Design strategies of AuNPs-based nucleic acid colorimetric biosensors

Waveguide-Enhanced Nanoplasmonic Biosensor for Ultrasensitive and Rapid DNA Detection

DNA is fundamental for storing and transmitting genetic information. Analyzing DNA or RNA base sequences enables the identification of genetic disorders, monitoring gene expression, and detecting pathogens. Traditional detection techniques like polymerase chain reaction (PCR) and next-generation sequencing (NGS) have limitations, including complexity, high cost, and the need for advanced computational skills. Therefore, there is a significant demand for enzyme-free and amplification-free strategies for rapid, low-cost, and sensitive DNA detection. DNA biosensors, especially those utilizing plasmonic nanomaterials, offer a promising solution. This study introduces a novel DNA-functionalized waveguide-enhanced nanoplasmonic optofluidic biosensor using a nanogold-linked sorbent assay for enzyme-free and amplification-free DNA detection. Integrating plasmonic gold nanoparticles (AuNPs) with a glass planar waveguide (WG) and a microfluidic channel, fabricated through cost-effective, vacuum-free methods, the biosensor achieves specific detection of complementary target DNA sequences. Utilizing a sandwich architecture, AuNPs labeled with detection DNA probes enhance sensitivity by altering evanescent wave distribution and inducing plasmon resonance modes. The biosensor demonstrated exceptional performance in DNA detection, achieving a limit of detection (LOD) of 33.1 fg/mL (4.36 fM) with a rapid response time of approximately 8 min. This ultrasensitive, rapid, and cost-effective biosensor exhibits minimal background nonspecific adsorption, making it highly suitable for clinical applications and early disease diagnosis. The innovative design and fabrication processes offer significant advantages for mass production, presenting a viable tool for precise disease diagnostics and improved clinical outcomes.

Nanomaterials revolutionize biosensing: 0D-3D designs for ultrasensitive detection of microorganisms and viruses

Various diseases caused by harmful microorganisms and viruses have caused serious harm and huge economic losses to society. Thus, rapid detection of harmful microorganisms and viruses is necessary for disease prevention and treatment. Nanomaterials have unique properties that other materials do not possess, such as a small size effect and quantum size effect. Introducing nanomaterials into biosensors improves the performance of biosensors for faster and more accurate detection of microorganisms and viruses. This review aims to introduce the different kinds of biosensors and the latest advances in the application of nanomaterials in biosensors. In particular, this review focuses on describing the physicochemical properties of zero-, one-, two-, and three-dimensional nanostructures as well as nanoenzymes. Finally, this review discusses the applications of nanobiosensors in the detection of microorganisms and viruses and the future directions of nanobiosensors.

Advancements in Biosensors for Point-of-Care Testing of Nucleic Acid

Rapid, low-cost and high-specific diagnosis based on nucleic acid detection is pivotal in both detecting and controlling various infectious diseases, effectively curbing their spread. Moreover, the analysis of circulating DNA in whole blood has emerged as a promising noninvasive strategy for cancer diagnosis and monitoring. Although traditional nucleic acid detection methods are reliable, their time-consuming and intricate processes restrict their application in rapid field assays. Consequently, an urgent emphasis on point-of-care testing (POCT) of nucleic acids has arisen. POCT enables timely and efficient detection of specific sequences, acting as a deterrent against infection sources and potential tumor threats. To address this imperative need, it is essential to consolidate key aspects and chart future directions in POCT biosensors development. This review aims to provide an exhaustive and meticulous analysis of recent advancements in POCT devices for nucleic acid diagnosis. It will comprehensively compare these devices across crucial dimensions, encompassing their integrated structures, the synthesized nanomaterials harnessed, and the sophisticated detection principles employed. By conducting a rigorous evaluation of the current research landscape, this review will not only spotlight achievements but also identify limitations, offering valuable insights into the future trajectory of nucleic acid POCT biosensors. Through this comprehensive analysis, the review aspires to serve as an indispensable guide for fostering the development of more potent biosensors, consequently fostering precise and efficient POCT applications for nucleic acids.

A highly sensitive and selective colorimetric aptasensor for detecting sulfadiazine in river waters based on gold nanoparticles synthesized from discarded Longan seed extract

Gold nanoparticles (AuNPs) were extensively employed for in-situ detection sulfadiazine (SDZ) residues, yet current synthesis methods suffer from complex procedures, reagent pollution of the environment, and low particle quality. This study presents a novel synthesis method using discarded longan seed extract as a reducing agent to synthesized high-quality AuNPs, and then can be used for in-situ SDZ detection. Response surface methodology (RSM) was employed to optimize synthesis parameters, which resulted in five optimal combinations that enhanced the flexibility of synthesis. These AuNPs, ranging in size from 18.26 nm to 33.8 nm with zeta potentials from - 29.5 mV to - 14.3 mV, were successfully loaded with functional groups from longan seed extract. In the detection of SDZ, the colorimetric aptasensor demonstrated excellent sensitivity and selectivity over other antibiotics with a limit of detection and quantification at 70.98 ng·mL-1 and 236.59 ng·mL-1 in the concentration range of 200-800 ng·mL-1. Recoveries of spiked SDZ samples ranged from 97.90% to 106.7%, with RSD values below 9.25%. Meanwhile, the aptasensor exhibited exceptional diagnostic efficacy (AUC: 0.976) compared to UV absorption methods in the ROC evaluation. In conclusion, this study highlights the potential of using AuNPs synthesized from longan seed extract coupled with aptamer technology as a straightforward detection method for SDZ in river water, offering promising applications in environmental monitoring.

Hemin/G-quadruplex and AuNPs-MoS2 based novel dual signal amplification strategy for ultrasensitively sandwich-type electrochemical thrombin aptasensor

In this work, a novel sandwich-type electrochemical aptasensor based on the dual signal amplification strategy of hemin/G-quadruplex and AuNPs-MoS2 was designed and constructed, which realized the highly sensitive and specific detection of thrombin (TB). In this aptasensor, the 15-mer TB-binding aptamer (TBA-1) modified with thiol group was immobilized on the surface of AuNPs modified glassy carbon electrode (AuNPs/GCE) as capturing elements. Another thiol-modified 29-mer TB-binding aptamer (TBA-2) sequence containing G-quadruplex structure for hemin immobilization was designed. The formed hemin/G-quadruplex/TBA-2 sequence was further combined to the AuNPs decorated flower-like molybdenum disulfide (AuNPs-MoS2) composite surface via Au-S bonds, acting the role of reporter probe. In presence of the target TB, the sandwich-type electrochemical aptamer detection system could be formed properly. With the assistance of the dual signal amplification of AuNPs-MoS2 and hemin/G-quadruplex toward H2O2 reduction, the sandwich-type electrochemical aptasensor was successfully constructed for sensitive detection of TB. The results demonstrate that the fabricated aptasensor displays a wide linear range of 1.0 × 10-6 ∼ 10.0 nM with a low detection limit of 0.34 fM. This proposed aptasensor shows potential application in the detection of TB content in real biological samples with high sensitivity, selectivity, and reliability.

Freeze-Driven Synthesis of DNA Hairpin-Conjugated Gold Nanoparticle Biosensors for Dual-Mode Detection

Freeze-based immobilization of deoxyribonucleic acid (DNA) oligonucleotides on gold nanoparticles (AuNPs) is highly efficient for single-stranded oligonucleotides but typically does not accommodate structures such as snap-cooled DNA hairpins (Sc-HPs) and snap-cooled molecular beacons (Sc-MBs) frequently used for biorecognition applications. Recognizing this limitation, we have developed a modified, freeze-based technique specifically designed to enable the adsorption of such hairpin oligonucleotides onto AuNP surfaces while ensuring that they retain their biosensing capabilities. Successful hairpin oligonucleotide conjugation of varying lengths to a wide range of AuNP diameters was corroborated by dynamic light scattering, ζ-potential, and UV-vis spectrophotometry. Moreover, we conducted a thorough evaluation of this modified method, confirming the retention of the sensing functions of Sc-HPs and Sc-MBs. This advancement not only offers a more efficient route for DNA hairpin conjugation but also elucidates the underlying biorecognition functions, with implications for broader applications in molecular diagnostics.

Hydrogen Bonding-Induced Aggregation of Chiral Functionalized AuNS@Ag NPs for Photothermal Enantioanalysis

Toward the challenges of signaling transduction amplified in enantioselective recognition, we herein devised an innovative strategy for highly selective recognition of amino acids and their derivatives, leveraging photothermal effects. In this approach, bifunctional l-ascorbic acid is employed to reduce silver ions in situ on Au nanostars. Simultaneously, its oxidate (l-dehydroascorbic acid) is bonded to the silver shell as a chiral selector to prepare chiral nanoparticles (C-AuNS@Ag NPs) with the ability to recognize stereoisomers and sensitively modulate the photothermal effect. l-Dehydroascorbic acid can selectively capture one of the enantiomers of the two forms through hydrogen bonding and drive aggregation of the nanoparticles, which sharply enhances the photothermal effect. Consequently, the two forms of the system exhibit a significant temperature difference, which enables the discrimination and quantification of enantiomers. Our strategy verifies that six chiral amino acids and their derivatives can be discriminated with enantioselective response values of up to 79. Additionally, the chiral recognition mechanism was revealed through density functional theory (DFT) calculations, providing a paradigm shift in the development of enantiomeric recognition strategies.

Double phage displayed peptides co-targeting-based biosensor with signal enhancement activity for colorimetric detection of Staphylococcus aureus

The development of simple, fast, sensitive, and specific strategies for the detection of foodborne pathogenic bacteria is crucial for ensuring food safety and promoting human health. Currently, detection methods for Staphylococcus aureus still suffer from issues such as low specificity and low sensitivity. To address this problem, we proposed a sensitivity enhancement strategy based on double phage-displayed peptides (PDPs) co-targeting. Firstly, we screened two PDPs and analyzed their binding mechanisms through fluorescent localization, pull-down assay, and molecular docking. The two PDPs target S. aureus by binding to specific proteins on its outer membrane. Based on this phenomenon, a convenient and sensitive double PDPs colorimetric biosensor was developed. Double thiol-modified phage-displayed peptides (PDP-SH) enhance the aggregation of gold nanoparticles (AuNPs), whereas the specific interaction between the double PDPs and bacteria inhibits the aggregation of AuNPs, resulting in an increased visible color change before and after the addition of bacteria. This one-step colorimetric approach displayed a high sensitivity of 2.35 CFU/mL and a wide detection range from 10-2 × 108 CFU/mL. The combination with smartphone-based image analysis improved the portability of this method. This strategy achieves the straightforward, highly sensitive and portable detection of pathogenic bacteria.

A comprehensive review on enzyme-based biosensors: Advanced analysis and emerging applications in nanomaterial-enzyme linkage

Biosensors with nanomaterials and enzymes detect and quantify specific targets in samples, converting recognition into measurable signals. The study explores the intrinsic synergy between these elements for detecting and quantifying particular targets in biological and environmental samples, with results demonstrated through bibliometric analysis and a comprehensive review of enzyme-based biosensors. Using WoS, 57,331 articles were analyzed and refined to 880. Key journals, countries, institutions, and relevant authors were identified. The main areas highlighted the multidisciplinary nature of the field, and critical keywords identified five thematic clusters, revealing the primary nanoparticles used (CNTs, graphene, AuNPs), major application fields, basic application themes, and niche topics such as sensitive detection, peroxidase activity, and quantum dot utilization. The biosensor overview covered nanomaterials and their primary applications, addressing recent advances and inherent challenges. Patent analysis emphasized the U.S. leadership in the industrial sector, contrasting with China's academic prominence. Future studies should focus on enhancing biosensor portability and analysis speed, with challenges encompassing efficient integration with recent technologies and improving stability and reproducibility in the nanomaterial-enzyme interaction.

A review of nanomaterials for biosensing applications

A biosensor is a device that reacts with the analyte to be analyzed, detects its concentration, and generates readable information, which plays an important role in medical diagnosis, detection of physiological indicators, and disease prevention. Nanomaterials have received increasing attention in the fabrication and improvement of biosensors due to their unique physicochemical and optical properties. In this paper, the properties of nanomaterials such as the size effect, optical and electrical properties, and their advantages in the field of biosensing are briefly summarized, and the application of nanomaterials can effectively improve the sensitivity and reduce the detection limit of biosensors. The advantages of commonly used nanomaterials such as gold nanoparticles (AuNPs), carbon nanotubes (CNTs), quantum dots (QDs), graphene, and magnetic nanobeads for biosensor applications are also reviewed. Besides, the two main types of biosensors using nanomaterials involved in their construction and their working principles are described, and the toxicity and biocompatibility of nanomaterials and the future direction of nanomaterial biosensors are discussed.

Enhancement of telomerase extension via quadruple nucleic acid recycling to develop a novel colorimetric biosensing method for kanamycin assay

BACKGROUND

Colorimetric biosensors have important value for antibiotic residue testing. However, many previous methods were constructed based on the optical density change of certain unstable single-colored products with poor discrimination for visual measurements. Moreover, their low extinction coefficients usually result in low sensitivity of biosensors. In addition, many conventional signal amplification strategies often involve sophisticated nanomaterial preparation, inconvenient multi-step assay manipulation and limited signal amplification ability. Therefore, the development of new colorimetric biosensing strategies with excellent visual discrimination, high sensitivity and convenient manipulation is highly desirable.

RESULTS

We designed a target recycling accelerated cascade DNA walking amplification mechanism to trigger a telomerase extension-related enzymatic reaction, and developed a novel colorimetric biosensing strategy for kanamycin (Kana) assay. The target recycling was induced by an exonuclease III-assisted aptamer recognition reaction, which could also trigger the successive DNA walking at the streptavidin (SA)- and magnetic bead (MB)-based tracks. This not only caused the quantitative exposure of the telomeric substrate primers on MB surfaces but also released another strand to accelerate the SA-based DNA walking. By using the telomerase extension product to link numerous alkaline phosphatases and induce the plasmonic property change of gold nanobipyramids (Au NBPs), a colorimetric signal output strategy was constructed. This method could be applied for the high-resolution visual screening of Kana, and it also showed a very low detection limit of 17.6 fg mL-1 for assaying Kana over a wide, five-order-magnitude linear range.

SIGNIFICANCE

The quadruple nucleic acid recycling-enhanced telomerase extension resulted in the ultrahigh sensitivity of the method and also excluded the sophisticated manipulations involved in conventional biosensing strategies. The multiple enzyme catalysis-induced plasmonic property change of Au NBPs realized the stable and multicolor visual signal transduction. Together with its low cost, simple operation, high selectivity, excellent repeatability, and reliable performances, this method exhibits great potential for use in practical applications.

A Novel Aptamer Biosensor Based on a Localized Surface Plasmon Resonance Sensing Chip for High-Sensitivity and Rapid Enrofloxacin Detection

Enrofloxacin, a fluoroquinolone widely used in animal husbandry, presents environmental and human health hazards due to its stability and incomplete hydrolysis leading to residue accumulation. To address this concern, a highly sensitive aptamer biosensor utilizing a localized surface plasmon resonance (LSPR) sensing chip and microfluidic technology was developed for rapid enrofloxacin residue detection. AuNPs were prepared by the seed method and the AuNPs-Apt complexes were immobilized on the chip by the sulfhydryl groups modified on the end of the aptamer. The properties and morphologies of the sensing chip and AuNPs-Apt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, and scanning electron microscope (SEM), respectively. The sensing chip was able to detect enrofloxacin in the range of 0.01-100 ng/mL with good linearity, and the relationship between the response of the sensing chip and the concentration was Δλ (nm) = 1.288log ConENR (ng/mL) + 5.245 (R2 = 0.99), with the limit of detection being 0.001 ng/mL. The anti-interference, repeatability, and selectivity of this sensing chip were studied in detail. Compared with other sensors, this novel aptamer biosensor based on AuNPs-Apt complexes is expected to achieve simple, stable, and economical application in the field of enrofloxacin detection.

Recent advances of biosensors on microneedles

Biosensors have attracted a considerable attention in recent years due to their enormous potential to provide insights into the physical condition of individuals. However, the widespread use of biosensors has experienced difficulties regarding the stability of the biological response and the poor miniaturization and portability of biosensors. Hence, there is an urgent need for more reliable biosensor devices. Microneedle (MN) technology has become a revolutionary approach to biosensing strategies, setting new horizons for improving existing biosensors. MN-based biosensors allow for painless injection, and in situ extraction or monitoring. However, the accuracy and practicality of detection need to be improved. This review begins by discussing the classification of MNs, manufacturing methods and other design parameters to develop a more accurate MN-based detection sensing system. Herein, we categorize and analyze the energy supply of wearable biosensors. Specifically, we describe the detection methods of MN biosensors, such as electrochemical, optical, nucleic acid recognition and immunoassays, and how MNs can be combined with these methods to detect biomarkers. Furthermore, we provide a detailed overview of the latest applications (drug release, drug detection, etc.). The MN-based biosensors are followed by a summary of key challenges and opportunities in the field.

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.

Recent Advances in Fluorescent Nanoprobes for Food Safety Detection

Fluorescent nanoprobes show similar fluorescence properties to traditional organic dyes, but the addition of nanotechnology accurately controls the size, shape, chemical composition, and surface chemistry of the nanoprobes with unique characteristics and properties, such as bright luminescence, high photostability, and strong biocompatibility. For example, modifying aptamers or antibodies on a fluorescent nanoprobe provides high selectivity and specificity for different objects to be tested. Fluorescence intensity, life, and other parameters of targets can be changed by different sensing mechanisms based on the unique structural and optical characteristics of fluorescent nanoprobes. What's more, the detection of fluorescent nanoprobes is cost-saving, simple, and offers great advantages in rapid food detection. Sensing mechanisms of fluorescent nanoprobes were introduced in this paper, focusing on the application progress in pesticide residues, veterinary drug residues, heavy metals, microbes, mycotoxins, and other substances in food safety detection in recent years. A brief outlook for future development was provided as well.

Aptamer-Based Point-of-Care Devices: Emerging Technologies and Integration of Computational Methods

Recent innovations in point-of-care (POC) diagnostic technologies have paved a critical road for the improved application of biomedicine through the deployment of accurate and affordable programs into resource-scarce settings. The utilization of antibodies as a bio-recognition element in POC devices is currently limited due to obstacles associated with cost and production, impeding its widespread adoption. One promising alternative, on the other hand, is aptamer integration, i.e., short sequences of single-stranded DNA and RNA structures. The advantageous properties of these molecules are as follows: small molecular size, amenability to chemical modification, low- or nonimmunogenic characteristics, and their reproducibility within a short generation time. The utilization of these aforementioned features is critical in developing sensitive and portable POC systems. Furthermore, the deficiencies related to past experimental efforts to improve biosensor schematics, including the design of biorecognition elements, can be tackled with the integration of computational tools. These complementary tools enable the prediction of the reliability and functionality of the molecular structure of aptamers. In this review, we have overviewed the usage of aptamers in the development of novel and portable POC devices, in addition to highlighting the insights that simulations and other computational methods can provide into the use of aptamer modeling for POC integration.

Dual-amplification colorimetric detection of bisphenol A based on catalytic hairpin assembly and DNAzyme-caused fragment self-assembly hybridization chain reaction

An efficient and innovative strategy for colorimetric detection of bisphenol A (BPA) is shown here based on target-induced catalytic hairpin assembly (CHA) and DNAzyme-caused fragment self-assembly hybridization chain reaction (HCR). BPA can bind with its aptamer hairpin to trigger CHA, thus forming Y-shaped DNA nanostructures with an enzyme-strand (E-DNA) tail. Subsequently, the E-DNA can cyclically cleave the substrate hairpin, generating many fragments which can cause self-assembly HCR to form long strand DNA. Finally, the formed long strand DNA can hybridize with short single strand DNA on AuNPs, causing the color change of AuNPs from red to blue. Six important detection conditions of the proposed aptasensor were optimized. Under optimal conditions, the biosensor has high sensitivity for BPA detection at concentrations ranging from 0.8 pM to 500 pM and the detection limit is as low as 0.2 pM, providing a promising prospective ultrasensitive detection of BPA.

Electrical Nanobiosensors for Nucleic Acid Based Diagnostics

Recent advances in nanotechnologies have promoted the iterative updating of nucleic acid sensors. Among various sensing technologies, the electrical nanobiosensor is regarded as one of the most promising prospects to achieve rapid, precise, and point-of-care nucleic acid based diagnostics. In this Perspective, we introduce recent progresses in electrical nanobiosensors for nucleic acid detection. First, the strategies for improving detection performance are summarized, including chemical amplification and electrical amplification. Then, the detection mechanism of electrical nanobiosensors, such as electrochemical biosensors, field-effect transistors, and photoelectric enhanced biosensors, is illustrated. At the same time, their applications in cancer screening, pathogen detection, gene sequencing, and genetic disease diagnosis are introduced. Finally, challenges and future prospects in clinical application are discussed.

Plasmonic Cross-Linking Colorimetric PCR for Simple and Sensitive Nucleic Acid Detection

Simple, low-cost, and accurate nucleic acid assay platforms hold great promise for point-of-care (POC) pathogen detection, disease surveillance, and control. Plasmonic photothermal polymerase chain reaction (PPT-PCR) is a powerful and efficient nucleic acid amplification technique, but it lacks a simple and convenient analysis method for POC applications. Herein, we propose a novel plasmonic cross-linking colorimetric PCR (PPT-ccPCR) assay by integrating plasmonic magnetic nanoparticle (PMN)-based PPT-PCR with gold nanoparticle (AuNP)-based cross-linking colorimetry. AuNPs form assembled structures with the PMNs in the presence of amplicons and collect in a magnetic field, resulting in color changes to the supernatant. Target DNA with concentrations as low as 5 copies/μL can be visually detected within 40 min. The achieved limit of detection was 1.8 copies/μL based on the absorption signals. This simple and sensitive strategy needs no expensive instrumentation and demonstrates high potential for POC detection while enabling further applications in clinical diagnostics.

Construction of multiple modes using gold nanoparticles as probes for the rapid detection of fenpyroximate

Herein, three patterns for the detection of fenpyroximate based on the response signal of gold nanoparticles are described. The strong interaction between the guanidine group of arginine-modified gold nanoparticles and the ester group of fenpyroximate led to the aggregation of the nanoparticles and to a variation of ultraviolet-visible light spectrum and color of the solution. Sensors were constructed based on the correlation of the concentration of fenpyroximate with the absorbance ratio (A₆₅₀/A₅₂₅) and the R value was obtained by extracting the color of the test solution by using a smartphone to take a photo of the solution, which was then analyzed by colorimeter software. The absorbance ratio increased linearly in the range of 0.225-0.375 mg L^-1 and the limit of detection was 0.215 mg L^-1, while the R value declined linearly in the range of 0.20-0.40 mg L^-1 and the limit of detection was 0.21 mg L^-1. Further, the gold nanoparticles could cause a fluorescence quenching of fluorescent dyes, such as rhodamine B, and it was found that the fluorescence could be quenched and then restored after aggregation; therefore, a fluorescence method based on fluorescence "off-on" was constructed, and the fluorescence quenching was found to increase linearly in the range of 0.0-1.0 mg L^-1 and the limit of detection was 0.013 mg L^-1. These three patterns indicated highly selective and sensitive response signals for fenpyroximate, and all were applied to the detection of fenpyroximate in apple juice, pear juice, and environmental water samples, with the results showing that the three methods could be mutually verified, with the recoveries ranging from 94.15% to 110.65%.

Nanozyme-based dual-signal sensing system for colorimetric and photothermal detection of AChE activity in the blood of liver-injured mice

Acetylcholinesterase (AChE), a crucial enzyme related to liver function, is involved in numerous physiological processes such as neurotransmission and muscular contraction. The currently reported techniques for detecting AChE mainly rely on a single signal output, limiting their high-accuracy quantification. The few reported dual-signal assays are challenging to implement in dual-signal point-of-care testing (POCT) because of the need for large instruments, costly modifications, and trained operators. Herein, we report a colorimetric and photothermal dual-signal POCT sensing platform based on CeO₂-TMB (3,3',5,5'-tetramethylbenzidine) for the visualization of AChE activity in liver-injured mice. The method compensates for the false positives of a single signal and realizes the rapid, low-cost portable detection of AChE. More importantly, the CeO₂-TMB sensing platform enables the diagnosis of liver injury and provides an effective tool for studying liver disease in basic medicine and clinical applications. Rapid colorimetric and photothermal biosensor for sensitive detection of acetylcholinesterase (I) and acetylcholinesterase levels in mouse serum (II).

Nanozyme-catalysed CRISPR-Cas12a system for the preamplification-free colorimetric detection of lead ion

CRISPR-based detection was often based on the target preamplification to realize the high sensitivity. Here, we prepared a CRISPR-Cas12a system for the colorimetric detection of lead ion (Pb²⁺) based on the assistance of DNAzyme and nanozyme instead of preamplification. The recognition between GR-5 DNAzyme and Pb²⁺ could trigger the CRISPR-Cas12a system. MnO₂ nanozymes connected with magnetic beads through single stranded DNA were prepared as the colorimetric signal probes and catalyst of CRISPR-Cas12a system for the strong oxidase-like activity inducing the color change of 3,3',5,5'-tetramethylbenzidine. The nanozyme-catalysed CRISPR-Cas12a system could be used to detect Pb²⁺ through the color change with high specificity and sensitivity. The linear range of this approach was 0.8 nM-2500 nM, with a limit of detection of 0.54 nM. This method was applied for the detection of the Pb²⁺ in food samples indicating good accuracy and anti-interference ability.

A high performance dual-mode biosensor based on Nd-MOF nanosheets functionalized with ionic liquid and gold nanoparticles for sensing of ctDNA

A dual-mode biosensor constructed based on photoelectrochemical (PEC) and electrochemical (EC) property was developed for assaying circulating tumor DNA (ctDNA), which is commonly used for triple-negative breast cancer diagnosis. Ionic liquid functionalized two-dimensional Nd-MOF nanosheets were successfully synthesized through a template-assisted reagent substituting reaction. Nd-MOF nanosheets integrated with gold nanoparticles (AuNPs) were able to improve photocurrent response and supply active sites for assembling sensing elements. To achieve selective detection of ctDNA, thiol-functionalized capture probes (CPs) were immobilized on the Nd-MOF@AuNPs modified glassy carbon electrode surface, thereby generating a "signal-off" photoelectrochemical biosensor for ctDNA under visible light irradiation. After the recognition of ctDNA, ferrocene-labeled signaling probes (Fc-SPs) were introduced into the biosensing interface. After hybridization between ctDNA and Fc-SPs, the oxidation peak current of Fc-SPs generated from square wave voltammetry can be employed as a "signal-on" electrochemical signal for ctDNA quantification. Under the optimized conditions, a linear relationship was obtained to the logarithm of ctDNA concentration in between 1.0 fmol L^-1 to 10 nmol L^-1 for the PEC model and 1.0 fmol L^-1 to 1.0 nmol L^-1 for the EC model. The dual-mode biosensor can provide accurate results for ctDNA assays, effectively eliminating the probable occurrence of false-positive or false-negative results in single-model assays. By switching DNA probe sequences, the proposed dual-mode biosensing platform can serve as a strategy for detecting other DNAs and possesses broad applications in bioassay and early disease diagnosis.

Recent Progress on Optical Biosensors Developed for Nucleic Acid Detection Related to Infectious Viral Diseases

Optical biosensors have many advantages over traditional analytical methods. They enable the identification of several biological and chemical compounds directly, instantly, and without the need of labels. Their benefits include excellent specificity, sensitivity, compact size, and low cost. In this review, the main focus is placed on the nucleic acid-based optical biosensor technologies, including colorimetric, fluorescence, surface plasmon resonance (SPR), Evanescent-Wave Optical, Fiber optic and bioluminescent optical fibre. The fundamentals of each type of biosensor are briefly explained, and particular emphasis has been placed on the achievements which have been gained in the last decade on the field of diagnosis of infectious viral diseases. Concluding remarks concerning the perspectives of further developments are discussed.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Optical reflectometric measurement of SARS-CoV-2 (COVID-19) RNA based on cationic cysteamine-capped gold nanoparticles

The coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged as a major public health outbreak in late 2019 and was proclaimed a global pandemic in March 2020. A reflectometric-based RNA biosensor was developed by using cysteamine-stabilized gold nanoparticles (cysAuNPs) as the colorimetric probe for bioassay of COVID-19 RNA (SARS-CoV-2 RNA) sequence. The cysAuNPs aggregated in the presence of DNA probes via cationic and anionic electrostatic attraction between the positively charged cysteamine ligands and the negatively charged sugar-phosphate backbone of DNA, whilst in the presence of target RNAs, the specific recognition between DNA probes and targets depleted the electrostatic interaction between the DNA probes and cysAuNPs signal probe, leading to dispersed particles. This has rendered a remarkable shifting in the surface plasmon resonance (SPR) on the basis of visual color change of the RNA biosensor from red to purplish hue at the wavelength of 765 nm. Optical evaluation of SARS-CoV-2 RNA by means on reflectance transduction of the RNA biosensor based on cysAuNPs optical sensing probes demonstrated rapid response time of 30 min with high sensitivity, good linearity and high reproducibility across a COVID-19 RNA concentration range of 25 nM to 200 nM, and limit of detection (LOD) at 0.12 nM. qPCR amplification of SARS-CoV-2 viral RNA showed good agreement with the proposed RNA biosensor by using spiked RNA samples of the oropharyngeal swab from COVID-19 patients. Therefore, this assay is useful for rapid and early diagnosis of COVID-19 disease including asymptomatic carriers with low viral load even in the presence of co-infection with other viruses that manifest similar respiratory symptoms.

Nanomaterials assisted exosomes isolation and analysis towards liquid biopsy

Exosomes has attracted tremendous research interests as they are emerging as a new paradigm of liquid biopsy. Although the concentration of exosomes in blood is relatively abundant, there still exists various vesicle-like nanoparticles, such as microvesicles, apoptotic bodies. It's an urgent need to isolate and enrich exosomes from the complex contaminants in biofluid samples. Moreover, the expressing level of exosomal biomarkers varies a lot, which make the sensitive molecular detection of exosomes in high demand. Unfortunately, the efficient isolation and sensitive molecular quantification of exosomes is still a major obstacle hindering the further development and clinical application of exosome-based liquid biopsy. Nanomaterials, with unique physiochemical properties, have been widely used in biosensing and analysis aspects, thus they are thought as powerful tools for effective purification and molecular analysis of exosomes. In this review, we summarized the most recent progresses in nanomaterials assisted exosome isolation and analysis towards liquid biopsy. On the one hand, nanomaterials can be used as capture substrates to afford large binding area and specific affinity to exosomes. Meanwhile, nanomaterials can also be served as promising signal transducers and amplifiers for molecular detection of exosomes. Furthermore, we also pointed out several potential and promising research directions in nanomaterials assisted exosome analysis. It's envisioned that this review will give the audience a complete outline of nanomaterials in exosome study, and further promote the intersection of nanotechnology and bio-analysis.

Biometric Photoelectrochemical-Visual Multimodal Biosensor Based on 3D Hollow HCdS@Au Nanospheres Coupled with Target-Induced Ion Exchange Reaction for Antigen Detection

Three-dimensional (3D) hollow photoactive nanomaterials can enhance light capture due to the light scattering benefiting from the unique hollow nanostructures, which contributes to the decrease in energy loss and the electron-hole recombination during the process of photoelectric conversion. Herein, a 3D hollow HCdS@Au nanosphere synthesized by the templated-assisted method and photodeposition is employed to construct a multimodal sensing platform by combining the photoelectrochemical (PEC) biosensor with colorimetric analysis and photothermal imaging. In the presence of target carcinoembryonic antigen (CEA), a sandwich structure is formed on magnetic beads based on the dual-aptamer recognition, followed by the initiation of rolling circle amplification (RCA) to bind numerous CuO-DNA probes. Upon stimulation by chlorhydric acidic, a large number of Cu²⁺ is released from CuO, which could interact with yellow HCdS@Au on electrode to produce dark CuS by ion exchange. As a result, with increased CEA level, the photocurrent is weakened and the color of electrode interface is changed from yellow to dark, which thus facilitates the PEC and colorimetric detection of CEA. Simultaneously, the formed CuS with highly photothermal effect can achieve qualitative visual analysis of CEA using a portable infrared thermal imager. This work exhibits an excellent performance for sensitive and selective detection of CEA in the dynamic working range from 0.015 to 2.4 ng/mL with a detection limit as low as 3.5 pg/mL. Moreover, the proposed PEC biosensor is successfully applied to CEA determination in human serum, which holds great promise in accurate analysis of biomarkers and early diagnosis of diseases in the clinic.

Modular Label-Free Electrochemical Biosensor Loading Nature-Inspired Peptide toward the Widespread Use of COVID-19 Antibody Tests

Limitations of the recognition elements in terms of synthesis, cost, availability, and stability have impaired the translation of biosensors into practical use. Inspired by nature to mimic the molecular recognition of the anti-SARS-CoV-2 S protein antibody (AbS) by the S protein binding site, we synthesized the peptide sequence of Asn-Asn-Ala-Thr-Asn-COOH (abbreviated as PEP2003) to create COVID-19 screening label-free (LF) biosensors based on a carbon electrode, gold nanoparticles (AuNPs), and electrochemical impedance spectroscopy. The PEP2003 is easily obtained by chemical synthesis, and it can be adsorbed on electrodes while maintaining its ability for AbS recognition, further leading to a sensitivity 3.4-fold higher than the full-length S protein, which is in agreement with the increase in the target-to-receptor size ratio. Peptide-loaded LF devices based on noncovalent immobilization were developed by affording fast and simple analyses, along with a modular functionalization. From studies by molecular docking, the peptide-AbS binding was found to be driven by hydrogen bonds and hydrophobic interactions. Moreover, the peptide is not amenable to denaturation, thus addressing the trade-off between scalability, cost, and robustness. The biosensor preserves 95.1% of the initial signal for 20 days when stored dry at 4 °C. With the aid of two simple equations fitted by machine learning (ML), the method was able to make the COVID-19 screening of 39 biological samples into healthy and infected groups with 100.0% accuracy. By taking advantage of peptide-related merits combined with advances in surface chemistry and ML-aided accuracy, this platform is promising to bring COVID-19 biosensors into mainstream use toward straightforward, fast, and accurate analyses at the point of care, with social and economic impacts being achieved.

RGB color analysis of formaldehyde in vegetables based on DNA functionalized gold nanoparticles and triplex DNA

A highly sensitive and selective RGB color analysis for the detection of formaldehyde (FA) was developed by using a DNA functionalized gold nanoparticle (AuNPs-DNA) probe. When complementary oligonucleotides (oligo 2 and oligo 3) and a silver ion (Ag⁺) were added to the AuNPs-DNA solution, triplex DNA was formed, resulting in the aggregation of AuNPs, and accompanied by a solution color change from red to purple. With the addition of formaldehyde, it reacted with Ag⁺, decreased the stability of triplex DNA between AuNPs-DNA, induced the dispersion of AuNPs, and the color of AuNPs recovered to red. Therefore, the formaldehyde concentration could be estimated with the RGB (red, green, blue) values of the AuNP solution by using a smartphone application (APP). The R value of the system was proportional to the concentration of formaldehyde within the range of 0.23-4.50 mg L^-1, with a detection limit of 0.14 mg L^-1. The method has been successfully applied to detect the residues of formaldehyde in vegetable samples and has the potential of the on-site determination of formaldehyde.

Materials with Tunable Optical Properties for Wearable Epidermal Sensing in Health Monitoring

Advances in wearable epidermal sensors have revolutionized the way that physiological signals are captured and measured for health monitoring. One major challenge is to convert physiological signals to easily readable signals in a convenient way. One possibility for wearable epidermal sensors is based on visible readouts. There are a range of materials whose optical properties can be tuned by parameters such as temperature, pH, light, and electric fields. Herein, this review covers and highlights a set of materials with tunable optical properties and their integration into wearable epidermal sensors for health monitoring. Specifically, the recent progress, fabrication, and applications of these materials for wearable epidermal sensors are summarized and discussed. Finally, the challenges and perspectives for the next generation wearable devices are proposed.

Nucleic Acids Detection for Mycobacterium tuberculosis Based on Gold Nanoparticles Counting and Rolling-Circle Amplification

Tuberculosis (TB) is a common infectious disease caused by Mycobacterium tuberculosis, which usually disturbs the lungs, and remains the second leading cause of death from an infectious disease worldwide after the human immunodeficiency virus. Herein, we constructed a simple and sensitive method for Mycobacterium tuberculosis-specific DNA detection with the dark-field microscopic imaging of gold nanoparticles (AuNPs) counting strategy and rolling-circle amplification (RCA). Taking advantage of RCA amplification, one target molecule produced hundreds of general oligonucleotides, which could form the sandwich structure with capture-strand-modified magnetic beads and AuNPs. After magnetic separation, AuNPs were released and detected by dark-field imaging; about 10 fM Mycobacterium tuberculosis-specific DNA target can still be differentiated from the blank. No significant change of the absorbance signals was observed when the target DNA to genomic DNA ratio (in mass) was from 1:0 to 1:10⁶. The spike recovery results in genomic DNA from human and Klebsiella pneumoniae suggested that the proposed method has the feasibility for application with biological samples. This proposed method is performed on an entry-level dark-field microscope setup with only a 6 μL detection volume, which creates a new, simple, sensitive, and valuable tool for pathogen detection.

Selection and Characterization of DNA Aptamers for Constructing Aptamer-AuNPs Colorimetric Method for Detection of AFM1

Aflatoxin M1 (AFM1), one of the most toxic mycotoxins, is a feed and food contaminant of global concern. To isolate the ssDNA aptamer of AFM1, synthesized magnetic graphene oxide nanomaterials, 12 rounds of subtractive systematic evolution of ligands by exponential enrichment (SELEX) selection were carried out. As a result, 24 candidate aptamers were selected, and their sequence similarity exceeded 97%. Their binding affinity and specificity were further examined by fluorescence and biofilm interferometry (BLI) methods. One aptamer (Apt-5) against AFM1 with a high affinity and specificity was isolated and demonstrated to be the optimal aptamer, whose dissociation constant reached the nanomolar level, Kd = 8.12 ± 1.51 nM. Additionally, molecular docking studies were used to predict the possible binding sites and mechanisms of the two. Based on Apt-5, an unlabeled aptamer-AuNPs colorimetric method was established to detect AFM1 in milk with a linear range of 0.078-10 ng/mL, and the actual detection limit was 0.078 ng/mL. These results demonstrated that this detection technique could be useful for the quantitative determination of AFM1 in milk and dairy products.

The Integration of Gold Nanoparticles with Polymerase Chain Reaction for Constructing Colorimetric Sensing Platforms for Detection of Health-Related DNA and Proteins

Polymerase chain reaction (PCR) is the standard tool in genetic information analysis, and the desirable detection merits of PCR have been extended to disease-related protein analysis. Recently, the combination of PCR and gold nanoparticles (AuNPs) to construct colorimetric sensing platforms has received considerable attention due to its high sensitivity, visual detection, capability for on-site detection, and low cost. However, it lacks a related review to summarize and discuss the advances in this area. This perspective gives an overview of established methods based on the combination of PCR and AuNPs for the visual detection of health-related DNA and proteins. Moreover, this work also addresses the future trends and perspectives for PCR-AuNP hybrid biosensors.

Advanced screening and tailoring strategies of pesticide aptamer for constructing biosensor

The rapid development of aptamers has helped address the challenges presented by the wide existed pesticides contaminations. Screening of aptamers with excellent performance is a prerequisite for successfully constructing biosensors, while further tailoring of aptamers with enhanced activity greatly improved the assay performance. Firstly, this paper reviewed the advanced screening strategies for pesticides aptamers, including immobilization screening that preserves the native structures of targets, non-immobilized screening based on nanomaterials, capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX), virtual screening in silico, high-throughput selection, and rational secondary library generation methods, which contributed significantly to improve the success rate of screening, reduce the screening time, and ensure aptamer binding affinity. Secondly, the precise tailoring strategies for pesticides aptamers were modularly elaborated, containing deletion, splitting, elongation, and fusion, which provided various advantages like cost-efficiency, enhanced binding affinity, and new derived functional motifs. Thirdly, the developed aptamer-based biosensors (aptasensors) for pesticide detection were systematically reviewed according to the different signal output modes. Finally, the challenges and future perspectives of pesticide detection are discussed comprehensively.

Selection and identification of high-affinity aptamer of Kunitz trypsin inhibitor and their application in rapid and specific detection

Kunitz trypsin inhibitor (KTI), a harmful protein, seriously affects food hygiene and safety. Therefore, a sensitive, efficient, and rapid method for KTI detection is urgently needed. Aptamers are short and single-stranded (ss) DNA that recognize target molecules with high affinity. This work used graphene oxide-SELEX (GO-SELEX) to screen KTI aptamers. The positive and reverse screening was designed to ensure the high specificity and affinity of the selected aptamers. After 10 rounds of screening, multiple nucleic acid chains were obtained, and the chains were sequenced. Three aptamers with better affinity were obtained, and the values of the dissociation constant (K d) were calculated to be 52.6 nM, 22.7 nM, and 67.9 nM, respectively. Finally, a colorimetric aptamer biosensor based on gold nanoparticles (AuNPs) was constructed. The biosensor exhibited a broader linear range of 30-750 ng/ml, with a lower detection limit of 18 ng/ml, and the spiked recovery rate was between 98.2% and 103.3%. This experiment preliminary demonstrated the potential of the application of KTI aptamer in the real sample tests.

A label-free colorimetric aptasensor based on split aptamers-chitosan oligosaccharide-AuNPs nanocomposites for sensitive and selective detection of kanamycin

Herein, the split aptamers, chitosan oligosaccharide, and AuNPs were combined as nanocomposites that present different formations to develop a label-free colorimetric aptasensor for rapid detection of small molecules. Kanamycin was chosen as a model target. Computational studies were performed to assist in the design of orientated immobilization of the split aptamers onto the AuNPs surface. Chitosan oligosaccharide was initially applied as an aggregation inducer of AuNPs, and chitopentaose was screened as the optimal. Under optimized conditions, the proposed aptasensor showed high sensitivity and selectivity, with a limit of detection of 20.58 nM, a linear range of 25-800 nM, and good recoveries of 98.49-104.9% and 85.69-107.0% when employed to detect kanamycin in tap water and milk samples, respectively. Only 55 min was needed for the whole assay. More importantly, this study can serve as a novel and robust reference for the aptasensing detection of other small molecules.

Emerging roles of the aptasensors as superior bioaffinity sensors for monitoring shellfish toxins in marine food chain

Shellfish toxins are derived from harmful algae and are easily accumulated in environment and marine food through the food chain, exposing high risks on human health. Preliminary rapid screening is one of the most effective monitoring ways to reduce the potential risks; however, the traditional methods encounter with many limitations, such as complicated procedures, low sensitivity and specificity, and ethical problems. Alternatively, bioaffinity sensors are proposed and draw particular attention. Among them, the aptasensors are springing up and emerging as superior alternatives in recent years, exhibiting high practicability to analyze shellfish toxins in real samples in the marine food chain. Herein, the latest research progresses of aptasensors towards shellfish toxins in the marine food chain in the past five years was reviewed for the first time, in terms of the aptamers applied in these aptasensors, construction principles, signal transduction techniques, response types, individual performance properties, practical applications, and advantages/disadvantages of these aptasensors. Synchronously, critical discussions were given and future perspectives were prospected. We hope this review can serve as a powerful reference to promote further development and application of aptasensors to monitor shellfish toxins, as well as other analytes with similar demands.

Mimetic peroxidase based on a gold amalgam for the colorimetric sensing of trace mercury(ii) in water samples

A simple and effective AuNPs/H-rGO/CC colorimetric sensing interface was constructed for the sensitive, selective, and facile determination of Hg2+ in water samples.

Bimetallic molecularly imprinted nanozyme: Dual-mode detection platform

Molecularly imprinted polymer nanozyme (MIL-101(Co,Fe)@MIP) with bimetallic active sites and high-efficiency peroxidase-like (POD-like) activity were synthesized for the ratiometric fluorescence and colorimetric dual-mode detection of vanillin with high selectivity and sensitivity. Compared with the monometallic nanozyme, the POD-like activity of bimetallic nanozyme was greatly enhanced by changing the electronic structure and surface structure. Ratiometric fluorescence and colorimetric dual-mode detection of vanillin in aqueous solution was realized by vanillin entering specific imprinted cavities and blocking the molecular channels on the surface of MIL-101(Co,Fe)@MIP and the dual-mode visual detection was also realized. The limits of detection were as low as 104 nM and 198 nM, respectively. The method proposed in this paper was applied to the real samples of ice cream and candy. And the recoveries were between 93.3% and 105.5%, which also reached a satisfactory degree. The further detection of dexamethasone and prednisone, two drugs belonging to glucocorticoid, proved that the nanozyme analysis method based on MIL-101(Co,Fe)@MIP could be developed into a sensing platform.

Advances in Colorimetric Assay Based on AuNPs Modified by Proteins and Nucleic Acid Aptamers

This review is focused on the biosensing assay based on AuNPs (AuNPs) modified by proteins, peptides and nucleic acid aptamers. The unique physical properties of AuNPs allow their modification by proteins, peptides or nucleic acid aptamers by chemisorption as well as other methods including physical adsorption and covalent immobilization using carbodiimide chemistry or based on strong binding of biotinylated receptors on neutravidin, streptavidin or avidin. The methods of AuNPs preparation, their chemical modification and application in several biosensing assays are presented with focus on application of nucleic acid aptamers for colorimetry assay for determination of antibiotics and bacteria in food samples.

Dual colorimetric strategy for specific DNA detection by nicking endonuclease-assisted gold nanoparticle signal amplification

The continuous spread of invasive alien species, as zebra mussel (Dreissena polymorpha), is a major global concern and it is urgent to stop it. Early stages of an invasion are crucial and challenging; however, detection tools based on environmental DNA analysis are promising alternatives. We present an alternative DNA target amplification strategy for signal enhancement followed by dual-mode colorimetric naked eye and optical smartphone analysis for the early detection of zebra mussel environmental DNA. Target amplification was designed based on the nicking endonuclease probe cleavage upon probe and complementary target hybridization. The cleaved/intact probe interacts with DNA-modified nanoparticles for colorimetric detection. We have demonstrated that enzyme amplification strategy enhanced 12-fold the sensitivity by naked eye detection, achieving a detection limit of ~8 nM (4.48×10¹⁰ copies) in controlled conditions, whereas target in complex environmental samples allowed the detection of 22.5 nM (1.26×10¹¹ copies). Competitive assays also showed that the system can discriminate specific zebra mussel DNA sequences from other DNA sequences. Additionally, smartphone analysis for DNA quantification further improved the sensitivity of its detection by 130-fold, more than 2 orders of magnitude, when applied to environmental samples. The limit of detection to 0.17 nM (9.52×10⁸ copies) is based on RGB coordinates, which is especially relevant to monitor early aggregation stages, being more accurate and reducing naked eye detection subjectivity. DNA extracted from zebra mussel meat, zebra mussel contaminated river water, and non-contaminated river water samples were successfully tested. Dual-mode colorimetric detection is useful in field analysis without the need for expensive laboratory equipment.

Transcription-Based Amplified Colorimetric Thrombin Sensor Using Non-Crosslinking Aggregation of DNA-Modified Gold Nanoparticles

Gold nanoparticles (AuNPs) have been employed as colorimetric biosensors due to the color difference between their dispersed (red) and aggregated (blue) states. Although signal amplification reactions triggered by structural changes of the ligands on AuNPs have been widely used to improve measurement sensitivity, the use of ligands is limited. In this study, we designed a AuNP-based signal-amplifying sandwich biosensor, which does not require a conformational change in the ligands. Thrombin was used as a model target, which is recognized by two different probes. In the presence of the target, an extension reaction occurs as a result of hybridization of the two probes. Then RNA synthesis is started by RNA polymerase activation due to RNA promoter duplex formation. The amplified RNA drives aggregation or dispersion of the AuNPs, and a difference of the color if the AuNP solution is observed. As this detection system does not require a conformational change in the ligand, it can be generically applied to a wide range ligands.

Nucleic Acid Amplification Techniques in Immunoassay: An Integrated Approach with Hybrid Performance

An immunoassay is mostly employed for the direct detection of food contaminants, and a molecular assay for targeting nucleic acids employs amplification techniques for distinguishing genes. The integration of an immunoassay with nucleic acid amplification techniques inherits the direct and rapid performance of an immunoassay and the ultrasensitive merit of a molecular assay. Enthusiastic attention has been attracted in recent years on the utilization of isothermal amplification techniques in an immunoassay, as well as the employment of a lateral flow immunoassay in a molecular assay. Thus, this Review discussed these kinds of approaches from two categories: immuno-nucleic acid amplification (I-NAA) and nucleic acid amplification-immunoassay (NAA-I). The advantages, drawbacks, and future developments were discussed for a comprehensive understanding.

Hairpin DNA-Mediated isothermal amplification (HDMIA) techniques for nucleic acid testing

Nucleic acid detection is of great importance in a variety of areas, from life science and clinical diagnosis to environmental monitoring and food safety. Unfortunately, nucleic acid targets are always found in trace amounts and their response signals are difficult to be detected. Amplification mechanisms are then practically needed to either duplicate nucleic acid targets or enhance the detection signals. Polymerase chain reaction (PCR) is one of the most popular and powerful techniques for nucleic acid analysis. But the requirement of costly devices for precise thermo-cycling procedures in PCR has severely hampered the wide applications of PCR. Fortunately, isothermal molecular reactions have emerged as promising alternatives. The past decade has witnessed significant progress in the research of isothermal molecular reactions utilizing hairpin DNA probes (HDPs). Based on the nucleic acid strand interaction mechanisms, the hairpin DNA-mediated isothermal amplification (HDMIA) techniques can be mainly divided into three categories: strand assembly reactions, strand decomposition reactions, and strand creation reactions. In this review, we introduce the basics of HDMIA methods, including the sensing principles, the basic and advanced designs, and their wide applications, especially those benefiting from the utilization of G-quadruplexes and nanomaterials during the past decade. We also discuss the current challenges encountered, highlight the potential solutions, and point out the possible future directions in this prosperous research area.