Photothermal neural interface technology: Controlling neural activity using light and heat

The limitations of conventional neuron stimulation methods were challenged by a novel light-based neuromodulation platform that is highly applicable to brain disease treatment and brain research. The aim of this study is to regulate the electrical activity of neurons using the photothermal effect of gold nanoparticles (gold nanorods or nanostars) absorbing a specific wavelength, ultimately controlling the function of neuronal circuits.

Article  |  Spring 2018

Imagine being able to regulate the activity of nerve cells through light. The ability to control the activity of neurons by turning on and off external light will be useful for studying brain function. Neurons are the basic unit of the brain, which controls the senses and organs of the human body through electrical signals and enables mental functions such as emotion, memory, and learning. To study brain function and treat diseases, it is imperative to control the electrical activity of individual neurons and their networks.

Electrical stimulation has been the prevalent method in research and clinical practice for past several decades. Recently, optical stimulation techniques have emerged as complementary methods to overcome some of the limitations of the electrical method.

Professor Yoonkey Nam and his team in Neural Engineering Laboratory (http://neuros.kaist.ac.kr) of the Department of Bio and Brain Engineering have developed a new technology that regulates the activity of neurons using local surface plasmonic resonance (LSPR) of gold nanoparticles that generate heat upon exposure to light. The research team developed a new neuronal activity control system by applying gold nanoparticles, which were originally proposed for treating cancers, to nerve cells. The stimulation of neurons using light stimuli can provide a high spatial and temporal resolution as compared with conventional electrical and chemical stimuli and also does not require genetic modification of neurons used in the field of optogenetics.

In 2014, the team reported their first finding on the photothermal inhibition of neural activity using rod-shaped gold nanoparticles to absorb near-infrared light of wavelength of 785 nm. In 2016, they developed a microelectrode array platform using gold nanorods that can be used for electrical recordings as well as optical neural stimulation. They demonstrated that the gold nanorods can be coated on a microelectrode chip capable of measuring the activity of neuron cells, and then cultured neurons to inhibit the activity of neurons by the same light stimuli.

 

In the most recent study, the team introduced gold nanostars for photothermal neural stimulation. They improved the biocompatibility of the nanoparticles by using ‘green chemicals’ in the synthesis process, which will be important for future clinical uses. When uniformly coated with gold nanostructured particles on a microelectrode chip, they found that the same amount of light stimuli generated more heat than gold nanorod particles, and the activity of the neuron was similarly inhibited in proportion to the intensity of light. Despite the delivery of heat to the cell membrane, the team could not find any harmful effect in the stimulation range they used to induce neural inhibition. Through this approach, the team increased the cell affinity between existing cells and gold nanoparticles and at the same time improved the efficiency of light stimulation-thermal conversion, thereby increasing the efficiency of the nerve cell activation suppression method.

Original papers:
http://pubs.acs.org/doi/abs/10.1021/nn5020775
http://pubs.acs.org/doi/abs/10.1021/acsnano.5b07747
https://doi.org/10.1016/j.biomaterials.2017.10.041