Chemistry Reference
In-Depth Information
individual molecules and other processes inside cells. For applications
where visualization of different cellular components is necessary or
when there is a need for detection of trace amount of molecules, it was
thought that labeling the molecule of interest with fluorescent dyes
will address this need, and hence fluorescence microscopy came into
play. Fluorescence microscope excites fluorescent molecules used to
label cells known as fluorophores with a particular wavelength and
detects the fluorescence, which is of another wavelength.
Initially, organic dyes such as fluorescein isothiocyanate (FITC),
rhodamine, and coumarin were used for fluorescence labeling due
to its various advantageous properties such as small size, ease of
attachment to biomolecules, and high quantum yield. However, they
suffer from limitations such as low photostability, which hinders
long-term monitoring, and also overlap of excitation and emission
spectra for some organic dyes. The emergence of fluorescent
tags of biological origin such as green fluorescent protein (GFP)
and DsRed provides the advantages of themselves being able to
genetically fuse to the protein of interest so that the protein can be
tracked in real time. But they too face some shortcomings such as
low quantum yield and low fluorescence lifetime. Recently, many
types of fluorescent nanoparticles were developed to overcome the
limitations of the earlier fluorescent probes. A main class is polymeric
nanoparticles, where organic dyes were encapsulated in polymers to
increase stability and amplify signals. However, they were not stable
enough for long-term studies. The next class comprises fluorescent
semiconductor crystals, also known as quantum dots, which have
gained tremendous popularity. Their color output can be tuned
by changing their sizes, and they have good photostability with
narrow emission spectrum. But they too face some problems such
as photoblinking and high cytotoxicity. Studies are under way to
overcome these problems. The final class of nanoparticles consists
of rare earth fluorides, which are believed to have many superior
properties compared to their predecessors.
3.2
Rare Earth Nanoparticles
Rare earth elements constitute a class of elements found in the 6th
and 7th periods of the periodic table along with lanthanum and
actinium. It is divided into two main series known as the lanthanide
