Chemical
and colloidal stability in complex aqueous media are among
the main challenges preventing nanoparticles from successfully entering
into the biomedical field. Small core–shell upconversion nanoparticles
(UCNPs) NaYF4:Yb,Er@NaYF4 of 12 nm in diameter
with a high surface-to-volume ratio are utilized to demonstrate that
self-assembling phospholipid bilayers (PLMs) have several benefits
compared to common ligand-exchange and ligand-addition particle coatings
such as poly(acrylic acid) and amphiphilic polymers. An efficient
hydrophobic barrier against water quenching and toward particle disintegration
is formed by PLM. Particles with this functionalization have a higher
upconversion luminescence in aqueous media in contrast to common surface
ligands. They attract with better colloidal stability in phosphate
buffer, in a wide pH range, in high ionic solutions, and in complex
cell media, as is required for biological applications. Moreover,
kidney cells (NRK) are not affected by these stable PLM-coated UCNPs
as first cell viability tests reveal.
Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted a lot of interest due to their benefits in biological applications: They are not suffering from intermittence and provide nearly background-free luminescence. The progress in synthesis nowadays enables access to complex core-shell particles of controlled size and composition. Nevertheless, the frequently used doping ratio dates back to where mostly core-only particles of relatively large size have been studied. Especially at low power excitation as needed in biology, a decrease in particle size leads to a drastic decrease in the upconversion efficiency. An enhancement strategy based on an increased absorption rate of near-infrared light provided by an increase of the sensitizer content, together with the simultaneous blocking of the energy migration pathways to the particle surface, is presented. NaYbF 4 (20%Er) particles of 8.5 nm diameter equipped with an about 2 nm thick NaYF 4 shell show significantly enhanced upconversion luminescence in the red (660 nm) compared to the most commonly used particles with only 20% Yb 3+ and 2% Er 3+ . The impact of size, composition, and core-shell architecture on photophysical properties are studied. The findings demonstrate that an increase in doping rates enables the design of small, bright UCNPs useful for biological applications.
The increasing popularity of nanoparticles in many applications has led to the fact that these persistent materials pollute our environment and threaten our health. An online sensor system for monitoring the presence of nanoparticles in fresh water would be highly desired. We propose a label-free sensor based on SPR imaging. The sensitivity was enhanced by a factor of about 100 by improving the detector by using a high-resolution camera. This revealed that the light source also needed to be improved by using LED excitation instead of a laser light source. As a receptor, different self-assembled monolayers have been screened. It can be seen that the nanoparticle receptor interaction is of a complex nature. The best system when taking sensitivity as well as reversibility into account is given by a dodecanethiol monolayer on the gold sensor surface. Lanthanide-doped nanoparticles, 29 nm in diameter and with a similar refractive index to the most common silica nanoparticles were detected in water down to 1.5 µg mL−1. The sensor can be fully regenerated within one hour without the need for any washing buffer. This sensing concept is expected to be easily adapted for the detection of nanoparticles of different size, shape, and composition, and upon miniaturization, suitable for long-term applications to monitor the quality of water.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.