Immobilized ferrocene and glucose oxidase on titanium(IV) oxide grafted onto a silica gel surface and its application as an amperometric glucose biosensor

The voltammograms obtained with an electrode containing carbon paste with ferrocene immobilized on a titanium-oxide/silica gel material showed good response and stability in aqueous media. From pH 4 to 8 the electrode response remained almost constant, but a small shift in the midpoint potential towards more positive values was observed when the pH was decreased. The nature of the cation does not affect the voltammetric response. However, the nature of the anion affects the midpoint potential significantly. Cyclic voltammetry investigation showed that the electrode with immobilized glucose oxidase is an excellent biosensor. The mechanism of the electron transfer was proposed as being electron tunneling by the flavin of the enzyme to mediator, and the high current level is assigned to the high surface area of the silica matrix. The amperometric measurements showed a linear response in the range from 1.0 x 10(-4) to 8.0 x 10(-4) M. Above this range, saturation of the enzyme was observed. The response time was about 15 s. Determination of glucose in blood serum showed an excellent correlation when compared with Merck's Kit method. The immobilized material presented an excellent stability mantaining the same activity for at least six months.