An electrochemical immunosensor for detection of aflatoxin B1 (AFB1) in food samples was developed. The sensor is composed by cysteine monolayer immobilized on gold electrode surface with subsequent bind to monoclonal antibody (MAb-Cys-modified electrode). The AFB1 detection was evaluated by cyclic voltammetry and impedance spectroscopy in the frequency range of 100 mHz-100 kHz. Samples of rice were spiked with AFB1 to evaluate the sensitivity of the sensor. Impedance spectra could be fitted to a Randles equivalent circuit containing a constant phase element. Atomic force microscope (AFM) images showed MAb-AFB1 complex immobilized across the electrode surface. The electron transfer resistance (Rct) increase was attributed to a decrease in the charge permeability of the MAb-AFB1-Au surface to a redox probe K4[Fe(CN)6]4-/K3[Fe(CN)6]3-. The surface coverage exhibited a linear relationship as function of toxin concentration and is found to be 0.75 at 30 µg mL-1. The obtained sensor is a promising candidate for detection of AFB1 in rice with sensitivity and specificity.

Dielectric characterization has been applied as a convenient tool for evaluation of transport and polarization mechanisms in soft materials. In this work, we have explored the study of charge transport mechanisms in alginate hydrogel containing neomycin-loaded liposomes. For comparison, drug release kinetic was evaluated by using UV-Vis spectrophotometry and electrical impedance spectroscopy (EIS) at different external direct current (DC) polarization (100 mV and 1 V). The charge transfer resistance (Rct) was proportional to DC electrical stimulation and inversely to the amount of released neomycin. Optical and electrical measurements confirmed the dependence of neomycin release under influence of electrical potentials. The kinetic profile of these systems was described by zero-order model. In addition, the Korsmeyer-Peppas model also suggested a diffusion mechanism based on super case II transport (non-Fickian). These results encouraged the use of EIS as a “dark" spectroscopy technique, since EIS is effective for studies of release kinetics controlled by DC external electrical excitation.