BUFFALO, N.Y. -- Efficient and highly scalable new chemical
synthesis methods developed at the University at Buffalo's
Institute for Lasers, Photonics and Biophotonics have the potential
to revolutionize the production of quantum dots for bioimaging and
A patent has been filed on the methods, which were described
last month in papers in the Journal of the American Chemical
Society and Applied Physics Letters.
Quantum dots are tiny semiconductor particles generally no
larger than 10 nanometers that can be made to fluoresce in
different colors depending on their size. Scientists are interested
in quantum dots because they last much longer than conventional
dyes used to tag molecules, which usually stop emitting light in
seconds. Quantum dots also are of great interest for energy
applications because they can produce electrons when they absorb
light, making possible extremely efficient solar-energy
Both fabrication methods developed by the UB researchers involve
using a single container, or "pot," and take just a few hours to
The UB scientists report that one of their rapid-solution
synthesis methods enabled them to prepare robust, water-dispersible
quantum dots for bioimaging, while the other one allowed them to
prepare organically soluble quantum dots ready to be sequestered
into a polymer host.
The new synthesis methods are truly scalable and can be used to
produce large quantities of quantum dots, according to Paras N.
Prasad, Ph.D., executive director of the UB Institute for Lasers,
Photonics and Biophotonics, SUNY Distinguished Professor in the
Department of Chemistry, and co-author on both papers.
"This fast-reaction chemistry will allow us to exploit the true
potential of quantum dots, whether it be for delivery into human
cells for imaging biological processes in unprecedented detail or
for the development of far more efficient devices for solar
conversion," he said.
On Aug. 17, the UB researchers reported in a paper in the
Journal of the American Chemical Society what is believed to be the
first successful demonstration of so-called III-V semiconductor
quantum dots as luminescence probes for bioimaging that appear to
be non-toxic. "Three-five," and other such classifications refer to
the position on the periodic table of the elements that make up
Until now, only II-VI quantum dots have been produced for these
applications. However, they are highly toxic to humans.
Composed of indium phosphide, the nanocrystals developed at UB
demonstrate luminescence efficiencies comparable to other quantum
dots, but they also emit light in longer wavelengths in the red
region of the spectrum.
"This is a key advantage because red-light emission means these
quantum dots will be capable of imaging processes deeper in the
body than commercially available quantum dots, comprised of cadmium
selenide, which emit mostly in the lower wavelength range," said
Like those cadmium selenide quantum dots, the nanocrystals also
exhibit two-photon excitation, absorbing two photons of light
simultaneously, which is necessary for high-contrast imaging.
The UB group's quantum dots are composed of an indium phosphide
core surrounded by a zinc selenide shell to protect the surface. An
organic group then is attached to this shell, as well as a
targeting group, in this case, folic acid. Folate receptors are
targeted commonly by drugs in diseases such as cancers of the
breast, ovary, prostate and colon.
In their experiments, UB researchers showed that the quantum dot
system recognized the folate receptor and then penetrated the cell
membrane, Prasad explained.
The entire system is water dispersible, which is critical,
Prasad said, if quantum dots are to be widely used for
The other scalable chemical fabrication procedure developed by
the UB researchers allowed them to prepare quantum dot-polymer
nanocomposites that absorb photons in the infrared region.
The work was described in the paper, "Efficient photoconductive
devices at infrared wavelengths using quantum dot-polymer
nanocomposites," published online Aug. 11 in Applied Physics
"Current solar cells act only in the green region, thus
capturing only a fraction of the available light energy," Prasad
said. "By contrast, we have shown that these lead selenide quantum
dots can absorb in the infrared, allowing for the development of
photovoltaic cells that can efficiently convert many times more
light to usable energy than can current solar cells."
In addition to broadening the applications for solar energy in
general, the UB research is likely to have applications to
nighttime imaging systems used by the military that must absorb and
emit light in the infrared.
"Because of the efficient photon harvesting ability of quantum
dots, in the immediate future we will be able to incorporate a few
different types of them simultaneously into a plastic host material
so that an efficient and broad band active solar device is
possible," said Yudhisthira Sahoo, Ph.D., research assistant
professor in the UB Department of Chemistry and co-author on the
Co-authors with Prasad on the paper in the Journal of the
American Chemical Society are Dhruba J. Bharali, Ph.D., and Derrick
W. Lucey, Ph.D., postdoctoral associates, and Haridas E. Pudavar,
Ph.D., senior research scientist, all of the Department of
Chemistry in the UB College of Arts and Sciences, and Harishankar
Jayakumar, a graduate student in the Department of Electrical
Engineering in the UB School of Engineering and Applied
The research was supported by a Defense University Research
Initiative in Nanotechnology (DURINT) grant from the Air Force
Office of Scientific Research and by the John R. Oishei Foundation,
as well as by UB's New York State Center of Excellence in
Bioinformatics and Life Sciences.
Co-authors with Prasad and Sahoo on the Applied Physics Letters
paper are K. Roy Choudhury, graduate student in the Department of
Physics in the UB College of Arts and Sciences, and T.Y.
Ohulshanskyy, Ph.D., senior research scientist in the UB Department
of Chemistry. The research was supported by the DURINT grant and by
the National Science Foundation.
Research at UB's Institute for Lasers, Photonics and
Biophotonics has been supported by special New York State funding
sponsored by State Sen. Mary Lou Rath.
The University at Buffalo is a premier research-intensive
public university, the largest and most comprehensive campus in the
State University of New York.