Metal oxide barium strontium titanate thin films for electrical immunosensing applications

Immunosensors based on antigen-antibody interaction have attracted intensive research interest in recent years because of their advantages of low cost, ease of miniaturization and label-free operation in the clinical/home-based point-of-care (POC) as well as many other applications. Considerable research activities have been carried out using metal oxide materials, such as SiO ₂, TiO ₂, SiN, Ta ₂O ₅, ZnO, Al ₂O ₃, SrTiO ₃ (strontium titanate) and BST (barium strontium titanate) as the insulator layer on top of electrode for biosensing applications using electrical means of measurements. Owing to its good dielectric properties, the sol-gel derived BST thin films have been proven to be good candidate for immunosensing applications. An immunosensor platform based on such BST thin film has been developed. Detailed chemical surface modification protocol for antigen/antibody immobilization was also implemented. The sensors showed promising sensitivity for human IgG detection using ac impedimetric measurements. The immunosensor is based on non-faradaic process that requires no reagents or labels, and this proved to be more amenable to POC applications. An improved immunosensor device based on the interdigitated microelectrodes and BST thin films showed improved sensitivity and repeatability, reduced sensing area and analyte requirement. Realistic clinical samples for dengue infection detection have also been tested using such platform. The results showed very promising sensitivity towards low concentration detection. The sensor platform also possessed long-term storage stability when stored dry at 4 °C. To highlight the novel approaches for this BST sensing platform, the chapter begins with a general description of the development of metal oxide based immunosensors. Next the fabrication of the BST thin film based immunosensor and chemical surface modification procedures are explained. Thereafter, the unique sensing performance and sensing mechanism with equivalent circuit modeling of are presented.