Exploring the brain's microcircuitry has traditionally been done by lining up tiny electrodes within or near single neurons to probe their electrical activity. Though well established, this method is invasive and often noisy because of background electrical activity in the brain. A number of alternative approaches use optical probes that can detect neuronal activity with light, but these methods often require labeling neural cells with electrically-sensitive dyes that may be toxic to neurons.
Brown Researchers have imbedded gold nanoparticles into tissue culture and shown that they can measure the electrical activity of live neurons. The technique takes advantage of a phenomenon known as surface plasmon polariton resonance, a sharp spectroscopic resonance at visible/near-infrared wavelengths. Basically, the gold nanoparticles are used to optically sense the local electric fields produced when nearby neurons fire. The neuronal activity modulates the electron density at the surface of the nanoparticle, which causes an observable spectral shift that they can monitor. They presented their experiments at the Conference on Lasers and Electro-Optics (CLEO) in San Francisco, May 2008.