▎ 摘　　要

In this study, graphene oxide (GO) has been reduced in two different ways for the production of oppositely charged reduced graphene oxide (rGO) sheets. One reduction route consisted of the covalent modification of GO with (3-aminopropyl) triethoxysilane and subsequent chemical reduction to produce positively charged rGO. In the second route employed, GO was reduced in a domestic microwave oven, in which the presence of urea doped the material with nitrogen, increasing its electrical conductivity considerably. Multilayers of oppositely charged rGO were manufactured using the layer-by-layer (LbL) assembly technique. The kinetics and growth of multi layers were monitored by UV-Vis absorption spectroscopy and quartz crystal microbalance. rGO multilayers on the interdigitated gold electrodes originate high conductive films, in which the number of deposited layers controls the conductivity. As a solution-gated field-effect transistor, the devices presented high trans conductance; (90 mu S and 55 mu S for holes and electrons, respectively). Upon modification of the LbL films with papain, used as a biological recognition element, the devices were capable of detecting Cystatin C protein (a chronic renal disease biomarker) in synthetic urine in concentrations as low as 5 ng.mL(-1). Therefore, the proposed transistors proposed here represent interesting alternatives as novel sensors and biosensors platforms.