Dual-mode DNA walker-based optical fiber biosensor for ultrasensitive detection of microRNAs.

We present a novel dual-mode DNA-walker based optical fiber biosensor (DMDW-Opt biosensor) for sensitive assay of micro-RNAs in bio-samples. In the sensor system, we develop a new strategy for the cascade amplification, DNA-walker/rolling cycle amplification (RCA), by the use of the residue track of the walker. The strategy can significantly improve the response of the sensor and avoid any tedious operation procedure. Dual-mode readouts, i.e., fluorescence and chemiluminescence, are measured independently without interfering with each other to achieve reliable and accurate analysis. Optical fibers with the surface modified by gold nanoparticles are utilized as the support for fabrication of the sensor, which would be benefit for developing miniaturized and portable sensing devices. The performance of the proposed method is evaluated by using micro-RNAs (MiR-155 and MiR-21) as the analytical target. The method is successfully applied for accurate determination of micoRNAs in human serum and MCF-7 cells. Our method can perform sensitive assays of MiR-155 with limit-of-detection as low as 97.72 fM and 11.22 fM, MiR-21 with limit-of-detection as low as 107.15 fM and 8.32 fM for the fluorescence- and the chemiluminescence-readout respectively, and the biosensor exhibits excellent specificity, reproducibility and storage stability, indicating its valuable potential applications for sensing trace-amount targets in complicated real samples.

Nano-channel confined biomimetic nanozyme/bioenzyme cascade reaction for long-lasting and intensive chemiluminescence.

We present here a novel nano-channel confined biomimetic nanozyme/bioenzyme system, which is prepared by co-immobilizing polyoxometalates (vanadomolybdophosphoric heteropoly acid, PMoV2) and glucose oxidase (GOx) in the nano-scale channel of core-shell mesoporous silica (CSMS) microspheres. The biomimetic dual-enzyme nanoreactors (CSMS@PMoV2@GOx) is used for producing long-lasting chemiluminescence (CL) emission. With glucose and luminol in the reaction mixture, hydrogen peroxide (H2O2) is formed in mesoporous channels by GOx catalysis and then is consumed immediately by PMoV2 to induce CL emission. Confined in nano-size channels of CSMS materials, the biomimetic cascade reactions can induce a long-lasting CL emission with a flat period over 12 h. The proposed CSMS@PMoV2@GOx system has excellent reproducibility and storage stability, and has been applied for glucose sensing in human serum samples with satisfactory accuracy. Our study provides a new glow-type CL system based on nanozyme/bioenzyme cascade reactions confined in nano-scale channels of CSMS microspheres, and will also shed a light on potential application of functional polyoxometalates immobilized in mesoporous materials, which would be of great value in various fields including bioassays and heterogeneous catalysis.

Polyoxometalates as catalysts for fluorescence amplification in rapid and sensitive detection of artemisinin.

The combination therapy based on artemisinin is the most effective method to treat malaria. Sensitive, rapid and accurate detection of artemisinin is very important to monitor clinical pharmaceutical effect as well as the drug quality control. In this work, catalytic performance of polyoxometalates (POMs), vanadomolybdophosphoric heteropoly acid (H5PMo10V2O40, PMoV2) and tungstophosphoric heteropoly acid (Na5PW11O39Cu, PW11Cu), are investigated. It is indicated that the POMs exhibit peroxidase-like activity, which efficiently catalyze the artemisinin/thiamine reaction to produce fluorescent product thiochrome. With the usage of the POMs as the catalyst in combination with fluorescent probes, we propose a method for highly sensitive and rapid determination of artemisinin. When PMoV2 and PW11Cu are used as catalysts, the linear ranges are 1.0 × 10-6-1.0 × 10-1 mM and 5.0 × 10-6-9.0 × 10-1 mM, and the detection limits are as low as 0.5 nM and 1 nM, respectively. The method is successfully applied to determine artemisinin in human plasma and Artemisia annua. L leaves with good accuracy.

Enzyme-like catalysis of polyoxometalates for chemiluminescence: Application in ultrasensitive detection of H2O2 and blood glucose.

We show that vanadomolybdophosphoric heteropoly acid (H5PMo10V2O40, PMoV2), one of the polyoxometalates (POMs), presents peroxidase-like activity that can catalyze the luminol/H2O2 reaction to generate chemiluminescence (CL) emission. Based on this foundation, we report an enzyme-free luminol/H2O2/PMoV2 CL system that can be utilized for the ultrasensitive detection of H2O2. The CL intensity exhibits good linear dependence on H2O2 concentration in a wide range up to 5000 nM with a limit-of-detection of 5 nM. The method was successfully used for the determination of glucose in human serum. Our study paves the way for the application of functional POM materials in a variety of biosensing assays, such as the determination of cholesterol, uric acid, lactate, etc., in which H2O2 is a product of oxidoreductase enzymes.