Luminescent carbon dots provide nontoxic alternative to silicon
Noting the toxicity and potential environmental hazard of silicon-based
semiconductor quantum dots, researchers at Clemson University in South Carolina
have created carbon nanodots with photoluminescence that is dependent upon particle
size and surface passivation.
Silicon nanostructures are strongly luminescent
when their surfaces are oxidized, and the researchers, led by chemistry professor
Ya-Ping Sun, theorized that carbon would act similarly. They report in the May 23
ASAP edition of the Journal of the American Chemical Society that, to test
this, they used a Q-switched Nd:YAG laser at 1064 nm to ablate nanoscale particles
from a pressed, baked, cured and annealed mixture of graphite and cement.
The resulting particles were not photoluminescent
but became so when passivated with such organic molecules as a diamine-terminated
oligomeric form of polyethylene glycol or polypropionylethyleneimine-co-ethyleneimine.
The dots emitted from the visible to the near-infrared, with larger dots less luminescent
than smaller ones and different passivating molecules yielding different emission
curves. Because the passivation process was organic, the dots could be conjugated
with bioactive molecules for bioimaging. Multiplexing of the dots could create
different labels simultaneously. The details of how this might be done still must
be worked out.
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