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Gold Nanoparticles Prove to Be Hot Stuff

From NIST Tech Beat: August 31, 2006

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Contact: Laura Ost
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gold nanobead temp grad
A gold nanobead, trapped with 205 milliwatts of infrared laser light, heats up to about 75 degrees C or 167 degrees F (shown in dark red) and the temperature in the surrounding area gradually cools off (the purple area is about 27 degrees C or 81 degrees F).
                   
Credit: Yeonee Seol/JILA
                   
View hi-resolution image
             

Gold nanoparticles are highly efficient and sensitive  “handles” for biological molecules being manipulated and tracked by lasers, but  they also can heat up fast—by tens of degrees in just a few nanoseconds—which  could either damage the molecules or help study them, according to scientists  at JILA, a joint institute of the National Institute of Standards and  Technology (NIST) and University of Colorado at Boulder.

             

Biophysicists often study nanoscale and even picoscale mechanics  by using lasers to both apply force to and track the position of fragile  biomolecules such as DNA or protein by manipulating a tiny sphere—typically  polystyrene—attached to the molecule. The JILA team would like to find new  microsphere materials that can be trapped by laser radiation pressure more  efficiently, which would enable faster measurements and detection of smaller  motions at the same laser power. As described in the Aug. 15 issue of Optics Letters,* the JILA team  demonstrated that 100-nanometer-wide gold beads, as expected because of their  metallic nature, can be trapped and detected six times more easily than  polystyrene particles of a similar size.

             

However, the scientists also found that gold absorbs light  and heats up quickly, by a remarkable 266 degrees (Celsius) per watt of laser  power, at the wavelength most often used in optical traps. Unless very low  laser power is used, the heat could damage the molecules under study. Thus,  gold beads would not be useful for temperature-sensitive experiments or  applying force to molecules. But the heating effect could be useful in raising  local temperatures in certain experiments, such as heating a protein just  enough to allow scientists to watch it unfold, the paper suggests.

             

The work was supported by a W.M. Keck grant in the RNA  Sciences, a Burroughs Wellcome Fund Career Award in the Biomedical Sciences, a  National Institutes of Health training grant, the National Science Foundation,  and NIST.

             
* Y. Seol, A.E. Carpenter, T.T. Perkins. 2006. Gold  nanoparticles: enhanced optical trapping and sensitivity coupled with  significant heating. Optics Letters. Aug. 15.