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Multiplexed DNA target detection is of great significance in many fields including clinical diagnostics, environmental monitoring, biothreat detection and forensics. Although the emergence of DNA chip technology has accelerated this process, it is still a challenge to perform ultrasensitive DNA assay at low attomol concentrations so that DNA detection can be directly achieved without a PCR protocol. In this work, an oligonucleotide-functionalized silver nanoparticle tag has been successfully developed for multiplexed DNA electrochemical detection with ultrahigh sensitivity. The multiprobes containing oligo(d)A and the reporting probes were anchored onto the silver nanoparticles, followed by hybridizing with the silver nanoparticle conjugate modified with oligo(d)T. The hybridization-induced tag was found to show an aggregated nanostructure 10 times larger than the individual nanoparticle, as revealed by TEM. For sandwich-based assays, the tag was specifically coupled to a gold electrode surface via target DNA. Compared to a single nanoparticle label, this novel tag has shown excellent electroactive property and produces 103-fold amplification in the differential pulse voltammetric (DPV) method. Hepatitis B virus (HBV) sequence was employed as a sample model, and we have achieved a detection limit of 5 aM (~120 molecules in 40 [mu]L volume), demonstrating ultrasensitive measurement for DNA. The property of the electrochemical process involving silver aggregates was further investigated and the integrative oxidation of the silver tag was observed. We further demonstrated the multiplexed DNA target detection using array chips functionalized with Herpes simplex virus (HSV), Epstein--Barr virus (EBV) and cytomegalovirus (CMV) sequences, which shows effective recognition of the relative sequences individually or simultaneously. The method offers a uniquely new approach for DNA detection with ultrahigh sensitivity as well as advantages of rapidity, throughput, and miniaturization. 10.1021/ac101193e

Nanozymes with cascade catalytic reactions gain advantages over natural enzymes by simplifying the preparation, decreasing the cost, and enhancing the local concentrations of the intermediates and the stability. However, in vivo applications of such cascade nanozymes are hampered due to the low catalytic activity in the complex physiological microenvironment. Substantial research work is currently devoted to exploiting light-driven catalytic kinetic acceleration of nanozymes via hot electron injection from plasmonic nanoparticles. Here, a near-infrared (NIR) light-driven plasmon-enhanced cascade nanozyme with a formulation of Au@Pt0.46Ag0.54 is developed for efficient synergistic cancer therapy. This nanozyme possesses catalase, oxidase, and peroxidase activities and is capable of converting hydrogen peroxide to oxygen and reactive oxygen species through cascade reactions. Both in vitro and in vivo experimental measurements reveal that 808 nm NIR-laser-driven hot electron injection not only obviously enhanced the catalytic activities of the nanozyme but also triggered efficient photothermal conversion, which successfully achieved synergetic catalytic therapy/photothermal therapy for cancer treatment. This strategy of tailoring multi-metal cascade nanozyme techniques opens up avenues for realizing multistep reactions with high catalytic kinetics and provides an innovative way for therapeutic systems with clinical significance. [ABSTRACT FROM AUTHOR]

We report a simple electrochemical method for the identification of properties of peripheral nerve fibers, based on the detection of a neurotransmitter enzyme, acetylcholinesterase (ACHE). A poly(diallydimethylammonium) (PDDA) adulterated poly(dimethylsiloxane) (PDMS) film is spin-coated on the surface of gold electrodes. Gold nanoparticles (AuNPs) are in situ synthesized on the polymer film, which act as 'electron antennae' between the film and the electrode surface and also provide a biocompatible interface. This PDMS--PDDA/AuNPs film shows different adsorption sites to choline oxidase (ChO) and ACHE; after incubation with ChO, the polymer--gold nanocomposite film also shows excellent adsorption ability to ACHE. Moreover the adsorption sites of AChE would not be blocked by bovine serum albumin (BSA) which provides a good platform for the quantitative amperometric determination of AChE via the oxidation of the enzymatically generated [H.sub.2][O.sub.2] in the bienzyme system in the presence of acetylcholine. The detection limit is down to 1.0 unit/mL. The polymer--gold nanocomposite film shows excellent anti-interference ability to the coexistent electroactive substances such as ascorbic acid. Thus it was applied to determine AChE in peripheral nerve fibers homogenates and identify the motor and sensory fibers for the first time. Compared with histochemical staining methods, the electrochemical technique shows good accurate rate and faster response, which has good potential for a clinical application.

A versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels has been developed for sensitive protein detection. This sandwich-type sensor is fabricated on an indium tin oxide chip covered with a well-ordered gold nanoparticle monolayer. Gel imaging systems were successfully introduced to develop a novel high-efficient optical immunoassay, which could perform simultaneous detection for the samples with a series of different concentrations of a target analyte. The linear range of this assay was between 0.1 and 500 ng/mL, and the assay sensitivity could be further increased to 0.005 ng/mL with the linear range from 0.005 to 100 ng/mL by stripping voltammetric analysis. The immunosensor showed good precision, high sensitivity, acceptable stability, and reproducibility and could be used for the detection of real sample with consistent results in comparison with those obtained by the ELISA method.

Mercaptoacetic acid (RSH)-capped CdS nanocrystals (NCs) was demonstrated to be electrochemically reduced during potential scan and react with the coreactant [S.sub.2][O.sup.2-.sub.8] to generate strong electrochemiluminescence (ECL) in aqueous solution. Based on the ECL of CdS NCs, a novel label-free ECL biosensor for the detection of low-density lipoprotein (LDL) has been developed by using self-assembly and gold nanoparticle amplitication techniques. The bio-sensor was prepared as follows: The gold nanoparticles were first assembled onto a cysteamine monolayer on the gold electrode surface. This gold nanoparticle-covered electrode was next treated with cysteine and then reacted with CdS NCs to afford a CdS NC-electrode. Finally, apoB-100 (ligand of LDL receptor) was covalently conjugated to the CdS NC-electrode. The modification procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy, respectively. The resulting modified electrode was tested as ECL biosensor for LDL detection. The LDL concentration was measured through the decrease in ECL intensity resulting from the specific binding of LDL to apoB-100. The ECL peak intensity of the biosensor decreased linearly with LDL concentration in the range of 0.025-16 ng m[L.sup.-1] with a detection limit of 0.006 ng m[L.sup.-1]. The CdS NCs not only showed high ECL intensity and good biocompafibility but also could provide more binding sites for apoB-100 loading. In addition, the gold nanoparticle amplification for protein ECL analysis was applied to the improvement of the detection sensitivity. Thus, the biosensor exhibited high sensitivity, good reproducibility, rapid response, and long-term stability.

In this work, we establish an indirect amperometric detection method via mounting a single carbon fiber disk working electrode in the end part of a microchannel. This in-channel configuration for microchip capillary electrophoresis brings about that the potential of the working electrode in the case of electrochemical reduction reaction is coupled by the separation electric field, while the potential of the working electrode in the case of electrochemical oxidation reaction is not coupled by the separation electric field. Such a special performance provides a convenient and sensitive approach for indirectly detecting nonelectroactive analytes that relies on amperometric response of dissolved oxygen in solution and directly detecting electroactive analytes based on their own amperometric response on the carbon fiber electrode. This method has shown its essential importance in the analysis of inorganic cations, biomolecules, and electroosmotic flow rates. Based on preliminary results, a detection limit of 1.0 [micro]M for [K.sup.+] and [Na.sup.+] have been achieved.

The fabrication and surface morphology of methylene blue (MB)/perfluorosulfonated ionomer (Nafion) modified microcylinder carbon fiber electrode were studied. The stability of the modified electrode is good. The extraction coefficient K of MB between Nafion film and solution is [approximately]110, and the diffusion coefficient of MB in Nafion film is [approximately]5.3 X [10.sup.-9] [cm.sup.2]/s. The MB/Nafion modified microcylinder electrode shows significant electrocatalytic activity for the oxidation of hemoglobin in weak acid media; it can be used for the determination of hemoglobin in the range of 5.0-50 [[micro]molar] with a relative standard deviation of 3.5% at 6.0 [[micro]molar] HB. A satisfactory result has been obtained for the determination of hemoglobin in clinical blood samples.