Development of a FPW allergy biosensor for human IgE detection by MEMS and cystamine-based SAM technologies

Conventional allergy detecting kits usually require a large number of expensive testing samples, time-consuming procedures and complex instruments. To overcome these disadvantages, this study presents a high-sensitivity flexural plate-wave (FPW)-based allergy biosensor with integrated cystamine self-assembled monolayer (SAM) for detecting the concentration of immunoglobulin E (IgE) in human serum. The ultrasonic flexural plate-waves were respectively launched and received by two Cr/Au interdigital transducers (IDTs) located on the left and right side of the Si/SiO2/Si3N4/Cr/Au/ZnO floating thin plate. A 4.625-nm height cystamine SAM and a 1.078-nm height glutaraldehyde cross-linking layer were developed for the immobilization of IgE antibody and their surface chemical composition and structural perturbation changes were analyzed by Auger electron spectroscopy (AES) and Fourier transform-infrared (FT-IR) spectroscopy, respectively. Using atomic force microscopy (AFM), this work investigates the molecular topographies of the cystamine SAM, glutaraldehyde, IgE antibody and IgE antigen layers and the number of bonded IgE antibody/antigen pairs. A FPW-based allergy biosensor with very high mass-sensitivity (−8.52 × 107 cm2 g−1) and low operating frequency (8.75 MHz) of human IgE antigen was demonstrated.