Operation of acoustic plate mode immunosensors in complex biological media

Acoustic wave based immunosensors have proven to facilitate the in situ detection of marker-free proteins in real time, However, the vast majority of these studies focuses on the interaction of a single type of antigen with immobilized receptors in pure buffer solutions. In an effort to evaluate the potential of acoustic plate mode immunosensors for operation in more complex biological environments, antigen/antibody reactions have been studied in pure buffer solution, in the presence of cells, and in human serum. It has been observed that the devices do not respond to cell adsorption and that antigen/antibody reactions can successfully be detected even if a thick layer of cells is deposited on the sensing surface. By varying the frequency of operation, it was shown that the sensitivity of the devices toward nonspecific protein adsorption is reduced at high frequencies of operation. Thus, spurious immunosensor response caused by nonspecific adsorption processes can be suppressed by appropriately selecting device frequency. Using immunoglobulin G with minimum cross reactivity with human serum proteins, antigen/antibody reactions have also been monitored in human serum. While the observed frequency shifts are comparable to those measured in pure buffer solutions, the binding process is accompanied by additional acoustic loss, indicating changes in the viscoelastic properties of the interfacial layer.