Upconversion nanoparticles — new types of luminescent nanomaterials that release high-energy photons after laser light stimulation — can penetrate deeper into tissue and are more photochemically stable than conventional bioimaging agents, such as quantum dots and organic dyes.
Luminescent nanocrystals doped or impregnated with small amounts of rare-earth ytterbium (Yb) ions are particularly effective at photon upconversion. The specific lasers used to excite Yb dopants, however, can also heat water molecules in biological samples causing cell death or tissue damage.
Now, Xiaogang Liu from the A*STAR Institute of Materials Research and Engineering in Singapore and co-workers have synthesized a rare-earth-doped nanocrystal that can be excited at wavelengths within a safer ‘biological window’, thanks to a layered, core–shell design1.
Luminescent nanocrystals require ‘sensitizer’ components to absorb photons and transfer energy to activator sites, which emit the desired light radiation. Liu and co-workers investigated a different rare-earth dopant, neodymium (Nd), which absorbs the short-wavelength laser light that excites water molecules, thus avoiding overheating effects. Unfortunately, Nd can be doped into nanocrystals only at very low concentrations before cross-interactions with activators begin to extinguish the luminescence. This makes Nd-doped nanoparticles weak emitters compared to Yb-based biomarkers.
To resolve this problem, the researchers produced spherical nanoparticles containing layers with starkly different concentrations of Nd ions. They doped small amounts of Nd, Yb, and activator ions into nanocrystals of sodium yttrium fluoride (NaYF4), a material with a strong upconversion efficiency. They then synthesized a shell layer around the low-doped core containing a significantly higher Nd dopant concentration of 20 per cent. In this arrangement, the shell layer effectively harvests light and then transfers energy to the core, where low sensitizer concentrations minimize luminescence reduction.
The experiments revealed that the core–shell design dramatically improved the nanocrystals’ bioimaging capabilities — the new material had better light-harvesting capabilities than nanoparticles doped with pure Nd or Yb and achieved emission intensities seven times higher than pure NaYF4. Mechanistic studies showed that energy transfer between Nd and Yb ions in the nanoparticle core was key to overcoming the limitations of low dopant concentrations.
Next, the team tested their new materials by imaging an array of cervical cancer cells. While typical laser irradiation for Yb-doped biomarkers killed the cells within five minutes, the shorter wavelengths used for Nd-doped core–shell nanoparticles kept the cells viable over the same time.
“We plan to further improve the upconversion efficiency of our nanoparticles and use them for both bioimaging and drug delivery,” says Liu.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering
Xie, X., Gao, N., Deng, R., Sun, Q., Xu, Q.-H. & Liu, X. Mechanistic investigation of photon upconversion in Nd3+-sensitized core–shell nanoparticles. Journal of the American Chemical Society 135, 12608–12611 (2013).
New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University
Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology