(E-172) Flexible neural probe for the selective in-vivo recording of acetylcholine

Introduction:: In the brain, acetylcholine (ACh) functions simultaneously as a neuromuscular transmitter and neuromodulator, thus playing critical roles in learning, memory, motivation, and muscle control. Alterations in ACh concentration in the cerebral cortex were correlated to dementia and Alzheimer's disease, psychiatric disorders, anxiety, and depression. Therefore, tools for selective sensing of ACh are crucial for a fundamental biological understanding of the role of this neurotransmitter in disease progression, as well as the rational design and testing of therapeutics that interact with cholinergic receptors. Here, I am taking an innovative approach to fabricating a biocompatible and biorthogonal sensor for the in-vivo recording of ACh levels in the brain tissue to address current challenges in ACh detection, including low selectivity in biofluids.

Materials and Methods:: I am utilizing a superhydrophobic sensing membrane. First, I am fabricating a flexible perylene-based neural probe and integrating it with a newly developed superhydrophobic fluorophilic receptor selective toward ACh. Fluorocarbons (not to be mistaken with fluorescent compounds) have gained much attention due to their superiority over traditional lipophilic polymers for applications such as superhydrophobic dielectric coatings, surfactants, biocompatible, nontoxic artificial blood, and biocompatible biofouling resistant coatings on medical devices. However, applying fluorous compounds for sensing is underexplored. Due to the low polarity, low polarizability, and poor coordinating nature of the fluorous phase, they can enhance the selectivity of potentiometric sensing electrodes. Our work showed that the fluorous phase could expand the selectivity of potentiometric sensors by several orders of magnitude, achieving an unprecedented selectivity toward ions of interest. We fabricated a flexible neural probe by applying carbon-based conductive ink to the 100% mercerized 250 µm thick cotton thread. Next, the fabricated conductive threads were modified with the ACh selective membrane precursor. The ACh-selective probes were insulated with parylene coating separating the sensing zone (1.0 cm) and electrical connection (1.0 cm). The potential measurements were performed using a 16-channel potentiometer relative to a commercial reference electrode. All measurements were performed at room temperature with freshly prepared solutions. Synthetic biofluids were prepared based on physiologically relevant composition.

Results, Conclusions, and Discussions:: Our preliminary results indicated that this new platform improves the limit of detection and sensor selectivity by three orders of magnitude. This innovation will generate the first flexible ACh probe capable of ACh detection in its physiological range (1 nM to 1 mM) in the complex brain environment, paving the way for biocompatible, biofouling-resistant sensing platforms for neural recordings. This sensor can be used in a plug-and-play mode, where no genetic expression or staining is needed. The ACh levels can be read after insertion in the appropriate region in the brain. First, we assessed the performance of polymeric ACh-selective precursor, which illustrated 56.75±0.18 mV/decade sensitivity. Next, the fluorocarbon-based sensor feasibility was validated by comparing the obtained sensitivity, 60.78±3.36 mV/decade for ACh (theoretical Nerstian value 59.2 mV/decade) with a detection limit of 59 nM (Fig 1.A). We then compared the selectivity of fluorocarbon-based probes with conventional electrodes, where we observed three orders of magnitude improvement toward sodium, potassium, and calcium as physiologically relevant interfering ions. Next, we assessed the performance of our electrodes in artificial cerebrospinal fluid, in which we achieved an 830 nM detection limit (Fig 1.B). The fabricated flexible ACh-selective neural probes illustrated a promising potential to be incorporated into in-vivo studies (Fig 1.C). The fabricated platform technology enables a more detailed study of cholinergic signaling and provides a companion diagnostic tool for early neurodegenerative disease detection.

Acknowledgements (Optional): : FA, AS would like to acknowledge the Viterbi Graduate School Fellowship

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