Amperometric bioelectrode for specific human immunoglobulin G determination: optimization of the method to diagnose...

Bioelectrodes to detect immunoglobulin G (IgG) antibodies occurring in sera of patients suffering from American trypanosomiasis were assembled. The device consisted of a gold electrode modified with a thiol sensitized with parasite proteins. The assemblage was accomplished by adsorbing IgG antibodies from confirmed infected patients followed by adsorption of anti-human IgG labeled with a redox enzyme. The appliance was used as a working electrode in a three-electrode cell containing a soluble charge-transfer mediator, also behaving as enzyme cosubstrate. The method is based on the measurement of the catalytic current after addition of the enzyme substrate, occurring when a positive serum is used to build up the biosensor. The discrimination efficiency between positive and negative sera was 100% for the samples studied. A 0.9525 correlation coefficient was obtained for results acquired by using this approach and one commercial diagnostic kit. The reproducibility, evaluated by the percentage coefficient of variation, varied between 7 and 20%. The sensitivity was 12.4 ng mL(-1) IgG, which is in the same order as that obtained with the commercial kit. Stability of the device was studied for a 7-day period and the results showed no significant change (p = 0.218). Leishmaniasic sera showed cross-reactivity when total parasite homogenate was used as antigen.