High Bandwidth Power Electronics and Magnetic Nanoparticles for Multichannel Magnetogenetic Neurostimulation

Objective: We present a power electronic system and magnetic nanoparticles for multiplexed magnetogenetic neurostimulation with three channels spanning a wide frequency range and rapid channel switching capability. This enables selective heating of magnetic nanoparticles with different coercivity using various frequency-amplitude combinations of the magnetic field. Such multiplexed operation could provide the technical means for selective magnetogenetic neurostimulation beyond its spatial focality limits. Approach: The electronic system uses a hybrid of silicon metal-oxide-semiconductor and gallium-nitride field-effect transistors, which generate the required high-amplitude current up to 500 A in the sub-MHz range and the high-frequency current in the MHz range, respectively. Via three discrete resonance capacitor banks, the system generates an alternating magnetic field in the same liquid-cooled field coil at three distinct frequency channels spanning 50 kHz to 4 MHz. Fast switching between channels is achieved with high-voltage contactors connecting the coil to different capacitor banks. We characterized the system by the output channels' frequencies, field strength, and switching time, as well as the system's overall operation stability. Three types of iron oxide nanoparticles with different coercivity are developed to form three magnetothermal channels. Specific absorption rate and infrared thermal imaging measurements are performed with the nanoparticles to characterize their heating and demonstrate selective actuation for all three channels. Main results: The system achieved the desired target field strengths for three frequency channels (70 kA/m at 50 kHz, 10 kA/m at 500 kHz, and 1 kA/m at more than 2 MHz), with rapid switching speed between channels on the order of milliseconds. The system can operate continuously for at least two hours at 30% duty cycle with 125 Arms load in the coil, corresponding to a stimulation protocol of cycling the three channels at target strength with 3 s pulses and 7 s interpulse intervals. The nanoparticles were heated with selectivity between 2.3 and 9 times for their respective frequency channel. The system's intended use was thus validated with three distinct channels available for magnetothermal heating. Significance: We describe the first combination of a power electronic system and magnetic nanoparticles that achieves three stimulation channels. Selective actuation of nanoparticles is demonstrated for each channel using the same field coil, including a novel composition responding to magnetic fields in the MHz range. This approach could improve the speed and flexibility of frequency-multiplexed magnetogenetic neural stimulation.