Aptasensors: a review

Parametric Cyclic Voltammetric Analysis of an Electrochemical Aptasensor for Staphylococcus aureus Iron-Regulated Surface Determinant Protein A Detection

Rapid and reliable detection of pathogens requires precise and optimized analytical techniques to address challenges in food safety and public health. This study focuses on the parametric characterization of an electrochemical aptasensor for Staphylococcus aureus (S. aureus) iron-regulated surface determinant protein A (IsdA) using cyclic voltammetry (CV) analysis, which offers a robust method for evaluating electrode modifications and electrochemical responses. Key parameters were optimized to ensure maximum sensitivity, including an aptamer concentration of 5 μM, an incubation time of 4 h, a potential range from -0.1 to 0.9 V, and a scan rate of 0.05 V/s. The aptasensor achieved stability and peak performance at pH 7.5 and 25 °C. These conditions were critical for detecting the IsdA protein as a biomarker of S. aureus. The aptasensor applicability was demonstrated by successfully detecting S. aureus in food samples such as milk and apple juice with high specificity and reliability. Zeta potential measurements confirmed the layer-by-layer charge dynamics of the AuNPs-aptamer-IsdA system. This work emphasizes the importance of CV in understanding the performance of the electrochemical sensor, and supports the aptasensor as a practical, sensitive, and portable tool for addressing critical gaps in foodborne pathogen detection.

Sandwich-type electrochemical aptasensor based on hemin-graphite oxide as a signal label and rGO/MWCNTs/chitosan/carbon quantum dot modified electrode for sensitive detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is a pathogenic bacterium that causes severe infections and its rapid and reliable diagnosis is essential for effective control and treatment. In this study, we present an electrochemical aptasensor based on a signal amplification strategy for the detection of A. baumannii, the high specificity and affinity of the aptamer for the target make it favorable for signal amplification. This allows for a highly sensitive and selective detection of the target. The aptasensor is based on a carbon screen-printed electrode (CSPE) that has been modified with a nanocomposite consisting of multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. Additionally, the self-assembled aptamers were immobilized on hemin-graphite oxide (H-GO) as a signal probe. The composition of the nanocomposite (rGO-MWCNT/CS/CQD) provides high conductivity and stability, facilitating the efficient capture of A. baumannii onto the surface of the aptasensor. Also, aptamer immobilized on Hemin-graphite oxide (H-GO/Aptamer) was utilized as an electrochemical signal reporter probe by H reduction. This approach improved the detection sensitivity and the aptamer surface density for detecting A. baumannii. Furthermore, under optimized experimental conditions, the aptasensor was demonstrated to be capable of detecting A. baumannii with a linear range of (10 - 1 × 107 Colony-forming unit (CFU)/mL) and a limit of detection (LOD) of 1 CFU/mL (σ = 3). One of the key features of this aptasensor is its ability to distinguish between live and dead bacteria cells, which is very important and critical for clinical applications. In addition, we have successfully detected A. baumannii bacteria in healthy human serum and skim milk powder samples provided using the prepared electrochemical aptasensor. The functional groups present in the synthetic CQD, rGO-MWCNT, and chitosan facilitate biomolecule immobilization and enhance stability and activity. The fast electron-transfer kinetics and high conductivity of these materials contribute to improved sensitivity and selectivity. Furthermore, The H-GO/Aptamer composite's large surface area increases the number of immobilized secondary aptamers and enables a more stable structure. This large surface area also facilitates more H loading, leading to signal amplification.

Sandwich-type aptamer-based biosensors for thrombin detection

Thrombin, a proteolytic enzyme, plays an essential role in catalyzing many blood clotting reactions. Thrombin can act as a marker for some blood-related diseases, such as leukemia, thrombosis, Alzheimer's disease and liver disease. Therefore, its diagnosis is of great importance in the fields of biological and medical research. Biosensors containing sandwich-type structures have attracted much consideration owing to their superior features such as reproducible and stable responses with easy improvement in the sensitivity of detection. Sandwich-type platforms can be designed using a pair of receptors that are able to bind to diverse locations of the same target. Herein, we investigate recent advances in the progress and applications of thrombin aptasensors containing a sandwich-type structure, in which two thrombin-binding aptamers (TBAs) identify different parts of the thrombin molecule, leading to the formation of a sandwich structure and ultimately signal detection. We also discuss the pros and cons of these approaches and outline the most logical approach in each section.

17β-estradiol biosensors based on different bioreceptors and their applications

17β-Estradiol (E2) is a critical sex steroid hormone, which has significant effects on the endocrine systems of both humans and animals. E2 is also believed to play neurotrophic and neuroprotective roles in the brain. Biosensors present a powerful tool to detect E2 because of their small, efficient, and flexible design. Furthermore, Biosensors can quickly and accurately obtain detection results with only a small sampling amount, which greatly meets the detection of the environment, food safety, medicine safety, and human body. This review focuses on previous studies of biosensors for detecting E2 and divides them into non-biometric sensors, enzyme biosensors, antibody biosensors, and aptamer biosensors according to different bioreceptors. The advantages, disadvantages, and design points of various bioreceptors for E2 detection are analyzed and summarized. Additionally, applications of different bioreceptors of E2 detection are presented and highlight the field of environmental monitoring, food and medicine safety, and disease detection in recent years. Finally, the development of E2 detection by biosensor is prospected.

Aptasensors: employing molecular probes for precise medical diagnostics and drug monitoring

Accurate detection and monitoring of therapeutic drug levels are vital for effective patient care and treatment management. Aptamers, composed of single-stranded DNA or RNA molecules, are integral components of biosensors designed for both qualitative and quantitative detection of biological samples. Aptasensors play crucial roles in target identification, validation, detection of drug-target interactions and screening potential of drug candidates. This review focuses on the pivotal role of aptasensors in early disease detection, particularly in identifying biomarkers associated with various diseases such as cancer, infectious diseases and cardiovascular disorders. Aptasensors have demonstrated exceptional potential in enhancing disease diagnostics and monitoring therapeutic drug levels. Aptamer-based biosensors represent a transformative technology in the field of healthcare, enabling precise diagnostics, drug monitoring and disease detection.

Aptamer-Protein Interactions: From Regulation to Biomolecular Detection

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

Gold-coated tilted fiber Bragg gratings for lead ion sensing

Surface plasmon resonance sensor based on gold-coated tilted fiber Bragg gratings (SPR-TFBGs) are perfectly suited for fine refractometry. Thanks to the functionalization of the gold layer, they can be used for label-free biosensing. They have been largely used for the specific detection of proteins and cells. In this work, we experimentally demonstrate that they are enough sensitive to detect a very small entity like an environmental pollutant. In this context, we report here a bio-functionalization of the SPR-TFBG with thrombin aptamers for lead ion detection. We used aqueous solutions of lead ions with increasing concentrations from 0.001 ppb to 10 ppb. Based on the affinity bending of Pb2+ ions to the thrombin aptamer, we experimentally demonstrated low detection level of lead ion concentration (0.001 ppb) while the saturation limit is meanly fixed by the physical dimension of the sensor and the binding efficiency.

Paper-Based Aptasensors: Working Principles, Detection Modes, and Applications

Aptamers are short oligonucleotides designed to possess high binding affinity towards specific target compounds (ions, molecules, or cells). Due to their function and unique advantages, aptamers are considered viable alternatives to antibodies as biorecognition elements in bioassays and biosensors. On the other hand, paper-based devices (PADs) have emerged as a promising and powerful technology for the fabrication of low-cost analytical tools, mainly intended for on-site and point-of-care applications. The present work aims to provide a comprehensive overview of paper-based aptasensors. The review describes the fabrication methods and working principles of paper-based devices, the properties of aptamers as bioreceptors, the different modes of detection used in conjunction with aptasensing PADs, and representative applications for the detection of ions, small molecules, proteins, and cells. The future challenges and prospects of these devices are also discussed.

Recent Advances of Biosensors for Detection of Multiple Antibiotics

The abuse of antibiotics has caused a serious threat to human life and health. It is urgent to develop sensors that can detect multiple antibiotics quickly and efficiently. Biosensors are widely used in the field of antibiotic detection because of their high specificity. Advanced artificial intelligence/machine learning algorithms have allowed for remarkable achievements in image analysis and face recognition, but have not yet been widely used in the field of biosensors. Herein, this paper reviews the biosensors that have been widely used in the simultaneous detection of multiple antibiotics based on different detection mechanisms and biorecognition elements in recent years, and compares and analyzes their characteristics and specific applications. In particular, this review summarizes some AI/ML algorithms with excellent performance in the field of antibiotic detection, and which provide a platform for the intelligence of sensors and terminal apps portability. Furthermore, this review gives a short review of biosensors for the detection of multiple antibiotics.

Defective porphyrin-based metal-organic framework nanosheets derived from V2CTx MXene as a robust bioplatform for impedimetric aptasensing 17β-estradiol

An electrochemical aptasensor was prepared for the efficient, sensitive, and selective detection of 17β-estradiol. The sensor was based on a defective two-dimensional porphyrin-based metal-organic framework derived from V₂CT_x MXene. The resulting metal-organic framework nanosheets benefited from the advantages of V₂CT_x MXene nanosheets and porphyrin-based metal-organic framework, two-dimensional porphyrin-based metal-organic framework nanosheets demonstrated amplified electrochemical response and enhanced aptamer-immobilization ability compared with V₂CT_x MXene nanosheets. The sensor's detection limit was ultralow at 0.81 fg mL^-1 (2.97 fM), and the 17β-estradiol concentration range was wide, thereby outperforming most reported aptasensors. The high selectivity, superior stability and reproducibility, and excellent regeneration performance of the constructed aptasensor indicated its remarkable potential application for 17β-estradiol determination in diverse real samples. This aptasensing strategy can be used to analyze other targets by replacing the corresponding aptamer.

A signal-off aptasensor for the determination of Acinetobacter baumannii by using methylene blue as an electrochemical probe

An electrochemical aptasensor has been developed to detect Acinetobacter baumannii (A. baumannii). The proposed system was developed by modifying carbon screen-printed electrodes (CSPEs) with a synthesized MWCNT@Fe₃O₄@SiO₂-Cl nanocomposite and then binding A. baumannii-specific aptamer using covalent immobilization on the modified electrode surface and the interaction of methylene blue (MB) with Apt as an electrochemical redox indicator. As a result of the incubation of the A. baumannii bacteria as a target on the proposed aptasensor, a cathodic peak current density (J_pc) of MB decreased due to the formation of the Apt-A. baumannii complex and MB being released from the immobilized Apt on the surface of the modified electrode. In addition to increasing the electron transfer kinetics, the nanocomposite provides a relatively stable matrix to improve the loading Apt sequence. The suggested aptasensor was demonstrated to be capable of detecting A. baumannii with a linear range of 10.0-1.0 × 10⁷ colony-forming unit (CFU) mL^-1 and a detection limit of 1 CFU mL^-1 (S/N = 3) using differential pulse voltammetry (DPV) studies at a working potential of ~0.29 V and a scan rate of 100 mV s^-1. The outcomes revealed that the aptasensor exhibited high A. baumannii detection sensitivity, stability, reproducibility, and specificity.

Aptamers Targeting Membrane Proteins for Sensor and Diagnostic Applications

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

Recent advances in optical aptasensors for biomarkers in early diagnosis and prognosis monitoring of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) accounts for approximately 90% of all primary liver cancers and is one of the main malignant tumor types globally. It is essential to develop rapid, ultrasensitive, and accurate strategies for the diagnosis and surveillance of HCC. In recent years, aptasensors have attracted particular attention owing to their high sensitivity, excellent selectivity, and low production costs. Optical analysis, as a potential analytical tool, offers the advantages of a wide range of targets, rapid response, and simple instrumentation. In this review, recent progress in several types of optical aptasensors for biomarkers in early diagnosis and prognosis monitoring of HCC is summarized. Furthermore, we evaluate the strengths and limitations of these sensors and discuss the challenges and future perspectives for their use in HCC diagnosis and surveillance.

Sandwich-Type Electrochemical Aptasensor for Highly Sensitive and Selective Detection of Pseudomonas Aeruginosa Bacteria Using a Dual Signal Amplification Strategy

An electrochemical aptasensor developed to realize the detection of Pseudomonas aeruginosa (P. aeruginosa) bacteria based on a signal amplification strategy. The carbon screen-printed electrode (CSPE) surface was modified by MIL-101(Cr)/Multi-walled carbon nanotubes (MWCNT), which significantly increased the effective surface area of the electrode, thus resulting in further F23 aptamer immobilization at the surface of the modified electrode. As a result, the P. aeruginosa can be efficiently captured onto the surface of the aptasensor. Moreover, aptamer immobilized on the two-dimensional graphitic carbon nitride complex with silver nanoparticles (AgNPs/c-g-C₃N₄/Apt) was used as an electrochemical signal label, connected to P. aeruginosa bacteria at the modified electrode. This strategy increased the aptamer surface density and the sensitivity for detecting P. aeruginosa. Also, the resultant material was thoroughly characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis techniques. A highly sensitive voltammetric aptasensor for P. aeruginosa detection was obtained via this strategy at the limit of detection of 1 Colony-forming unit (CFU)/mL (σ = 3). Therefore, this proposed strategy with dual signal amplification can be a promising platform for simple, practical, reliable, and sensitive method for P. aeruginosa.

Aptamer-based rapid diagnosis for point-of-care application

Aptasensors have attracted considerable interest and widespread application in point-of-care testing worldwide. One of the biggest challenges of a point-of-care (POC) is the reduction of treatment time compared to central facilities that diagnose and monitor the applications. Over the past decades, biosensors have been introduced that offer more reliable, cost-effective, and accurate detection methods. Aptamer-based biosensors have unprecedented advantages over biosensors that use natural receptors such as antibodies and enzymes. In the current epidemic, point-of-care testing (POCT) is advantageous because it is easy to use, more accessible, faster to detect, and has high accuracy and sensitivity, reducing the burden of testing on healthcare systems. POCT is beneficial for daily epidemic control as well as early detection and treatment. This review provides detailed information on the various design strategies and virus detection methods using aptamer-based sensors. In addition, we discussed the importance of different aptamers and their detection principles. Aptasensors with higher sensitivity, specificity, and flexibility are critically discussed to establish simple, cost-effective, and rapid detection methods. POC-based aptasensors' diagnostic applications are classified and summarised based on infectious and infectious diseases. Finally, the design factors to be considered are outlined to meet the future of rapid POC-based sensors.

Role of Estradiol Hormone in Human Life and Electrochemical Aptasensing of 17β-Estradiol: A Review

Estradiol is known as one of the most potent estrogenic endocrine-disrupting chemicals (EDCs) that may cause various health implications on human growth, metabolism regulation, the reproduction system, and possibly cancers. The detection of these EDCs in our surroundings, such as in foods and beverages, is important to prevent such harmful effects on humans. Aptamers are a promising class of bio-receptors for estradiol detection due to their chemical stability and high affinity. With the development of aptamer technology, electrochemical aptasensing became an important tool for estradiol detection. This review provides detailed information on various technological interventions in electrochemical estradiol detection in solutions and categorized the aptasensing mechanisms, aptamer immobilization strategies, and electrode materials. Moreover, we also discussed the role of estradiol in human physiology and signaling mechanisms. The level of estradiol in circulation is associated with normal and diseased conditions. The aptamer-based electrochemical sensing techniques are powerful and sensitive for estradiol detection.

Recent Progresses in Development of Biosensors for Thrombin Detection

Thrombin is a serine protease with an essential role in homeostasis and blood coagulation. During vascular injuries, thrombin is generated from prothrombin, a plasma protein, to polymerize fibrinogen molecules into fibrin filaments. Moreover, thrombin is a potent stimulant for platelet activation, which causes blood clots to prevent bleeding. The rapid and sensitive detection of thrombin is important in biological analysis and clinical diagnosis. Hence, various biosensors for thrombin measurement have been developed. Biosensors are devices that produce a quantifiable signal from biological interactions in proportion to the concentration of a target analyte. An aptasensor is a biosensor in which a DNA or RNA aptamer has been used as a biological recognition element and can identify target molecules with a high degree of sensitivity and affinity. Designed biosensors could provide effective methods for the highly selective and specific detection of thrombin. This review has attempted to provide an update of the various biosensors proposed in the literature, which have been designed for thrombin detection. According to their various transducers, the constructions and compositions, the performance, benefits, and restrictions of each are summarized and compared.

Quartz Crystal Microbalance-Based Aptasensors for Medical Diagnosis

Aptamers are important materials for the specific determination of different disease-related biomarkers. Several methods have been enhanced to transform selected target molecule-specific aptamer bindings into measurable signals. A number of specific aptamer-based biosensors have been designed for potential applications in clinical diagnostics. Various methods in combination with a wide variety of nano-scale materials have been employed to develop aptamer-based biosensors to further increase sensitivity and detection limit for related target molecules. In this critical review, we highlight the advantages of aptamers as biorecognition elements in biosensors for target biomolecules. In recent years, it has been demonstrated that electrode material plays an important role in obtaining quick, label-free, simple, stable, and sensitive detection in biological analysis using piezoelectric devices. For this reason, we review the recent progress in growth of aptamer-based QCM biosensors for medical diagnoses, including virus, bacteria, cell, protein, and disease biomarker detection.

Recent advances in CRISPR-based systems for the detection of foodborne pathogens

There has long been a need for more advanced forms of pathogen detection in the food industry. Though in its infancy, biosensing based on clustered regularly interspaced short palindromic repeats (CRISPR) has the potential to solve many problems that cannot be addressed using conventional methods. In this review, we briefly introduce and classify the various CRISPR/Cas protein effectors that have thus far been used in biosensors. We then assess the current state of CRISPR technology in food-safety contexts; describe how each Cas effector is utilized in foodborne-pathogen detection; and discuss the limitations of the current technology, as well as how it might usefully be applied in other areas of the food industry. We conclude that, if the limitations of existing CRISPR/Cas-based detection methods are overcome, they can be deployed on a wide scale and produce a range of positive food-safety outcomes.

An entropy driven catalytic reaction powered DNA motor for simultaneous detection of ochratoxin A and chloramphenicol in food

An entropy driven catalytic reaction powered DNA motor was proposed for simultaneous detection of ochratoxin A (OTA) and chloramphenicol (CAP) in food. The dumbbell hairpin structure was formed by the two aptamers of OTA and CAP. The dumbbell hairpin can be opened by the interaction of OTA and CAP with their aptamers. The tails of the end of dumbbell hairpin sequence can induce the entropy driven catalytic reactions on the AuNPs, causing the sustained releasing of the fluorophore labeled DNA sequences. The recovery of fluorescent intensities can be used for quantitative detection of OTA and CAP. The limit of detection reached 2 pM for OTA and 6 pM for CAP respectively, which was great improved by entropy driven amplification of the self-powdered DNA motor. This strategy is simple and sensitive and only needs one-step operation. It exhibits promising potentiality in food quality control and food security supervision.

Construction and bioapplications of aptamer-based dual recognition strategy

Aptamer-based dual recognition strategy, using dual aptamers or the cooperation of aptamers with other recognition elements, can better utilize the advantages of each recognition molecule and increase the design flexibility to effectively overcome the limitations of a single molecule recognition strategy, thereby improving the sensitivity and selectivity and facilitating the regulation of biological process. Hence, this review systematically tracks the construction and application of dual aptamers recognition strategy in the versatile detection of protein biomarkers, pathogenic microorganisms, cancer cells, and the treatment of some diseases and, more importantly, in functional regulation and imaging of cell-surface protein receptors. Then, the cooperation of aptamers with other recognition elements are briefly introduced. Potential challenges facing this field have been highlighted, aiming to expand bioanalytical applications of aptamer-based dual or multiple recognition strategies and meet the growing demand for precision medicine.

Recent Advances in Aptasensor for Cytokine Detection: A Review

Cytokines are proteins secreted by immune cells. They promote cell signal transduction and are involved in cell replication, death, and recovery. Cytokines are immune modulators, but their excessive secretion causes uncontrolled inflammation that attacks normal cells. Considering the properties of cytokines, monitoring the secretion of cytokines in vivo is of great value for medical and biological research. In this review, we offer a report on recent studies for cytokine detection, especially studies on aptasensors using aptamers. Aptamers are single strand nucleic acids that form a stable three-dimensional structure and have been receiving attention due to various characteristics such as simple production methods, low molecular weight, and ease of modification while performing a physiological role similar to antibodies.

Aptamer Applications in Neuroscience

Being the predominant cause of disability, neurological diseases have received much attention from the global health community. Over a billion people suffer from one of the following neurological disorders: dementia, epilepsy, stroke, migraine, meningitis, Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, Huntington's disease, prion disease, or brain tumors. The diagnosis and treatment options are limited for many of these diseases. Aptamers, being small and non-immunogenic nucleic acid molecules that are easy to chemically modify, offer potential diagnostic and theragnostic applications to meet these needs. This review covers pioneering studies in applying aptamers, which shows promise for future diagnostics and treatments of neurological disorders that pose increasingly dire worldwide health challenges.

Nanomaterial-based aptasensors as an efficient substitute for cardiovascular disease diagnosis: Future of smart biosensors

As a major cause of deaths in developed countries, cardiovascular disease (CVD) has been a big burden for human health systems. Its early and rapid detection is crucial to efficiently apply appropriate on time therapy and to ultimately reduce the associated mortality rate. Aptamers, known as single-stranded DNA/RNA or oligonucleotides containing receptors and/or catalytic properties, have been widely employed in biodetection platforms due to their beneficial properties. Like antibodies, aptamers have served as artificial target receptors in affinity biosensors. Currently, advanced biosensors with improved sensitivity and specificity are fabricated by the synergistic combination of aptamers and diverse nanomaterials. Herein, we review the current development and applications of nanomaterial-based aptasensors for the recognition of CVD biomarkers with special emphasis on electrochemical and optical technologies. The performance of aptasensors has been assessed further in terms of key quality assurance metrics along with discussions on recent technologies developed for the amplification of signals with enhanced portability.

Surface enhanced Raman scattering for the multiplexed detection of pathogenic microorganisms: towards point-of-use applications

Surface enhanced Raman scattering (SERS) is a technique that demonstrates a number of advantages for the rapid, specific and sensitive detection of pathogenic microorganisms. In this review, an overview of label-free and label-based SERS approaches, including microfluidics, nucleic acid detection and immunoassays, for the multiplexed detection of pathogenic bacteria and viruses from the last decade will be discussed, as well as their transition into promising point-of-use detection technologies in industrial and medical settings.

Machine Learning Enhances the Performance of Bioreceptor-Free Biosensors

Since their inception, biosensors have frequently employed simple regression models to calculate analyte composition based on the biosensor's signal magnitude. Traditionally, bioreceptors provide excellent sensitivity and specificity to the biosensor. Increasingly, however, bioreceptor-free biosensors have been developed for a wide range of applications. Without a bioreceptor, maintaining strong specificity and a low limit of detection have become the major challenge. Machine learning (ML) has been introduced to improve the performance of these biosensors, effectively replacing the bioreceptor with modeling to gain specificity. Here, we present how ML has been used to enhance the performance of these bioreceptor-free biosensors. Particularly, we discuss how ML has been used for imaging, Enose and Etongue, and surface-enhanced Raman spectroscopy (SERS) biosensors. Notably, principal component analysis (PCA) combined with support vector machine (SVM) and various artificial neural network (ANN) algorithms have shown outstanding performance in a variety of tasks. We anticipate that ML will continue to improve the performance of bioreceptor-free biosensors, especially with the prospects of sharing trained models and cloud computing for mobile computation. To facilitate this, the biosensing community would benefit from increased contributions to open-access data repositories for biosensor data.

Advances in Gold Nanoparticles-Based Colorimetric Aptasensors for the Detection of Antibiotics: An Overview of the Past Decade

Misuse of antibiotics has recently been considered a global issue because of its harmful effects on human health. Since conventional methods have numerous limitations, it is necessary to develop fast, simple, sensitive, and reproducible methods for the detection of antibiotics. Among numerous recently developed methods, aptasensors are fascinating because of their good specificity, sensitivity and selectivity. These kinds of biosensors combining aptamer with colorimetric applications of gold nanoparticles to recognize small molecules are becoming more popular owing to their advantageous features, for example, low cost, ease of use, on-site analysis ability using naked eye and no prerequisite for modern equipment. In this review, we have highlighted the recent advances and working principle of gold nanoparticles based colorimetric aptasensors as promising methods for antibiotics detection in different food and environmental samples (2011–2020). Furthermore, possible advantages and disadvantages have also been summarized for these methods. Finally, the recent challenges, outlook, and promising future perspectives for developing novel aptasensors are also considered.

Recent Developments in Aptasensors for Diagnostic Applications

Aptamers are exciting smart molecular probes for specific recognition of disease biomarkers. A number of strategies have been developed to convert target-aptamer binding into physically detectable signals. Since the aptamer sequence was first discovered, a large variety of aptamer-based biosensors have been developed, with considerable attention paid to their potential applications in clinical diagnostics. So far, a variety of techniques in combination with a wide range of functional nanomaterials have been used for the design of aptasensors to further improve the sensitivity and detection limit of target determination. In this paper, the advantages of aptamers over traditional antibodies as the molecular recognition components in biosensors for high-throughput screening target molecules are highlighted. Aptamer-target pairing configurations are predominantly single- or dual-site binding; the design of recognition modes of each aptamer-target pairing configuration is described. Furthermore, signal transduction strategies including optical, electrical, mechanical, and mass-sensitive modes are clearly explained together with examples. Finally, we summarize the recent progress in the development of aptamer-based biosensors for clinical diagnosis, including detection of cancer and disease biomarkers and in vivo molecular imaging. We then conclude with a discussion on the advanced development and challenges of aptasensors.

Advances in Optical Aptasensors for Early Detection and Diagnosis of Various Cancer Types

Cancer is a life-threatening concern worldwide. Sensitive and early-stage diagnostics of different cancer types can make it possible for patients to get through the best available treatment options to combat this menace. Among several new detection methods, aptamer-based biosensors (aptasensors) have recently shown promising results in terms of sensitivity, identification, or detection of either cancerous cells or the associated biomarkers. In this mini-review, we have summarized the most recent (2016-2020) developments in different approaches belonging to optical aptasensor technologies being widely employed for their simple operation, sensitivity, and early cancer diagnostics. Finally, we shed some light on limitations, advantages, and current challenges of aptasensors in clinical diagnostics, and we elaborated on some future perspectives.

Application of Multiplexed Aptasensors in Food Contaminants Detection

The existence of contaminants in food poses a serious threat to human health. In recent years, aptamer sensors (aptasensors) have been developed rapidly for the detection of food contaminants because of their high specificity, design flexibility, and high efficiency. However, the development of high-throughput, highly sensitive, on-site, and cost-effective methods for simultaneous detection of food contaminants is still restricted due to multiple signal overlap or mutual interference and cross-reaction between different analytes with similar molecular structures. To overcome these problems, this Review summarizes some effective strategies from the articles published in recent years about multiplexed aptasensors for the simultaneous detection of food contaminants. This work focuses on the application of multiplexed aptasensors to simultaneously detect antibiotics, pathogens, and mycotoxins in food. These aptasensors mainly contain fluorescent aptasensors, electrochemical aptasensors, surface-enhanced Raman scattering-based aptasensors, microfluidic chip aptasensors, and paper-based multiplexed aptasensors. In addition, this Review also covers the application of nucleic acid cycle amplification and nanomaterial amplification strategies to improve the detection sensitivity. Finally, the limitations and challenges in the design of multiplexed aptasensor are also taken into account.

Electrochemical Aptasensors Based on Hybrid Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique variety of properties and morphology of the structure that make it possible to extend the performance of existing and design new electrochemical biosensors. High porosity, variable size and morphology, compatibility with common components of electrochemical sensors, and easy combination with bioreceptors make MOFs very attractive for application in the assembly of electrochemical aptasensors. In this review, the progress in the synthesis and application of the MOFs in electrochemical aptasensors are considered with an emphasis on the role of the MOF materials in aptamer immobilization and signal generation. The literature information of the use of MOFs in electrochemical aptasensors is classified in accordance with the nature and role of MOFs and a signal mode. In conclusion, future trends in the application of MOFs in electrochemical aptasensors are briefly discussed.

Graphene-family materials in electrochemical aptasensors

The study of graphene-based carbon nanocomposites has remarkably increased in recent years. Functionalized graphene-based nanostructures, including graphene oxide and reduced graphene oxide, have great potential as new innovative electrode materials in the fabrication of novel electrochemical sensors. Electrochemical sensors based on aptamers attracted great attention because of their high sensitivity and selectivity, and simple instrumentation, as well as low production cost. Aptamers as a potent alternative to antibodies are functional nucleic acids with a high tendency to specific analytes. Electrochemical aptasensors show specific recognition ability for a wide range of analytes. Although aptamers are selected in vitro in contrast to antibodies, they are interesting due to advantages like high stability, easy chemical modifications, and the potential to be employed in nanostructured device fabrication or electrochemical sensing devices. Recently, new nanomaterials have shown a significant impact on the production of electrochemical sensors with high efficiency and performance. This review aims to give an outline of electrochemical aptasensors based on the graphene family materials and discuss the detection mechanism in this type of aptasensors. The present review summarizes some of the recent achievements in graphene-based aptasensors and includes their recent electroanalytical applications. Graphical Abstract Graphical Abstract.

Impedimetric Determination of Kanamycin in Milk with Aptasensor Based on Carbon Black-Oligolactide Composite

The determination of antibiotics in food is important due to their negative effect on human health related to antimicrobial resistance problem, renal toxicity, and allergic effects. We propose an impedimetric aptasensor for the determination of kanamycin A (KANA), which was assembled on the glassy carbon electrode by the deposition of carbon black in a chitosan matrix followed by carbodiimide binding of aminated aptamer mixed with oligolactide derivative of thiacalix[4]arene in a cone configuration. The assembling was monitored by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. In the presence of the KANA, the charge transfer resistance of the inner interface surprisingly decreased with the analyte concentration within 0.7 and 50 nM (limit of detection 0.3 nM). This was attributed to the partial shielding of the negative charge of the aptamer and of its support, a highly porous 3D structure of the surface layer caused by a macrocyclic core of the carrier. The use of electrostatic assembling in the presence of cationic polyelectrolyte decreased tenfold the detectable concentration of KANA. The aptasensor was successfully tested in the determination of KANA in spiked milk and yogurt with recoveries within 95% and 115%.

Aptamer based recognition of cancer cells: Recent progress and challenges in bioanalysis

Rapid and accurate monitoring of cancer cells with high sensitivity is essential for a successful cancer treatment. As high-affinity nucleic acid ligands, aptamers can improve the properties of detection methods by conjugating with intracellular or extracellular cancer biomarkers. Despite the advances in the early detection and treatment of cancer cells, lacking effective early detection tools is one of the causes of a high mortality rate. Aptasensors, which are based on the specificity of aptamer-target recognition, with transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. In this review, some selective and sensitive methods were summarized based on advanced nanomaterials towards aptasensing of cancer cells, such as blood, breast, cervical, colon, gastric, liver, and lung cancer cells. This review summarizes advances from 2010 to June 2020 in the development of aptasensors for cancer cell detection. Various aptasensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and opportunities to integrate aptasensing platforms into point-of-care solutions. Finally, the advantages and limitations of aptamer-based aptasensing strategies were reviewed.

Advances in aptasensor technology

Aptasensors form a class of biosensors that function on the basis of a biological recognition. An aptasensor is advantageous because it incorporates a unique biologic recognition element, i.e., an aptamer, coupled to a transducer to convert a biological interaction to readable signals that can be easily processed and reported. In such biosensors, the specificity of aptamers is comparable to and sometimes even better than that of antibodies. Using the SELEX technique, aptamers with high specificity and affinity to various targets can be isolated from large pools of different oligonucleotides. Nowadays, new modifications of the SELEX technique and, as a result, easy generation and synthesis of aptamers have led to the wide application of these materials as biological receptors in biosensors. In this regard, aptamers promise a bright future. In the present research a brief account is initially provided of the recent developments in aptasensors for various targets. Then, immobilization methods, design strategies, current limitations and future directions are discussed for aptasensors.

Specific monitoring of aflatoxin M1 in real samples using aptamer binding to DNFS based on turn-on method: A novel biosensor

In the present work, a novel biocompatible scaffold was fabricated for the DNA aptamer immobilization. For the first time, amino-functionalized dendritic fibrous nanosilica (KCC-1-nPr-NH₂ ) and gold nanoparticle supported by chitosan (AuNPs-CS) were synthesized and electrodeposited successfully on the surface of the glassy carbon electrode by chronoamperometry technique. Unique oligonucleotide of aflatoxin M1 (5'-ATC CGT CAC ACC TGC TCT GAC GCT GGG GTC GAC CCG GAG AAA TGC ATT CCC CTG TGG TGT TGG CTC CCG TAT) labeled by toluidine blue was immobilization on the prepared interface. Hence, a novel aptamer-based bioassay was formed for highly sensitive quantitation of AFM1 using cyclic voltammetry and differential plus voltammetry. The structure and morphology of GQDs-CS/KCC-1-nPr-NH₂ were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, atomic force, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The achieved low limit of quantification of apta-assay for detection of AFM1 was 10fM. Also, calibration curve was linear from 0.1μM to 10fM in real samples. The proposed apta-assay has acceptable long-term stability. Designed aptasensor has a lot of remarkable advantages including excellent selectivity, sensitivity, and stability that could be used as facile bio-device for the determination of AFM1 in milk samples.

A Fluorescent Sensor Based on Reversible Addition-Fragmentation Chain Transfer Polymerization for the Early Diagnosis of Non-small Cell Lung Cancer

We propose a novel, ultrasensitive and low-cost sensor using reversible addition-fragmentation chain transfer (RAFT) polymerization as a signal amplification strategy for the detection of CYFRA 21-1 DNA fragment, a tumor marker of non-small cell lung carcinoma. The peptide nucleic acid (PNA) probes were firstly immobilized on magnetic beads (MBs) to capture the CYFRA 21-1 DNA specifically. After hybridization, CPAD was tethered to the hetero duplexes through carboxylate-Zr⁴⁺-phosphate chemistry. Subsequently, a number of fluorescent tags were introduced to the heteroduplexes through RAFT polymerization, leading to an amplification of the fluorescence signal. The sensor demonstrates a low limit of detection (LOD) of 0.02 fM. It has great selectivity with respect to base mismatch DNA, and high anti-interference ability in normal human serum. Overall findings of the study suggest that proposed sensor holds enormous potential to be used as a tool for the early-stage diagnosis of lung cancers.

Determination of aflatoxin M1 using an aptamer-based biosensor immobilized on the surface of dendritic fibrous nano-silica functionalized by amine groups

Aflatoxins are potential food pollutants produced by fungi. Among them, aflatoxin M1 (AF M1) is the most toxic. A great deal of concern is associated with AF M1 toxicity. Aflatoxins are potential food pollutants produced by fungi. Among them, aflatoxin M1 (AF M1) is the most toxic. A great deal of concern is associated with AF M1 toxicity. In the present work, a novel aptamer-based bioassay was developed for monitoring aflatoxin M1 (AF M1) in real samples. A chitosan-modified graphene quantum dot (GQD-CS) nanocomposite was used as a biocompatible substrate coated with dendritic fibrous nanosilica functionalized by amine groups (KCC-1-NH₂-Tb). Accordingly, an innovative biocompatible polymeric matrix was prepared for aptamer immobilization. The unique oligonucleotide of AF M1 (5'-ATC CGT CAC ACC TGC TCT GAC GCT GGG GTC GAC CCG GAG AAA TGC ATT CCC CTG TGG TGT TGG CTC CCG TAT) labelled by toluidine blue was immobilized on the engineered interface. Hence, a novel aptamer-based bioassay was formed for the highly sensitive quantitation of AF M1 using cyclic voltammetry and differential pulse voltammetry techniques. The structure and morphology of GQDs-CS/KCC-1-NH₂-Tb was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, atomic force and scanning electron microscopy and energy-dispersive X-ray spectroscopy. The toxicity tests, which were performed by MTT assays, revealed the biocompatible nature of KCC-1-NH₂-Tb. The engineered aptasensor demonstrated excellent behaviour toward the determination of AF M1, where the low limit of quantification was 10 fM. The proposed aptamer-based bioassay was successfully used for the monitoring of AF M1 in milk samples. This work provides a beneficial reference for the sensing of other toxins in food/pharmaceutical assays and veterinary medicine.

Label-free cocaine aptasensor based on a long-period fiber grating

In this Letter, we combined a promising bioreceptor, a cocaine aptamer MN6, with an ultrasensitive optical platform long-period fiber grating (LPFG) to create a new cocaine biosensor. The cocaine induces a conformational rearrangement of the aptamer which changes the refractive index around the LPFG producing a measurable shift of the transmission spectrum. We were able to track subtle interaction between the receptor and cocaine molecules over a concentration range of 25 to 100 μM. The presented biosensor does not require labeling or signal enhancement, resulting in a simple user-friendly device.

Aptamers and Aptasensors for Highly Specific Recognition and Sensitive Detection of Marine Biotoxins: Recent Advances and Perspectives

Marine biotoxins distribute widely, have high toxicity, and can be easily accumulated in water or seafood, exposing a serious threat to consumer health. Achieving specific and sensitive detection is the most effective way to prevent emergent issues caused by marine biotoxins; however, the previous detection methods cannot meet the requirements because of ethical or technical drawbacks. Aptamers, a kind of novel recognition element with high affinity and specificity, can be used to fabricate various aptasensors (aptamer-based biosensors) for sensitive and rapid detection. In recent years, an increasing number of aptamers and aptasensors have greatly promoted the development of marine biotoxins detection. In this review, we summarized the recent aptamer-related advances for marine biotoxins detection and discussed their perspectives. Firstly, we summarized the sequences, selection methods, affinity, secondary structures, and the ion conditions of all aptamers to provide a database-like information; secondly, we summarized the reported aptasensors for marine biotoxins, including principles, detection sensitivity, linear detection range, etc.; thirdly, on the basis of the existing reports and our own research experience, we forecast the development prospects of aptamers and aptasensors for marine biotoxins detection. We hope this review not only provides a comprehensive summary of aptamer selection and aptasensor development for marine biotoxins, but also arouses a broad readership amongst academic researchers and industrial chemists.