Flexible Acetylcholine Neural Probe with a Hydrophobic Laser-Induced Graphene Electrode and a Fluorous-Phase Sensing Membrane

This work develops the first laser-induced graphene (LIG)-based electrochemical sensor with a superhydrophobic fluorous membrane for a flexible acetylcholine (ACh) sensor. ACh regulates several physiological functions, including synaptic transmission and glandular secretion. The ACh sensing membrane is doped with a fluorophilic cation-exchanger that can selectively measure ACh based on the inherent selectivity of the fluorous phase for hydrophobic ions, such as ACh. The fluorous-phase sensor improves the selectivity for ACh over Na⁺ and K⁺ by 2 orders of magnitude (compared to traditional lipophilic membranes), thus lowering the detection limit in artificial cerebrospinal fluid (aCSF) from 331 to 0.38 <b><i>μ</i></b> M, thereby allowing measurement in physiologically relevant ranges of ACh. Engraving LIG under argon creates a hydrophobic surface with a 133.7° contact angle, which minimizes the formation of a water layer. The flexible solid-contact LIG fluorous sensor exhibited a slope of 59.3 mV/decade in aCSF and retained function after 20 bending cycles, thereby paving the way for studying ACh's role in memory and neurodegenerative diseases.