An implantable ionic liquid-gel microelectrode for in vivo monitoring of K⁺ levels in the living rat brain

The exploration of new interfaces for in vivo analysis holds great promise for electrochemical acquisition of chemical signals involved in brain events. In this study, we designed and created an implantable electrode using a liquid/liquid (L/L) interface concept to monitor in vivo variations of K⁺ in the living brain. Poly(1-butyl-3-vinylimidazolium bis(trifluoro-methylsulfonyl)imide) (PB) and an ionic liquid of 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide (C₁₀M) were optimized to form a uniform ionic liquid gel (ILG), which exhibits a wide potential window and remarkably enhances interfacial mechanical stability. Furthermore, the specific ionophore [2.2.3]-triazacryptand (TAC) was optimized and incorporated into the ILG (ILG-TAC) to molecularly tailor the micro-interface between the gel phase and water phase. The developed implantable ILG-TAC electrode demonstrated high selectivity for K⁺, and good anti-biofouling capability with a signal deviation less than 8.5% over 50 days of continuous implantation. This ion-transfer-based sensing strategy introduces a novel approach for in vivo analysis, especially beneficial for detecting redox inactive species.