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.
A nanoengineered
interface fabricated by self-assembly enables
the online determination of vitamin B12 via a simple luminescence
readout in serum without any pretreatment. The interplay of Tm3+-doped NaYF4 nanoparticles (UCNPs) and a gold
nanotriangle array prepared by nanosphere lithography on a glass slide
is responsible for an efficient NIR to UV upconversion. Hot spots
of the gold assembly generate local electromagnetic-field enhancement,
favoring the four-photon upconversion process at the low-power excitation
of approximately 13 W·cm–2. An improvement
by about 6 times of the intensity for the emission peaking at 345
nm is achieved. The nanoengineered interface has been applied in a
proof-of-concept sensor for vitamin B12 in serum, which is known as
a marker for the risk of cancer; Alzheimer disease; or, during pregnancy,
neurological abnormalities in newborn babies. Vitamin B12 can be detected
in serum down to 3.0 nmol·L–1 by a simple intensity-based
optical readout, consuming only 200 μL of a sample, which qualifies
as easy miniaturization for point-of-care diagnostics. Additionally,
this label-free approach can be used for long-term monitoring because
of the high photostability of the upconversion nanoparticles.
…c onsisting of oleate and dodecylamine provides excellent colloidal stability and versatility to nanoparticles with upconversion luminescence.T his surface modification strategy can be achieved in af ast and easy one-step reaction, as demonstrated by MaríaJ .Marín, Thomas Hirsch et al. in their Research Article (e202305165).
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