Development of a Surface Acoustic Wave Immunosensor

In this paper the first application of horizontal polarized surface acoustic waves (HP-SAW) in LiTaO3 for an immunosensor is presented. A SAW device with two paths, a sensitive path and a reference path operating in liquid at 345 MHz, is used as the sensor. Antigens and antibodies were both immunoglobulins. The antibodies were immobilized via protein A on the sensitive path with a mass density of 0.4 ng/mm2, as shown by ELISA measurements. A theoretical detection limit of ∼33 pg and a high sensitivity of 110 kHz/(ng/mm2) could be derived from the experiments. High signal enhancement factors of 4.5 and 12 are achievable by gold colloid labeled antigens with colloid diameters of 5 and 10 nm, respectively. Specificity of the antibody was demonstrated by a preabsorption experiment. As a further antibody/antigen system the binding of the anti-human serum albumin (HSA) to HSA was examined.