Shining Light On The Brain's Activity

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.

Now Jiayi Zhang, Tolga Atay, and Arto Nurmikko at Brown University have created a new type of dye-free optical probe that can directly sense naturally occurring neural activity. They 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 the researchers can monitor.

This study "Detection of Neural Cell Activity Using Plasmonic Gold Nanoparticles" was presented at the 2008 Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS) May 4-9 at the San Jose McEnery Convention Center in San Jose, California.