Surface modification of neural interfaces for electrical and optical measurements of neural activities

Abstract

The neural interface is one of the most important parameter that influences the quality of neural activity recording. Thus, it is essential to construct highly sensitive neural interfaces. In this dissertation, I focused on the surface modification of neural interfaces for electrical and optical recordings of neural activities. First, the mechanically stable platinum black microelectrode was developed. The polydopamine and platinum black hybrids were fabricated by the electrochemical layer-by-layer coating. The electrical properties of hybrids were comparable to conventionally used platinum black microelectrodes, and the hybrids endured the harsh external physical agitations. The developed polydopamine-platinum black hybrids were also efficient for recording electrical activities of cultured neural networks. Second, the improvements of the electrical properties of conducting polymer microelectrodes were achieved through polydopamine incorporation. Polydopamine itself is not conductive material but polydopamine incorporated PEDOT showed a high level of charge injection limit and low level of impedance. Also, they were appropriate for recording and stimulation of neural networks. Third, the optical imaging system providing high-speed recording was constructed. Utilizing a digital micromirror for light pattern generator, targeted areas were serially illuminated with high frame rate. A photomultiplier tube recorded the fluorescence signals from targets with the high sampling frequency. The performance of the system was confirmed by calcium and voltage imaging of cultured neural networks. Forth, gold nanoplasmonic substrates were fabricated to enhance the efficiency of optical imaging of neural activities. GNRs were synthesized to have similar spectral properties with the voltage dye, a widely used voltage sensitive dye di-8-ANEPPS, and immobilized on culture substrates. Layer-by-layer coating of polyelectrolytes was conducted to construct a spacer between GNRs and fluorophores that controls the distance. The voltage sensitive dye loaded neurons showed enhanced fluorescence signals when they were cultured on GNR substrates. The enhancement effect was 4.78 based on the increment of peak values, but it was difficult to find the enhancement effect on neural activity imaging.