Patterned Photothermal Neuromodulation using Inkjet-printed Thermo-plasmonic Gold Nanorods on Microelectrode Array Chips

Abstract

Event Abstract Back to Event Patterned Photothermal Neuromodulation using Inkjet-printed Thermo-plasmonic Gold Nanorods on Microelectrode Array Chips Hongki Kang1, 2, Gu-Haeng Lee1, Hyunjun Jung1, 3, 4, Jee Woong Lee1, 3, 4 and Yoonkey Nam1, 3, 4* 1 Department of Bio and Brain Engineering, College of Engineering, KAIST, Republic of Korea 2 Department of Information and Communications Engineering, College of Engineering, KAIST, Republic of Korea 3 Information and Communications University, Information & Electronics Research Institute, KAIST, Republic of Korea 4 Information and Communications University, Department of Bio and Brain Engineering, Republic of Korea Photothermal neural activity modulation technique using thermo-plasmonic metal nanoparticles is a promising noninvasive stimulation method as there is no genetic modification required.[1] Various types of gold nanoparticles with near infrared light illumination have shown that spontaneous activities of cultured neurons on the microelectrode arrays (MEAs) can be instantaneously and temporarily inhibited during the light illumination. In order to apply this photothermal neuromodulation technique in more controlled ways (e.g., with high spatial selectivity, and precise intensity control), we need to develop a fabrication process that allows us to precisely deposit the plasmonic nanoparticles onto neural chips. In this work, we developed a patterned photothermal stimulation method by inkjet printing gold nanorods directly onto the MEA chips in the patterns we intend to apply the photothermal stimulation to the in vitro cultured neuronal network. We synthesized gold nanorod particles tuned for optical absorption peak in near infrared (NIR). The gold nanorod ink was formulated for stable piezoelectric inkjet printing. For good printing pattern fidelity and uniformity of the printed nanorods, we applied biocompatible polyelectrolyte layer-by-layer coating to the MEA chips (60MEA200/30IR-ITO-w/o, Multi Channel Systems).[2] The patterned nanorods were stably adhered to the MEA chip surface in the culture media owing to the electrostatic attraction between the coated surface and the nanoparticles. Using the inkjet printing process, we were able to fabricate micro patterns of the gold nanorods as small as 45 μm on the MEA chips. The temperature change upon NIR illumination was highly localized around the micro patterns. With resulting heat patterns as small as 45 μm, we have achieved that we can remotely activate thermal stimulation in very small areas precisely defined on the MEA with respect to the location of microelectrodes. In addition, thanks to the design freedom in inkjet printing, the arrangement of printed micro patterns on the MEA can be easily varied from chip-to-chip depending on the purpose of experiments. Hippocampal neurons, dissociated from embryonic day 18 Sprague-Dawley rat brain, were successfully cultured on the gold nanorod inkjet printed MEAs. Despite slight increase of the impedance of microelectrodes due to the polyelectrolyte coating, the MEA still showed low noise level (8 µVrms). Therefore, we confirmed that this additive fabrication process was compatible with the neuronal cell cultures on planar MEA chips and with the multichannel neural recording capability. By implementing patterned photothermal effect on a part of the entire electrode area in MEAs, we confirmed that we can selectively stimulate the cultured in vitro neuronal network while still successfully recording neural activities. Despite wide NIR illumination covering the entire electrode area, localized heat was only generated from the printed nanorods, and thus only the activities of neurons on or around the printing area were suppressed upon the illumination while other neurons far from the printing area were not significantly affected. Furthermore, even when the entire neuronal network was highly synchronized, we were able to temporarily perturb the network synchrony by partial area photothermal stimulation instead of completely turning off the entire channel areas. The patterned inhibitory stimulation can become a useful tool in studying neuronal network activities. Acknowledgements This work was supported by a National Research Foundation of Korea (NRF) grant (NRF-2018R1A2A1A05022604) funded by the Ministry of Science, ICT & Future Planning.