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Posted: February 25, 2010

Breakthrough to pave the way for greener, highly efficient production of nanocrystals

(Nanowerk News) Researchers from the National University of Singapore (NUS), in collaboration with counterparts from the Agency for Science, Technology and Research (A*STAR), Nanyang Technological University (NTU) and King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, have discovered a new synthetic strategy for controlling the properties of ultra-small luminescent nanocrystals that hold much potential for applications in advanced bio-imaging, sophisticated volumetric 3D image displays, and the treatment of diseases such as cancer and age-related macular degeneration (AMD).
Their findings will be published on 25 February 2010 in the leading scientific journal Nature.
Assistant Professors Liu Xiaogang and Zhang Chun, Dr Wang Feng, Dr Lu Yunhao and Ms Wang Juan from NUS, together with Associate Professor Hong Minghui and Dr Lim Chin Seong from A*STAR Data Storage Institute (DSI) had conducted this study in collaboration with counterparts from NTU and KAUST.
Significant cost and energy savings for industry
Used in a wide variety of imaging devices for the biomedicine and life sciences fields, upconversion nanocrystals had attracted significant research interest over the past decade, because of their ability to convert lower-energy near-infrared light into a visible emission. The visible emission from these nanocrystals under near-infrared light enhances their prospects as luminescent labels for biological specimens and is less harmful to biological species than conventional ultraviolet excitation
However, the creation of ultra-small upconversion nanocrystals is a challenge, since high reaction temperatures and prolonged heat treatment associated with conventional methods generally result in enlarged crystal size.
Through manipulating the concentration of lanthanide ions that are introduced into the crystal structure, the team had developed a novel technology that makes it possible to simultaneously control the size, structure and colour emission of nanocrystals, while drastically reducing the required reaction time (from several days to less than two hours) and reaction temperature from 300 to 230 degrees Celsius), compared to conventional methods.
The dramatically shortened reaction time and lowered reaction temperature would potentially lead to substantial cost and energy savings in the expensive process of manufacturing nanocrystals.
In addition, the new technique pioneered by the team makes it possible to do away with the need to use hazardous metals or solvents, making it a more environmentally friendly method in comparison with existing methods.
Applications for 3D image displays and biomedicine
The ultra-small nanocrystals resulting from the team’s technology can be readily incorporated into the equipment used to produce volumetric 3D displays, as they enable the production of 3D displays using a single beam, in contrast to conventional methods that rely on the intersection of two separate laser beams and that incur problems of misalignment of the two beams and blurred images.
Moreover, the incorporation of gadolinium ions, which are attracted to external magnetic fields, also enables the nanocrystals to be used in magnetic resonance imaging (MRI) probes for biological sensing.
The team is currently exploring applications of these upconversion nanocrystals for photodynamic therapy, which is used in treatment of a wide variety of cancersas well as age-related macular degeneration, as the use of near-infrared excitation is very advantageous with its high depth of penetration in biological cells.
Source: A*STAR
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