Shengyuan Deng

A glucose biosensor based on direct electrochemistry of glucose oxidase immobilized on nitrogen-doped carbon nanotubes

A novel biosensor for glucose was prepared by immobilizing glucose oxidase (GOx) on nitrogen-doped carbon nanotubes (CNx-MWNTs) modified electrode. The CNx-MWNTs membrane showed an excellent electrocatalytic activity toward the reduction of O(2) due to its diatomic side-on adsorption on CNx-MWNTs. The nitrogen doping accelerated the electron transfer from electrode surface to the immobilized GOx, leading to the direct electrochemistry of GOx. The biofunctional surface showed good biocompatibility, excellent electron-conductive network and large surface-to-volume ratio, which were characterized by scanning electron microscopy, contact angle and electrochemical impedance technique. The direct electron transfer of immobilized GOx led to stable amperometric biosensing for glucose with a linear range from 0.02 to 1.02 mM and a detection limit of 0.01 mM (S/N=3). These results indicated that CNx-MWNTs are good candidate material for construction of the third-generation enzyme biosensors based on the direct electrochemistry of immobilized enzymes.

Electrochemical synthesis of reduced graphene sheet-AuPd alloy nanoparticle composites for enzymatic biosensing

A simple, fast, green and controllable approach was developed for electrochemical synthesis of a novel nanocomposite of electrochemically reduced graphene oxide (ERGO) and gold-palladium (1:1) bimetallic nanoparticles (AuPdNPs), without the aid of any reducing reagent. The electrochemical reduction efficiently removed oxygen-containing groups in ERGO, which was then modified with homogeneously dispersed AuPdNPs in a good size distribution. ERGO-AuPdNPs nanocomposite showed excellent biocompatibility, enhanced electron transfer kinetics and large electroactive surface area, and were highly sensitive and stable towards oxygen reduction. A biosensor was constructed by immobilizing glucose oxidase as a model enzyme on the nanocomposites for glucose detection through oxygen consumption during the enzymatic reaction. The biosensor had a detection limit of 6.9μM, a linear range up to 3.5mM and a sensitivity of 266.6μAmM(-1)cm(-2). It exhibited acceptable reproducibility and good accuracy with negligible interferences from common oxidizable interfering species. These characteristics make ERGO-AuPdNPs nanocomposite highly suitable for oxidase-based biosensing.

Ultrasensitive Immunoassay of Protein Biomarker Based on Electrochemiluminescent Quenching of Quantum Dots by Hemin Bio-Bar-Coded Nanoparticle Tags

A hemin bio-bar-coded nanoparticle probe labeled antibody was designed by the assembly of antibody and alkylthiol-capped bar-code G-quadruplex DNA on gold nanoparticles and the interaction of hemin with the DNA to form a G-quadruplex/hemin bio-bar-code. An ultrasensitive immunoassay method was developed by combining the labeled antibody with an electrochemiluminescent (ECL) immunosensor for protein. The ECL immunosensor was constructed by a layer-by-layer modification of carbon nanotubes, CdS quantum dots (QDs), and capture antibody on a glassy carbon electrode. In air-saturated pH 8.0 PBS the immunosensor showed a carbon-nanotube-enhanced cathodic ECL emission of QDs. Upon the formation of immunocomplex, the ECL intensity decreased owing to the consumption of ECL coreactant in bio-bar-code electrocatalyzed reduction of dissolved oxygen. Using α-fetoprotein as model analyte, the quenched ECL could be used for immunoassay with a linear range of 0.01 pg mL(-1) to 1 ng mL(-1) and a detection limit of 1.0 fg mL(-1). The wide detection range and high sensitivity resulted from the enhanced ECL emission and highly efficient catalysis of the bio-bar-code. The immunosensor exhibited good stability and acceptable fabrication reproducibility and accuracy, showing great promise for clinical application.

Electrochemiluminescent Quenching of Quantum Dots for Ultrasensitive Immunoassay through Oxygen Reduction Catalyzed by Nitrogen-Doped Graphene-Supported Hemin

A hemin functionalized graphene sheet was prepared via the noncovalent assembly of hemin on nitrogen-doped graphene. The graphene sheet could act as an oxygen reduction catalyst to produce sensitive electrochemiluminescent (ECL) quenching of quantum dots (QDs) due to the annihilation of dissolved oxygen, the ECL coreactant, by its electrocatalytic reduction. With the use of the catalyst with high loading of hemin as a signal tag of the secondary antibody, a novel ultrasensitive immunoassay method for biomarker detection was proposed. In an air-saturated pH 8.0 buffer, the immunosensor constructed by a stepwise immobilization of bidentate-chelated CdTe QDs and capture antibody showed an intensive cathodic ECL irradiation, which could be scavenged upon the formation of the catalyst-bound sandwich immunocomplex. With the use of the carcinoembryonic antigen as a model analyte, the immunoassay method showed a linear range from 0.1 pg mL(-1) to 10 ng mL(-1) and a detection limit of 24 fg mL(-1). The immunosensor exhibited good stability, acceptable fabrication reproducibility, and practicability. The electrocatalytic reduction-based ECL quenching strategy provided a powerful avenue for the design of the ultrasensitive detection method, showing great promise for clinical application.

Amplified electrochemiluminescence of quantum dots by electrochemically reduced graphene oxide for nanobiosensing of acetylcholine.

A signal amplification system for electrochemiluminescence (ECL) of quantum dots (QDs) was developed by using electrochemically reduced graphene oxide (ERGO) to construct a nanobiosensing platform. Due to the structural defects of GO, the ECL emission of QDs coated on GO modified electrode was significantly quenched. After the electrochemical reduction of GO, the restoration of structural conjugation was observed with spectroscopic, morphologic and impedance techniques. Thus in the presence of dissolved O₂ as coreactant, the QDs/ERGO modified electrode showed ECL intensity increase by 4.2 and 178.9 times as compared with intrinsic QDs and QDs/GO modified electrodes due to the adsorption of dissolved O₂ on ERGO and the facilitated electron transfer. After choline oxidase (ChO) or ChO-acetylcholinesterase was further covalently cross-linked on the QDs/ERGO modified electrode, two ECL biosensors for choline and acetylcholine were fabricated, which showed the linear response ranges and detection limits of 10-210 μM and 8.8 μM for choline, and 10-250 μM and 4.7 μM for acetylcholine, respectively. This green and facile approach to prepare graphene-QDs system could be of potential applications in electronic device and bioanalysis.

Pt-dispersed flower-like carbon nanosheet aggregation for low-overpotential electrochemical biosensing

A Pt nanoparticle-decorated flower-like carbon nanosheet aggregation (FCNA) was prepared via one-step ethylene glycol method. The aggregation was characterized with scanning electron micrographs, X-ray photoelectron spectra, X-ray diffraction and electrochemical impedance spectra. When the aggregation was immobilized on a glassy carbon electrode, the dense dispersion of Pt nanoparticles (Pt NPs) on the carbon nanosheets of FCNA could combine the good conductivity of FCNA with the excellent catalytic activity of Pt NPs for the electroreduction of oxygen at a low overpotential, which led to a method for electrochemical detection of oxygen from 6.3 to 69.3 μM. Using glucose oxidase (GOx) as a model, the resulting GOx/Pt/FCNA nanocomposite-based amperometric biosensor showed a linear response to glucose ranging from 0.5 to 8.0 mM with a detection limit of 0.3 mM at a S/N ratio of 3. The designed biosensor was of excellent performance with high selectivity, acceptable recovery and good repeatability, and could be successfully applied in the detection of glucose in human serum. The FCNA could be expected as a carrier for the preparation of other metal nanoparticle-dispersed aggregations and biosensing applications.

Platinum nanodendrite functionalized graphene nanosheets as a non-enzymatic label for electrochemical immunosensing

An ultrasensitive immunosensing method was developed using platinum nanodendrite functionalized graphene nanosheets (PtNDs@GS) as a non-enzymatic label for the electrochemical detection of human immunoglobulin G (HIgG). The PtNDs@GS hybrid was prepared in situ by reducing K2PtCl4 with ascorbic acid in an aqueous solution of reduced graphene oxide, and characterized by scanning electron microscopy, transmission electron microscopy and spectral techniques. The disposable immunosensor was constructed by coating a polyethylene glycol film on a screen-printed carbon working electrode and then immobilizing the capture antibody on the film. After binding with the antigen for further capture of the PtNDs@GS labelled antibody, PtNDs@GS was introduced as an electrochemical tag to produce a large electrocatalytic current towards the reduction of dissolved oxygen for signal amplification. Compared with the enzyme-based immunosensor, PtNDs@GS as non-enzymatic tag exhibited many advantages. This method showed a good linearity in the concentration range of 1 pg mL-1 to 10 ng mL-1, with a detection limit of 0.87 pg mL-1. PtNDs@GS as non-enzymatic label provides a versatile method for constructing ultrasensitive immunosensors, and demonstrates proof-of-concept in immunosensing.