ABSTRACT
A surface-modified electrode, PVA/laccase-Au-NPs/Pt, was prepared to sense ascorbic acid (H2A) in this study. An amount of the following composite, PVA/laccase-Au-NPs/Pt, the polyvinyl acetate (PVA) was employed as a surfactant to adhere the substrate, Pt; then the laccase peptides were spun inside the PVA fiber to wind around the immobilized Au-NPs and construct a hierarchical structure. The PVA shell layer was in charge of sensing H2A and transmitting electrical signals, i.e. transducing redox reaction of H2A. Inside the core region, laccase peptides were responsible for transducing electrons and the Au-NPs collected and relayed them to the substrate of the Pt electrode. It was found that the sensing mechanism for the transducing laccase molecules involved a long-chain electron transmission and peroxide bridging, and for the sensed object, H2A, is related to a sequential discharge of two electrons. According to a test of the catalytic activity, the sensitivity increased with the increase of the doped Au-NPs up to a maximum amount and then decreased because excess Au-NPs tended to agglomerate and obstruct the relaying electrons. The response time and sensitivity were measured to be ca. 40 s and 1.8 µA cm-2 ppm. The surface-modified electrode, PVA/laccase-Au-NPs/Pt, was found to show good selectivity among several disturbing reagents and good stability for 76 days.
ABSTRACT
Electrodes of ruthenium oxide modified nickel were prepared by a thermal decomposition method. The stoichiometry of the modifier, RuOx, was quantitatively determined to be a meta-stable phase, RuO5. The electrodes were employed to sense ascorbic acid in alkaline solution with a high sensitivity, 296 µAcm-2 mM-1, and good selectivity for eight kinds of disturbing reagents. We found that the ascorbic acid was oxidized irreversibly in solution. To match with the variation of the morphology, the sensitivity reached a maximum when the RuOx segregated with a nano-crystalline feature. We find that the substrate oxidized as the deposited RuOx grew thicker. The feature of the deposited RuOx changed from nano-particles to small islands resulting from the wetting effect of the substrate oxide, NiO; meanwhile the sensitivity decreased dramatically. The endurance of the RuOx/Ni electrode also showed a good performance after 38 days of successive test.