Studies of Sol−Gel Ceramic Film Incorporating Methylene Blue on Glassy Carbon: An Electrocatalytic System for the Simultaneous Determination of Ascorbic and Uric Acids

In this work, we investigated the immobilization of methylene blue in a methyltrimethoxysilane sol−gel ceramic film on a glassy carbon electrode. Up to a certain saturation level, under our conditions, it was found that the methylene blue was tightly held and did not leach out into aqueous solutions, even with continuous immersion for up to 1 month. The electrochemical behavior of the immobilized methylene blue was then studied. pH variation revealed that there were two distinct redox couples whose existences were pH-dependent. The methylene blue/sol−gel film was also examined as an electrocatalytic system for ascorbic and uric acid oxidations. It was revealed that this system was highly sensitive for ascorbic and uric acid sensing (practical determination limits of 5.00 nM and 1.00 nM for ascorbic acid and uric acid, respectively) and also allowed simultaneous determination of these biomolecules. The simultaneous determination of these two analytes in a human urine sample was demonstrated. The stability of the methylene blue/sol−gel film/glassy carbon electrode sensing system was good, with up to at least a month of continual operation.