Abstract
Optical activation of neurons requires genetic manipulation or the use of chemical photoactivators with undesirable side effects. As a solution to these disadvantages, here, we demonstrate optically evoked neuronal activity in mouse cortical neurons in acute slices and in vivo by nonlinear excitation of gold nanoparticles. In addition, we use this approach to stimulate individual epitheliomuscular cells and evoke body contractions in Hydra vulgaris. To achieve this, we use a low-power pulsed near-infrared excitation at the double-wavelength of the plasmon resonance of gold nanoparticles, which enables optical sectioning and allows for high spatial precision and large penetration depth. The effect is explained by second-harmonic Mie scattering, demonstrating light absorption by a second-order nonlinear process, which enables photothermal stimulation of the cells. Our approach also minimizes photodamage, demonstrating a major advancement towards precise and harmless photoactivation for neuroscience and human therapeutics.
Highlights
The interaction of light with metal nanoparticles (NPs) has been of great interest for both fundamental research and a wide variety of applications[1,2,3]
For metallic NPs, the excitation of the surface plasmons is confined to their curved geometries, resulting in the socalled localized surface plasmon resonance (LSPR)
In the case of the small Au NPs used in this study, the absorption of NIR excitation light in the specimen is dominated by a second-order nonlinear process occurring in the NPs, where a fraction of the excitation light is converted into a second-harmonic (SH) component[17,18]; high spatial resolution is achieved
Summary
The interaction of light with metal nanoparticles (NPs) has been of great interest for both fundamental research and a wide variety of applications[1,2,3]. In the case of the small Au NPs used in this study, the absorption of NIR excitation light in the specimen is dominated by a second-order nonlinear process occurring in the NPs, where a fraction of the excitation light is converted into a second-harmonic (SH) component[17,18]; high spatial resolution is achieved. Following this approach, we used small spherical Au NPs for nonlinear photoactivation of mouse neurons in slices and in vivo and epitheliomuscular cells of Hydra vulgaris with high spatial resolution. This technique, using fs-pulsed NIR excitation of Au NPs, is in many aspects advantageous compared to currently available methods to optically activate neurons
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