Gravimetric biosensor based on a 1.3 GHz AlN shear-mode solidly mounted resonator

Abstract

We investigate the performance of solidly mounted resonators based on Ir/tilted-AlN/Ir piezoelectric stacks as biosensors. These films are deposited by varying the pressure, the cathode power and the tem- perature of a two-step process based on depositing (00 • 2)-tilted AlN active layers over an (10 • 3)-oriented AlN seed layer. To minimize the influence of the temperature coefficient of frequency on the stability of the biosensor, we use insulating acoustic mirrors made of layers of SiO 2 and amorphous TaO x with non- /4 thicknesses, which enables to reduce the TCF to − 14 ppm/ ◦ C. The mass loading of the resonators with SiO 2 thin films results in a sensitivity of 1800 kHz/pg • cm 2 . Surface functionalization consists on the binding of silane groups on plasma oxidized SiO 2 surfaces. After a glutaraldehyde link, streptavidin is bonded to the surface to receive biotinylated receptors for several species. We test thrombin-binding aptamer (TBA29 against thrombin, and IgG antibody against immunoglobulin). The sensors response to species of different molecular weight like TBA-29 (9.75 kDa) or IgG antibody (150 kDa) is monitored. Finally, we assess the response of the biosensors to different thrombin concentrations (ranging from 4 nM to 270 nM) on surfaces functionalized with the TBA29 aptamer.