A portable colorimetric point-of-care testing platform for MicroRNA detection based on programmable entropy-driven dynamic DNA network modulated DNA-gold nanoparticle hybrid hydrogel film

A portable point-of-care testing platform for rapid and sensitive miRNA-21 detection for heart failure diagnosis

BACKGROUND

MicroRNAs (miRNAs) play a pivotal role in various physiological and pathological processes. In particular, miRNA-21 holds significant potential as a novel biomarker for the diagnosis of heart failure. The development of miRNA detection methods is rapidly advancing, with point-of-care testing (POCT) platforms garnering considerable attention. However, traditional methods are often hampered by their reliance on expensive instruments and complex procedures, limiting clinical applicability. Therefore, there is an urgent need to develop a simple, portable, sensitive, and rapid POCT platform for miRNA-21 detection.

RESULTS

In this work, we proposed a portable POCT platform using a colorimetric biosensor specifically sensitive for miRNA-21. The platform utilized 3,3',5,5'-tetramethylbenzidine as the signaling molecule, and a Linear G-quadruplex loaded with Blocker Nanostructures (LGBN) generated by the RCA reaction as the probe. Furthermore, changes in primary color channels (R/G/B) of TMB for miRNA-21 detection were analyzed via smartphone-based digital image recognition. Under optimal conditions, the platform showed a linear detection range between 0.01 nM and 1 nM, with limits of detection of 8.3 pM (colorimetric methods) and 9.5 pM (digital image colorimetry). Moreover, the colorimetric biosensor exhibited excellent specificity and resistance to interference, successfully detecting miRNA-21 in serum samples from heart failure patients.

SIGNIFICANCE

This detection method has an accuracy consistent with RT-qPCR results, providing a novel and practical approach with POCT for miRNA-21 detection.

A CRISPR/Cas12a-based colorimetric AuNPs biosensor for naked-eye detection of pathogenic bacteria in clinical samples

Pathogenic bacteria, such as Pseudomonas aeruginosa, pose significant threats to public health due to their multidrug resistance and association with severe infections. Rapid and reliable detection methods are crucial for timely treatment and effective infection control, especially in resource-limited settings. In this study, we developed a CRISPR/Cas12a-based colorimetric biosensor that leverages Cas12a's trans-cleavage activity to release left single-stranded DNA (lDNA). The released lDNA facilitates hybridization with clDNA-functionalized gold nanoparticles (AuNPs), resulting in a visible color change. The biosensor achieved a detection limit of 100 CFU/reaction for P. aeruginosa within 2 hours, with excellent specificity and robustness, as validated in spiked sputum and blood samples. Clinical testing using 32 blood samples (13 positive, 19 negative) confirmed its high diagnostic accuracy, achieving an AUC of 1 in ROC curve analysis. The platform's simplicity, robustness, and programmability suggest its broad potential for rapid infectious disease diagnostics, particularly in low-resource settings.

A Dual-Capture and Dual-Output 3D DNA Walker System Integrated with Ligases Enables Ultrasensitive Detection of Single-Nucleotide Polymorphisms

DNA walkers, as structurally and functionally programmable signal amplification tools, exhibit great potential for application in the field of biosensing. Traditional DNA walkers often rely on enzymes for operation, posing compatibility challenges, while the handful of existing enzyme-free DNA walkers demonstrate limited performance. To address this, we innovatively developed an efficient enzyme-free 3D DNA walker with dual capture and dual output capabilities. Coupled with ligase chain reaction (LCR), this system facilitates highly sensitive and specific detection of single nucleotide polymorphisms (SNPs). Specifically, LCR precisely identifies single-base mutations, effectively transmitting biological information. The 3D DNA walker system is based on entropy-driven circuit cycling reaction technology. In this system, LCR products serve as the driving strands for the DNA walker, independently binding to track strands and walking legs immobilized on gold nanoparticles, forming a unique dual signal capture mechanism. Each track strand carries two signal chains, significantly enhancing signal amplification efficiency. Benefiting from this novel enzyme-free 3D DNA walker strategy, our biosensing system exhibits exceptional sensitivity to mutant targets (MT), detecting MT at concentrations as low as 30.3 aM and distinguishing heterozygous samples with a 0.01% mutation frequency. Furthermore, this system has been successfully applied to genotyping and mutation abundance assessment of genomes from fresh soybean leaves, demonstrating its vast potential for practical applications. In summary, this research pioneers a novel enzyme-free 3D DNA walker with dual capture and dual output capabilities, and develops an ultrasensitive genotyping tool. This provides strong technical support for the advancement of genetic research.

Structure-switching G-quadruplex: An efficient CRISPR/Cas12a signal reporter for label-free colorimetric biosensing

G-quadruplex is widely used as a signal reporter for colorimetric biosensor construction. However, the effectiveness of CRISPR/Cas12a in trans-cleaving G-quadruplexes is significantly influenced by their resistance to nuclease, resulting in a weak colorimetric signal response. Herein, a structure-switching G-quadruplex regulated by transducer DNA is used as a signal reporter to construct CRISPR/Cas12a-based biosensors. The transducer DNA lacks a stable secondary structure, enabling efficient cleavage by CRISPR/Cas12a, which subsequently affects the catalytic activity of the G-quadruplex/hemin DNAzyme. We used microRNAs (miRNAs) and ATP as model targets to develop a label-free colorimetric detection platform. By optimizing the DNA sequences and reaction conditions, the biosensors exhibit excellent detection selectivity and sensitivity. The reliability of the proposed method was validated by its consistency with RT-qPCR for miRNAs detection and a commercial chemiluminescence kit for ATP assay, demonstrating its potential in clinical diagnosis and bioanalytical studies. The assay is concise and cost-effective because it does not require DNA labeling, magnetic separation, or enzymatic DNA amplification. Our design strategy avoids the use of G-quadruplex as a cleavage substrate for CRISPR/Cas12a while ensuring an efficient response of the G-quadruplex/hemin DNAzyme to CRISPR/Cas12a system, addressing the issue of G-quadruplex resistance to CRISPR/Cas12a nuclease activity.

DNA Hydrogels in Tissue Engineering: From Molecular Design to Next-Generation Biomedical Applications

DNA hydrogels have emerged as promising materials in tissue engineering due to their biocompatibility, programmability, and responsiveness to stimuli. Synthesized through physical and chemical crosslinking, these hydrogels can be categorized into functionalized types, such as those based on aptamers, and stimuli-responsive types that react to pH, temperature, and light. This review highlights their applications in tissue engineering, including drug delivery, cell culture, biosensing, and gene editing. DNA hydrogels can encapsulate therapeutic agents, support cell growth, and respond dynamically to environmental changes, making them ideal for tissue engineering. A comprehensive bibliometric analysis is included, identifying key research trends and emerging areas of interest in DNA hydrogel design, synthesis, and biomedical applications. The analysis provides a deeper understanding of the field's development and future research directions. Challenges such as mechanical strength, stability, and biosafety persist, but the integration of AI in hydrogel design shows promise for advancing their functionality in clinical applications.

A dual-trigger entropy driven circuit based on competitive hybridization for highly specific enzyme-free detection of single nucleotide polymorphisms

Single nucleotide polymorphisms (SNPs) play a pivotal role in the detection of major diseases and the breeding of molecular designs. However, current SNP detection methods often rely heavily on expensive proteases, or alternatively, enzyme-free detection methods grapple with limited specificity. Addressing this issue, our study presents an enzyme-free, highly specific, simple, and efficient detection platform. First, we introduced additional base mismatches into the traditional entropy-driven circuit (EDC) reaction to establish a foundational distinction between mutant (MT) and wild-type (WT) sequences. On this basis, we introduced the concept of competitive hybridization and developed a dual-trigger EDC (DEDC) reaction platform, which responded to both wild-type targets (WT) and mutant targets (MT). By strategically leveraging the signals from both WT and MT, we constructed a ratiometric signal output mode, substantially enhancing the discrimination factor between WT and MT and maximizing the specificity of the detection system. Within the DEDC reaction system, the sole driving force is the increase in the system's entropy, with no enzymes involved throughout the entire process, thereby achieving simple and efficient specific detection of SNPs. Notably, MT, previously considered an interference in assays, is repurposed as a trigger signal, making DEDC particularly suitable for the identification of heterozygous samples with low mutational abundances. By analyzing the performance of this platform and using it for genotyping detection of soybean real genome samples, the practical application potential of the CTMSD platform was verified. The CTMSD platform based on EDC reactions has the potential to become a universal biosensing paradigm for future biochemical applications.

Fluorescent biosensor for ultra-stability detection of Pax-5a based on a double cascade amplification strategy

The development of B-lymphoblastic leukemia is tightly associated with aberrant expression of Pax-5a. This work presented a novel dual signal amplification strategy-based Pax-5a detection method by combining the rolling circle amplification reaction (RCA) and the Entropy-driven toehold-mediated strand displacement (ETSD). Particularly noteworthy is the employed ETSD, which effectively improves the rate and stability of the reaction due to its unique entropy-driven principle. The uniqueness of this method is the combination of two amplification techniques, each utilizing its own strengths to achieve our intended purpose. This sensing method has been effectively used to determine the Pax-5a gene which with a reliable linear correlation for detection within a range and achieving a detection limit of 3.34 pM, calculated using the formula (3σ/S). Furthermore, even in 1 % of human serum samples, the biosensor can identify the target gene with exceptional sensitivity. The recovery rates fall within the range of 96.68-101.76 %, with a relative standard deviation (RSD) of 5.47 %. The method has a strong specificity based on sequence-specific hybridization of nucleic acids, thereby effectively preventing potential false-positive results. This fluorescent biosensor has a high detection capability for Pax-5a, and offers stable results. It provides a new way for early clinical diagnosis of acute lymphoblastic leukemia.

Redox-stimulated catalytic DNA circuit for high-fidelity imaging of microRNA and in situ interpretation of the relevant regulatory pathway

Biomolecules play essential roles in regulating the orderly progression of biochemical reaction networks. DNA-based biocircuits supplement an attractive and ideal approach for the visual imaging of endogenous biomolecules, yet their sensing performance is commonly encumbered by the undesired signal leakage. To solve this issue, here we proposed a glutathione (GSH)-activated DNA circuit for achieving the spatio-selective microRNA imaging through the successive response of a GSH-specific activation procedure and a non-enzymatic catalytic signal amplification procedure. In this design, by incorporating a disulfide bond into the pre-sealed nucleic acid probe, the uncontrolled circuitry leakage could be effectively ameliorated. In target cancer cells with high-abundant GSH and miR-21, endogenous GSH recognized and cleaved the pre-installed disulfide bond within DNA probes, thereby restoring the activity of circuitry components. The miR-21 then catalyzed the specific operation of circuitry for generating an amplified readout signal. We demonstrate that this system not only enables the effective discriminations of various cell types, but also contributes to the exploration of the correlationship between GSH and miR-21. This on-site activated DNA circuit can be extended to the robust analysis and exploration of different biomolecular interactions, offering a reliable reference for the in-depth understanding of biochemical interaction networks.

Breaking barriers in cancer diagnosis: unveiling the 4Ms of biosensors

Cancer, an insidious affliction, continues to exact a heavy toll on humanity, necessitating early detection and nuanced comprehension of its intricacies for effective treatment. Recent strides in micro and nanoscale electronic chip fabrication have revolutionized biosensor technology, offering promising avenues for biomedical and telemedicine applications. Micro Electromechanical System (MEMS)-based integrated circuits (ICs) represent a paradigm shift in detecting chemical and biomolecular interactions pertinent to cancer diagnosis, supplanting conventional methodologies. Despite the wealth of research on biosensors, a cohesive framework integrating Material, Mechanism, Modeling, and Measurement (4M) dimensions is often lacking. This review aims to synthesize these dimensions, exploring recent breakthroughs in biosensor design and development. Categorized based on electromechanical integration, material selection, and fabrication processes, these biosensors bridge crucial knowledge gaps within the research community. A comparative analysis of sensing methods in point-of-care (PoC) technology provides insights into their practicality and efficacy. Moreover, we critically evaluate biosensor limitations, pivotal in addressing challenges hindering their global commercialization.

Entropy-Driven Circuit Integrated with Ligases to Regulate DNA-AuNP Network Disintegration for Colorimetric Detection of Single Nucleotide Polymorphisms

In recent years, entropy-driven circuit (EDC) dynamic DNA networks have garnered significant attention in nucleic acid detection owing to their simplicity, efficiency, and flexible design. Nevertheless, conventional EDC reactions face a constraint in achieving optimal signal amplification due to a solitary and feeble driving force. To overcome this limitation, we innovatively devised a gold nanoparticle (AuNP) dispersion-enhanced EDC (Au-EDC) approach, pioneering a novel colorimetric signal amplification and output system. The system was harmoniously integrated with the ligase chain reaction (LCR) for precise single nucleotide polymorphism (SNP) genotyping. Specifically, LCR was selectively executed solely on the positive strand of the mutant target (MT), facilitating precise point-to-strand information transduction. Subsequently, the LCR product triggered the Au-EDC cycling reaction, causing the DNA-AuNPs network to progressively disintegrate and release a pronounced colorimetric signal. This strategic design ingeniously harnessed the entropy increase that occurs as AuNPs undergo a transition from aggregated to dispersed states, offering a supplemental impetus for the EDC cycle. The integrated LCR-Au-EDC system excelled in detecting MT at concentrations as low as 320 fM and differentiating pooled samples with mutation frequencies as low as 0.1%. Moreover, the system accurately performed SNP genotyping on the real genomes derived from soybean leaves. Consequently, this study not only develops a colorimetric signal amplification and output sensing system based on EDC reactions but also provides a cost-effective and efficient SNP genotyping tool.

Colorimetric, Quantitative, and Portable Liquid Crystal Elastomer Biosensing of Cholesterol and Malathion

Cholesteric liquid crystal elastomers (CLCEs) possess a unique characteristic that allows the manipulation of the reflected color by adjusting the spacing between layers. This attribute can create a reliable and cost-effective colorimetric sensing platform for the on-site detection of various substances. In this study, CLCE films were coupled with cross-linked poly(acrylic acid) (CLCE-PAA) or poly(dimethylaminoethyl methacrylate) (CLCE-PDA) films to monitor cholesterol and malathion levels, respectively. In both cases, the color change is recorded by a mobile phone camera, and the reflectance wavelength is measured spectrophotometrically. For on-site detection, a smartphone application was used to capture the film's image, process the color data into hue (H) values, and calculate the corresponding concentration of the tested analyte via an analysis program. Cholesterol and malathion can be detected within a linear range of 0.2-1.0 mM and 1-10,000 ng/mL, respectively. The corresponding recoveries for actual sample analysis were 86-115% and 87-122% for cholesterol and malathion, respectively. This system offers a practical solution for on-site testing of cholesterol and malathion in biological and environmental samples.

Oligoadenine Strand Functionalized Polyacrylamide Hydrogel Film Exhibiting pH-Triggered High-Degree Inverse Shape Deformations

Smart shape-memory DNA hydrogels, which can respond to various types of external stimuli and undergo macroscopic shape deformations, have shown great potential in various applications. By constructing free-standing films, the deformation and response properties of these hydrogels can be further enhanced, and visualized deformation can be achieved. However, DNA hydrogels that can exhibit rapid and high-degree shape deformations, such as the inverse shape deformations, are still lacking. Herein, free-standing oligoadenine strand-functionalized polyacrylamide hydrogel films were developed that can exhibit reversible and high degree of inverse shape deformation upon cyclic pH changes. The oligoadenine strands exhibit a pH-stimulated reversible conformational transition between a flexible single-stranded state and parallel duplex A-motif structures, resulting in their role change in the film from negatively charged side chains to "head-to-head" crosslinking structures, driving a high degree of inverse shape deformation with a relative bending angle change of 223.7 % of the film, which is more than 5 times that of a film driven by pH-responsive i-motif structures, facilitating the development of bilayer hydrogel film actuators with potential in flexible sensors and robots.

Entropy driven-based catalytic biosensors for bioanalysis: From construction to application-A review

The rapid advancement of precision medicine and the continuous emergence of novel pathogens have presented new challenges for biosensors, necessitating higher requirements. Target amplification technology serves as the core component in biosensor construction. Enzyme-based amplification methods are often sensitive and selective but involve relatively complex operational steps, whereas enzyme-free amplification methods offer simplicity but frequently fail to meet both sensitivity and selectivity simultaneously. Existing research has confirmed that entropy-driven catalyst (EDC) biosensors not only fulfills the demands for sensitivity and selectivity concurrently but also offers ease of operation and flexibility in construction. In this review, we summarize the key advantages of EDC, explore how to construct DNA nanomachines based on these advantages to achieve intracellular detection and simultaneous detection of multiple targets, as well as point-of-care testing (POCT) to address practical issues in clinical diagnosis and treatment. We also anticipate potential challenges, propose corresponding solutions, and outline future development directions for EDC-based biosensors in practical clinical applications. We firmly believe that EDC sensors will emerge as a crucial branch within the realm of biosensor development.

An intelligent fluorescence sensing platform based on entropy-driven toehold-mediated strand displacement cycle reaction for point-of-care testing of miRNA

BACKGROUND

MicroRNA (miRNA) has gradually become an emerging biomarker for early diagnosis and prognosis of various diseases due to its specific gene expression and high stability. With the development of molecular diagnosis and point-of-care testing (POCT) technology, developing simple, fast, sensitive, efficient, and low-cost miRNA sensors is of great significance for clinical applications and emergency rapid diagnosis. At present, entropy-driven toehold mediated chain displacement reaction, as a promising enzyme free isothermal amplification technique, is an important tool for ultra-sensitive biosensing applications.

RESULTS

In this study, we used gold nanoparticles (AuNPs) as carriers and quenchers, modified them using self-assembled triple chain composite substrates AuNPs@A@B1/B2, and used dual reporter molecules for cascade cyclic amplification to amplify fluorescence signals, which proposed a fluorescent biosensor based on this reaction and build an intelligent fluorescence sensing platform for rapid detection of miRNA. We designed a highly specific self-programmable sensor using the acute ischemic stroke (AIS) biomarker miRNA-125a-5p as a sample, and achieved sensitive detection of miRNA in the range of 0.01 μM∼10 μ M under optimal conditions. It broke through the traditional detection limitations of weak signals and liberated the fluorescence detection environment.

SIGNIFICANCE

In summary, this creative miRNA biosensor combined with POCT has demonstrated extraordinary detection potential, broad application prospects in the early diagnosis and prognosis monitoring of AIS, provides a novel miRNA universal detection strategy for the fields of biological and life sciences.

Application of smart-responsive hydrogels in nucleic acid and nucleic acid-based target sensing: A review

In recent years, nucleic acid-related sensing and detection have become essential in clinical diagnostics, treatment and genotyping, especially in connection with the Human Genome Project and the COVID-19 pandemic. Many traditional nucleic acid-related sensing strategies have been employed in analytical chemistry, including fluorescence, colorimetric and chemiluminescence methods. However, their key limitation is the lack of understanding of the interaction during analysis, particularly at the 3D matrix level close to biological tissue. To address this issue, smart-responsive hydrogels are increasingly used in biosensing due to their hydrophilic and biocompatible properties. By combining smart-responsive hydrogels with traditional nucleic acid-related sensing, biological microenvironments can be mimicked, and targets can be easily accessed and diffused, making them ideal for nucleic acid sensing. This review focuses on utilizing smart-responsive hydrogels for nucleic acid-related sensing and detection, including nucleic acid detection, other nucleic acid-based analyte detection and nucleic acid-related sensing platforms applying nucleic acid as sensing tools in hydrogels. Additionally, the analytical mechanisms of smart-responsive hydrogels with the combination of various detection platforms such as optical and electrochemical techniques are described. The limitations of using smart-responsive hydrogels in nucleic acid-related sensing and proposed possible solutions are also discussed. Lastly, the future challenge of smart-responsive hydrogels in nucleic acid-related sensing is explored. Smart-responsive hydrogels can be used as biomimetic materials to simulate the extracellular matrix, achieve biosensing, and exhibit great potential in nucleic acid-related sensing. They serve as a valuable complement to traditional detection and analytical methods.

Point-of-care testing for early-stage liver cancer diagnosis and personalized medicine: Biomarkers, current technologies and perspectives

Liver cancer is a highly prevalent and lethal form of cancer worldwide. In the absence of early diagnosis, treatment options for this disease are severely restricted. Recent advancements in genomics and bioinformatics have facilitated the discovery of a multitude of novel biomarkers that accurately depict an individual's disease diagnosis, progression, and treatment response. Leveraging these breakthroughs, personalized medicine employs an individual's biomarker profile to enable early detection of liver cancer and inform decisions regarding treatment selection, dosage determination, and prognosis assessment. The current lack of readily applicable, timely, and economically viable tools for biomarker analysis has hindered the incorporation of personalized medicine into regular clinical procedures. Over the past decade, significant advancements have been achieved in the field of molecular point-of-care testing (POCT) and amplification techniques, leading to substantial improvements in the diagnosis of liver cancer and the implementation of precision medicine. Instrument-free PCR technology or plasma PCR technology can shorten the complex procedure of in vitro detection of nucleic acid-based biomarkers. Also, compared to traditional ELISA, various nanomaterials modified with monoclonal antibodies to target proteins for recognition, capture, and detection have improved the efficiency of protein-based biomarker detection. These advances have reduced the time and cost of clinical detection of early-stage hepatocellular carcinoma and improved the efficiency of timely diagnosis and survival of suspected patients while reducing unnecessary testing costs and procedures. This review aims to provide a comprehensive overview of the current and emerging biomarkers employed in the early detection of liver cancer, as well as the advancements in point-of-care molecular testing technology and platforms. The primary objective is to assess their potential in facilitating the implementation of personalized medicine. This review ultimately revealed that the diagnosis of early-stage hepatocellular carcinoma not only requires sensitive biomarkers, but its various modifications and changes during the progression of cirrhosis to early-stage hepatocellular carcinoma will be a greater focus of our attention in the future. The rapid development of POCT has facilitated the opportunity to readily detect liver cancer in the general population in the future, and the integration of multi-pathway multiplexing and intelligent algorithms has improved the sensitivity and accuracy of early liver cancer biomarker detection. It is expected that the integration of point-of-care technology will be instrumental in the widespread adoption of personalized medicine in the foreseeable future.

A colour sensor integrated into a microcontroller platform as a reliable tool for measuring pH changes in biochemistry applications

Colorimetry is a widely used technique for optical detection in point-of-care testing and on-site detection. Although some studies employ a multiplex approach to analyse coloured solutions, many still analyse one sample at a time. We have prepared a simple and affordable colorimetric assay based on a TCS34725 colour sensor (ams-OSRAM) integrated into an M5Stack module and an RGB LED module both inserted into a 3D printed frame. We found that the colorimetric assay can be easily transferred to a colour sensing platform, and the signal range obtained using the prepared colorimeter is more than 200 times larger than that obtained using digital image colorimetry (DIC) for the same samples containing cholinesterase or urease as a model enzyme providing a change in pH of the processed solution. The assay appears to be ready for practical use.

Entropy-Driven Catalytic G-Quadruple Cycle Amplification Integrated with Ligases for Label-Free Detection of Single Nucleotide Polymorphisms

G-Quadruplex/thioflavin (G4/THT) has become a very promising label-free fluorescent luminescent element for nucleic acid detection due to its good programmability and compatibility. However, the weak fluorescence efficiency of single-molecule G4/THT limits its potential applications. Here, we developed an entropy-driven catalytic (EDC) G4 (EDC-G4) cycle amplification technology as a universal label-free signal amplification and output system by properly programming classical EDC and G4 backbone sequences, preintegrated ligase chain reaction (LCR) for label-free sensitive detection of single nucleotide polymorphisms (SNPs). First, the positive strand LCR enabled specific transduction and preliminary signal amplification from single-base mutation information to single-strand information. Subsequently, the EDC-G4 cycle amplification reaction was activated, accompanied by the production of a large number of G4/THT luminophores to output fluorescent signals. The EDC-G4 system was proposed to address the weak fluorescence of G4/THT and obtain a label-free fluorescence signal amplification. The dual-signal amplification effect enabled the LCR-EDC-G4 detection system to accurately detect mutant target (MT) at concentrations as low as 22.39 fM and specifically identify 0.01% MT in a mixed detection pool. Moreover, the LCR-EDC-G4 system was further demonstrated for its potential application in real biological samples. Therefore, this study not only contributes ideas for the development of label-free fluorescent biosensing strategies but also provides a high-performance and practical SNP detection tool in parallel.

SERS biosensors based on catalytic hairpin self-assembly and hybridization chain reaction cascade signal amplification strategies for ultrasensitive microRNA-21 detection

A highly sensitive surface-enhanced Raman scattering (SERS) biosensor has been developed for the detection of microRNA-21 (miR-21) using an isothermal enzyme-free cascade amplification method involving catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR). The CHA reaction is triggered by the target miR-21, which causes hairpin DNA (C1 and C2) to self-assemble into CHA products. After AgNPs@Capture captures the resulting CHA product, the HCR reaction is started, forming long-stranded DNA on the surface of AgNPs. A strong SERS signal is generated due to the presence of a large amount of the Raman reporter methylene blue (MB) in the vicinity of the SERS "hot spot" on the surface of AgNPs. The monitoring of the SERS signal changes of MB allows for the highly sensitive and specific detection of miR-21. In optimal conditions, the biosensor exhibits a satisfactory linear range and a low detection limit for miR-21 of 42.3 fM. Additionally, this SERS biosensor shows outstanding selectivity and reproducibility. The application of this methodology to clinical blood samples allows for the differentiation of cancer patients from healthy controls. As a result, the CHA-HCR amplification strategy used in this SERS biosensor could be a useful tool for miRNA detection and early cancer screening.

Nanoenzyme Hydrogel Film-Based Portable Point-of-Care Testing Platform for Double-Signal Visual Detection of PSA

The development of the Point-of-Care Testing (POCT) platform that combines convenience and cost-effectiveness is crucial for enabling the visual detection of disease biomarkers. In this work, a POCT platform for the sensitive in situ detection of prostate specific antigen (PSA) with dual-signal output was constructed by functionalizing the Eppendorf (EP) tube. This was achieved through the modification of aptamer hairpin probes (AHPs) on the lid of the EP tube and the assembly of a nanoenzyme hydrogel film on its inner wall. The target could trigger the release of Ag+ by AHP and subsequently activate Ag+-dependent DNAzyme (Ag-DNAzyme). This would initiate the cleavage of the DNA-Au/Pt NP hydrogel network, leading to the release of Au/Pt NPs. The released Au/Pt NPs exhibit both peroxidase (POD)-like and catalase (CAT)-like activity to produce a colorimetric response and induce liquid flow under pressure. Therefore, the target can be measured visually and quantitatively through colorimetric analysis and the measurement of total dissolved solids (TDS) using a pressure-triggered liquid flow device integrated into the platform. The designed platform is distinguished by its simplicity, specificity, cost-effectiveness, and remarkable sensitivity. It allows for the visual detection of PSA within concentration ranges of 0.5-100 ng/L (colorimetric) and 3-100 ng/L (TDS reading), boasting detection limits as low as 0.15 ng/L (colorimetric) and 0.57 ng/L (TDS reading). The strategy of target-triggered nanoenzyme release significantly enhances sensitivity and provides a guiding approach for visual biomarker detection.

Highly sensitive miRNA-21 detection with enzyme-free cascade amplification biosensor

In this study, we present an enzyme-free fluorescence biosensor for the highly sensitive detection of miRNA-21, a crucial biomarker in clinical diagnosis. Our innovative approach combines catalytic hairpin assembly (CHA) and entropy-driven amplification into a cascade amplification strategy. MicroRNA initiates the catalytic hairpin assembly reaction, liberating the trigger region needed for the entropy-driven amplification reaction. This triggers a series of strand displacement reactions, resulting in the separation of the fluorescence resonance energy transfer pair and an amplified fluorescence signal from FAM. Our cascade amplification strategy achieves ultra-sensitive microRNA detection, with an impressive limit of detection (LOD) of 1.3 fM, approximately 100-fold lower than CHA alone. Additionally, we successfully applied this biosensor for microRNA quantification in human serum and cell lysates, demonstrating its practicality and potential for early diagnosis.

Glucose-metabolism-triggered colorimetric sensor array for point-of-care differentiation and antibiotic susceptibility testing of bacteria

Simple and sensitive discrimination of multiple bacteria and antimicrobial susceptibility test (AST) are significant for food safety, clinical diagnosis and treatment. Herein, based on different metabolic ability of bacteria on glucose, we presented a colorimetric sensor array for point-of-care testing (POCT) of multiple bacteria with methyl red (MER), bromothymol blue (BTB) and bromocresol green (BCG) as probes. Different bacteria resulted in different color changes of three probes, which was converted to RGB (Red (R)/Green (G)/Blue (B)) signals by the color recognizer APP loaded on smartphone. The sensor array performed differentiation of eleven species of bacteria, achieving the quantitative analysis of individual bacteria in tap water and differentiation of bacterial mixtures. Interestingly, the sensor array can be used for AST and evaluating minimal inhibitory concentration (MIC) of antibiotics to bacteria. The research provided meaningful guidance for distinguishing multiple bacteria and evaluating MIC, presenting great potential in practical application.

A microfluidic concentration gradient colorimetric system for rapid detection of nitrite in surface water

A microfluidic concentration gradient colorimetric detection system consisting of a microfluidic concentration gradient colorimetric detection chip, a self-built colorimetric signal acquisition box and a self-written smartphone APP was constructed for the rapid, in-field and visual quantitative detection of nitrite. Specifically, nitrite with initial concentration of C0 can be automatically diluted into 8 concentration gradients characterized by arithmetic series, and the concentrations are 0, 0.20 C0, 0.33 C0, 0.46 C0, 0.59 C0, 0.72 C0, 0.86 C0 and C0. The colorimetric signal acquisition box avoided the interference of light spots on data acquisition. Under the optimal experimental conditions, the quantitative detection of nitrite was achieved by the proposed two-step colorimetric method based on the inhibition of AuNPs signal amplification, and the limit of detection (LOD) was 0.14 mg/L. The microfluidic concentration gradient colorimetric detection system was able to detect nitrite as low as 0.43 mg/L and showed a good specificity. The practical application was investigated by analyzing 10 actual samples of river and lake water, pure water and tap water. The recoveries of the microfluidic concentration gradient colorimetric detection system ranged from 94.92% to 105.60%, which indicates that the method had a good application prospect in the detection of practical samples.

Target-Responsive DNA Nanoclaw for the On-Site Identification of Chinese Medicines with Naked Eye

The identification of Chinese medicinal herbs occupies a crucial part in the development of the food and drug market. Although molecular identification based on real-time PCR offers good versatility and uniform digital standards compared with traditional methods, such as morphology, the dependence on large-scale equipment hinders spot detection and marketable applications. In this study, we developed a DNA nanoclaw for colorimetric detection and visible on-site identification of Chinese medicines. When specific miRNA is present, the DNAzyme is activated and cleaves the substrate strand, triggering the catalytic hairpin assembly (CHA) reaction and forming branched DNA junctions on AuNP-I. This can then capture AuNP-II through hybridization and facilitate their aggregation, resulting in a noticeable color change that is observable to the naked eye. By harnessing the dual amplification of DNAzyme and CHA, this highly sensitive nanoprobe successfully achieved specific identification of Chinese medicines. This offers a new perspective for on-site testing in the herbal market.

Precise quantification of microRNAs based on proximity ligation of AuNPs-immobilized DNA probes

MiRNAs are critical regulators of target gene expression in many biological processes and are considered promising biomarkers for diseases. In this study, we developed a simple, specific, and sensitive miRNA detection method based on proximity ligation reaction, which is easy to operate. The method uses a pair of target-specific DNA probes immobilized on the same gold nanoparticles (AuNPs), which hybridize to the target miRNA. Hybridization brings the probes close together, allowing the formation of a continuous DNA sequence that can be amplified by Quantitative Real-time PCR (qPCR). This method eliminates the need for complex reverse transcription design and achieves high specificity for discriminating single base mismatches between miRNAs through a simple procedure. This method can sensitively measure three different miRNAs with a detection limit of 20 aM, providing high versatility and sensitivity, even distinguishing single-base variations among members of the miR-200 family with high selectivity. Due to its high selectivity and sensitivity, this method has important implications for the investigation of miRNA biological functions and related biomedical research.

Exo I signal amplification of a DNA hydrogel film combined with capillary self-driven action for EpCAM detection

Target-responsive aptamer hydrogels are increasingly used in the field of analytical sensing with different morphologies developed by various strategies. Herein, we developed a DNA hydrogel film combined with capillary self-driven action for the specific detection of the tumor marker EpCAM and further introduced Exo I for signal amplification. EpCAM aptamer was used as a crosslinking agent to construct the DNA hydrogel film. When EpCAM was present, it competed for binding with the EpCAM aptamer, resulting in a permeability change of the DNA hydrogel film attached to one end of the capillary, and leading to different solution flow rates through the capillaries that can be utilized for the quantitative detection of EpCAM. This method did not require any instrument and was easy to use. The distance the solution travelled through the capillary was quantified as the concentration of EpCAM, and only a small amount of DNA hydrogel was required for each detection. The detection limit of EpCAM was as low as 0.018 ng mL-1, while offering the advantages of good stability and specificity, and showing great potential in point-of-care testing.

A Cas12a-based platform combined with gold nanoparticles for sensitive and visual detection of Alternaria solani

Alternaria solani (A. solani), the causal agent of early blight in potatoes, poses a serious and persistent threat to potato production worldwide. Therefore, developing a method that can accurately detect A. solani in the early stage to avoid further spread is urgent. However, the conventional PCR-based method is not appropriate for application in the fields. Recently, the CRISPR-Cas system has been developed for nucleic acids analysis at point-of-care. Here, we propose a gold nanoparticles-based visual assay combining loop-mediated isothermal amplification with CRISPR-Cas12a to detect A. solani. After optimization, the method could detect 10-3 ng/μL genomic gene of A. solani. The specificity of the method was confirmed by discriminating A. solani from other three highly homologous pathogens. We also developed a portable device that could be used in the fields. By integrating with the smartphone readout, this platform holds significant potential in high-throughput detection of multiple pathogens in the fields.

Advances in Point-of-Care Testing of microRNAs Based on Portable Instruments and Visual Detection

MicroRNAs (miRNAs) are a class of small noncoding RNAs that are approximately 22 nt in length and regulate gene expression post-transcriptionally. miRNAs play a vital role in both physiological and pathological processes and are regarded as promising biomarkers for cancer, cardiovascular diseases, neurodegenerative diseases, and so on. Accurate detection of miRNA expression level in clinical samples is important for miRNA-guided diagnostics. However, the common miRNA detection approaches like RNA sequencing, qRT-PCR, and miRNA microarray are performed in a professional laboratory with complex intermediate steps and are time-consuming and costly, challenging the miRNA-guided diagnostics. Hence, sensitive, highly specific, rapid, and easy-to-use detection of miRNAs is crucial for clinical diagnosis based on miRNAs. With the advantages of being specific, sensitive, efficient, cost-saving, and easy to operate, point-of-care testing (POCT) has been widely used in the detection of miRNAs. For the first time, we mainly focus on summarizing the research progress in POCT of miRNAs based on portable instruments and visual readout methods. As widely available pocket-size portable instruments and visual detection play important roles in POCT, we provide an all-sided discussion of the principles of these methods and their main limitations and challenges, in order to provide a guide for the development of more accurate, specific, and sensitive POCT methods for miRNA detection.

Amplification-free electrochemical biosensor detection of circulating microRNA to identify drug-induced liver injury

Drug-induced liver injury (DILI) is a major challenge in clinical medicine and drug development. There is a need for rapid diagnostic tests, ideally at point-of-care. MicroRNA 122 (miR-122) is an early biomarker for DILI which is reported to increase in the blood before standard-of-care markers such as alanine aminotransferase activity. We developed an electrochemical biosensor for diagnosis of DILI by detecting miR-122 from clinical samples. We used electrochemical impedance spectroscopy (EIS) for direct, amplification free detection of miR-122 with screen-printed electrodes functionalised with sequence specific peptide nucleic acid (PNA) probes. We studied the probe functionalisation using atomic force microscopy and performed elemental and electrochemical characterisations. To enhance the assay performance and minimise sample volume requirements, we designed and characterised a closed-loop microfluidic system. We presented the EIS assay's specificity for wild-type miR-122 over non-complementary and single nucleotide mismatch targets. We successfully demonstrated a detection limit of 50 pM for miR-122. Assay performance could be extended to real samples; it displayed high selectivity for liver (miR-122 high) comparing to kidney (miR-122 low) derived samples extracted from murine tissue. Finally, we successfully performed an evaluation with 26 clinical samples. Using EIS, DILI patients were distinguished from healthy controls with a ROC-AUC of 0.77, a comparable performance to qPCR detection of miR-122 (ROC-AUC: 0.83). In conclusion, direct, amplification free detection of miR-122 using EIS was achievable at clinically relevant concentrations and in clinical samples. Future work will focus on realising a full sample-to-answer system which can be deployed for point-of-care testing.