Surface modification of ZnO nanostructured electrodes with thiol and phosphonic acid moieties for biosensing applications

Abstract

The analytical performance of affinity immunoassay based biosensor systems is determined by the efficiency of capture probe immobilization, which in turn depends on the stability of surface modification. In this study, we investigate the functionalization of nanostructured ZnO surfaces through two types of crosslinker molecules – DSP that favors thiol chemistry and 11-AUPA that favors phosphonic acid bonding. The type of interaction and surface composition of functionalized ZnO surfaces were evaluated using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements. The crosslinker interaction with ZnO surfaces and subsequent biomolecular binding events influence the inherent electrical properties at the ZnO electrode–electrolyte interface. The changes in charge perturbations due to these events are leveraged for the sensing of target biomolecules, and cardiac troponin-I (cTnI) is investigated using Electrochemical Impedance Spectroscopy and Mott–Schottky measurements. Our results demonstrate that Zn–S formation is more sensitive for the detection of cTnI as compared to the ZnO–AUPA interactions. The dynamic range of detection is from 0.1 pg mL⁻¹ to 100 000 pg mL⁻¹ with a limit of detection at 0.1 pg mL⁻¹ in human serum.