Sn–Fe cyanogels noncovalently grafted to carbon nanotubes in a versatile biointerface design: an efficient matrix and a facile platform for glucose oxidase immobilization

Abstract

Enzyme immobilization is a powerful strategy adapted to effectively maximize the bioactivity, specificity and stability of an isolated enzyme. In this study, we demonstrate a novel and scalable procedure for facile enzyme immobilization, in which three-dimensional porous Sn–Fe hydrogels were applied to incorporate the enzyme to construct a sensing interface for an amperometric biosensor. The process was initiated from the electrodeposition of Prussian Blue (PB) on multi-walled carbon nanotube (MWCNT)-modified gold electrodes, sequentially capped with tin tetrachloride (SnCl₄) solution followed by the addition of a freshly-made homogeneous mixture of enzyme and potassium ferrocyanide solution, leading to instant formation of hydrated three-dimensional (3D) porous Sn–Fe cyanogel networks, deeply set outside the produced rough layer of the MWCNT–PB complexes, providing a desirable microenvironment for the entrapped enzyme. The structural morphology and electrochemical properties of the as-prepared Sn–Fe cyanogels noncovalently grafted to MWCNTs with functionalities of electrodeposited PB were well characterized by scanning electron microscopy (SEM), ultraviolet visible spectroscopy (UV-vis) and cyclic voltammetry. The results indicate that the modified electrode with a multilayer configuration was well-organized, as proposed, and exhibited good electrical conductivity and stable catalytic activity to H₂O₂ electro-reduction due to the functional layer of PB. When glucose oxidase (GOx) was selected as a model enzyme, the resulting glucose biosensor exhibited a relatively low detection limit of 0.1 μM (S/N 3) with a good sensitivity of 1.68 μA mM⁻¹ cm⁻² and improved stability. The results suggest that the Sn–Fe cyanogels, with sufficient interfacial adhesion, hold promise as an attractive support material.