SPECTROSCOPY/NANOTECHNOLOGY/POINT-OF-CARE DIAGNOSTICS: Nanotechnology boosts Raman signal in noise-free, ‘lab on a bubble’ approach

You’ve heard of a lab on a chip: Now a group of researchers have developed a “lab on a bubble” approach to quickly concentrate samples in order to detect biological molecules. The method is promising for point-of-care diagnostics.1

The team, which involves the University of Wyoming (Laramie, WY), and coatings and materials company iFyber (Ithaca, NY), used paramagnetic 50-μm-diameter silica beads that attach to 50-nm-diameter gold nanoparticles in the presence of a compound of interest. When they captured the beads using a magnet and directed Raman laser light to them, the compound adsorbed onto the gold nanoparticles to produce a characteristic surface-enhanced Raman scattering (SERS) signal that happens to be relatively noise-free.

Hollow silicon dioxide spheres (top) covered with gold nanoparticles grab an analyte from solution (center) and then float to the top (bottom) for easy characterization
Hollow silicon dioxide spheres (top) covered with gold nanoparticles grab an analyte from solution (center) and then float to the top (bottom) for easy characterization. (Image courtesy of the Journal of the American Chemical Society)

The nanoparticle-covered spheres rise to the surface when mixed into a sample, so the approach works with relatively small sample volumes. Without the beads, the nanoparticles would drift in and out of the detection area instead of collecting within the laser’s beam—which would generate noise. In addition, the spheres prevent the gold from aggregating, and thus the method produces about 28 times larger SERS signals than do gold nanoparticles alone. The researchers used the “lab on a bubble” method to measure known concentrations of cyanide ions, and were able to achieve 173 ppt sensitivity—similar to that produced by gold nanoparticles only.

1. V.L. Schmit et al., J. Am. Chem. Soc., doi:10.1021/ja208463f (2011).

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