Hongfang Zhang

Enzymatically induced formation of neodymium hexacyanoferrate nanoparticles on the glucose oxidase/chitosan modified glass carbon electrode for the detection of glucose.

The formation of neodymium hexacyanoferrate (NdHCF) nanoparticles (NPs) on the surface of glucose oxidase/chitosan (GOx/CHIT) modified glass carbon electrode induced by enzymatic reaction was described and characterized. CHIT can be used not only as enzyme immobilizer, but also to provide active sites for NPs growth. Results showed that the optimized conditions of the GOx/CHIT film induced NdHCF NPs for the biosensing of glucose were 1.0mM Nd(3+) and 20.0mM Fe(CN)(6)(3-). The biocatalyzed generation of NdHCF NPs enabled the development of an electrochemical biosensor for glucose. The calculated apparent Michaelis-Menten constant was 7.5mM. The linear range for glucose detection was 0.01-10.0mM with the correlation coefficient of 0.9946, and the detection limit was 5 microM (S/N=3). Furthermore, this system avoids the interferences of other species during the biosensing process and can be used for the determination of glucose in human plasma samples.

DNA as a linker for biocatalytic deposition of Au nanoparticles on graphene and its application in glucose detection

Taking advantages of the striking properties of both self-assembly and biocatalysis, a highly sensitive glucose electrochemical biosensor was proposed by using DNA–GE as biocatalysis target-guide to deposit Au nanoparticles (AuNPs). AuNPs interacted with thiol and amino groups of DNA strands, which make the reaction much easier and faster. Furthermore, the proposed AuNPs/glucose oxidase (GOx)/DNA–GE/glassy carbon (GC) modified electrode achieved the direct electrochemistry and electrocatalysis of GOx. The growth of AuNPs was confirmed by scanning electron microscopy and electrochemical methods. The characterizations of the electrode modified after each assembly step and the content of AuNPs on the electrode surfaces during the growth process were investigated by cyclic voltammetry. The amount of AuNPs was relative to the amount of glucose oxidized accompanying with the biocatalytic process of GOx. The biosensor showed a linearity with glucose concentration in the range of 0.8–50 μM with a detection limit of 0.3 μM (S/N = 3). The sensitivity was 2.4 × 104 μA mM−1. The combination of self-assembly and biocatalysis offers the new design of enzymatic biosensors with potential applications in direct electrochemistry and biocatalysis.

Facile and controllable preparation of glucose biosensor based on Prussian blue nanoparticles hybrid composites.

A glucose biosensor based on polyvinylpyrrolidone (PVP) protected Prussian blue nanoparticles (PBNPs)-polyaniline/multi-walled carbon nanotubes hybrid composites was fabricated by electrochemical method. A novel route for PBNPs preparation was applied in the fabrication with the help of PVP, and from scanning electron microscope images, Prussian blue particles on the electrode were found nanoscaled. The biosensor exhibits fast current response (<6 s) and a linearity in the range from 6.7x10(-6) to 1.9x10(-3) M with a high sensitivity of 6.28 microA mM(-1) and a detection limit of 6x10(-7) M (S/N=3) for the detection of glucose. The apparent activation energy of enzyme-catalyzed reaction and the apparent Michaelis-Menten constant are 23.9 kJ mol(-1) and 1.9 mM respectively, which suggests a high affinity of the enzyme-substrate. This easy and controllable construction method of glucose biosensor combines the characteristics of the components of the hybrid composites, which favors the fast and sensitive detection of glucose with improved analytical capabilities. In addition, the biosensor was examined in human serum samples for glucose determination with a recovery between 95.0 and 104.5%.

A novel electrochemical immunosensor based on nonenzymatic Ag@Au-Fe3O4 nanoelectrocatalyst for protein biomarker detection

A hybrid nanostructure of Fe3O4 nanospheres and Ag@Au nanorods prepared by polydopamine coating was utilized as nanoelectrocatalyst to construct a novel sandwich-type electrochemical immunosensor. Ag@Au-Fe3O4 nanohybrid modified electrode exhibited much better electrocatalytic activity toward the reduction of hydrogen peroxide than Fe3O4 nanospheres or Ag@Au nanorods due to the synergetic catalytic effect. The immunosensor was prepared by immobilizing the capture antibodies on the amine-terminated nanocomposite of carbon nanofibers-chitosan, whilst the trace tag was prepared by loading detection antibodies on the Ag@Au-Fe3O4 nanocomposite. After the parameter optimization, the amperometric signal increased linearly with human IgG concentration in the broad range of 0.1pgmL(-1) to 5μgmL(-1) with a detection limit of 50fgmL(-1). Meanwhile, the enzyme-free catalyst based immunosensor also showed acceptable selectivity, reproducibility and stability.

Enzymatic deposition of Au nanoparticles on the designed electrode surface and its application in glucose detection

This paper reported the enzymatic deposition of Au nanoparticles (AuNPs) on the designed 3-mercapto-propionic acid/glucose oxidase/chitosan (MPA/GOD/Chit) modified glassy carbon electrode and its application in glucose detection. Chit served as GOD immobilization matrix and interacted with MPA through electrostatic attraction. AuNPs, without nano-seeds presented on the electrode surface, was produced through the glucose oxidase catalyzed oxidation of glucose. The mechanism of production of AuNPs was confirmed to be that enzymatic reaction products H(2)O(2) in the solution reduce gold complex to AuNPs. The characterizations of the electrode modified after each assembly step was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy showed the average particle size of the AuNPs is 40nm with a narrow particle size distribution. The content of AuNPs on the electrode surfaces was measured by differential pulse stripping voltammetry. The electrochemical signals on voltammogram showed a linear increase with the glucose concentration in the range of 0.010-0.12mM with a detection limit of 4μM. This provided a method to the determination of glucose.

Ultrasensitive electrical biosensing of syphilis DNA using target-guided formation of polyaniline based on enzyme-catalyzed polymerization

An ultrasensitive assay for electrical biosensing of syphilis DNA was proposed by using target-guided formation of polyaniline (PANI) based on an enzymatically catalyzed method. The sensitive biodetection relies on the DNA hybridization and biotin-streptavidin interaction. After coupling of biotinylated catalase with streptavidin-modified hybrids, a head-to-tail structure of PANI templated by hybridized DNA was formed. The current response of PANI was linearly related to target DNA concentration between 1.0 pM and 1.0 nM with a correlation coefficient of 0.998. The detection limit was determined to be 0.5 pM with the signal-to-noise ratio of 3. The synergistic performances of DNA hybridization, strong biotin-streptavidin binding ability, and highly efficient polymerization provide a general platform for simple, highly sensitive and selective biosensor for the detection of the specific polA gene fragment of T. pallidum. It is expected that the proposed biosensor holds great promise for diagnosing disease in practice.

Silver deposition directed by self-assembled gold nanorods for amplified electrochemical immunoassay

A novel electrochemical immunoassay was developed based on the signal amplification strategy of silver deposition directed by gold nanorods (AuNRs), which was in-situ assembled on the sandwich immunocomplex. The superstructure formed by the self-assembly of AuNRs provided abundant active sites for the nucleation of silver nanoparticles. In this pathway, the stripping current of silver was greatly enhanced. Using human immunoglobulin G (HIgG) as a model analyte, the ultrasensitive immunoassay showed a wide linear range of six orders of magnitude from 0.1 fg mL(-1) to 100 pg mL(-1), with the low detection limit down to 0.08 fg mL(-1). The practicality of this electrochemical immunoassay for detection of HIgG in serum was validated with the average recovery of 93.9%. In addition, this enzyme-free immunoassay also has the advantages of acceptable reproducibility and specificity, and thus this immunosensing protocol can be extended to the detection of other low-abundant protein biomarkers.

An ultrasensitive electrochemical immunosensor for the detection of human immunoglobulin G based on Ag@BSA microspheres

A novel human immunoglobulin G (HIgG) electrochemical immunosensor was developed based on nanosilver-doped bovine serum albumin microspheres (Ag@BSA). The immunosensor was prepared step-wise by first modifying the electrode with β-cyclodextrin functionalized gold nanoparticles followed by the immobilization of captured antibodies and then the formation of a sandwich-type immunocomplex to introduce Ag@BSA bionanoprobes on the sensor surface. The amplification pathway using the stripping voltammetric measurement of silver ions released from Ag@BSA to monitor the immunoreaction was first adopted. The immunosensor exhibited a large dynamic range of 1 fg mL−1 to 10 pg mL−1 and an ultralow detection limit of 0.5 fg mL−1 to HIgG. Moreover, the immunosensor also showed acceptable stability and reproducibility. This biosensor was applied to the detection of the HIgG level in real serum samples.

A sensitive hydrogen peroxide sensor based on leaf-like silver

A novel non-enzymatic hydrogen peroxide sensor based on leaf-like silver was constructed. The leaf-like silver was synthesized on the surface of L-cysteine (L-cys) by electrodeposition. Scanning electron microscopy and electrochemical techniques were used to characterize the leaf-like silver nanoparticles. The sensor showed high electrocatalytic activity towards the reduction of hydrogen peroxide. A wide linear range of 2.5?1.5?mM with a low detection limit of 0.7??M was obtained. Excellent electrocatalytic activity, large surface-to-volume ratio and efficient electron transport properties of leaf-like silver have enabled stable and highly sensitive performance for the non-enzymatic hydrogen peroxide sensor.