Gold nanoparticles can be attached to neurons and used to stimulate the cells, without introducing any genes.

Current 'optogenetic' methods use light to excite specific neurons, but genes must first be inserted into the cells to make them sensitive to light. To develop an alternative method, Francisco Bezanilla at the University of Chicago in Illinois, David Pepperberg at the University of Illinois at Chicago and their colleagues used molecules including antibodies to attach 20-nanometre-wide gold spheres to three different ion channels on the surface of cultured neurons. When the researchers flashed a millisecond pulse of light, the gold heated up, causing most of the neurons to fire. The same thing happened when they injected the nanoparticles into a specific region of a mouse brain slice.

Neuron http://doi.org/2sj (2015)