2. What are quantum dots?
Nanocystals made up of semiconductor
materials .
Glow on introducing with light source such as
ultraviolet(UV)rays.
Diameter range 2-10 nm.
Have quantum mechanical properties.
Discovered by Alexei Ekimov on matrix and
L.E. Brus in colloidal solutions.
3. Properties that enables its
application
Can emit light of different colours on varying its
size (Confinement effect).
Since the size is smaller , larger its band gap;
greater the energy to excite the electron from
ground valence band to the exited conduction
band.
Large Q.D. produce light with long wavelength
while small do opposite.
In terms of colour large Q.D. emit red colour while
small Q.D. emits blue colour.
By combining a range of different sized Q.D.
Entire light spectrum can be obtained .
5. Characteristics
Optical property due to their high extinction.
Zero dimensions give it a sharper density of
states than higher dimensional structures.
High quality Q.D. have broad exicitation
profiles and narrow emission spectra.
6. Application of quantum dots
Optical application
Q.D. can be used in optical applications where
precise control of light is needed .
A thin layer of Q.D. has been developed so it can
be fitted on top of fluorescent or LED lamp and
convert its light from bluish to warmer, redder
colour.
The improved photostability of quantum dots, for
example, allows the acquisition of many
consecutive focal-plane images that can be
reconstructed into a high-resolution 3-D image.
7. Semiconductor quantum dots have also been
employed for in vitro imaging of pre-labeled
cells.
As donor fluorophores in Förster resonance
energy transfer , where the large extinction
coefficient and spectral purity of these
fluorophores make them superior to molecular
fluorophore.
8. Cell imaging
Multicolor labeling of cells is a powerful technique
for visualizing many of these structures
simultaneously, such as cytoskeletal proteins or
organelles, and to elucidate intracellular
processes.
Potential cancer treatments
Q.D. can be designed to accumulate particular
part of body and deliver anti cancer drug bound to
them.
Target specific ,more precise than conventional
drugs and reduced side effect.
9. Organic dyes (in vivo imaging)
Used as nanoscopic light bulbs and colour
specific cells to be studied under microscope.
As sensors for chemical and biological warfare
agents such as anthrax.
Are bright produce any colour of visibility and
lasts indefinitely (photo stable).
In food science
Detect pathogenic bacteria , proteins.
10. Tumor targetting
The use of quantum dots for tumor targeting
under in vivo conditions employ two targeting
schemes:
Active targeting - quantum dots are
functionalized with tumor-specific binding sites
to selectively bind to tumor cellstive targeting
and passive targeting.
Passive targeting uses the enhanced
permeation and retention of tumor cells for the
delivery of quantum dot probes.
11. Toxicity
Quantum dot probes exhibit in vivo toxicity.
EX. CdSe nanocrystals are highly toxic to cultured
cells under UV illumination, because the particles
dissolve in a process known as photolysis to
release toxic cadmium ions into the culture
medium.
The toxicity arises primarily from two sources:
1. The semiconductor materials that commonly
constitute the QD core (and sometimes the
overcoating shell) which can leach under certain
circumstances.
2. The generation of reactive and free radical
species during excitation.
12. Cell squeezing
Quantum dots can be efficiently delivered
without inducing aggregation, trapping material
in endosomes, or significant loss of cell
viability.
Diagnostics
The unique properties of QDs have been
investigated almost exclusively for two
techniques that require the use of diagnostic
fluorophores: immunolabeling and nucleic acid
detection.
13. Nucleic acid detection
By combining the ability to multiplex with the
increased sensitivity derived from QD’s
photostability to improve detection and reduce
both the sample and probe concentrations
required.
EX. Gerion and coworkers demonstrated single
nucleotide polymorphism (SNP) of p53 tumor
suppressor gene mutations and multiallele
detection of hepatitis B and C virus genes with
a commercial scanner and two colors of QDs .
14. Immunolabelling
Use of antibody-driven specific binding to a target
protein or biomolecule and the visualization of this
event with some form of QD labeling.
Biosensors
Due to their unique physical and optical properties,
colloidal QDs have been used to develop new
methods of biosensing.
By attaching biomolecules to the QD surface, it is
possible to generate complex bioconjugates that
merge biological specificity and function with the
desirable optical characteristics of QDs.
Known as “nanosensors.”
15. Conclusion
We can conclude that Q.D. are leading research
tool helpful in many prospects such as
research related to human health and disease
as well as research related to other sectors
such as robotics , electronics, environment
and so on.
