Diseño de nuevos (bio)sensores electroquímico basados en el uso de compósitos de grafito modificados con grafeno y nanopartículas de magnetita

Abstract

In this thesis were developed electrochemical sensors based on the employment of graphite powder composites modified either with electro-generated nanoparticles of Fe304 or graphene, for the quantification of bioanalytes of clinical relevance like hydrogen peroxide, glucose and dopamine. The excelent electrocatalytic properties of the Fe304 nanoparticles dispersed in the composite made possible the amperometric detection of hydrogen peroxide at very low potentials (-0,100 V) with the consequent improvement in the sensibility and selectivity of the sensor. The simultaneous incorporation of different proteins (insulin, glucose oxidase, ovolizocim, mucin, albumin and casein) and Fe304 in the composite allowed to obtain a drastic improvement in the reduction signal of hydrogen peroxide, due to the considerable increment in the exposed electrocatalytic surface area The presence of the proteins within the composite favors a more efficient dispersion of the Fe304 nanoparticles, which in turns produce a considerable increment in the exposed electrocatalytic surface area augmenting the electro-analytical signal. The synergic effect between the Fe304 nanoparticles and the proteins resulted in a significant decrease in the charge transfer resistance towards hydrogen peroxide reduction, thus, in an important increment in thesensitivity and repeatability of the amperometric response. This effect was highly dependent on the Fe304/protein proportions and protein nature. Due to the good response obtained with the aboye mentioned modified electrode for the amperometric reduction of hydrogen peroxide, we incorporated the enzyme glucose oxidase to obtain an amperometric biosensor for glucose. The analytical signal was obtained from the amperometric reduction of enzimatically-generated hydrogen peroxide. A sensitive, stable, reproducible and fast biosensor for the detection of glucose was obtained, allowing its use for direct quantification of glucose in human blood serum, with an excellent correlation with the conventional spectrophotometric technique. Another aspect addressed in this thesis was the study of a new electrode for the development of electrochemical sensors based in the incorporation of chemically reduced graphene oxide in graphite composites. Through the employment of medium exchange adsorptive stripping voltammetry, the determination of submicromoiar leveis of dopamine was achieved, even in excess of ascorbic acid and serotonin. The sensors proposed in this thesis, represent a strategy with a great potentiality for future development of electrochemical (bio)sensors using other biorecognition molecules and new transduction schemes.