Constructing DNAzyme-driven three-dimensional DNA nanomachine-mediated paper-based photoelectrochemical device for ultrasensitive detection of miR-486-5p.

As a unique class of dynamic nanostructures, biomimetic DNA walking machines that exhibit geometrical complexity and nanometre precision have gained great success in photoelectrochemical (PEC) bioanalysis. Despite certain achievements, the slow reaction kinetics and low processivity severely restrict the amplification efficiency of the DNA walker-mediated biosensors. Herein, by taking advantage of efficient DNA rolling machines, a three-dimensional (3D) DNA nanomachine-mediated paper-based PEC device for speedy ultrasensitive detection of miR-486-5p was successfully constructed. To achieve it, a novel In2S3/SnS2 sensitized heterojunction was firstly in-situ grown on the Au-modified paper fibers and implemented as the photoanode with effective separation of photogenerated carriers to achieve an enhanced initial photocurrent. Subsequently, the copper hexacyanoferrate(II)-modified CuO nanosphere was introduced as a multifunctional signal regulator via the competitive capture of electron donors and photon energy with the photoelectric layer for efficiently quenching the PEC signal. With the introduction of targets, the DNAzyme-driven DNA nanomachine with editable motion modes was gradually activated and it could continuously cleave the tracks DNA labeled quenching probes, finally achieving the recovery of PEC signal. As a proof of concept, the elaborated paper-based PEC device presented a wide linear range from 0.1 fM to 100 pM and a detection limit of 35 aM for miR-486-5p bioassay. This work provides an innovative insight to the exploitation of DNA nanobiotechnology and nucleic acid signal amplification strategy.

Tetrahedral DNA Nanostructure-Engineered Paper-Based Sensor with an Enhanced Antifouling Ability for Photoelectrochemical Sensing.

Herein, a newly designed two-in-one tetrahedral DNA (TDN) nanostructure with an antifouling surface and backbone-rigidified interfacial tracks was developed for highly sensitive and selective detection of miRNA-182-5p. The well-regulated TDN tracks were assembled onto the surface of the TiO2/MIL-125-NH2-functionalized paper electrode, which efficiently avoided the obstacle of DNA strand tangling and decreased the probability of suspension during the walking process, thus greatly promoting the moving efficiency of DNA walkers. More interestingly, the TDN-modified sensing interfaces demonstrated incomparable antifouling ability against protein samples and interfering miRNAs due to the strong hydrophilic capacity and special molecular conformations, which addressed the dilemma of low sensitivity from traditional antifouling coating strategies. As a proof of concept, the designed bifunctional tetrahedron-modified paper-based photoelectrochemical sensor was successfully used to quantify miRNA-182-5p with a low detection limit of 0.09 fM and high specificity and was validated for monitoring of miRNA-182-5p in real samples. This TDN-engineered biointerface could be used as a universal platform for tracking various targets by substituting the biorecognition events, providing great promise for bioanalysis and clinical diagnosis.

Photothermal-Reagent-Triggered Visual Thermoresponsive and Quantized Photoelectrochemical Dual-Signal Assay.

In vitro biosensing chips are urgently needed for early-stage diagnosis and real-time surveillance of epidemic diseases. Herein, a versatile zone with photothermal effects is implanted in the miniature space of a collapsible lab-on-paper photoelectrochemical biosensor for on-site detection of microRNA-141 in body fluids, which can flexibly interconnect the traditional photocurrent signal with functional temperature response. The visualized thermoresponsive results are enhanced by the exciton energy conversion between Fe3O4 nanoparticles (Fe3O4 NPs) and formed Prussian blue nanoparticles under near-infrared irradiation, which not only presents heat energy gradient variations but also generates color changes. Significantly, the controlled release of Fe3O4 NPs is actuated by a target-triggered enzyme assist strand displacement cycle strategy to efficiently improve the accuracy of target temperature signal prediction, which can concurrently mediate photoelectric signal attenuation via promoting the rapid recombination of photoexcited charge carriers on the CuInS2/CoIn2S4 electrode surface, affording dependable ultrasensitive detection results. Benefitting from the ingenious design of the versatile thermoresponsive-photoelectric sensing platform, the preliminary screening and ultrasensitive quantitative analysis can be simultaneously achieved in a single-drop sample. As a consequence, speedy prediction results and satisfied monitoring data are acquired in the ranges of 0.5 pM to 2 nM and 0.001 pM to 5 nM by measuring the temperature change and photocurrent intensity. By right of these advantages, such research paves a prospective paradigm for the manufacture of a visual, rapid, broad-spectrum, and reliable real-time surveillance platform, which allows it to be a promising candidate for epidemic disease home diagnosis and intelligent diagnosis.

Paper-Based Bipolar Electrode Electrochemiluminescence Platform Combined with Pencil-Drawing Trace for the Detection of M.SssI Methyltransferase.

Herein, a hand-drawing paper-based bipolar electrode (BPE) electrochemiluminescence (ECL) platform for M.SssI methyltransferase (M.SssI MTase) assay was proposed via employing high electrocatalytic Pt@CeO2 as an ECL co-reaction accelerator and pencil-drawing graphite electric circuits as wires and electrodes. Notably, the introduction of pencil-drawing trace not only simplified the manufacturing process but also reduced the cost and saved fabricating time. Meanwhile, Pt@CeO2 with good electrocatalytic activity and satisfactory chemical stability was used at the anode of the closed BPE-ECL device to accelerate the oxidation rate of uric acid. Due to the balanced charges of the bipolar electrode, the ECL response of the MnS: CdS@ZnS/S2O82- system emitted on the cathode was enhanced. In situ growth of gold nanoparticles in the two electrode areas was convenient for DNA immobilization. With the above points in mind, the specific DNA double strands functionalized via Pt@CeO2 were employed to identify M.SssI MTase. The unmethylated DNA double strands were cut by HpaII endonuclease, resulting in the quenching of the ECL signal. Under the optimal conditions, sensitive detection of M.SssI MTase in a wide linear range of 0.01-100 U·mL-1 with a satisfactory detection limit of 0.008 U·mL-1 was realized. The reliable and versatile BPE-ECL tool for the determination of M.SssI MTase with easy-to-operate pencil-drawing traces and independent solution systems provides a new opportunity to develop paper-based devices applied in early disease diagnosis and pathogenesis research.

A Target-Driven Self-Feedback Paper-Based Photoelectrochemical Sensing Platform for Ultrasensitive Detection of Ochratoxin A with an In2S3/WO3 Heterojunction Structure.

Currently, developing versatile, easy-to-operate, and effective signal amplification strategies hold great promise in photoelectrochemical (PEC) biosensing. Herein, an ultrasensitive polyvinylpyrrolidone-treated In2S3/WO3 (In2S3-P/WO3)-functionalized paper-based PEC sensor was established for sensing ochratoxin A (OTA) based on a target-driven self-feedback (TDSF) mechanism enabled by a dual cycling tactic of PEC chemical-chemical (PECCC) redox and exonuclease III (Exo III)-assisted complementary DNA. The In2S3-P/WO3 heterojunction structure with 3D open-structure and regulable topology was initially in situ grown on Au nanoparticle-functionalized cellulose paper, which was served as a universal signal transducer to directly record photocurrent signals without complicated electrode modification, endowing the paper chip with admirable anti-interference ability and unexceptionable photoelectric conversion efficiency. With the assistance of Exo III-assisted cycling process, a trace amount of OTA could trigger substantial signal reporter ascorbic acid (AA) generated by the enzymatic catalysis of alkaline phosphatase, which could effectively provoke the PECCC redox cycling among the tris(2-carboxyethyl)phosphine acid, AA, and ferrocenecarboxylic at the In2S3-P/WO3 photoelectrode, initiating TDSF signal amplification. Based on the TDSF process induced by the Exo III-assisted recycling and PECCC redox cycling strategy, the developed paper-based PEC biosensor realized ultrasensitive determination of OTA with persuasive selectivity, high stability, and excellent reproducibility. It is believed that the proposed paper-based PEC sensing platform exhibited enormous potential for the detection of other targets in bioanalysis and clinical diagnosis.

Engineering paper-based visible light-responsive Sn-self doped domed SnO2 nanotubes for ultrasensitive photoelectrochemical sensor.

Exploring novel photoactive materials with high photoelectric conversion efficiency plays a crucial role in enhancing the analytical performance of paper-based photoelectrochemical (PEC) biosensor. SnO2, which possesses higher photostability and electron mobility, can be regarded as a promising photoactive material. Herein, paper-based one dimensional (1D) domed SnO2 nanotubes (NTs) have been developed with the template-consumption strategy. What's more, their growth mechanism has also been proposed based on the controllable experiments. At first, the paper-based 1D ZnO nanorods (NRs) as the typical amphoteric oxide are prepared and serve as the sacrifice templates which can be etched by the generated alkaline environment during the formation of SnO2. At a certain stage, all the ZnO NRs can be completely etched by controlling the experimental conditions, resulting in the forming of vertically distributed hollow SnO2 NTs. Furthermore, the Sn self-doping strategy is also proposed to suppress the recombination of charge carriers and broaden the light response range by introducing the impurity energy levels. Profiting from such doping strategy, the prominent photocurrent signal is obtained compared with pure paper-based SnO2 NTs. Ultimately, an innovative visible light responsive paper-based Sn-doping SnO2-x NTs are developed and employed as the photoelectrode for the PEC biosensor using the alpha fetoprotein (AFP) as the model analyte. Under the optimal conditions, the ultrasensitive AFP sensing is realized with the linear range and detection limitation of 10 pg mL-1 to 200 ng mL-1 and 3.84 pg mL-1, respectively. This work provides a judiciously strategy for developing novel photoactive materials for paper-based PEC bioanalysis.