Gold Nanofilm Coated Microelectrode Array Chip for Photothermal Inhibition of Cultured Hippocampal Neurons
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1
Korea Advanced Institute of Science and Technology, Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology, Korea
Motivation
Stimulating neurons with light by use of gold nanoparticles has a great deal of advantages such as high spatial and temporal resolution, compared to conventional electrical and chemical methods. In addition, it is not necessary to genetically modify the neurons for stimulating their neural activities. Recently, our group developed a novel photothermal stimulation technique by using gold nanorods upon irradiation of near-infrared (NIR) light [1, 2]. However, the synthesis of gold nanorods requires cytotoxic chemicals such as cetyltrimethylammonium bromide(CTAB), and takes a total of 5~6 days for stabilization and treatment of the surface. In this study, we suggest a less time-consuming and simple method for suppressing hippocampal neurons cultured in vitro by making use of the photothermal property of gold nanofilms (Figure 1(a)).
Material and Methods
Hippocampal neurons from embryonic day 18 Sprague Dawley rat were cultured on a 60-electrode microelectrode array (MEA) with 30-¥ìm size electrodes. All of electrodes were electroplated with platinum black, and MEA substrate was coated with various thickness of gold nanofilm by sputtering(SPT-20, COXEM). Sputtering time was 20, 90, 110, 200, and 210 seconds and current was 3, 5 and 7 mA. Then poly-D-lysine was coated to enhance cell adhesion. The NIR laser of various power densities (0 ~ 15 mW/mm2) with a pulse width (20 sec off, 10 sec on) was exposed to the neurons. The spontaneous activity inhibition test was repeated 30 times at each laser power density. Extracellular spike signals were recorded (gain 1000, 150 Hz-5.5 kHz, sampling frequency 25 kHz) and six standard deviation of background noise level was used as a spike threshold. We compared the firing rate during photostimulation with before stimulation for the same period.
Results and Discussion
The UV-Vis absorption spectrum graph showed that 40-nm and 80-nm thick gold nanofilm absorbed more than 20-nm thick gold nanofilm at 785 nm wavelength (data not shown). But MEA chips that are coated by gold nanofilms whose thickness went over 40 nm had an electrical short problem (data not shown). The 20-nm thick gold nanofilm was the most efficient in the temperature change than other thickness conditions at every NIR laser power density in air (Figure 1(b)). Figure 1(c) shows different levels of neural suppression when varying thickness of gold nanofilms (10 nm, 20 nm) were irradiatied by NIR (785 nm) laser. Whereas the 10-nm thick gold nanofilm led to a gradual decrease in the spike rate at varying laser powers, the 20-nm brought about a much more sudden decrease. This finding indicates that 10-nm thick gold nanofilm could be utilized for controlling the degree of neural suppression by modulating the laser powers accordingly, and the 20-nm for accomplishing the suppression effect at a minimum laser power (at 3 mW/mm2, the spike firing rate was suppressed by as much as 90.62 ¡¾ 3.76% (mean ¡¾ SEM)). Each thickness of gold nanofilm has its own merits; the 10 nm allows for an accurate modulation of neural activities, and the 20 nm the suppression of neural activities to a large extent at a very low laser power.
Figure 1. Properties of gold nanofilms and neural activity changes under NIR light stimulation. (a) Scheme of gold nanofilm-mediated photothermal stimulation. (b) Temperature changes of various thickness of gold nanofilm coated chips at different light densities in air condition. (c) Spike rate change by photothermal stimulation of the gold nanofilm coated chips with different laser power densities (mean¡¾SEM, 0 ~ 15 mW/mm2).
Conclusion
In summary, we introduced an easy and fast method of making a platform for the investigation of neural suppression. We also demonstrated that the photothermal inhibition effect can be controlled by changing the thickness of gold nanofilms and NIR laser power densities. This method could be applied in neuroscience research and the treatment of complex brain disorders such as epilepsy. However, further study of the relationship between the cells and the light exposed area should be performed to understand how the generated heat is delivered into the cellular membrane.
Acknowledgements: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) (NRF-2015R1A2A1A09003605).
References:
[1] S. Yoo, S. Hong, Y. Choi, J.-H. Park, and Y. Nam, ¡°Photothermal Inhibition of Neural Activit y with Near-Infrared-Sensitive Nanotransducers,¡± ACS Nano, vol. 8, no. 8, pp. 8040?8049, Aug. 2014.
[2] S Yoo, R Kim, JH Park, Y Nam, ¡°Electro-optical Neural Platform Integrated with Nanoplasmonic Inhibition Interface¡±, ACS Nano 2016 Mar 09;10(4);4274-81.
Keywords:
hippocampal neurons,
Near infrared,
Gold nanofilm,
photothermal inhibition
Conference:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays, Reutlingen, Germany, 28 Jun - 1 Jul, 2016.
Presentation Type:
oral
Topic:
MEA Meeting 2016
Citation:
Jee-woong
L and
Nam
Y
(2016). Gold Nanofilm Coated Microelectrode Array Chip for Photothermal Inhibition of Cultured Hippocampal Neurons.
Front. Neurosci.
Conference Abstract:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays.
doi: 10.3389/conf.fnins.2016.93.00107
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Received:
22 Jun 2016;
Published Online:
24 Jun 2016.
*
Correspondence:
Dr. Lee Jee-woong, Korea Advanced Institute of Science and Technology, Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea, holybio@kaist.ac.kr