Desenvolvimento de microssensores eletroquímicos para aplicações em estudos envolvendo amostras de interesse biológico utilizando a microscopia eletroquímica de varredura

Abstract

This thesis presents some approaches to manufacturing miniaturized electrochemical sensors aiming at applications in biological samples. Potentiometric pH sensors were fabricated from IrOx films using two different strategies. In the first one, the device was manufactured in a micropipette and was applied in SECM studies involving the pH determination of some biological samples. These devices showed a super-Nernstian and stable response, even in complex samples. Thus, it was found that adjacent regions of C2C12 cells undergo a pH decrease after stimulation with caffeine.In another study, significant pH changes were noticed in the midgut of some lepidopteran order larvae throughout their developmental stages. However, in general, the medium tends to remain alkaline. The second approach involved the development of Si microneedles using MEMS technology. These devices were also surface-modified with a pH-sensitive IrOx film. The geometry and mechanical stability of the microneedles make these devices very promising for in vivo application studies. A Ca 2+ ion-selective membrane electrode was fabricated in a micropipette and used to assess the Ca 2+ permeation through alginate/gelatin hydrogels. It was found that the presence of magnetic nanoparticles in the hydrogel composition increases the permeation of Ca 2+ , while caffeine has the opposite effect, but to a minor extent. Finally, the SECM technique was used to evaluate the electrocatalytic properties of nanostructured materials. In the first study, a nanoporous gold microelectrode was used to map the dopamine diffusion, simulating its release by a cell. In the last two studies, kinetic parameters of these surfaces´ reactivity were obtained by approach curves, and the catalytic activity promoted by these surfaces was confirmed.