Latex piezoelectric immunoassay: detection of agglutination of antibody-bearing latex using a piezoelectric quartz crystal.

A method for immunoassay of CRP (C-reactive protein) was developed using a piezoelectric quartz crystal. Previous immunoassays using a piezoelectric crystal have required the formation of a thin film on the crystal, to which an antibody is affixed. The occurrence of antigen-antibody reaction increases the weight attached to the crystal surface, which causes a reduction in the oscillation frequency. In our method, the frequency reduction was observed using antibody-bearing latex without any film. One possible mechanism of the frequency change is that the crystal acts as a sensing apparatus for viscosity or density change in the solution due to aggregation of latex particles. The detection limit was almost the same as that for latex photometric immunoassay (LPIA). The present method has been designated as latex piezoelectric immunoassay (LPEIA).