Tiny gold particles are heated using infrared light from an optical tweezer and the hot gold particle is brought closer and closer towards an artificial cell membrane. When you know how the lipids melt you can observe them and calculate the exact temperature of the particles. |
Tiny
gold particles are good for transferring heat and could be a promising
tool for creating localized heating in, for example, a living cell. In
new experiments, researchers at the Niels Bohr Institute have measured
the temperature of nano-sized gold particles with extreme precision and
have examined their ability to melt the lipid membranes surrounding
cells, paving the way for dissolving sick cells. The results have been
published in the esteemed journal Nano Letters.
Gold
nano-particles have a strong interaction with light in relation to
their size and it is precisely their physical size that gives them
different colours. Its colour is the result of how strongly a gold
particle scatters and absorbs light at different wavelengths. Therefore,
when the light heats up the gold particle, the colour has significance
for its temperature.
The
research was conducted in the Optical Tweezers Group at the Niels Bohr
Institute. Optical tweezers are sophisticated instruments, which using
an extremely focused laser light can trap and hold gold particles on a
nanometer scale. A nanometer is a thousandth of a millimeter and
therefore very small. The gold particles are between 60 and 200
nanometers in size.
“The
particles can be heated using infrared light from the optical tweezers
and by turning the light up and down you can control the heat”, explains
PhD student in biophysics, Anders Kyrsting, who conducted the research
along with his colleagues from the Optical Tweezers group.
But
exactly how hot do the extremely small gold particles get? It is
important to know the precise temperature in order to have complete
control over the situation. The particles are too small to measure
directly, so you can instead measure indirectly by their effect.
Kyrsting
brought the hot gold particles closer and closer towards an artificial
cell membrane comprised of lipids. When quite close the lipids melt and
if you know exactly when certain lipids melt you can use this to
calculate the temperature of the gold particles. It turns out that the
gold particles are able to reach several hundred degrees at a light
intensity of less than 1 watt.
Gentle and effective
Having
a hot particle means that you have a tool that you can use – a tiny
little heat source, which is well-defined. By melting the lipids in a
cell membrane the cell will be dissolved – killed. But only that cell.
“The
heat decreases so rapidly that at just a radius of a gold particle from
the surface, the heat is half the temperature than it is at the
surface. That is to say, that a typical cell length away from the
particle the heat will have decreased so much that it is harmless”,
explains Kyrsting.
“The
technique can also be used as a tool for changing temperatures in a few
microseconds. When the temperature from the surface of a heated gold
nanoparticle decreases several hundred degrees per micrometer, it is,
for example, possible to have two separate states – a liquid and a more
solid form in artificial cell systems consisting of small lipid
vesicles. Here the border surface between the two states will be very
clear-cut, which is useful if you want to study cell membranes”,
explains Kyrsting.
Source: Niels Bohr Institute
