HCR/DNAzyme-triggered cascaded feedback cycle amplification for self-powered dual-photoelectrode detection of femtomolar HPV16

A novel amplification strategy based on target-induced multicomponent nuclease-mediated catalytic hairpin assembly for fluorescent DNA sensor

Ochratoxin A (OTA) is a highly hazardous mycotoxin widely found in food ingredients and processed products. In response to the demand for food safety, there is an urgent need to establish a highly sensitive, reliable, and cost-effective method for the detection of OTA. In this study, a simple, enzyme-free, sensitive cascade amplification fluorescent strategy was developed to detect OTA based on a magnetic separation system-assisted, multicomponent nuclease (MNAzyme) and its induced catalytic hairpin assembly (CHA). The formation of a stable active MNAzyme was induced by the presence of the target, and the MNAzyme specifically cleaved multiple hairpin H1 to produce sDNA fragments. The sDNA could initiate the mismatched CHA cycle, leading to the production of a large number of H2-H3 complexes, with carboxyfluorescein (FAM) moving away from the quench group (BHQ1), and the fluorescent signal being significantly amplified. The constructed fluorescent aptasensor has a good linear range (0.5-100 ng/mL) and detection limit (0.45 ng/mL). The developed sensor was successfully applied to detect OTA in corn flour and black tea samples.

Interface self-shelling effect-mediated photoinduced carrier transport and multiplexed signal amplification mechanism in self-powered photoelectrochemical biosensing

In the realm of biomedical diagnostics, the development of sensitive and specific detection methods for cancer biomarkers is of paramount importance. Herein, we report on the design and implementation of a self-powered photoelectrochemical (PEC) sensor that harnesses amplified photocathode signals for the deterioration of carbohydrate antigen 125 (CA125) associated with ovarian cancer. This self-powered sensing platform integrates Cu2O/Cu3SnS4 heterojunction and ZnIn2S4 sensitized TiO2 with flower-like structure as photocathode and photoanode. Moreover, the PEC biosensor introduces the interface shedding effect to overcome the limitations of weak or unstable photocathode PEC signals. When MnO2 nanoparticles are used as the quenching source, the cathode photocurrent experiences a reduction to a certain extent owing to the phenomenon of competitive light absorption. To enhance the application for efficient CA125 detection, the interface self-shelling effect is introduced. The effect is implemented through the hydrolysis reaction of Acetylcholinesterase (AChE), producing thiocholine (TCh) as the interface detachment initiator. Which resulting in the detachment of layer modifiers, including MnO2, from the electrode surface and achieving the effect of significant enhancement of the photoelectric signal. Therefore, multiple signal amplification effects synergistically enhanced the photoelectric response. The self-powered PEC biosensing with a wide linear range of 0.001 U/mL-200 U/mL and a low detection limit of 0.32 mU/mL, which shows excellent performance in terms of sensitivity, specificity, and stability, making it a promising candidate for point-of-care diagnostics.

The Trend of Nonenzymatic Nucleic Acid Amplification: Strategies and Diagnostic Application

Nonenzymatic nucleic acid amplification reactions, especially nonenzymatic DNA amplification reactions (NDARs), are thermodynamically driven processes that operate without enzymes, relying on toehold-mediated strand displacement (TMSD) and branch migration. With their sensitive and efficient signal amplification capabilities, NDARs have become essential tools for biomarker detection and intracellular imaging. They encompass four primary amplification methods: catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), DNAzyme-based amplification, and entropy-driven circuits (EDC). Based on amplification mechanisms, NDARs can be categorized into three types: stimuli-responsive NDARs, which employ single amplification strategies triggered by specific stimuli like pH, light, or biomolecules; cascade NDARs, which integrate two or more amplification reactions for stepwise signal enhancement; and autocatalytic NDARs, which achieve exponential amplification through self-sustained cycling. These advanced designs progressively improve amplification efficiency, enhance sensitivity, and minimize background noise, enabling precise detection of proteins, viruses, and nucleic acids as well as applications in cancer cell imaging and therapy. Compared with classical NDARs, these approaches significantly reduce signal leakage, offering broader applicability in diagnostics, imaging, and therapeutic contexts. This review summarizes recent advancements, addresses existing challenges, and explores future directions, providing insights into the development and applications of NDARs.

Advancements in fluorescent nanobiosensors for HPV detection: from integrating nanomaterials to DNA nanotechnology

Human papillomavirus (HPV) is a leading cause of cervical cancer and other malignancies, necessitating the development of highly sensitive and specific detection tools. This review explores recent advancements in fluorescent nanobiosensors (FNBS) for HPV detection, focusing on the integration of nanomaterials and DNA nanotechnology, highlighting their contributions to improving sensitivity, specificity, and point-of-care (POC) usability. The review critically evaluates a range of nanomaterial-based FNBS, including those employing quantum and carbon dots, nanoclusters, nanosheets, and nanoparticles, discussing their underlying signal amplification mechanisms, target recognition strategies, and limitations related to toxicity, stability, and reproducibility. Furthermore, it examines the application of diverse DNA nanotechnology, such as DNA origami, DNAzyme, catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), and DNA hydrogel in improving FNBS performance. It also addresses the current challenges in clinical translation, emphasizing the necessity for large-scale production methods and thorough clinical validation to ensure biosafety. It also outlines the potential of innovative technologies, such as CRISPR-Cas-based diagnostics and artificial intelligence, to further revolutionize HPV detection and enable accessible, cost-effective screening, particularly in resource-limited settings. This review provides a valuable resource for researchers and clinicians seeking to develop next-generation FNBS for improved HPV diagnostics and cervical cancer prevention.

Rapid Recognition and Monitoring of Multiple Core Biomarkers with Point-of-Care Importance through Combinatorial DNA Logic Operation

The early diagnosis of a disease relies on the reliable identification and quantitation of multiple core biomarkers in real-time point-of-care (POC) testing. To date, most of the multiplex photoelectrochemical (PEC) assays are inaccessible to home healthcare due to cumbersome steps, long testing time, and limited detection efficiency. The rapid and fast-response generation of independent photocurrent for multiple targets is still a great challenge. Herein, a combinatorial DNA logic operation-guided multiplex PEC sensor is constructed to facilely distinguish and simultaneously monitor two core biomarkers that are essential for identifying asymptomatic Alzheimer patients and predicting the progression of the disease. The aptamers of amyloid-β oligomers (AβO) and Tau441 protein are simply integrated at the high-performance In-TBAPy photocathode. In the presence of AβO and Tau441 protein, the aptamer-target affinity complexes are formed and subsequently detached from the electrode surface, resulting in an increase of photocurrent. Through programming concatenated DNA molecular circuits, a 2-target input OR logic gate not only simplifies the manufacturing process of the multiplex PEC sensor but also realizes rapid and intelligent multiple-target recognition. As a conceptual prototype for the development of more sophisticated and complicated logic devices, the proposed DNA molecular logic system may open a new horizon for rapid disease diagnosis and POC analysis.

Cas12a/crRNA recognition initiated self-priming mediated chain extension for colorimetric cell-free DNA (cfDNA) analysis

Cell-free DNA (cfDNA) has attracted increasing attention as a promising biomarker in liquid biopsy due to its crucial role in disease diagnosis. However, previous cfDNA detection methods are commonly based on the development of target-specific primers and integrated signal amplification strategies, which may induce false-positive results. This paper presents a sensitive yet accurate method for cfDNA detection that combines phosphorothioated-terminal hairpin creation with a self-priming extension process. This approach initiates a self-priming mediated chain extension-based signal cycle following the trans-cleavage of H0@MBs when the CRISPR-Cas12a complex is activated by target cfDNA, resulting in the production of a substantial quantity of pyrophosphate. A pyrophosphate sensing probe (pp probe) was utilized, facilitating both high-efficiency and stable colorimetric signaling. This innovative technique for colorimetric detection of target cfDNA demonstrated exceptional sensitivity with a low limit of detection of 1.04 fM and greatly enhanced selectivity, with the complete detection process taking around 60 min. In addition, this technique is capable of detecting cfDNA from the culture medium of HEK293 cells, indicating its clinical application potential. Compared with the previous CRISPR-Cas system-based cfDNA method that necessitates an amplification step before detection, Cas12a was directly used to identify a target sequence that can avoid false target amplification. This technique is simple, accurate, and rapid, engineered to identify cancer-associated cfDNA via a highly sensitive colorimetric change, which is expected to be beneficial for applications requiring point-of-care cancer detection.

Self-powered multifunctional platform based on dual-photoelectrode for dual-mode detection and inactivation of Salmonella enteritidis

Self-powered photoelectrochemical (PEC) sensing is a novel sensing modality. The introduction of dual-mode sensing and photoelectrocatalysis in a self-powered system enables both detection and sterilization purposes. To this end, herein, a self-powered multifunctional platform for the photoelectrochemical-fluorescence (PEC-FL) detection and in-situ inactivation of Salmonella enteritidis (SE) was constructed. The platform utilized Bi4NbO8Cl/V2CTx/FTO as a photoanode and CuInS2/FTO as a photocathode and incubated quantum dot (QDs) signaling probes on the surface of the photocathode. During detection, the system drives the transfer of photogenerated electrons between the dual photoelectrodes through the Fermi energy level difference. The photoanode amplifies the photoelectric signal, while the photocathode is solely dedicated to the immune recognition process. QDs provide an additional fluorescence signal to the system. Under optimal experimental conditions, the multifunctional platform achieves detection limits of 3.2 and 5.3 CFU/mL in PEC and FL modes respectively, with a detection range of 2.91 × 102 to 2.91 × 108 CFU/mL. With the application of an external bias voltage, it further promotes electron transfer between the dual photoelectrodes, inhibits the recombination of photogenerated electrons and holes. It generates a significant amount of superoxide radicals (·O2-) in the cathodic region, resulting in strong sterilization efficiency (99%). The constructed self-powered multifunctional platform exhibits high sensitivity and sterilization efficiency, it provides a feasible and effective strategy to enhance the comprehensive capability of self-powered sensors.

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au-S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

Exonuclease-III Assisted the Target Recycling Coupling with Hybridization Chain Reaction for Sensitive mecA Gene Analysis by Using PGM

In the field of neonatal infections nursing, methicillin-resistant Staphylococcus aureus (MRSA) is a major bacterial pathogen. Here, we present a portable biosensor for MRSA detection that is both highly sensitive and portable, owing to its implementation on the personal glucose meter (PGM) platform. The H probe was fixed on the magnetic bead for mecA gene analysis. A blunt 3' terminus appeared in the MBs-H probe when the mecA gene was present. Exonuclease-III (Exo-III) recognized the blunt terminus and cleaved it, freeing the mecA gene and so facilitating target recycling. In the meantime, the remaining H probe-initiated hybridization chain reaction (HCR) led to the desired signal amplification. Portable quantitative detection of mecA gene is possible because PGM can read the quantity of invertase tagged on HCR product. After optimizing several experimental parameters, such as the concentration of Exo-III and incubation time, the constructed sensor is extremely sensitive, with a detection limit of 2 CFU/mL. The results from this sensitive PGM-based sensor are in agreement with those obtained from plate counting methods, suggesting that it can be used to accurately assess the MRSA content in artificial clinical samples. In addition, the PGM sensor can significantly cut down on time spent compared to plate counting techniques. The manufactured sensor provides a promising option for accurate identification of pathogenic bacteria.

Dual-sensitized heterojunction Ag2S/ZnS/NiS composites with entire visible-light region absorption for ultrasensitive photoelectrochemical detection of tobramycin

In this study, an ultrasensitive photoelectrochemical (PEC) aptasensor based on dual-sensitized heterojunction Ag2S/ZnS/NiS composites as a signal probe was proposed for the detection of tobramycin (TOB) by combining a cascaded quadratic signal amplification strategy. Specifically, compared to the limited visible light-harvesting capability of single sensitized composites, Ag2S/ZnS/NiS composites with p-n and n-n heterojunction could greatly improve the light energy utilization to tremendously strengthen the optical absorption in the entire visible-light region. Moreover, dual-sensitized heterojunction could effectively hinder the rapid recombination of photoelectrons and holes (carriers) to obtain a good photocurrent for improving the sensitivity of the aptasensor. Furthermore, a cascaded quadratic signal amplification strategy was applied to convert trace target TOB into plentiful gold nanoclusters (Au NCs) labelled double-stranded DNA for the construction of PEC aptasensor, with a broad linear detection range from 0.01 to 100 ng mL-1 and a low detection limit of 3.38 pg mL-1. Importantly, this study provided a versatile and sensitive PEC biosensing platform for TOB analysis, and demonstrated its successful application for TOB detection in milk samples. This protocol provides a novel dual-sensitized heterojunction composites to develop a highly efficient and harmfulless PEC aptasensor, which is expected to be used in food safety, environmental monitoring and other areas.

Target Recognition Triggered Split DNAzyme based Colorimetric Assay for Direct and Sensitive Methicillin-Resistance Analysis of Staphylococcus aureus

The accurate and rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) holds significant clinical importance. This work presents a new method for detecting methicillin-resistant Staphylococcus aureus (S. aureus) in clinical samples. The method uses an aptamer-based colorimetric assay that combines a recognizing probe to identify the target and split DNAzyme to amplify the signal, resulting in a highly sensitive and direct analysis of methicillin-resistance. The identification of the PBP2a protein on the membrane of S. aureus in clinical samples leads to the allosterism of the recognizing probe, and thus provides a template for the proximity ligation of split DNAzyme. The proximity ligation of split DNAzyme forms an intact DNAzyme to identify the loop section in the L probe and generates a nicking site to release the loop sequence ("3" and "4" fragments). The "3" and "4" fragments forms an intact sequence to induce the catalytic hairpin assembly, exposing the G-rich section. The released the G-rich sequence of LR probe induces the formation of G-quadruplex-hemin DNAzyme as a colorimetric signal readout. The absorption intensity demonstrated a strong linear association with the logarithm of the S. aureus concentration across a wide range of 5 orders of magnitude dynamic range under the optimized experimental parameters. The limit of detection was calculated to be 23 CFU/ml and the method showed high selectivity for MRSA.

Ultrathin mesoporous BiOCl nanosheets-mediated liposomes for photoelectrochemical immunoassay with in-situ signal amplification

Designing new biochemical sensors and achieving selectivity and high-sensitivity analysis is one of main research directions for immunoassays. Herein, a liposome-amplification photoelectrochemical (PEC) immunoassay was developed using ultrathin mesoporous bismuth chloride oxide nanosheets (BiOCl MSCN) for the highly selective and sensitive detection of carcinoembryonic antigen (CEA). Based on good photocurrent response of BiOCl MSCN toward dopamine, a liposome-conjugated secondary antibody loaded with dopamine was added for specific recognition in the presence of CEA. After the lysis treatment, the liberated dopamine was injected into the three-electrode electrolytic cell to enhance the photocurrent of BiOCl MSCN. Under the optimized conditions, the constructed liposome-mediated PEC immunoassay showed high sensitivity against CEA, with a dynamic response in the linear range of 0.05 ng mL-1 to 100 ng mL-1 and a detection limit of 35 pg mL-1. The present study proposes a new approach to the liposome-mediated PEC immunoassay constructed on ultrathin mesoporous BiOCl nanosheets, which can be used to target further the study of the sensing mechanism.