Determination of microbes and immunoglobulins using a piezoelectric biosensor

Abstract

Determination of the pathogenic microbe Candida albicans and specific immunoglobulins was performed using a piezoelectric crystal sensor system. The system consisted of an oscillator, a frequency counter, and a modified piezoelectric crystal device. Piezoelectric crystals were coated with immobilized anti- Candida antibody or protein A and used as immunoassay sensors by measuring the resonance frequency shift of the piezoelectric devices associated with a mass change at the surface. The frequency shift correlated with a C. albicans concentration in the range of 10 6−5 X 10 8 cells-cm -3 and a human IgG concentration in the range of 10 −6-10 −2 mg-ml −1. The analysis pattern of mouse IgG sub-classes, obtained by using a buffer solution with stepped pH gradient, showed three peaks for IgG 1, IgG 2a and IgG 2b. Auger electron spectroscopy was applied to examine the effect of anodic oxidation of the Pd electrode on the quartz crystal which was used for immobilization. This data indicated that the oxidized electrode surface had a higher oxygen content compared with the non-treated electrode. Two immobilizing methods using γ-aminopropyltriethoxysilane and 2,2,2-trifluoroethanesulfonyl chloride were used and gave similar frequency shift values.