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Figure 2: Biomedical applicatons of lanthanide-doped upconversion nanopartcles include sensing, cellular imaging, deep tssue imaging and in vivo therapy. tssue imaging and in vivo therapeutcs stable luminescent nanopartcles currently in use are excited by a 980 nm (see Figure 2). suitable for biological environments. laser. This might cause an overheatng This is achieved by modifying the efect due to the strong absorpton of Due to its low auto-fuorescence, surface conditon of small partcles, water and the scatering of biological upconversion nanosensors can greatly which allows for the coupling of Au tssue. We have a design for the improve the limit of detecton. We nanopartcles with hairpin DNA. synthesis of Nd -doped core-shell 3+ have developed a series of hybrid These biocompatble nanopartcles nanopartcles to overcome this issue. upconversion nanomaterials for high- are suitable as probes for deep-tssue These nanopartcles can be efciently sensitvity detecton of target species imaging and therapeutc applicatons. excited at 800 nm which reduces water in vitro and in vivo. This includes metal This method also overcomes the absorpton, minimising overheatng ions, small molecules, reactve nitrogen problem of nanopartcles tending to problems. and oxygen species. In partcular, cluster together and other associated our recent demonstraton on the issues. More importantly, our Outlook use of a chromophore-conjugated experimental studies revealed that upconversion nanosensor shows the DNA strands, bound to the surface Although there has been great progress the rapid detecton of Peroxynitrite, of gold nanopartcles, retained their in the use of upconversion nanopartcles (ONOO ) with a low detecton limit biological functonality. This means for biological applicatons, several - (down to 0.08 mm). These nanoprobes that the nanopartcle can be used challenges stll remain. One major enable real-tme monitoring of for target strand hybridisaton and challenge is to improve the brightness paracetamol-induced liver damage in molecular recogniton. By combining of the nanopartcles. This is largely living animals, providing a convenient single-band ant-Stokes near-infrared constrained by their narrow band screening platorm for harmful efects emission and the photothermal efect absorpton and low conversion of synthetc drug molecules [2]. mediated by the coupling of gold to efciency. Another challenge is on upconversion nanopartcles, these improving the stability of nanopartcles Another promising biological hairpin DNA-conjugated nanoprobes in a physiological environment through applicaton is the use of upconversion have proven efectve for simultaneous surface functonalisaton. This would probes for deep-tssue imaging deep-tssue imaging and targeted drug require a deeper understanding of the and therapy in vivo. We have delivery in vivo [3]. interacton between biomolecules and developed a way to produce highly the partcle’s surface. Most upconversion nanopartcles LIU Xiaogang is a Professor with the Department of Chemistry, NUS. He holds a joint appointment at the Insttute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR). His research interests include lanthanide-doped optcal nanomaterials, supramolecular chemistry, and surface science for catalysis, sensors and biomedical applicatons. Please visit this website htp://liuxg. science.nus.edu.sg for more informaton. References [1] Zhou B; et al., “Controlling upconversion nanocrystals for emerging applicatons” NATURE NANOTECHNOLOGY Volume: 10 Issue: 11 Pages: 924-936 DOI: 10.1038/NNANO.2015.251 Published: 2015. [2] J. Peng; et al., “Real-tme in vivo hepatotoxicity monitoring through chromophore-conjugated photon-upconvertng nanoprobes” ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 56 Issue: 15 Pages: 4165-4169 DOI: 10.1002/ anie.201612020 Published: 2017. [3] S. Han; et al., “Gold and hairpin DNA functonalizaton of upconversion nanocrystals for imaging and in vivo drug delivery“, ADVANCED MATERIALS Volume: 29 Issue: 18 DOI:10.1002/adma.201700244 Published: 2017. ADVANCES IN SCIENCE | VOL. 22 | NUMBER 1 | JUNE 2017 9
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