Adrian Marcelo Granero

Development of an amperometric biosensor based on peroxidases to quantify citrinin in rice samples.

An amperometric biosensor based on horseradish peroxidase (EC1.11.1.7,H2O2-oxide-reductases) to determine the content of citrinin mycotoxin in rice samples is proposed by the first time. The method uses carbon paste electrodes filled up with multi-walled carbon nanotubes embedded in a mineral oil, horseradish peroxidase, and ferrocene as a redox mediator. The biosensor is covered externally with a dialysis membrane, which is fixed to the body side of the electrode with a Teflon laboratory film, and an O-ring. The reproducibility and the repeatability were of 7.0% and 3.0%, respectively, showing a very good biosensor performance. The calibration curve was linear in a concentration range from 1 to 11.6nM. The limits of detection and quantification were 0.25nM and 0.75nM, respectively. For comparison, the citrinin content in rice samples was also determined by fluorimetric measurements. A very good correlation was obtained between the electrochemical and spectrophotometric methods.

Electrochemical Reduction of the Mycotoxin Citrinin at Bare and Modified with Multi-Walled Carbon Nanotubes Glassy Carbon Electrodes in a Non-Aqueous Reaction Medium

-1 tanto em eletrodo de carbono vitreo (GC) nao modificado quanto em eletrodo GC modificado com nanotubos de carbono de paredes multiplas foi investigado por voltametria ciclica e eletrolise a potencial controlado. Os resultados obtidos permitiram inferir um mecanismo de eletroreducao complexo com etapas quimicas e eletroquimicas, acopladas a reacao inicial de transferencia de eletron. Citrinina apresentou pico catodico unico que corresponde no minimo a duas etapas de reducao envolvendo um eletron e duas reacoes quimicas homogeneas, segundo mecanismo de autoprotonacao do tipo ECEC (transferencia de eletron acoplada com aceitacao de proton). As reacoes quimicas se originam nas transferencias de proton intermolecular do substrato para os seus produtos intermedios basicos de reducao, caracterizando um mecanismo de autoprotonacao. Analise cinetica por procedimentos de simulacao de resultados voltametricos permitiu uma caracterizacao completa do mecanismo de reducao heterogeneo de citrinina. Electrochemical reduction mechanism of citrinin in acetonitrile plus 0.1 mol L -1 (C4H9)4NClO4 at both bare and modified with multi-walled carbon nanotube glassy carbon (GC) electrodes was investigated by cyclic voltammetry and controlled potential electrolysis. Results allowed to infer a complex electroreduction mechanism with chemical and electrochemical steps coupled to the initial electron transfer reaction. Citrinin shows a single cathodic peak that corresponds at least to two electron reduction steps and two homogeneous chemical reactions, conforming to an ECEC (electron-transfer coupled with proton acceptance) self-protonation mechanism. The chemical reactions are originated in the intermolecular proton transfers from the substrate to its basic reduction intermediates, featuring a self-protonation mechanism. Kinetics analysis by simulation procedures of voltammetric results permitted a fully characterization of the mechanism of citrinin heterogeneous reduction.