Noise Mitigation Strategies for Silicon-Based Active Neural Optrode

In recent years, optogenetic-based neural regulation technologies have attracted extensive attention. Among them, the active neural optrode integrated with optical stimulating micro-laser diode (LD)/light-emitting diode (LED) and electrical recording microelectrodes presents significant advantages. However, the performance of the neural optrode is still hindered by high amplitude noises generated by micro-LD/LED and silicon substrate. A silicon optrode with heavy-doped probes, LD-coupled optical fiber, and electrochemical modified microelectrodes is here developed for low-noise and high-fidelity optical modulation. First, the electromagnetic interference (EMI) free and high-efficiency optical stimulation is realized by adopting an optical coupling module with microfabricated locating slot. Second, the photovoltaic (PV) noise and the photoelectrochemical (PEC) noise are significantly decreased by an order of magnitude through combination of heavy doping and electrochemical modification of the optrode. More importantly, it is confirmed for the first time that the PV and PEC noise can be further reduced by an order of magnitude through LD driving pulse shaping. Finally, the in vivo acute recording experiments show that the light-induced photoelectric noise (
$< 50 \mu \text{V}$
) has little influence on the firing rate (1.2 spikes/s) and signal-to-noise ratio (SNR = 4.9) of the recorded signals accompanied by optical stimulation. The results indicate that the developed noise mitigation strategies are promising for optogenetics-based neural circuit research.