Nanocrystals with Core-Shell Design Prevent Cells from Overheating in Bioimaging Tests
13 February 2014
Researchers at the A*STAR Institute of Materials Research and Engineering in Singapore have synthesized a rare-earth-doped nanocrystal that can be stimulated at wavelengths and reduce the overheating of cells during bioimaging tests thanks to their layered, core-shell structure.
Luminescent nanocrystals need "sensitizer" components to start absorbing photons and transmit energy to activator sites that release the required amount of light radiation. In order to offset the overheating effects after laser light simulation, the team led by Xiaogang Lui examined the properties of neodymium (Nd), a rare-earth dopant absorbing the short-wavelength laser light that excites water molecules. Nd, however, can be doped into nanocrystals at very low concentrations only, unlike ytterbium (Yb) ions that generally have strong upconversion currency, which makes Nd-doped nanoparticles weaker emitters than Yb-based biomarkers, Phys.org reports.
In order to overcome these limitations, the researchers generated spherical nanoparticles built up by layers containing different concentrations of Nd ions. The researchers doped small amounts of Nd, Yb and activator ions into nanocrystals of sodium yttrium fluoride (NaYF4), a substance known for its exceptional upconversion properties. The low-doped core was then rounded by a shell layer with higher Nd dopant concentration, which helped absorb light and transfer energy to the core, where low sensitizer concentrations pared down luminescence reduction.
The tests established that the core-shell design significantly enhances nanocrystals' bioimaging properties, chiefly thanks to the energy transfer between Nd and Yb ions in the nanoparticle core that helped address issues stemming from low dopant concentrations.
The team then tested the new materials by imaging cervical cancer cells, establishing that they remained viable when the shorter wavelengths for Nd-doped core-shell nanoparticles were used, unlike the experiments when Yb-doped biomarkers were applied, as their typical laser irradiation killed the cells within five minutes.