Chemistry Reference
In-Depth Information
the particles by ligand attraction, and layer-by-layer assembly of
oppositely charged polyions on the surface of nanoparticles, have also
been developed [27, 28]. Apart from the above methods, coating the
surface of nanoparticles with an amorphous layer of silica has gained
prominence and is being routinely used. Van Veggel
. coated a
layer of silica on nanoparticles via surface silanization [9]. Coating
the hydrophobic surface of nanoparticles with silica and coating
individual nanoparticles rather than their aggregates is a difficult
task. Li
et al
nanoparticles with a thin
layer of silica with tunable thickness and good monodispersity [29].
Recently, a mesoporous layer of silica coating was also performed
to facilitate the loading of therapeutic molecules such as drug or
gene into the pores of nanoparticles for simultaneous delivery and
imaging experiments [30].
Sometimes, the core of nanoparticles is first coated with
another layer of host material or an inert crystalline material before
functionalization. This is done to passivate the ligands on the surface
of the core, to fill the surface defects and to prevent fluorescence
quenching by impurities attached on the surface [31, 32]. This helps
to enhance the fluorescence of nanoparticles and provides a core-
shell structure to nanoparticle (as shown in Fig. 3.3).
Chapter 2 provides a more detailed discussion on rare earth
surface modification and functionalization.
et al
. reported the coating of NaYF
4
3.5
Applications
Rare earth-based nanoparticles have been investigated in a
wide range of biological applications ranging from imaging,
immunocytochemistry, DNA detection, and the like. This section
will provide in-depth discussions of the applications of these
nanoparticles in fluorescence microscopy. Fluorescence microscopy
involves the visualization of cells or cellular components with
subcellular resolution by labeling them with fluorescent probes.
Initially, wide-field fluorescence microscopes were used and later
laser scanning confocal microscopy was developed, which overcame
some of the earlier limitations, followed by two photon microscopy,
Total Internal Reflection Microscopy (TIRF), and Photoactivation
Localization Microscopy (PALM). All these techniques have their
own advantages and limitations. Even though they have very good
