Theoretical Study on Gold-Nanorod-Enhanced Near-Infrared Neural Stimulation

Abstract

Over the past decade, optical methods have emerged for modulating brain functions as an alternative to electrical stimulation. Among various optical techniques, infrared neural stimulation has been effective via a thermal mechanism enabling focused and noninvasive stimulation without any genetic manipulation, but it results in bulk heating of neural tissue. Recently, it has been shown that neural cells can be activated more efficiently by pulsed near-infrared (NIR) light delivered to gold nanorods (GNRs) near the neural cells. Despite its potential, however, the biophysical mechanism underlying this GNR-enhanced NIR stimulation has not been clearly explained yet. Here, we propose an integrative and quantitative model to elucidate the mechanism by modeling heat generated from interaction between NIR light and GNRs, the temperature-dependent ion channels (transient receptor potential vanilloid 1; TRPV1) in the neuronal membrane, and a heat-induced capacitive current through the membrane. Our results show that NIR pulses induce abrupt temperature elevation near the neuronal membrane and lead to both the TRPV1-channel and capacitive currents. Both current sources synergistically increase the membrane potential and elicit an action potential, and which mechanism is dominant depends on conditions such as the laser pulse duration and TRPV1 channel density. Although the TRPV1 mechanism dominates in most cases we tested, the capacitive current makes a larger contribution when a very short laser pulse is illuminated on neural cells with relatively low TRPV1 channel densities.

Current Review of Optical Neural Interfaces for Clinical Applications

“…When the light frequency is tuned to the surface plasmon resonance frequency of gold nanoparticles, they efficiently absorb the light to create localized thermal heat [ 86 ]. The local temperature elevation at the membrane produces a brief capacitive current and/or sustained current through a temperature-sensitive ion channel which both elevates the membrane potentials for neural activation [ 87 ].…”

“…Especially for the photothermal neural stimulation, thermal tissue damage is their biggest concern [ 50 , 201 ]. Since intrinsic methods of neuromodulation create bulk tissue heating, exogenous materials having good photothermal conversion efficiency are used to locally heat the neuronal membrane where it is known to be the photothermal neural activation area [ 87 ]. For the femtosecond laser stimulation, the ROS is produced, which causes problems in succession such as membrane barrier dysfunction and cell death by apoptosis [ 202 ].…”

Ultrasonic Retinal Neuromodulation and Acoustic Retinal Prosthesis

“…Over the past decade, impact of temperature elevation on neural activation has been studied in the optical stimulation [ 45 , 46 , 47 ]. Infrared light was found to cause a rapid increase in the temperature of the membrane, leading to neural excitation [ 45 , 48 , 49 ]. Two primary mechanisms of the opto-thermally driven neural excitation were hypothesized: (1) Change in the capacitance of the plasma membrane with temperature [ 45 , 48 , 49 ] and (2) temperature-triggered activation of the thermosensitive ion channels [ 50 , 51 ].…”

A Simple Capillary Blood Cell Flow Monitoring System using Magnetic Micro-Sensor: A Simulation Study

“…We first calculated the net charge of RBCs and WBCs, specifically the lymphocyte. The cell is modeled as three serially connected capacitors C bi , C i , and C o reflecting a lipid bilayer and electrical double layers of intracellular and extracellular regions, respectively, which are connected to an equivalent resistor (R Eq ) and a voltage source (V Eq ) in parallel [14][15][16]. Since three serially connected capacitors are simplified as an equivalent membrane capacitance (C RBC/WBC ), the net charge stored inside the cell is calculated by multiplying the C RBC/WBC and the transmembrane potential (V RBC/WBC ) ( Table 1).…”