Amino Acid-Based Imidazole Ionic Liquid: A Novel Soft Matrix for Electrochemical Biosensing Applications

Abstract

A new amino acid-based ionic liquid of 1-methyl-3-dodecane imidazolium aspartic acid ([Cₙmim]Asp IL, n = 4, 6, 8, 12, 14) was reported as a soft matrix to be used as a novel electrochemical glucose biosensor. [Cₙmim]Asp ILs were synthesized using a simple acid–base titration method and characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared (FT-IR) spectrum, scanning electron microscopy, negative-staining and cryogenic transmission electron microscopy, electrical conductivity, surface tension, dynamic light scattering, and UV–vis spectrum. [Cₙmim]Asp ILs possessed excellent conductivity and a large specific surface area, providing a biocompatible microenvironment to promote enzyme-catalyzed direct electron transfer while maintaining surface bioactivity and stability. It was found that the micelle structure could form in the [C₁₂mim]Asp IL solution when the concentration was beyond its critical micelle concentration. Glucose oxidase (GOx) could be uniformly dispersed and immobilized onto these micelles of the [C₁₂mim]Asp IL soft matrix through a hydrogen bond and physical absorption. Electrochemical experiments demonstrated that [C₁₂mim]Asp/GOx/Nafion/GCE achieved the best electrochemical performance toward glucose at a working potential of −0.33 V. The [C₁₂mim]Asp-based enzyme sensor displays a linear range response to glucose concentration from 0.001 to 0.58 and 0.58 to 12 mM and a low-end detection limit of 0.572 μM (S/N = 3). Additionally, the present glucose biosensor is robust to interfering molecules and shows acceptable reproducibility and practical application for real samples. The proposed amino acid-based ionic liquid can serve as a versatile and promising soft immobilization matrix for development of excellent biosensor applications.