Chemistry Reference
In-Depth Information
2.1.1 Luminescent Nanocrystals and Nanoparticles
The most prominent nanomaterials for bioanalysis at present are semiconductor
QDs. Rare-earth doped upconverting nanocrystals and precious metal nanoparticles
are becoming increasingly popular, yet they are still far from reaching the level of
use of QDs. Other luminescent nanoparticles like carbon-based nanoparticles start
to appear, but the synthesis and application of these materials are still in their
infancy and not significant for practitioners in the field of bioanalysis.
The photoluminescence of these nanoparticles has very different causes, depend-
ing on the type of nanomaterial: semiconductor QDs luminescence by recombina-
tion of excitons, rare-earth doped nanoparticles photoluminescence by atom orbital
(AO) transitions within the rare-earth ions acting as luminescent centers, and
metallic nanoparticles emit light by various mechanisms. Consequently, the optical
properties of luminescent nanoparticles can be very different, depending on the
material they consist of.
The optical properties of semiconductor QDs (Fig.
1a-c
, Tables
1
and
2
) are
controlled by the particle size, size distribution (dispersity), constituent material,
shape, and surface chemistry. Accordingly, their physico-chemical properties
depend to a considerable degree on particle synthesis and surface modification.
Typical diameters of QDs range between 1 and 6 nm. The most prominent optical
features of QDs are an absorption that gradually increases toward shorter
Fig. 1 Spectra of QDs and organic dyes. Absorption (
lines
) and emission (
symbols
) spectra of
representative QDs (a-c) and organic dyes (d-f). Reprinted by permission from Macmillan
Publishers Ltd: Nature Methods [
1
], copyright (2008)
Search WWH ::
Custom Search