Rafaela Fernanda Carvalhal

Electrochemical Detection in a Paper-Based Separation Device

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.

Surface plasmon resonance immunosensor for early diagnosis of Asian rust on soybean leaves.

Soybean rust (Asian rust) is a disease that occurs in soy cultures, negatively affecting pod formation and final grain weight and reducing value and product quality. Early identification of fungus in the plants prevents severe farming losses and spread to neighboring cultures. In this paper, a fast response sensor was developed based on surface plasmon resonance to detect Asian rust in soybean leaf extract at early stages of the disease. The antibody anti-Phakopsora pachyrhizi (pathogen) was covalently immobilized on a gold substrate via a self-assembled monolayer (SAM) of thiols using cysteamine-coupling chemistry. This immunosensor presented a linear response range for the antigen from 3.5 to 28.0 microg mL(-1) (r(2)=0.996). The effects of the antibody amount and the surface blocking to minimize non-specific adsorption on immunosensor response were evaluated. These studies provide new perspectives on using SPR technology for the development of a highly sensitive sensor for agricultural applications.

Development of a disposable amperometric biosensor for salicylate based on a plastic electrochemical microcell

The use of an amperometric biosensor for rapid salicylate determination in blood is described. Photolitography was used to make gold electrodes on a polyester film. The plastic microcell was characterized using cyclic voltammetry to demonstrate the electrochemical performance of the system. The biosensor was constructed by immobilizing salicylate hydroxylase onto the working electrode of the plastic electrochemical microcell. The optimized working conditions were 0.1 mol L(-1) phosphate buffer at pH 7.6 with 0.5 mmol L(-1) of NADH and 300 mV vs. Au as the applied potential. The resulting biosensor exhibited a high sensitivity (97.4 nA/mmol L(-1) salicylate) and an adequate linear response range (1.2x10(-4) to 1.0x10(-3)mol(-1)). The biosensor performance was verified by determining salicylate in spiked blood samples and the results were statistically equivalent to the values obtained from the standard Trinder spectrophotometric method, with a 95% confidence level. This study shows the potential development of a portable, inexpensive and disposable device for point-of-care monitoring.

Development of an electrochemical immunosensor for Phakopsora pachyrhizi detection in the early diagnosis of soybean rust

A ferrugem da soja e uma doenca que ocorre nas folhas da soja e e considerada muito agressiva, pois reduz a qualidade do grao final. A identificacao precoce do fungo na plantacao previne varias perdas para o agricultor bem como para as culturas vizinhas. Neste trabalho, um imunossensor foi desenvolvido sem a utilizacao de marcadores usando medidas de impedância para detectar a ferrugem asiatica nos extratos das folhas contaminadas nos estagios iniciais da doenca, antes do aparecimento dos sintomas. O anticorpo anti-micelio do fungo Phakopsora pachyrhizi (agente causador da doenca) foi imobilizado em substrato de ouro via formacao de monocamadas auto-organizadas de tiois e ligacoes covalentes com a biomolecula. O imunossensor apresentou um limite de deteccao de 385 ng mL-1. A otimizacao das condicoes experimentais e o bloqueio da superficie para minimizar ligacoes nao-especificas foram realizados. Este estudo proporcionou uma nova perspectiva da utilizacao do metodo para o diagnostico precoce da doenca.