Enhanced Protein Stability Using Room Temperature Ionic Liquid for Wearable Electrochemical Sweat-Based Biosensor

Wednesday, 4 October 2017: 11:40
Chesapeake J (Gaylord National Resort and Convention Center)
B. Jagannath (The University of Texas at Dallas), S. Muthukumar (EnLiSense LLC), R. D. Munje, and S. Prasad (The University of Texas at Dallas)
In this abstract we demonstrate the implementation of a hybrid aqueous/room temperature ionic liquid (RTIL) interface towards the development of a wearable biosensor for detection of inflammation through the use of a diagnostics protein biomarker. RTILs have low vapor pressure and a wide electrochemical window. RTILs are also known to stabilize proteins based on their physical properties such as hydrophobicity or hydrophilicity, viscosity and the chemical interaction of the RTIL with various functional groups of a protein. Typically, proteins are stable in RTILs with chaotropic cation and kosmotropic anion. Also, the interaction of anionic moiety with protein influences the protein stability as compared to the cationic moiety. We leverage the physicochemical properties of the RTIL, BMIM[BF4], along with its excellent electrochemical properties towards the development of a wearable electrochemical biosensor for the detection of IL-6 in human sweat. Firstly, the stability of α IL-6 antibody in RTIL was evaluated using optical techniques such as ATR-FTIR, dynamic light scattering (DLS) to determine any conformational changes or aggregation of the protein. ATR-FTIR temporal studies showed that the antibody was more stable in BMIM[BF4] (up to 96h) without any peak shifts as compared to PBS (up to 48h) and no aggregation in protein size was observed using DLS for up to 96h in BMIM[BF4]. Further, high zeta potential values for volumetric ratios ≥50% BMIM[BF4] in synthetic sweat(pH 2- 8) indicate that the protein does not aggregate in the presence of BMIM[BF4]. Once the enhanced stability of protein in BMIM[BF4] was confirmed, non-faradaic electrochemical impedance spectroscopy (EIS) was performed to assess the sensor performance metrics for detection of interleukin -6 (IL-6) in human sweat. The wearable sensor with metal-semiconductor electrode functionalized with IL-6 antibody in RTIL showed a limit of detection of 0.2pg/mL up to 24h, 2 pg/mL between 24- 48h, 5pg/mL between 48- 96h post-antibody functionalization. This LOD is below the physiological relevant range of 7-16 pg/mL. The linear dynamic range of the sensor obtained was 0.2- 200 pg/mL. This enhanced sensor performance is not only due to the protein stability maintained by the RTIL but also because of the electrochemical characteristics of RTIL that contributed to the enhanced electrical double layer post 96h immobilization. The physical, electrochemical along with protein stabilization properties of RTIL make it novel for electrochemical protein biosensing.