Environmental Engineering Reference
In-Depth Information
13.2.3 Nanoparticle Tracking Analysis (NTA) for Tracking
of the Brownian Motion
Nanoparticle Tracking Analysis (NTA) provides direct and real time visualization,
sizing, and counting of particulate materials between 10 nm and 1
m in liquid
suspension. The technique works on a particle-by-particle basis, relating the degree
of movement under Brownian motion to the sphere equivalent hydrodynamic
diameter particle size, allowing high resolution particle size distributions to be
obtained within minutes. Here we describe application of NTA to the analysis of
100 nm polystyrene nanospheres in liquid suspension. The technique can be
adapted for use with nearly all particulate materials with sizes between 10 nm
and 1
μ
μ
m.
Nanoparticle Tracking Analysis (NTA) has been introduced as an alternative
technique for dispersed submicron particles. Hereby, the particle size is derived
from the average displacement between successive photos due to Brownian motion.
As compared to DLS, NTA has the advantage that it has a higher resolution for
multimodal samples. In addition, it provides direct visual information from which
aggregation phenomena are visually observable [
6
].
13.2.4 Dynamic Light Scattering (DLS)
Dynamic light scattering is a new method for investigating macromolecular sys-
tems. The importance of the technique lies in its noninvasive character. It can be
employed on extremely small fluid volumes; the instrumentation is relatively
inexpensive and allows the rapid determination of diffusion coefficients as well
as providing information on relaxation time distributions for the macromolecular
components of complex systems.
DLS technique measures Brownian motion in the liquids and solutions. The
Brownian motion of molecules becomes more rapid when the size of particles
scattering light is smaller. DLS was discovered shortly after gas lasers were applied
as light sources in optical scattering investigations. Lasers are high intensity sharp
monochromatic light sources; as a consequence the spectral broadening of the low
intensity Rayleigh scattered radiation is relatively easy to detect.
DLS is most commonly used to analyze nanoparticles. Examples include deter-
mining nanogold size, protein size, latex size, and colloid size. In general, the
technique is best used for submicron particles and can be used to measure particle
with sizes less than a nanometer. In the domain of sizes ranging from nanometers to
microns, the distinction between a molecule (such as a protein or macromolecule)
and a particle (such as nanogold) becomes blurred, even if the measurements are
performed in liquid phase (such as in an emulsion). Dynamic light scattering can
also be used as a probe of complex fluids such as concentrated solutions. However,
this application is much less common than particle sizing.
