Covalent immobilization of cholesterol oxidase and poly(styrene-co-acrylic acid) magnetic microspheres on polyaniline films for amperometric cholesterol biosensing

Abstract

Magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs) were synthesized by co-precipitation (of Fe²⁺ and Fe³⁺) and surface-carboxylated by poly(styrene-co-acrylic acid) (PSA). Then they were thoroughly characterized by Scanning Electron Microscope and Transmission Electron Microscope analyses. Using glutaraldehyde cross-linking immobilization strategy, cholesterol oxidase (ChOx) was immobilized onto Fe₃O₄/PSA microspheres. The Fe₃O₄/PSA-ChOx has been successfully synthesized on the planar platinum polyaniline (PANi) modified electrode. PANi/Fe₃O₄/PSA-ChOx sensing properties were studied using cyclic voltammetric and chronoamperometric techniques. Under the optimized experimental conditions the biosensor shows excellent features, such as wide linear range, 0.2 to 1.8 mM (R² = 0.9901), low detection limit (0.02 mM), short response time (5–10 s), and high sensitivity (8796 μA mM⁻¹ cm⁻²). The interference test with selected organic compounds, such as glucose, ascorbic acid, uric acid, and acetaminophen indicated high selectivity of the above sensor. It can be proven that the proposed PANi/Fe₃O₄/PSA-ChOx based sensing concept could be successfully used for other biodetections.