The influence of different surface pretreatment procedures on the electrochemical response of a polycrystalline gold electrode was evaluated. Mechanical polishing with slurry alumina (M), chemical oxidation with H 2 SO 4 /H 2 O 2 (C), electrochemical polishing (potential cycling between À 0.1 V and 1.2 V vs. SCE) (E), chemical reduction with ethanol, and combinations among these treatments were employed to change the surface electrode characteristics. The efficiency of the proposed pretreatments was evaluated by electrochemical responses towards the redox couple ferri(II/III)-ammonium sulfate and by the formation of a self-assembly monolayer of 3-mercaptopropionic acid (3 MPA SAM) on gold electrodes. The procedure (C) allowed important gold surfaces activation. Using procedures (C) and (E) the roughness of polycrystalline gold surfaces was significantly minimized and more reproducible surfaces could be obtained. From the profile of reductive desorption of 3 MPA SAM it was possible to verify that reduced gold surfaces generated better packed monolayers than oxidized ones and a comparative study using CV and DPV techniques showed that between the two desorption peaks, the one localized at more negative potential values corresponds to the cleavage of Au-S bond from the chemisorbed thiol. In general, the improvement in the studied electrochemical responses could not only be attributed to an increase in the real surface area of the electrode, but to the chemical surface states set off by the pretreatment procedure.

Prototypes of microfluidic paper-based separation devices with amperometric detection were developed and evaluated. Photolithography was used to make a gold electrochemical microcell on polyester and that microcell was coupled to a strip of paper where a chromatographic separation occurs. The device performance was demonstrated with the separation and quantification of uric and ascorbic acid in mixtures. The method provides an analytical alternative for the determination of compounds where low cost and simplicity are essential.

O presente trabalho de revisão aborda os mais recentes avanços na tecnologia de biossensores alcançados através da montagem de biomoléculas associada com nanopartículas de ouro na construção de dispositivos analíticos. Esta revisão está dividida de acordo com a biomolécula empregada no desenvolvimento de biossensores: (i) compostos imunológicos; (ii) DNA/RNA funcionais; e (iii) enzimas e proteínas Heme. A fim de facilitar a compreensão, cada seção foi subdividida de acordo com o modo de transdução. Os imunossensores contendo nanopartículas de ouro têm uma ampla gama de aplicações nos campos alimentício, ambiental, farmacêutico, químico e de diagnósticos clínicos. As nanopartículas foram empregadas para melhorar o sinal analítico ou a imobilização dos imunocompostos. Em outra seção, os biossensores DNA/ RNA empregando nanoestruturas de ouro como labels e biossensores label-free associados a nanoestruturas de ouro como transdutores foram sistematicamente relatados para a rápida identificação de patógenos, espécies de interesse ambiental e diagnóstico clínico. A inclusão de nanopartículas de ouro em eletrodos modificados aumenta a transferência de elétrons entre o transdutor e a biomolécula proporcionando um melhor desempenho quando enzimas e proteínas redox heme são usados. Biossensores para a detecção e quantificação de glicose e peróxido de hidrogênio foram também discutidos.The present review discusses the latest advances in biosensor technology achieved by the assembly of biomolecules associated with gold nanoparticles in analytical devices. This review is divided in sections according to the biomolecule employed in the biosensor development: (i) immunocompounds; (ii) DNA/RNA and functional DNA/RNA; and (iii) enzymes and Heme proteins. In order to facilitate the comprehension each section was subdivided according to the transduction mode. Gold nanoparticles based immunosensors have a wide range of applications in food, environmental, pharmaceutical, chemistry and clinical diagnostics. The nanoparticles were employed to improve whether the analytical signal or the immunocompounds immobilization. In another section, biosensors based on DNA/RNA biomolecules employing gold nanostructures as labels and label-free funtional DNA/RNA biosensors associated to gold nanostructures as tranducers were systematically reported for rapid identification of pathogens, species of environmental interest and clinical diagnostics, respectively. The inclusion of gold nanoparticles in modified electrodes itself enhances the electron transfer between the transducer and biomolecules leading to improved bioanalytical devices when redox enzymes and heme proteins are used. Biosensors for the detection and quantification of glucose and hydrogen peroxide are discussed as well.

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