An aptamer-based hook-effect-recognizable three-line lateral flow biosensor for rapid detection of thrombin

Accurate Thrombin Monitoring Based on Proximity Ligation Assay-Assisted Rolling Circle Amplification (RCA)

Due to the fact that the expression level of thrombin affects the coagulation function of the injured tissue after trauma, it is considered as a very promising biomarker for the diagnosis and treatment of trauma. Nonetheless, sensitive, simple, and accurate thrombin detection continue to be extremely difficult. Here, using the two domains of thrombin as detection targets, we build a unique, accurate, isothermal thrombin analysis method. The method is constructed based on the integration of proximity ligation and rolling circle amplification (RCA). This approach specifically binds with the two functional domains of thrombin by using two intricately constructed probes. The technique has great accuracy thanks to proximity ligation, and the coupled RCA ensures acceptable sensitivity. With a limit of detection (LOD) of 0.23 pM, the method has demonstrated favorable detection persistence. Furthermore, the technique has a high selectivity for thrombin. Integrating merits including high sensitivity, low cost, and good portability, this method may enrich the arsenal for thrombin related applications.

CRISPR/Cas12a linked sandwich aptamer assay for sensitive detection of thrombin

BACKGROUND

Thrombin is a serine protease and hemostasis regulator with multiple functions and recognized as an important biomarker for diseases, and sensitive detection of thrombin is of significance for clinical diagnostics and disease monitoring. Recently, the target-triggered nonspecific single-stranded deoxyribonuclease activity of CRISPR/Cas system is discovered, making it become a powerful tool in assay developments due to the ease of signal amplification. In the short period of development, many CRISPR based nucleic acid detection methods have already played a critical role in clinical diagnostics. However, the application of CRISPR/Cas system for protein biomarkers remains limited.

RESULTS

Here we describe a CRISPR/Cas12a linked sandwich aptamer assay for detection of thrombin, which was based on the formation of a sandwich complex of target by using a capture aptamer or antibody coated on the microplate and a well-designed detection DNA strand. The detection DNA strand contained an anti-thrombin aptamer and an active DNA of Cas12a, thus the sandwich complex was labeled with the active DNA. The active DNA triggered activity of Cas12a in indiscriminately cleaving fluorophore and quencher labeled DNA reporters, causing significant fluorescence increase. Our method enabled sensitive detection of thrombin down to 10 pM, and it showed high selectivity for thrombin. The assay exhibited good performance in diluted serum samples, demonstrating the applicability for thrombin analysis in the real media.

SIGNIFICANCE

This assay combines the merits of high affinity of aptamer, trans-cleavage activity of Cas12a, high selectivity of sandwich format analysis, and high-throughput detection of microplate assay, and it shows promise in applications.

A nitrocellulose/cotton fiber hybrid composite membrane for paper-based biosensor

Nitrocellulose (NC) membrane was fabricated and tested for its potential use in various paper-based biosensors for use in point-of-care testing. However, contemporary technologies are complex, expensive, non-scalable, limited by conditions, and beset with potentially adverse effects on the environment. Herein, we proposed a simple, cost-effective, scalable technology to prepare nitrocellulose/cotton fiber (NC/CF) composite membranes. The NC/CF composite membranes with a diameter of 20 cm were fabricated in 15 min using papermaking technology, which contributes to scalability in the large-scale production of these composites. Compared with existing commercial NC membranes, the NC/CF composite membrane is characterized by small pore size (3.59 ± 0.19 μm), low flow rate (156 ± 55 s/40 mm), high dry strength (up to 4.04 MPa), and wet strength (up to 0.13 MPa), adjustable hydrophilic-hydrophobic (contact angles ranged from 29 ± 4.6 to 82.8 ± 2.4°), the good adsorption capacity of protein (up to 91.92 ± 0.07 μg). After lateral flow assays (LFAs) detection, the limit of detection is 1 nM, which is similar to commercial NC membrane (Sartorius CN 140). We envision the NC/CF composite membrane as a promising material for paper-based biosensors of point-of-care testing applications.

Aptasensors Are Conjectured as Promising ALT and AST Diagnostic Tools for the Early Diagnosis of Acute Liver Injury

Abnormal levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in human serum are the most sensitive indicator of hepatocellular damage. Because liver-related health problems are directly linked to elevated levels of ALT and AST, it is important to develop accurate and rapid methods to detect these enzymes for the early diagnosis of liver disease and prevention of long-term liver damage. Several analytical methods have been developed for the detection of ALT and AST. However, these methods are based on complex mechanisms and require bulky instruments and laboratories, making them unsuitable for point-of-care application or in-house testing. Lateral flow assay (LFA)-based biosensors, on the other hand, provide rapid, accurate, and reliable results, are easy to operate, and are affordable for low-income populations. However, due to the storage, stability, batch-to-batch variations, and error margins, antibody-based LFAs are considered unaffordable for field applications. In this hypothesis, we propose the selection of aptamers with high affinity and specificity for the liver biomarkers ALT and AST to build an efficient LFA device for point-of-care applications. Though the aptamer-based LFA would be semiquantitative for ALT and AST, it would be an inexpensive option for the early detection and diagnosis of liver disease. Aptamer-based LFA is anticipated to minimize the economic burden. It can also be used for routine liver function tests regardless of the economic situation in each country. By developing a low-cost testing platform, millions of patients suffering from liver disease can be saved.

Review on the Selection of Aptamers and Application in Paper-Based Sensors

An aptamer is a synthetic oligonucleotide, referring to a single-stranded deoxyribonucleic acid or ribonucleic acid ligand produced by synthesis from outside the body using systematic evolution of ligands by exponential enrichment (SELEX) technology. Owing to their special screening process and adjustable tertiary structures, aptamers can bind to multiple targets (small molecules, proteins, and even whole cells) with high specificity and affinity. Moreover, due to their simple preparation and stable modification, they have been widely used to construct biosensors for target detection. The paper-based sensor is a product with a low price, short detection time, simple operation, and other superior characteristics, and is widely used as a rapid detection method. This review mainly focuses on the screening methods of aptamers, paper-based devices, and applicable sensing strategies. Furthermore, the design of the aptamer-based lateral flow assay (LFA), which underlies the most promising devices for commercialization, is emphasized. In addition, the development prospects and potential applications of paper-based biosensors using aptamers as recognition molecules are also discussed.

Thrombin Determination Using Graphene Oxide Sensors with Co-Assisted Amplification

Graphene oxide (GO) is widely used in sensors. The detection of proteins based on bare GO has been developed; however, the detection sensitivity needs to be improved. In this paper, a novel GO-DNA sensor for thrombin detection was developed using an aptamer linked to the surface of GO. Polyethylene glycol (PEG) was further used to prevent thrombin from nonspecific adsorption and to improve the sensitivity of the sensor for detection of thrombin. In order to improve the limit of detection for thrombin, we developed a GO and RecJf exonuclease co-assisted signal amplification strategy, and a detection limit of 24.35 fM for thrombin was achieved using this strategy. The results show that it is a promising method in analytical applications.

Point-of-care COPD diagnostics: biomarkers, sampling, paper-based analytical devices, and perspectives

Chronic obstructive pulmonary disease (COPD) has become the third leading cause of global death. Insufficiency in early diagnosis and treatment of COPD, especially COPD exacerbations, leads to a tremendous economic burden and medical costs. A cost-effective and timely prevention requires decentralized point-of-care diagnostics at patients' residences at affordable prices. Advances in point-of-care (POC) diagnostics may offer new solutions to reduce medical expenditures by measuring salivary and blood biomarkers. Among them, paper-based analytical devices have been the most promising candidates due to their advantages of being affordable, biocompatible, disposable, scalable, and easy to modify. In this review, we present salivary and blood biomarkers related to COPD endotypes and exacerbations, summarize current technologies to collect human whole saliva and whole blood samples, evaluate state-of-the-art paper-based analytical devices that detect COPD biomarkers in saliva and blood, and discuss existing challenges with outlooks on future paper-based POC systems for COPD diagnosis and management.

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.

Mitigating hook effect in one-step quantitative sandwich lateral flow assay by timed conjugate release

Sandwich lateral flow assay (LFA) is one of the most successfully commercialized paper-based biosensors, which offers a rapid, low-cost, one-step assay. Despite its advantages, conventional sandwich LFA is fundamentally limited by the high-dose "hook" effect-a phenomenon that occurs at very high analyte concentrations and results in false-negative results. In this paper, we present a novel strategy of automatic timed detection antibody release to mitigate the hook effect in sandwich LFA without additional manual steps. We introduced an intermediate pad treated with saturated sucrose solution to regulate the flow between the nitrocellulose membrane and the conjugate pad in order to delay the reaction between detection antibodies and analytes. Using C-reactive protein (CRP) as a representative analyte, we demonstrated that our strategy exhibited a range of detection 10 times wider than that of our conventional LFA, without sacrificing the limit of detection. Comparing to other published strategies, our work could offer a one-step, cost-effective approach that is closely unified with the benefits of the LFA.

Aptamer duo-based portable electrochemical biosensors for early diagnosis of periodontal disease

Recently, point-of-care tests (POCT) have gained much attention due to their convenient, fast, simple, and easy characteristics. For POCT, portability is an essential feature. In this study, we have successfully fabricated a portable mini-potentiostat. Using chronoamperometry, electrical signals of this portable mini-potentiostat were measured, and the analytical performance of electrochemical aptasensors was compared with a benchtop potentiostat. The electrochemical signals measured by mini-potentiostat can be displayed on the screen of a smartphone. To verify the analytical performance of this portable electrochemical aptasensor platform with a mini-potentiostat, two well-known model protein biomarkers, vaspin, a type 2 diabetes biomarker, and thrombin, a biomarker for pulmonary metastasis and cardiovascular disease, were confirmed to be detected by using corresponding aptamer duo. After solid verification of this portable electrochemical aptasensor platform, we have successfully implemented this portable mini-potentiostat system to develop a portable sandwich-type binding pair of aptamers-based electrochemical biosensor, which can diagnose periodontal disease by measuring ODAM biomarker. The linear range of this ODAM biosensor was 0 to 15 nM with a detection limit of 0.02 nM and 1 nM in buffer and saliva, respectively. The sensitivity of this biosensor has been greatly enhanced, compared to previously developed surface plasmon resonance (SPR) or lateral flow assay (LFA) based aptasensors. This study showed that this new portable aptamer duo-based biosensor is expected to diagnose the early stage of periodontal diseases from real samples, such as saliva or gingival crevicular fluid in a short time as a point-of-care (POC) testing.

A simple strategy for signal enhancement in lateral flow assays using superabsorbent polymers

To enhance the sensitivity of lateral flow assays (LFAs), a simple strategy is proposed using a nitrocellulose membrane modified with a superabsorbent polymer (SAP). SAP was incorporated into a nitrocellulose membrane for the flow control of detection probes. When absorbing aqueous solutions, SAP promoted the formation of biomolecule complexes to achieve up to a tenfold sensitivity improvement for the detection of human IgG. The assay time was optimized experimentally and numerically to within 20 min using this strategy. Moreover, fluid saturation in LFAs modified with SAP was mathematically simulated to better understand the underlying process, and molecular dynamics simulations were carried out to determine the effect of SAP. The proposed design was also applied to samples spiked with human immunoglobulin-depleted serum to test its applicability. The strategy presented is unique in that it preserves the characteristics of conventional LFAs, as it minimizes user intervention and is simple to manufacture at scale.

Versatile CRISPR-Cas12a-Based Biosensing Platform Modulated with Programmable Entropy-Driven Dynamic DNA Networks

In addition to their roles as revolutionary genome engineering tools, CRISPR-Cas systems are also highly promising candidates in the construction of biosensing systems and diagnostic devices, which have attracted significant attention recently. However, the CRISPR-Cas system cannot be directly applied in the sensing of non-nucleic acid targets, and the needs of synthesizing and storing different vulnerable guide RNA for different targets also increase the application and storage costs of relevant biosensing systems, and therefore restrict their widespread applications. To tackle these barriers, in this work, a versatile CRISPR-Cas12a-based biosensing platform was developed through the introduction of an enzyme-free and robust DNA reaction network, the entropy-driven dynamic DNA network. By programming the sequences of the system, the entropy-driven catalysis-based dynamic DNA network can respond to different types of targets, such as nucleic acids or proteins, and then activate the CRISPR-Cas12a to generate amplified signals. As a proof of concept, both nucleic acid targets (a DNA target with random sequence, T, and an RNA target, microRNA-21 (miR-21)) and a non-nucleic acid target (a protein target, thrombin) were chosen as model analytes to address the feasibility of the designed sensing platform, with detection limits at the pM level for the nucleic acid analytes (7.4 pM for the DNA target T and 25.5 pM for miR-21) and 0.4 nM for thrombin. In addition, the detection of miR-21 or thrombin in human serum samples further demonstrated the applicability of the proposed biosensing platform in real sample analysis.

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.

Simultaneous Quantification of Ampicillin and Kanamycin in Water Samples Based on Lateral Flow Aptasensor Strip with an Internal Line

In this work, a simple and rapid method based on the lateral flow assay (LFA) has been developed for the detection of dual antibiotics. To achieve the quantitative assay and to reduce the non-specific adsorption, an internal system has been developed. A non-specific DNA was exploited as an internal standard and could be recognized by the DNA marker that was coated at the internal line. Two different kinds of aptamers were applied to recognize ampicillin (AMP) and kanamycin (KAM), and the distance between the detection line and conjugate pad was then optimized. Under the optimum conditions, the quantitative assays of AMP (R² = 0.984) and KAM (R² = 0.990) were achieved with dynamic ranges of 0.50 to 500.0 ng/L, and of 0.50 to 1000.0 ng/L, respectively. The LOQs of AMP and KAM were 0.06 ng/L and 0.015 ng/L, respectively. Finally, the proposed method has been successfully applied to analyze aquaculture water, tap water, and lake water, and hospital wastewater, indicating the established method could be used to monitor the environment.

Development of spike protein-based fluorescence lateral flow assay for the simultaneous detection of SARS-CoV-2 specific IgM and IgG

The pandemic outbreak of the 2019 coronavirus disease (COVID-19), which is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is still spreading rapidly and poses a great threat to human health. As such, developing rapid and accurate immunodiagnostic methods for the identification of infected persons is needed. Here, we proposed a simple but sensitive on-site testing method based on spike protein-conjugated quantum dot (QD) nanotag-integrated lateral flow immunoassay (LFA) to simultaneously detect SARS-CoV-2-specific IgM and IgG in human serum. Advanced silica-core@dual QD-shell nanocomposites (SiO2@DQD) with superior luminescence and stability were prepared to serve as fluorescent nanotags in the LFA strip and guarantee high sensitivity and reliability of the assay. The performance of the SiO2@DQD-strip was fully optimized and confirmed by using 10 positive serum samples from COVID-19 patients and 10 negative samples from patients with other respiratory diseases. The practical clinical value of the assay was further evaluated by testing 316 serum samples (114 positive and 202 negative samples). The overall detection sensitivity and specificity reached 97.37% (111/114) and 95.54% (193/202), respectively, indicating the huge potential of our proposed method for the rapid and accurate detection of SARS-CoV-2-infected persons and asymptomatic carriers.

A lateral flow strip for on-site detection of tobramycin based on dual-functional platinum-decorated gold nanoparticles

A novel lateral flow strip assay has been developed for rapid on-site detection of tobramycin. In this assay, unique dual-functional platinum-decorated gold nanoparticles (Au@Pt NPs) are synthesized by covering conventional gold nanoparticles (AuNPs) with an ultra-thin Pt film. Au@Pt NPs retain the plasmon activity of AuNPs and exhibit ultra-high catalytic activity that the Pt skin can achieve. The aptamer (Apt) specific for tobramycin and its complementary DNA (cDNA) are loaded on Au@Pt NPs as a duplex probe through the thiol group modified at the 5' end of the cDNA. When tobramycin is present, it binds specifically to the aptamer, resulting in its dehybridization from the cDNA and detachment from the surface of Au@Pt NPs. Then Au@Pt NPs can be captured by the fixed probe (DNA1) on the test zone (T zone) of the lateral flow strip through the hybridization between DNA1 and cDNA. The dual-functional Au@Pt NPs provide two different detection modes: one is based on the color of AuNPs (low sensitivity mode) and the other is based on the chromogenic reaction catalyzed by the Pt nanozyme (high sensitivity mode). The strip can complete the visual detection process of tobramycin within 10 min, and the cutoff values for the naked eye detection in the two modes are 60 nM and 5 nM, respectively. Furthermore, using a portable scanning reader and ImageJ software, quantitative detection can be achieved. The limits of detection (LOD) of the two modes are 0.09 nM and 0.02 nM, respectively. The strip has been successfully applied to detect tobramycin in different food samples. Therefore, Au@Pt NPs and the strip provide a highly sensitive, rapid and economical way for in-spot detection of tobramycin residues. The strip can be run in two modes, which can realize the on-demand adjustment of the detection performance and offer wider application prospects in diverse scenarios.

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.

A semi-dry chemistry hydrogel-based smart biosensing platform for on-site detection of metal ions

Balancing operability and performance has long been a focus of research in bioanalysis and biosensing. In this work, between the traditional wet chemistry and dry chemistry, we develop a semi-dry smart biosensing platform with favourable operability and performance for metal ions detection. This platform is based on the integration of a stimuli-responsive hydrogel with intelligent image recognition. The hydrogel consists of agarose as a matrix and well-designed fluorescent DNA probes as response elements. Target metal ions in a test sample can diffuse into the hydrogel and activate the DNA probes, outputting fluorescence signals for intelligent imaging. In this way, sensitive and convenient detection of metal ions such as potassium ions (K+) and mercury ions (Hg2+) can be achieved without the assistance of huge instruments and professional workers. The detection limits for K+ and Hg2+ are 0.34 mM and 5.6 nM, respectively. Detection of ions in serum and lake water is also available. Moreover, the hydrogel-based biosensing platform exhibits favorable selectivity, anti-degradation ability, and long-term stability. High-throughput testing can be also achieved by punching multiple test microwells in a single piece of hydrogel. The concept and successful practice of a semi-dry chemistry-based strategy make up for the shortcomings of wet chemistry and dry chemistry, and provide a promising approach for on-site testing.

Recent Advances in Electrochemical Sensors for the Detection of Biomolecules and Whole Cells

Electrochemical sensors are considered an auspicious tool to detect biomolecules (e.g., DNA, proteins, and lipids), which are valuable sources for the early diagnosis of diseases and disorders. Advances in electrochemical sensing platforms have enabled the development of a new type of biosensor, enabling label-free, non-destructive detection of viability, function, and the genetic signature of whole cells. Numerous studies have attempted to enhance both the sensitivity and selectivity of electrochemical sensors, which are the most critical parameters for assessing sensor performance. Various nanomaterials, including metal nanoparticles, carbon nanotubes, graphene and its derivatives, and metal oxide nanoparticles, have been used to improve the electrical conductivity and electrocatalytic properties of working electrodes, increasing sensor sensitivity. Further modifications have been implemented to advance sensor platform selectivity and biocompatibility using biomaterials such as antibodies, aptamers, extracellular matrix (ECM) proteins, and peptide composites. This paper summarizes recent electrochemical sensors designed to detect target biomolecules and animal cells (cancer cells and stem cells). We hope that this review will inspire researchers to increase their efforts to accelerate biosensor progress-enabling a prosperous future in regenerative medicine and the biomedical industry.

Reflector-less nanoparticles doped optical fiber biosensor for the detection of proteins: Case thrombin

A miniature biosensing platform based on MgO-based nanoparticle doped optical fiber was developed for the biomolecule detection. The technology used a single mode fiber with MgO-based nanoparticles doped core. The detection was based on collecting the Rayleigh backscattering signatures with increased gain upon the etching of the fiber 1-2 mm away from the tip. The shift from the backscattered signal with the maximum value of the cross-correlation was used to report the results. The sensor exhibited a sensitivity range from 0.75 nm/refractive index unit up to 19.63 nm/refractive index unit for a refractive index range from 1.3329 up to 1.37649. The deposition of the thin gold layer increased the overall sensitivity of the biosensor by 3.7 times for the etched part of the fiber with diameter 8-9 μm. The proposed biosensor was tested for the detection of thrombin molecule concentrations ranging from 0.625 μg/ml to 20 μg/ml. Thiol modified DNA specific aptamers were used to functionalize the gold coated surface of the fiber for the detection. The sensor showed detectable sensitivity and specificity as compared to the other control proteins. The proposed biosensing platform could be multiplexed and can be used in vivo for the detection in clinical settings due to its miniature size, biocompatibility of silica glass and reflector less set up.

A Rapid and Ultrasensitive Thrombin Biosensor Based on a Rationally Designed Trifunctional Protein

Rapid and sensitive detection of thrombin is imperative for the early diagnosis, prevention, and treatment of thrombin-related diseases. Here, an ultrasensitive and rapid thrombin biosensor is developed based on rationally designed trifunctional protein HTs, comprising three functional units, including a far-red fluorescent protein smURFP, hydrophobin HGFI, and a thrombin cleavage site (TCS). smURFP is used as a detection signal to eliminate any interference from the autofluorescence of sample matrix to increase detection sensitivity. HGFI serve as an adhesive unit to allow rapid immobilization of HTs on a multiwall plate. The TCS linking HGFI and smURFP function as a sensing element to recognize and detect thrombin. HTs immobilization is symmetrically optimized and characterized. Thrombin assay reveals the specific recognition of active thrombin in samples and the hydrolysis of the immobilized HTs, resulting in a decrease in the fluorescence intensity of the sample in a thrombin concentration-dependent manner. The limit of detection (LOD) is as low as 0.2 am in the serum. To the authors' knowledge, this is the lowest LOD ever reported for any thrombin biosensor. This study sheds light on the engineering of multifunctional proteins for biosensing.

Application of aptamers as molecular recognition elements in lateral flow assays

Owing to their ease in operation and fast turnaround time, lateral flow assays (LFAs) are increasingly being used as point-of-care diagnostic tests for variety of analytes. In a majority of these LFAs, antibodies are used as a molecular recognition element. Antibodies have a number of limitations such as high batch-to-batch variation, poor stability, long development time, difficulty in functionalization and need for ethical approval and cold chain. All these factors pose a great challenge to scale up the antibody-based tests. In recent years, the advent of aptamer technology has made a paradigm shift in the point-of-care diagnostics owing to the various advantages of aptamers over antibodies that favour their adaptability on a variety of sensing platforms including the lateral flow. In this review, we have highlighted the advantages of aptamers over antibodies, suitability of aptamers for lateral flow platforms, different types of aptamer-based LFAs and various labels for aptamer-based LFAs. We have also provided a summary of the applications of aptamer technology in LFAs for analytical applications.

Selection and application of aptamers with high-affinity and high-specificity against dinophysistoxin-1

Diarrhetic shellfish toxins (DSTs) are marine toxins distributed widely in the world, which pose a major threat to the health of mankind. Dinophysistoxin-1 (DTX-1) has the most potent toxicity in DSTs. However, the current detection methods have ethical problems and technical defects. Further research is needed, to develop a more suitable alternative to the supervision system. In this work, we successfully obtained an aptamer with high affinity and specificity bound to DTX-1 for the first time. After optimization, a core sequence of the aptamer with a higher K_D of 64 nM was obtained, while the binding mode of the core sequence and DTX-1 was explored. Based on this aptamer, we developed a biolayer interferometry (BLI) biosensor platform for DTX-1 detection. The aptasensor exhibited a broad detection range from 40 to 600 nM DTX-1 (linear range from 80 to 200 nM), and the low detection limit was 614 pM. Morever, the aptasensor showed good reproducibility and stability, which indicated that this novel aptasensor had broad development prospects for the sensitive and rapid detection of DTX-1.

For the first time, the aptamer of dinophysistoxin-1 was successfully obtained with high affinity and specificity by SELEX, and an aptasensor with a detection range from 40 to 600 nM was developed by biolayer interferometry.

A novel hybrid platform of g-C3N4 nanosheets /nucleic-acid-stabilized silver nanoclusters for sensing protein

The fabrication of nanomaterials-based sensing platform has attracted a great deal of interest due to their unique properties. Here, we report a novel hybrid platform of g-C₃N₄ nanosheets/DNA-stabilized Ag nanoclusters (CNNS/AgNCs) for sensing application. In this platform, the fluorescent AgNCs was synthesized using a pair of double-functional ssDNA sequence as a template, including the aptamer segment against thrombin and C-rich segment for AgNCs. Next, the interaction between the fluorescent Apt-AgNCs and CNNS was investigated. It is verified that DNA-stabilized AgNCs could absorb on the CNNS surface via the stronger π-π interaction to form the hybrid platform, whose fluorescence is quenched by CNNS through the photoelectron transfer effect (PET). When targets are introduced into the system, target/Apt-AgNCs complex will fall off from the CNNS surface, resulting in the fluorescence recovery. This hybrid platform can achieve the detection of biomolecule with high sensitivity and selectivity. Considering the fluorescence variability of DNA scaffold AgNCs, this hybrid platform is promising to extend to other target and even multi-target detection.

Highly sensitive detection of prostate cancer specific PCA3 mimic DNA using SERS-based competitive lateral flow assay

Accurate analysis of prostate cancer specific biomarkers plays an important role in the early diagnosis of prostate cancer. Traditional colorimetric lateral flow assay (LFA) has the limitations of low detection sensitivity and qualitative or semiquantitative detection. In this study, we developed a novel surface-enhanced Raman scattering (SERS)-based competitive LFA for the rapid and highly sensitive quantitative evaluation of prostate cancer antigen 3 (PCA3) mimic DNA. Herein, the competitive hybridization interaction with capture DNA between target PCA3 mimic DNA and reporter DNA-labeled SERS nanotags results in a change in the amount of SERS nanotags on the test line. The quantitative analysis of target PCA3 mimic DNA was realized by monitoring the Raman peak intensity of SERS nanotags on the test line. The limit of detection of PCA3 mimic DNA was estimated to be 3 fM, which is about three orders of magnitude more sensitive than that of a commercially available kit. By combining the outstanding characteristics of the well-established SERS-based competitive strategy and LFA platform, our design has strong potential for the early diagnosis of prostate cancer and other diseases.