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

The exploration of new interfaces for <i>in vivo</i> 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 <i>in vivo</i> 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 <i>in vivo</i> analysis, especially beneficial for detecting redox inactive species.