Search

Single nanoparticle collision (SNC) technology has attracted increasing attention to explore single nanoparticle electrochemistry. By improving the temporal resolution of electrochemical recording, several recent studies have uncovered the intermittent electron transfer processes during the SNC of single silver nanoparticles. The electrode current curve displayed multiple current peaks that were completely separated, instead of a single peak. In the present work, we employed surface plasmon resonance microscopy to monitor the collision and oxidation processes of single silver nanoparticles. Simultaneous optical and electrochemical recordings provided comprehensive capability to correlate the physical movement of nanoparticles (from optical signal) and the electron transfer activity (from electrochemical signal). While previous studies hypothesized the physical detachment of nanoparticles from the electrode due to electrostatic repulsion or Brownian motion, the optical imaging revealed that nanoparticles often remained in physical touch with the electrode even though no electron transfer was occurring. These results demonstrated that the electrical contact between nanoparticle and electrode, which could be rather stochastic due to thermal motion and micro‐convection, played critical roles in regulating the multi‐peak behavior of single silver nanoparticles. In touch: surface plasmon resonance microscopy is utilized to monitor collision and oxidation processes of single silver nanoparticles. Simultaneous optical and electrochemical recordings reveal that nanoparticles often remain in physical touch with the electrode even though no electron transfer is occurring. The electrical contact plays critical roles in regulating the multi‐peak behavior of single silver nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical method for the simultaneous detection of two different tumor markers, carcinoembryonic antigen (CEA) and α-fetoprotein (AFP), in one-pot, using CdS/DNA and PbS/DNA nanochains as labels was developed. Herein, magnetic beads (MBs) as bimolecule immobilizing carriers, were used for co-immobilization of primary anti-CEA and anti-AFP antibodies. The distinguishable signal labels were synthesized by in situ growth of CdS and PbS nanoparticles on DNA chains, respectively, which were further employed to label the corresponding secondary antibodies. A sandwich-type immunoassay format was formed by the biorecognition of the antigens and corresponding antibodies. The assay was based on the peak currents of Cd2+ and Pb2+ dissolved from CdS and PbS nanoparticles by HNO3 using square wave stripping voltammetry. Experimental results show that the multiplexed electrochemical immunoassay has enabled the simultaneous monitoring of CEA and AFP in a single run with wide working ranges of 0.1–100ngmL−1 for CEA and 0.5–200ngmL−1 for AFP. The detection limits reach to 3.3pgmL−1 for CEA and 7.8pgmL−1 for AFP. [Copyright &y& Elsevier]

Abstract: A novel DNAzyme-functionalized Pt nanoparticles/carbon nanotubes (DNAzyme/Pt NPs/CNTs) bioconjugate was fabricated as trace tag for ultrasensitive sandwich DNA detection. The Pt NPs/CNTs were prepared via layer-by-layer (LBL) assembly of the Pt NPs and polyelectrolyte on the carboxylated CNTs, followed by the functionalization with the DNAzyme and reporter probe DNA through the platinum—sulfur bonding. The subsequent sandwich-type DNA specific reaction would confine numerous DNAzyme/Pt NPs/CNTs bioconjugate onto the gold electrode surface for amplifying the signal. In the presence of 3,3′,5,5′ tetramethylbenzidine (TMB) which could be oxidized by the DNAzyme, electrochemical signals could be generated by chronoamperometry via the interrogation of reduction electrochemical signal of oxidized TMB. The constructed DNA sensor exhibited a wide linear response to target DNA ranging from 1.0fM to 10pM with the detection limit down to 0.6fM and exhibited excellent selectivity against even a single base mismatch. In addition, this novel DNA sensor showed fairly good reproducibility, stability, and reusability. [Copyright &y& Elsevier]

Abstract: On the basis of aptamer-based rolling circle amplification (RCA) and magnetic beads (MBs), a highly sensitive electrochemical method was developed for the determination of Ochratoxin A (OTA). Initially, an amino-modified capture DNA was immobilized onto MBs for the following hybridization with an OTA aptamer and a phosphate labeled padlock DNA. In the presence of OTA, the aptamer would dissociate from the bioconjugate, and the padlock DNA would subsequently hybridize with the capture DNA to form a circular template with the aid of the T4 ligase. Next, capture DNA would act as primer to initiate a linear RCA reaction and hence generate a long tandem repeated sequences by phi29 DNA polymerase and dNTPs. Then, two quantum dots (QDs) labeled DNA probes were tagged on the resulted RCA product to indicate the OTA recognition event by electrochemical readout. This strategy, based on the novel design of OTA-mediated DNA circularization, the combination of RCA and double signal probes introduction, could detect OTA down to the level of 0.2pgmL−1 with a dynamic range spanning more than 4 orders of magnitude. The proposed approach is tested to determine OTA in red wines and shows good application potential in real samples. [Copyright &y& Elsevier]

Abstract: A novel microfluidic immunoassay system for specific detection of hemoglobin A1c (HbA1c) was developed based on a three-component shell/shell/core structured magnetic nanocomposite Au/chitosan/Fe3O4, which was synthesized with easy handling feature of Fe3O4 by magnet, high affinity for gold nanoparticles of chitosan and good immobilization ability for anti-human hemoglobin-A1c antibody (HbA1c mAb) of assembled colloidal gold nanoparticles. The resulting HbA1c mAb/Au/chitosan/Fe3O4 magnetic nanoparticles were then introduced into microfluidic devices coupled with a gold nanoband microelectrode as electrochemical detector. After that, three-step rapid immunoreactions were carried out in the sequence of HbA1c, anti-human hemoglobin antibodies (Hb mAb) and the secondary alkaline phosphatase (AP)-conjugated antibody within 20min. The current response of 1-naphtol obtained from the reaction between the secondary AP-conjugated antibody and 1-naphthyl phosphate (1-NP) increased proportionally to the HbA1c concentration. Under optimized electrophoresis and detection conditions, HbA1c responded linearly in the concentration of 0.05–1.5μgmL−1, with the detection limit of 0.025μgmL−1. This system was successfully employed for detection of HbA1c in blood with good accuracy and renewable ability. The proposed method proved its potential use in clinical immunoassay of HbA1c. [Copyright &y& Elsevier]

Abstract: A new strategy for immobilization of horseradish peroxidase (HRP) has been presented by self-assembling gold nanoparticles on chitosan hydrogel modified Au electrode. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the deposited chitosan film with porous structure, which facilitates the assembly of gold nanoparticles and HRP. The resulting substrates were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The immobilized HRP displayed an excellent catalytic property to the reduction of H2O2 in the presence of methylene blue mediator. The resulting biosensor (HRP-modified electrode) showed a wide dynamic range of 8.0μM–15mM H2O2, and the linear ranges were 8.0μM–0.12mM and 0.50–12mM, with a detection limit of 2.4μM estimated at a signal-to-noise ratio of 3. Moreover, the biosensor remained about 85% of its original sensitivity after four weeks’ storage. [Copyright &y& Elsevier]