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

A new amino acid-based ionic liquid of 1-methyl-3-dodecane imidazolium aspartic acid (CnmimAsp IL, n = 4, 6, 8, 12, 14) was reported as a soft matrix to be used as a novel electrochemical glucose biosensor. CnmimAsp 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. CnmimAsp 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 C12mimAsp 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 C12mimAsp IL soft matrix through a hydrogen bond and physical absorption. Electrochemical experiments demonstrated that C12mimAsp/GOx/Nafion/GCE achieved the best electrochemical performance toward glucose at a working potential of −0.33 V. The C12mimAsp-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.