues, which is considered to be highly correlated with human tumors. Due to the detection of Mycoplasma hyorhinis mainly relies on PCR-based assay at present, thus it is critical for developing a novel assay for rapid detection and providing support diagnosis evidence. In our work, we screened and characterized a high affinity aptamer zyb1 that can recognize Mycoplasma hyorhinis based on infectious cell-SELEX. On this basis, we developed a lateral flow strip assay by using zyb1 and another aptamer AP15-1 to form a sandwich-type aptasensor. Using this new lateral flow strip assay biosensor, Mycoplasma hyorhinis could be detected within the detectable limit as low as 1 × 10³ CCU/mL. Therefore, our study successfully developed a convenient and effective lateral flow strip for Mycoplasma hyorhinis detection and demonstrated the potential of utilizing aptamer for the development of point-of-care testing products for mycoplasma detection.

Aptasensors for the detection of infectious pathogens: design strategies and point-of-care testing

The epidemic of infectious diseases caused by contagious pathogens is a life-threatening hazard to the entire human population worldwide. A timely and accurate diagnosis is the critical link in the fight against infectious diseases. Aptamer-based biosensors, the so-called aptasensors, employ nucleic acid aptamers as bio-receptors for the recognition of target pathogens of interest. This review focuses on the design strategies as well as state-of-the-art technologies of aptasensor-based diagnostics for infectious pathogens (mainly bacteria and viruses), covering the utilization of three major signal transducers, the employment of aptamers as recognition moieties, the construction of versatile biosensing platforms (mostly micro and nanomaterial-based), innovated reporting mechanisms, and signal enhancement approaches. Advanced point-of-care testing (POCT) for infectious disease diagnostics are also discussed highlighting some representative ready-to-use devices to address the urgent needs of currently prevalent coronavirus disease 2019 (COVID-19). Pressing issues in aptamer-based technology and some future perspectives of aptasensors are provided for the implementation of aptasensor-based diagnostics into practical application.

Lateral flow assays (LFA) as an alternative medical diagnosis method for detection of virus species: The intertwine of nanotechnology with sensing strategies

Viruses are responsible for multiple infections in humans that impose huge health burdens on individuals and populations worldwide. Therefore, numerous diagnostic methods and strategies have been developed for prevention, management, and decreasing the burden of viral diseases, each having its advantages and limitations. Viral infections are commonly detected using serological and nucleic acid-based methods. However, these conventional and clinical approaches have some limitations that can be resolved by implementing other detector devices. Therefore, the search for sensitive, selective, portable, and costless approaches as efficient alternative clinical methods for point of care testing (POCT) analysis has gained much attention in recent years. POCT is one of the ultimate goals in virus detection, and thus, the tests need to be rapid, specific, sensitive, accessible, and user-friendly. In this review, after a brief overview of viruses and their characteristics, the conventional viral detection methods, the clinical approaches, and their advantages and shortcomings are firstly explained. Then, LFA systems working principles, benefits, classification are discussed. Furthermore, the studies regarding designing and employing LFAs in diagnosing different types of viruses, especially SARS-CoV-2 as a main concern worldwide and innovations in the LFAs' approaches and designs, are comprehensively discussed here. Furthermore, several strategies addressed in some studies for overcoming LFA limitations like low sensitivity are reviewed. Numerous techniques are adopted to increase sensitivity and perform quantitative detection. Employing several visualization methods, using different labeling reporters, integrating LFAs with other detection methods to benefit from both LFA and the integrated detection device advantages, and designing unique membranes to increase reagent reactivity, are some of the approaches that are highlighted.

Aptamer-based diagnostic and therapeutic approaches in animals: Current potential and challenges

Fast and precise diagnosis of infectious and non-infectious animal diseases and their targeted treatments are of utmost importance for their clinical management. The existing biochemical, serological and molecular methods of disease diagnosis need improvement in their specificity, sensitivity and cost and, are generally not amenable for being used as points-of-care (POC) device. Further, with dramatic changes in environment and farm management practices, one should also arm ourselves and prepare for emerging and re-emerging animal diseases such as cancer, prion diseases, COVID-19, influenza etc. Aptamer – oligonucleotide or short peptides that can specifically bind to target molecules – have increasingly become popular in developing biosensors for sensitive detection of analytes, pathogens (bacteria, virus, fungus, prions), drug residues, toxins and, cancerous cells. They have also been proven successful in the cellular delivery of drugs and targeted therapy of infectious diseases and physiological disorders. However, the in vivo application of aptamer-mediated biosensing and therapy in animals has been limited. This paper reviews the existing reports on the application of aptamer-based biosensors and targeted therapy in animals. It also dissects the various modifications to aptamers that were found to be successful in in vivo application of the aptamers in diagnostics and therapeutics. Finally, it also highlights major challenges and future directions in the application of aptamers in the field of veterinary medicine.

Oligonucleotide aptamers for pathogen detection and infectious disease control

During an epidemic or pandemic, the primary task is to rapidly develop precise diagnostic approaches and effective therapeutics. Oligonucleotide aptamer-based pathogen detection assays and control therapeutics are promising, as aptamers that specifically recognize and block pathogens can be quickly developed and produced through simple chemical synthesis. This work reviews common aptamer-based diagnostic techniques for communicable diseases and summarizes currently available aptamers that target various pathogens, including the SARS-CoV-2 virus. Moreover, this review discusses how oligonucleotide aptamers might be leveraged to control pathogen propagation and improve host immune system responses. This review offers a comprehensive data source to the further develop aptamer-based diagnostics and therapeutics specific for infectious diseases.

Aptamer-based lateral flow assay on-site biosensors

The lateral flow assay (LFA) is a widely used paper-based on-site biosensor that can detect target analytes and obtain test results in several minutes. Generally, antibodies are utilized as the biorecognition molecules in the LFA. However, antibodies selected using an in vivo process not only may risk killing the animal hosts and causing errors between different batches but also their range is restricted by the refrigerated conditions used to store them. To avoid these limitations, aptamers screened by an in vitro process have been studied as biorecognition molecules in LFAs. Based on the sandwich or competitive format, the aptamer-based LFA can accomplish on-site detection of target analytes. Since aptamers have a distinctive ability to undergo conformational changes, the adsorption-desorption format has also been exploited to detect target analytes in aptamer-based LFAs. This paper reviews developments in aptamer-based LFAs in the last three years for the detection of target analytes. Three formats of aptamer-based LFAs, i.e., sandwich, competitive, and adsorption-desorption, are described in detail. Based on these formats, signal amplification strategies and multiplexed detection are discussed in order to provide an overview of aptamer-based LFAs for on-site detection of target analytes. In addition, the potential commercialization and future perspectives of aptamer-based LFAs for rapid detection of SARS-CoV-2 are given to support the COVID-19 pandemic.

Diverse high-affinity DNA aptamers for wild-type and B.1.1.7 SARS-CoV-2 spike proteins from a pre-structured DNA library

We performed in vitro selection experiments to identify DNA aptamers for the S1 subunit of the SARS-CoV-2 spike protein (S1 protein). Using a pool of pre-structured random DNA sequences, we obtained over 100 candidate aptamers after 13 cycles of enrichment under progressively more stringent selection pressure. The top 10 sequences all exhibited strong binding to the S1 protein. Two aptamers, named MSA1 (K_d = 1.8 nM) and MSA5 (K_d = 2.7 nM), were assessed for binding to the heat-treated S1 protein, untreated S1 protein spiked into 50% human saliva and the trimeric spike protein of both the wildtype and the B.1.1.7 variant, demonstrating comparable affinities in all cases. MSA1 and MSA5 also recognized the pseudotyped lentivirus of SARS-CoV-2 with respective K_d values of 22.7 pM and 11.8 pM. Secondary structure prediction and sequence truncation experiments revealed that both MSA1 and MSA5 adopted a hairpin structure, which was the motif pre-designed into the original library. A colorimetric sandwich assay was developed using MSA1 as both the recognition element and detection element, which was capable of detecting the pseudotyped lentivirus in 50% saliva with a limit of detection of 400 fM, confirming the potential of these aptamers as diagnostic tools for COVID-19 detection.

Role of plasmonics in detection of deadliest viruses: a review

Viruses have threatened animal and human lives since a long time ago all over the world. Some of these tiny particles have caused disastrous pandemics that killed a large number of people with subsequent economic downturns. In addition, the quarantine situation itself encounters the challenges like the deficiency in the online educational system, psychiatric problems and poor international relations. Although viruses have a rather simple protein structure, they have structural heterogeneity with a high tendency to mutation that impedes their study. On top of the breadth of such worldwide worrying issues, there are profound scientific gaps, and several unanswered questions, like lack of vaccines or antivirals to combat these pathogens. Various detection techniques like the nucleic acid test, immunoassay, and microscopy have been developed; however, there is a tradeoff between their advantages and disadvantages like safety in sample collecting, invasiveness, sensitivity, response time, etc. One of the highly resolved techniques that can provide early-stage detection with fast experiment duration is plasmonics. This optical technique has the capability to detect viral proteins and genomes at the early stage via highly sensitive interaction between the biological target and the plasmonic chip. The efficiency of this technique could be proved using commercialized techniques like reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) techniques. In this study, we aim to review the role of plasmonic technique in the detection of 11 deadliest viruses besides 2 common genital viruses for the human being. This is a rapidly moving topic of research, and a review article that encompasses the current findings may be useful for guiding strategies to deal with the pandemics. By investigating the potential aspects of this technique, we hope that this study could open new avenues toward the application of point-of-care techniques for virus detection at early stage that may inhibit the progressively hygienic threats.

Aptamers: The Powerful Molecular Tools for Virus Detection

Aptamers are short single-stranded DNA or RNA oligonucleotides selected by the technique of systematic evolution of ligands by exponential enrichment (SELEX). Aptamers have been demonstrated to bind various targets from small-molecule to cells or even tissues in the way of antibodies. Thus, they are called chemical antibodies. We summarize and evaluate recent developments in aptamer-based sensors (for short aptasensors) for virus detection in this review. These aptasensors are mainly classified into optical and electronic aptasensors based on the type of transducer. Nowadays, the smartphone has become the most widely used mobile device with billions of users worldwide. Considering the ongoing COVID-19 outbreak, smartphone-based aptasensors for a portable and point-of-care test (POCT) of COVID-19 detection will be of great importance in the future.

Integrating high-performing electrochemical transducers in lateral flow assay

Lateral flow assays (LFAs) are the best-performing and best-known point-of-care tests worldwide. Over the last decade, they have experienced an increasing interest by researchers towards improving their analytical performance while maintaining their robust assay platform. Commercially, visual and optical detection strategies dominate, but it is especially the research on integrating electrochemical (EC) approaches that may have a chance to significantly improve an LFA’s performance that is needed in order to detect analytes reliably at lower concentrations than currently possible. In fact, EC-LFAs offer advantages in terms of quantitative determination, low-cost, high sensitivity, and even simple, label-free strategies. Here, the various configurations of EC-LFAs published are summarized and critically evaluated. In short, most of them rely on applying conventional transducers, e.g., screen-printed electrode, to ensure reliability of the assay, and additional advances are afforded by the beneficial features of nanomaterials. It is predicted that these will be further implemented in EC-LFAs as high-performance transducers. Considering the low cost of point-of-care devices, it becomes even more important to also identify strategies that efficiently integrate nanomaterials into EC-LFAs in a high-throughput manner while maintaining their favorable analytical performance.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Development of nucleic acid aptamer-based lateral flow assays: A robust platform for cost-effective point-of-care diagnosis

Lateral flow assay (LFA) has made a paradigm shift in the in vitro diagnosis field due to its rapid turnaround time, ease of operation and exceptional affordability. Currently used LFAs predominantly use antibodies. However, the high inter-batch variations, error margin and storage requirements of the conventional antibody-based LFAs significantly impede its applications. The recent progress in aptamer technology provides an opportunity to combine the potential of aptamer and LFA towards building a promising platform for highly efficient point-of-care device development. Over the past decades, different forms of aptamer-based LFAs have been introduced for broad applications ranging from disease diagnosis, agricultural industry to environmental sciences, especially for the detection of antibody-inaccessible small molecules such as toxins and heavy metals. But commercial aptamer-based LFAs are still not used widely compared with antibodies. In this work, by analysing the key issues of aptamer-based LFA design, including immobilization strategies, signalling methods, and target capturing approaches, we provide a comprehensive overview about aptamer-based LFA design strategies to facilitate researchers to develop optimised aptamer-based LFAs.

Aptamer-Functionalized Microdevices for Bioanalysis

Aptamers have drawn great attention in the field of biological research and disease diagnosis for the remarkable advantages as recognition elements. They show unique superiority for facile selection, desirable thermal stability, flexible engineering, and low immunogenicity, complementing the use of conventional antibodies. Aptamer-functionalized microdevices offer promising properties for bioanalysis applications because of the compact sizes, minimal reaction volume, high throughput, operational feasibility, and controlled preciseness. In this review, we first introduce the innovative technologies in the selection of aptamers with microdevices and then highlight some advanced applications of aptamer-functionalized microdevices in bioanalysis field for diverse targets. Aptamer-functionalized microfluidic devices, microarrays, and paper-based and other interface-based microdevices are all bioanalysis platforms with huge potential in the near future. Finally, the major challenges of these microdevices applied in bioanalysis are discussed and future perspectives are also envisioned.