Guang-Chao Zhao

Electrocatalytic oxidation of nitric oxide at multi-walled carbon nanotubes modified electrode

Abstract In 0.1 mol/l KH 2 PO 4 –NaOH buffer solution (pH 7.0), the multi-walled carbon nanotubes (MWNTs) modified electrode exhibits high stability and strong catalytic effect toward the electrochemical oxidation of nitric oxide (NO). Upon further modification with a thin film of nafion which is capable of preventing interference from anions, especially nitrite, this modified electrode can be employed as a NO sensor in solution with fast response and high selectivity. The experimental conditions, such as supporting electrolyte and amounts of nafion, as well as scan rate have been optimized. The currents (measured by constant potential amperometry) increase linearly with the concentrations of NO in the range of 2×10 −7 –1.5×10 −4 mol/l . The calculated detection limit is 8.0×10 −8 mol/l . Moreover, the determination is free from the interference of nitrite and some biological substances. The experimental results show that NO might be adsorbed on the surface of electrode and then transfer electrons.

Direct electrocatalytic oxidation of nitric oxide and reduction of hydrogen peroxide based on α-Fe2O3 nanoparticles-chitosan composite

alpha-Fe(2)O(3) nanoparticles prepared using a simple solution-combusting method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on glass carbon electrode (GCE). The as-prepared alpha-Fe(2)O(3) nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanocomposite film exhibits high electrocatalytic oxidation for nitric oxide (NO) and reduction for hydrogen peroxide (H(2)O(2)). The electrocatalytic oxidation peak is observed at +0.82 V (vs. Ag/AgCl) and controlled by diffusion process. The electrocatalytic reduction peak is observed at -0.45 V (vs. Ag/AgCl) and controlled by diffusion process. This alpha-Fe(2)O(3)-CH/GCE nanocomposite bioelectrode has response time of 5 s, linearity as 5.0 x 10(-7) to 15.0 x 10(-6) M of NO with a detection limit of 8.0 x 10(-8) M and a sensitivity of -283.6 microA/mM. This alpha-Fe(2)O(3)-CH/GCE nanocomposite bioelectrode was further utilized in detection of H(2)O(2) with a detection limit of 4.0 x 10(-7) M, linearity as 1.0 x 10(-6) to 44.0 x 10(-6) M and with a sensitivity of 21.62 microA/mM. The shelf life of this bioelectrode is about 6 weeks under room temperature conditions.

Direct electrochemistry of hemoglobin at a graphene gold nanoparticle composite film for nitric oxide biosensing.

A simple two-step method was employed for preparing nano-sized gold nanoparticles-graphene composite to construct a GNPs-GR-SDS modified electrode. Hemoglobin (Hb) was successfully immobilized on the surface of a basal plane graphite (BPG) electrode through a simple dropping technique. Direct electrochemistry and electrocatalysis of the hemoglobin-modified electrode was investigated. The as-prepared composites showed an obvious promotion of the direct electro-transfer between hemoglobin and the electrode. A couple of well-defined and quasi-reversible Hb CV peaks can be observed in a phosphate buffer solution (pH 7.0). The separation of anodic and cathodic peak potentials is 81 mV, indicating a fast electron transfer reaction. The experimental results also clarified that the immobilized Hb retained its biological activity for the catalysis toward NO. The biosensor showed high sensitivity and fast response upon the addition of NO, under the conditions of pH 7.0, potential -0.82 V. The time to reach the stable-state current was less than 3 s, and the linear response range of NO was 0.72-7.92 μM, with a correlation coefficient of 0.9991.

Label-free detection of pathogenic bacteria via immobilized antimicrobial peptides.

A novel label-free strategy for the detection of bacteria was developed by using a specific antimicrobial peptide (AMP)-functionalized quartz crystal microbalance (QCM) electrode. This electrode interface was successfully applied to detect pathogenic Escherichia coli O157:H7 based on the specific affinity between the small synthetic antimicrobial peptide and the bacterial cell of pathogenic E. coli O157:H7. The concentrations of pathogenic E. coli O157:H7 were sensitively measured by the frequency response of the QCM with a detection limit of 0.4 cfu μL(-1). The detection can be fulfilled within 10 min because it does not require germiculture process. On the other hand, if the specific antimicrobial peptides were immobilized on a gold electrode, this label-free strategy can also be performed by electrochemical impedance spectroscopy (EIS). Compared with QCM technique, the EIS measurement gives a lower sensitivity and needs a longer assay time. The combination of antimicrobial peptides with the real-time responses of QCM, as well as electronic read-out monitoring of EIS, may open a new way for the direct detection of bacteria.

Ethylenediamine-assisted preparation of carbon nanofiber supported nickel oxide electrocatalysts for sensitive and durable detection of insulin

A uniform nickel oxide (NiO) nanoparticle decorated on carbon nanofibers (CNFs) hybrid with the assistance of ethylenediamine (EDA) following a simple on-spot pyrolysis route has been fabricated for insulin electrocatalytic oxidation. The fabricated hybrid displayed superior catalytic performance due to the synergetic effects between NiO nanoparticles and CNFs. Excellent analytical features, including high sensitivity (1.55 μA μM−1), short response time (<3 s), low detection limit (12.1 nM) and satisfactory linear dynamic range (20–1020 nM) were achieved. Moreover, this EDA-CNFs-NiO hybrid showed good stability and antifouling property in a 0.1 M NaOH electrolyte toward insulin after successive potential cycling, which is highly required for a promising insulin electrocatalyst.

Nano-encapsulant of ascorbic acid-loaded apoferritin-assisted photoelectrochemical sensor for protease detection

A signal-on photoelectrochemical (PEC) biosensor based on nano-encapsulant of ascorbic acid-loaded apoferritin-assisted for protease detection is described. The loaded ascorbic acid could be released from the central cavity of apoferritin into the buffer solution as sacrificial electron donor to capture the photo-generated holes of CdTe quantum dots when light is turned on. In this system, the biosensor relied on monitoring the photocurrent intensity as a result of enzymatic substrate proteolysis in the homogeneous aqueous solution. A low detection limit of 2.7ngmL-1 for trypsin in the linear range from 30 to 450ngmL-1 is achieved. We believe that such a sensing system not only holds the potential ability as a probe for trypsin activity assay, but also could be used for the corresponding inhibitor-screening. It might provide a potentially feasible alternative tool for determining trypsin in human serum in a clinical laboratory. The established method could open a different perspective for PEC enzyme detection and provide a new platform for future development of PEC analysis with other clinically important proteins.

Quenching of the electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(II) by caffeic acid.

Efficient quenching electrochemiluminescence (ECL) of the /tripropylamine (TPrA) system by a novel quencher Caffeic acid (CA) has been investigated. The quenching behaviors can be observed with a 100-fold excess of CA over . The mechanism of quenching is believed to involve energy transfer from the excited-state to the electro-chemical oxidation of CA, which was formed at the electrode surface. Photoluminescence experiments coupled with bulk electrolysis support formation of the oxidation product of CA upon electrochemical oxidation.

Direct electrochemistry of myoglobin in a room temperature ionic liquid aqueous solution and its catalysis to H2O2

Using 1-ethyl-2-methylimidazolium trifluoroacetate (EMImTfa) as the supporting electrolyte, a couple of well-defined and reversible redox peaks of Myb could be observed at the basal plane graphite (BPG) electrode through direct electron transfer between the protein and the BPG electrode, whose anodic and cathodic peak potentials were at −0.098 V and −0.144 V vs. Ag | AgCl, respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rates. Compared with the supporting electrolyte of phosphate buffer solution, EMImTfa played an important role for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of EMImTfa to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface could retain its biological activity and showed a remarkable electrocatalytic activity for the reduction of H2O2 in an EMImTfa aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of H2O2 in EMImTfa aqueous solution with a limit of detection of 3.24 × 10−8 M.