Ruthenium purple-containing zeolite modified electrodes and their application for the detection of glucose

Zeolite-entrapped ruthenium purple particles (denoted NaY \ RP) were prepar ed by exchanging Fe3+ into zeolite Y (NaY) and reacting further with ruthen ium hexacyanide (Ru(CN)(6)(4-)). Although XRD and diffuse-reflectance UV-vi s absorption analyses suggested that the RP(NaY) particles were basically a morphous, the resulting electrode prepared from these particles and glucose oxidase (GOx) displayed a remarkable sensitivity to glucose. The limiting current showed a linear relationship with the bulk activity of glucose up t o 4 mM (pH 5.1, phosphate), covering a range from 10(-6) to 10(-3) M. Flow- injection analysis, in addition, showed the detection limit reaching a leve l as low as 0.1 mu M. Data simulation showed that the electrode sensitivity followed an electrocatalytic (EC') mechanism based on the reduction of H2O 2 by the reduced ruthenium purple. Accordingly, the reaction rate constant (pseudo-first-order) and the effective activity of RP were determined to be 110 M-1 s(-1) (pH 5) and 1.5 x 10(-9) mol cm(-2), respectively. Electroche mical impedance spectroscopic (EIS) analysis showed that the charge-transfe r resistance of the cm zeolite-electrode decreased systematically with the stepwise addition of glucose into the system. The exchange rate constant (k (o)) and the diffusion coefficient of electrons (D-e) in the zeolite film w ere estimated to be 5 x 10(-6) cm s(-1) and 6 x 10(-10) cm(2) s(-1), respec tively. These experimental results suggested that the RP sites in the NaY \ RP particles were separated widely with the average distance between the a djacent RP sites estimated to be about 1 x 10(-4) cm or equivalent to 500 s upercages, which agreed well with the results obtained from data simulation . (C) 1999 Elsevier Science S.A. All rights reserved.