The probe is an optical fiber tapered to a tip measuring 100 nm with a thin coating of silver nanoparticles which induces what's called a surface-enhanced Raman scattering (SERS) effect. In ordinary Raman scattering, reflections of laser light from a target contain vibration energies unique to each compound in the sample, letting scientists identify the material.

In contrast, laser light emerging from the SERS nanoprobe creates rapid oscillations of the electrons in the silver nanoparticles. The oscillations produce a large electromagnetic field that adds to the Raman scattering signal. The nanoprobe works with any surface to induce the SERS effect. "The significance of this work is that we are now able to perform direct analysis of samples, even dry samples, with no preparation of the surface," says ORNL researcher Tuan Vo-Dinh. "Also, the small scale of the nanoprobe demonstrates the potential for detection in such nanoscale environments as at the intracellular level," he adds.

Usually, surface-enhanced scattering analysis requires that samples first be modified or treated, often by dilution or other means. The beauty of the ORNL nanoprobe is that it makes such preparations unnecessary.

Further work on the nanoprobe may make SERS more interesting as an ultrasensitive detection tool. Candidate applications range from environmental monitoring to intracellular sensing and medical diagnostics.