Biomedical Engineering Reference
In-Depth Information
8.1 Introduction
Light scattering causes many interesting phenomena in the universe.
For example, the blue color of the sky is caused by the scattering
of sunlight from the molecules and particles in the atmosphere.
1
Scattered light is emitted in all directions except the direction in
which incident light beams is propagated, and scattered light is
strongly related to the inhomogeneity of the medium.
2
Depending
on the size of the photon-interacted particles (
d
) and the wavelength
of incident light beams (
λ
), light scattering can be classiied into Mie
(
d
>>
λ
), Tyndall (
d
≈
λ
), and Rayleigh scattering (
d
≤ 0.05
λ
).
2
Despite
the wavelength difference between the incident and the scattered
beams, light scattering can also be divided into elastic scattering,
inelastic scattering, and quasi-elastic scattering.
3
Rayleigh scattering
is elastic, while both Raman and Brillouin scattering are inelastic.
Quasi-elastic scattering (dynamic light scattering) results from the
Brownian movement of the scatters.
3
Nanoparticles (NPs) of different sizes have unique optical and
electric properties, and can thus become promising RLS probes. It
is known that the RLS intensity is proportional to the sixth power of
the radius of the nanoparticles, and is inversely proportional to the
fourth power of the wavelength of incident light.
4,5
In addition, the
RLS intensity is proportional to the light intensity. Thus, NP size, as
well as the incident light's wavelength and intensity play important
roles in determining the RLS signals.
Both Au and Ag NPs have visible absorption and capability for
enhancing RLS signals. In addition to Au and Ag NPs, other NPs such
as AgCl, PbS, HgS, Ag
2
S, Fe
3
O
4
, CdTe, and C
60
also provide enhanced
RLS signals.
6-12
Due to its high sensitivity, RLS is a useful technique
for determining the concentrations of analytes of interest.
13,14
RLS
techniques, in conjunction with commercial spectroluorometers,
have been utilized in observing the formation of aggregated
chromophores in complex systems.
15-17
Moreover, RLS techniques
have proven themselves to be important and powerful tools for
the quantiication of nucleic acids, proteins, metallic ions, drugs
(in artiicial and real samples), and for characterization of the
aggregation and assembly of biological and chemical species.
18-22
This chapter briely describes the basic concepts of RLS. Au and
Ag NPs are the two most popular NPs used in RLS techniques, and
thus their RLS properties and use in RLS bioassays are discussed
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