Cholesterol biosensing with a polydopamine-modified nanostructured platinum electrode prepared by oblique angle physical vacuum deposition

Abstract

This paper reports a novel cholesterol biosensor based on nanostructured platinum (Pt) thin films prepared by Magnetron Sputtering (MS) in an oblique angle (OAD) configuration. Pt thin films were deposited onto a gold screen-printed electrode and characterized using Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Cyclic Voltammetry (CV), X-ray Photo-electron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and wetting analysis. Our results confirmed that the film is highly porous and formed by tilted nanocolumns, with an inclination of around 40° and a total thickness of 280 nm. XRD and CV analysis confirmed the polycrystalline nature of the Pt thin film. Cholesterol oxidase (ChOx) was covalently immobilized using a bioinspired polymer, polydopamine (PDA), via Schiff base formation and Michael-type addition. After being immobilized, ChOx displayed apparent activation energy of 34.09 kJ mol−1 and Michaelis constant (KM) values of 34.09 kJ mol−1 and 3.65 mM, respectively, confirming the high affinity between ChOx and cholesterol and the excellent ability of the PDA film for immobilizing biological material without degradation. Under optimized working conditions the developed biosensor presented a sensitivity of 14.3 mA M−1cm−2 (R2:0.999) with a linear range up to 0.5 mM and a limit of detection of 10.5 μM (S/N = 3). Furthermore, the biosensor exhibited a fast response (<8 s), good anti-interference properties and high stability after relatively long-term storage (2 months).