Environmental effects of chitosan as an immobilization medium for electrochemically active small molecules

Abstract

A number of challenges arise when using ferrocene as a component of electrochemical biosensors, including solubility in aqueous solutions. Therefore, entrapment of the biotin-ferrocene molecules within the chitosan film provides a route for immobilization on an electroactive surface such as an electrode while making the system water compatible. The use of the chitosan-ferrocene bioconjugate thin film on the electrode surface produces a signal that can be monitored in aqueous media. Herein, we discuss a series of modified ferrocene molecules that contain various linkers that provide non-covalent entanglement points to the chitosan medium. The electrochemical analysis and electron microscopy results show marked differences in the ferrocene loaded chitosan polymers when the termini of the ferrocene-linker vary between –SH and –NH₂. The –SH modified systems showed increased reversible and robust electrochemical signals relative to the –NH₂ congeners. Further studies showed that non-covalent impregnation strategy used is robust to degradation and less than 1% of the ferrocene molecules were leached over time. These results indicate that there are specific considerations needed when using chitosan-ferrocene systems as components in sensor arrays in future studies.