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

Abstract

Abstract Zeolite-entrapped ruthenium purple particles (denoted NaY ∣ RP) were prepared by exchanging Fe 3+ into zeolite Y (NaY) and reacting further with ruthenium hexacyanide (Ru(CN) 6 4− ). Although XRD and diffuse-reflectance UV-vis absorption analyses suggested that the RP (NaY) particles were basically amorphous, 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 to 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 level as low as 0.1 μM. Data simulation showed that the electrode sensitivity followed an electrocatalytic (EC′) mechanism based on the reduction of H 2 O 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 1.5×10 −9 mol cm −2 , respectively. Electrochemical impedance spectroscopic (EIS) analysis showed that the charge-transfer resistance of the 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 were estimated to be 5×10 −6 cm s −1 and 6×10 −10 cm 2 s −1 , respectively. These experimental results suggested that the RP sites in the NaY ∣ RP particles were separated widely with the average distance between the adjacent RP sites estimated to be about 1×10 −4 cm or equivalent to 500 supercages, which agreed well with the results obtained from data simulation.