Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rapid One-Pot Syntheses Developed For Quantum Dots

12.09.2005


New processes have applications in bioimaging and solar conversion



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 photovoltaic applications.
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 devices.



Both fabrication methods developed by the UB researchers involve using a single container, or "pot," and take just a few hours to prepare.

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 semiconductors.

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 Prasad.

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 bioimaging.

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 Letters.

"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 APL paper.

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 Sciences.

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.

Ellen Goldbaum | EurekAlert!
Further information:
http://www.buffalo.edu

More articles from Physics and Astronomy:

nachricht Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)

nachricht Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Smallest transistor worldwide switches current with a single atom in solid electrolyte

17.08.2018 | Physics and Astronomy

Robots as Tools and Partners in Rehabilitation

17.08.2018 | Information Technology

Climate Impact Research in Hannover: Small Plants against Large Waves

17.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>