Improving the functionality of microscale electrodes implanted in neural tissue with upconverting nanoparticles

In this research, the primary focus was on the development and characterization of a drug delivery system, that integrates micro electrocorticography (ECoG) arrays with upconverting nanoparticles (UCNP) to create a surface-modified, light-triggerable nanosystem for nervous tissue application. Methodology involves using a soft ECoG with a silicone substrate and Pt/Ir measuring sites. First the electrode surface is exposed to oxygen plasma then azide groups bind to it. Simultaneously, the UCNP exterior is modified with an aminosilane layer then a BCN-NHS linker compound. This linker attaches the UCNPs to the electrode surface. A tetrazine-kumarin-rhodol-based dye is then bound the UCNPs. This bond can be cleaved by the upconverted light, enabling controlled release. Results indicate successful covalent bond formations, confirmed by peaks in the Fourier-transformed infrared spectra, and the hydrophilicity/hydrophobicity changes of the electrode surface through contact angle measurements. Morphological analysis using scanning electron microscopy reveals satisfactory particle distribution even after mechanical testing. Electrochemical impedance spectroscopy suggests insignificant magnitude differences between modified and unmodified ECoGs, allowing for future electrophysiological measurements. Model drug release was first evaluated in a suspension, using UV/Vis spectroscopy. The chosen dye only exhibits fluorescence upon light-triggered cleavage of the linker bond. Afterwards applying the system to in vitro rat brain slices, then progressing to in vivo implantation in sleeping rats, results show that using two-photon microscopy the uncaged dye also gives a measurable signal between tissues. The ultimate objective is to transition from model dyes to real drugs, thus enabling the evocation and evaluation of the local neural responses.