SEM study of an Amperometric Biosensor for glucose determination in Apple juice

RISTOFF, M. E.; SORRIVAS, V.; LOZANO J. E.; CASERES, A.

RIO DE JANEIRO

Congreso; 17º INTERNAT. MICROSCOPY CONGRESS; 2010

SBMM

Amperometric biosensors function by the production of a current when a potential is applied between two electrodes. Research on amperometric biosensors attracts lots of current interest because of their potential applications in the food industry. A typical application for this simple type of devices is the determination of glucose concentrations by the use of an glucose oxidase immobilised on graphite [1]. The reaction results in a reduction of the oxygen concentration as it diffuses to the cathode, this being detected by a reduction in the current between the electrodes [2]. One problem of this technique is the lost of enzyme activity and the decrease of active surface affecting substrate diffusion. The objective of the present work was (i) to study electrode modifications using scanning electron microscopic (SEM) images taken of the graphite surface before and after immobilization and use. Carbon paste biosensors were prepared by hand-mixing glucose oxidase, graphite powder, paraffin, and ferrocene as mediator. Assay conditions were pH, 7; enzyme content, 10%; and applied voltage, 0.16V. Optimal working conditions were determined. The dispersion of enzyme in graphite was characterized using scanning electron microscopy (SEM, JEOL 6300F) [3]. The scanning electron microscopic (SEM) images were taken of the graphite surface before and after immobilization. Figure 1 shows SEM micrographs of lyophilized enzyme (1.a); graphite (1.b); glucose oxidase enzyme immobilized on the graphite sensor (1c); and a view of the electrode surface after its use for determining concentration of glucose. On the other hand, Fig. 2 shows the same information at lower magnification (7,00X). Results show the irregular distribution of glucose oxidase on graphite (Figs. 1c and 2c), associated to the reduction of the enzyme activity, and the layer of glucose covering the sensor (Figs 1d and 2d) building an additional resistance to the diffusion of glucose to the active enzyme surface. Therefore, SEM micrographs were employed to demonstrate the importance of surface properties in determining the response of the amperometric biosensor for glucose determination.