Towards the application of Al2O3/ZnO nanolaminates in immunosensors: total internal reflection spectroscopic ellipsometry based evaluation of BSA immobilization

Abstract

In this research Al₂O₃/ZnO nanolaminates were evaluated for possible application in the design of optical immunosensors. Total internal reflection ellipsometry (TIRE) was utilized to study the optical response during the formation of a bovine serum albumin (BSA) based monolayer on the surface of Al₂O₃/ZnO nanolaminates, which were pre-modified with a N-(3-aminopropyl)triethoxysilane (APTES) layer. The influence of the thicknesses of Al₂O₃ and ZnO layers on the performance of Al₂O₃/ZnO nanolaminate based structures has been assessed. This research has shown the noticeable contribution of multiple reflections from the interfaces between Al₂O₃ and ZnO for the enhancement of the optical response in a total internal reflection configuration. Al₂O₃/ZnO nanolaminates of 200 nm total thickness based on four 50 nm thick alternating Al₂O₃ and ZnO layers have shown better sensitivity than the nanolaminate based on two 100 nm oxide-layers. Real-time monitoring of the ellipsometric parameters Ψ(λ) and Δ(λ) has shown that BSA was successfully covalently attached to the nanolaminate/APTES surface. The surface concentration of immobilized BSA was evaluated from the real-time data of the ellipsometric parameters Ψ(λ) and Δ(λ). The expected advantages and disadvantages of Al₂O₃/ZnO nanolaminates during expected application in optical immunosensors are discussed.