Jun 5, 2008
Nano Satellites: Moon-shaped probes for exploring the cellular galaxy
Just as satellites are routinely sent to probe the depths of space, metallic nanoprobes may soon be able to provide detailed chemical maps of the space inside biological cells. And how appropriate, they’re moon shaped.
Researchers at the University of California-Berkeley recently published a study in Nanotechnology exploring the potential of moon-shaped gold nanoparticles, called nanocrescents. Through the phenomenon of plasmon resonance – the collective resonant oscillation of electrons in a metal – nanoparticles such as the nanocrescent can be used to focus and amplify light to nanometer-sized regions. The resulting highly enhanced and localized electromagnetic fields can then be used to provide valuable information about the local environment. Combined with spectroscopic techniques, such as surface-enhanced Raman spectroscopy (SERS) and plasmon resonance energy transfer (PRET), the nanoparticles can detect extremely low concentrations of molecules of interest – for example, a molecule that indicates a particular type of cancer, enzyme kinetics, metabolic activity, drug response or subcellular dynamics.
The Berkeley researchers demonstrated that the nanocrescent is a far more robust and tunable probe than spherical nanoparticles, the "gold standard" of nanoparticle probes. The nanocrescent is able to amplify light an order of magnitude higher than spherical nanoparticles, resulting in a 10,000-fold increase in the molecular sensitivity. By varying the nanocrescent geometry, such as the position of the cavity, the light frequency for resonance can be tuned to virtually any wavelength in the visible and near-infrared spectra, much like how a radio can be tuned to receive a specific frequency. Such tunability is essential, because there is only a limited "biological window" of wavelengths that will not harm cells and biological tissue.
Several research groups are currently fabricating nanocrescent-shaped particles, in the hope that soon we may be launching such nanosatellites to probe the molecular galaxy – the proteins, enzymes and cellular organelles – that make up each living cell.
About the author
B M Ross received BS and MS degrees from Pennsylvania State University in engineering science, and is a NSF graduate research fellow at the University of California-Berkeley in the Applied Science and Technology Graduate group. L P Lee is the Lloyd distinguished professor in the bioengineering department, director of the Biomolecular Nanotechnology Center, and co-director of the Berkeley Sensor & Actuator Center (BSAC) at the University of California-Berkeley.