The Brown University researchers -- Jiayi Zhang, Tolga Atay and Arto Nurmikko -- said they imbedded gold nanoparticles in tissue cultures and demonstrated the electrical activity of live neurons could be measured.

Exploring the brain's microcircuitry has traditionally been done with electrodes or optical devices using dyes, the researchers said. But the new dye-free optical probe can directly sense naturally occurring neural activity.

They said the technique takes advantage of a phenomenon known as surface plasmon polariton resonance -- a sharp spectroscopic resonance at visible/near-infrared wavelengths. The gold nanoparticles 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.

The researchers will present their findings next month in San Jose, Calif., during 2008 Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference.

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