The investigation of functionalized BST thin film surface for immunosensor application

In this contribution, the main goal is to develop a simple and effective surface modification and functionalization protocol on inorganic barium strontium titanate (BST) surfaces for immunosensing applications. We have successfully developed a four-step protocol; namely UV/Ozone activation, silanization, amino activation and antigen immobilization. The BST surface was initially exposed to UV/Ozone to create a hydroxyl layer that will render the surface highly hydrophilic. This surface has an advancing water contact angle of 19°, as compared to the original contact angle of 62° for the unmodified BST surface. Atomic force microscope (AFM) images showed dense coverage of the self assembled monolayer (SAM) and immobilized anti-human immunoglobulin G (anti-human IgG). Ellipsometer measurements on the thickness of the top organic layer confirmed the successful attachment of antigen and antigen-antibody conjugation. X-ray photoelectron spectroscopy (XPS) study revealed that the anti-human IgG was covalently immobilized onto the 3-aminopropyltrimethoxysilane (APTS)/glutaraldehyde modified surface. Specific antigen-antibody conjugation was also evident through fluorescence measurements. A near linear correlation range between the fluorescence intensity and anti-human IgG-FITC concentration on a logarithmic scale was observed. Through the step-by-step detail analyses with various surface characterization techniques, we conclude that the simple four-step surface modification protocol proposed is an efficient way for BST thin film surface modification and antigen/antibody immobilization. Preliminary impedance measurement results also showed good linear correlation between impedance with human IgG concentration.