President's Science Award 2016


Prof LIU Xiaogang
Department of Chemistry, Faculty of Science, National University of Singapore
Senior Scientist, Institute of Materials Research and Engineering, Agency for Science, Technology and Research

“For his outstanding research in developing rare-earth-doped nanocrystals that could be used as luminous tags for tracking cancer cells and deciphering various biologically relevant phenomena”


PSA LiuXiaogang

Prof Liu receiving the President's Science Award from President Tony TAN (Photo credit : A*STAR)


Over the past 10 years, Prof Liu Xiaogang has devoted himself to developing innovative methods for the synthesis of rare-earth-doped nanocrystals that can emit a palette of visible colours at a wavelength shorter than the excitation wavelength. This phenomenon is known as photon upconversion that makes the emitted light more energetic than the light absorbed.

Due to their good biocompatibility and small physical dimensions (several thousands of these nanomaterials could fit across the width of a human hair), upconversion nancrystals can be coupled to proteins or other biological macromolecular systems. They are particularly useful for bioimaging and biodetection because their high energy emissions can be clearly distinguished from background noise.  

In addition, these nanocrystals can be excited under near-infrared light – a spectral range which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation – and this property enhances their prospects as a biological tool to control and monitor the activities of individual cells in living tissue. Therefore, the discovery of these nanocrystals allows for tremendous improvements in our ability to make visible without much photodamage, and study complex biological systems such as proteins or cells over a long period of time. This is a feat virtually unachievable by conventional fluorescent imaging techniques.

Despite the enticing prospects, the applications of upconversion nanocrystals in biological and biomedical fields remained unclear in the early days of investigation. One major challenge was to devise methods for making materials with tunable sizes and shapes as well as a spectrum of emitting colours that are highly sought after for measuring multiple analytes in a single run. Another notable challenge was boosting the brightness of the nanocrystal emission at high dopant concentrations. High dopant concentration can lead to better light-harvesting capabilities, but cross-interactions will lead to the quenching of the generated light. This problem has provided a strong motivation for the materials science community to improve the nanocrystal’s light-harvesting capacities.

Indeed, much of the recent resurgence of upconversion came from the widespread research on controlled nanocrystals synthesis, together with the pressing demand for next-generation luminescent biomarkers that have very high photostability and long luminescence lifetime. Combined with advanced optical microscopies, these biomarkers could be utilised as a versatile platform for high resolution cell imaging and tumour targeting.

Prof Liu brings together a collaborative and multi-disciplinary team which has achieved a broad range of impactful inventions over the past 10 years. He has pioneered technologies for finely controlling upconversion emission colour, improving energy conversion efficiency, and interfacing living cells with upconversion nanocrystals. These fundamental breakthroughs have enabled new applications in anti-counterfeiting, volumetric 3D display, stem cell differentiation, optogenetics, drug delivery, and cancer therapy. More recently, he has demonstrated the use of upconversion nanothermometry as a useful tool to verify Einstein’s prediction made in 1907 that the instantaneous Brownian velocity is independent of particle size and shape under infinite dilution conditions. Better understanding of the Brownian motion of suspended nanoparticles in non-equilibrium systems would allow improved understanding of thermal conductivity, convective heat and mass transfer in various types of nano-fluids.

Prof Liu’s work on upconversion nanomaterials has inspired many researchers from a broad spectrum of disciplines, including chemistry, physics, materials and life sciences, and biomedical engineering, to join his efforts in expanding the upconversion field worldwide. The research on photon upconversion has flourished as one of the most exciting fields, as there are now over 120 groups in universities and research institutions around the world that are making valuable contributions to it.
Prof Liu’s list of accolades include the NUS Young Investigator Award (2006), BASF-SNIC (Singapore National Institute of Chemistry) Award in Materials Chemistry (2011), NUS Young Researcher Award (2011), and Royal Society of Chemistry Chemical Society Reviews Emerging Investigator Lectureship Award (2012). Based on The World’s Most Influential Scientific Minds 2014 report published by Thomson Reuters, he is among the top one percent of those cited in their fields for articles published from 2003 to 2013. He has served on a number of editorial advisory boards, including the Journal of the Chinese Chemical Society, Chemistry–An Asian Journal, ChemNanoMat, Nanoscale Horizons, and Advanced Optical Materials. He is currently the associate editor of Nanoscale (Royal Society of Chemistry) and Journal of Luminescence (Elsevier).

For his outstanding research in developing rare-earth-doped nanocrystals that could be used as luminous tags for tracking cancer cells and deciphering various biologically relevant phenomena, Prof Liu Xiaogang was awarded the 2016 President’s Science Award.


Article credit : A*STAR

The press release by A*STAR was published on 18 October 2016.