Latex piezoelectric immunoassay: Effect of interfacial properties

Latex piezoelectric immunoassay is a technique for detecting agglutination of antibody- or antigen-bearing latex by an immunoreaction using a piezoelectric quartz crystal; the agglutination decreases the oscillation frequency of the crystal. This is advantageous in that immobilization of antibody or antigen on the crystal surface is unnecessary. In this report, different kinds of chemical functional groups were immobilized on the electrode surface, allowing us to consider the effect of interfacial structure on the frequency change. Electrode modifications such as self-assembly of alkanethiol and aminoalkoxysilane monolayers, and polyethylenimine-glutaraldehyde coating as well as plasma treatment were examined. The sensitivity of the system was found to imitate the interfacial properties so that modification of the electrode surface could improve the response. Among the methods examined for this electrode surface modification, the polyethylenimine-glutaraldehyde modification had the advantages of high reproducibility, fast operation and simplicity. It was also suggested that the frequency change originated primarily from the immunoreaction at the interface.