Environmental Engineering Reference
In-Depth Information
s Nanoparticle Tracking Analysis (NTA) is a technique for charac-
terizing nanoparticles in their native suspension. This technique provides
multiparameter characterization of nanoparticles (down to 10-2,000 nm diameter)
achieved by video analysis of a laser illuminated sample through conventional
microscopy. Analysis of the Brownian motion of individual particles in the defined
field of view allows their size to be determined and their concentration. The
Brownian motion of particles (which appears as point scatters) is tracked separately
but simultaneously using a CCD camera, from which a high-resolution plot of
the particle-size distribution (and profile changes in time during, aggregation or
dissolution) is obtained. Sample pre-treatment is carried out only by dilution
with an appropriate solvent to acceptable concentrations (between 108 and 109
particles/ml, depending on the type of sample). All types of particles can be
measured provided they are sufficiently light to be spread visible. The technique
offers significant advantages over existing light scattering techniques for the char-
acterization of poly dispersed populations. Each particle is individually but simul-
taneously analyzed for: size, fluorescence, high resolution particle size distribution
profile, light scattering properties (refractive index), zeta potential through the
application of electric fields, and concentration (particles per milliliter) of any
given size class of nanomaterial. NTA is widely used as a preliminary character-
ization technique prior to exposure. This has been applied to a range of materials
including metals, metal oxides, and polymers.
NanoSight
'
13.3.1 Operating Principle
Nanoparticle Tracking Analysis (NTA) is a method that has gained popularity for
the study of nanoparticle dispersions. The NTA technique is centered on a sample-
analysis module in which a laser diode is configured to pass light through a 250
μ
l
liquid sample containing the nanoparticles. Particles in the beam are visualized by a
conventional optical microscope aligned normally to the beam axis (Fig.
13.1
). This
setup collects light scattered from every particle in the field of view as they move
rapidly under Brownian motion.
The nanoparticle-tracking-analysis (NTA) was development technology to visu-
alize and analyze—in terms of both size and scattered intensity—nanoscale parti-
cles in liquid with little preparation and at low cost. Analysis of a wide range of
particle types in a wide variety of solvents. The only user input required are the
sample temperature and solvent viscosity.
A finely focused, 635 nm (or for fluorescent studies 404 nm or 523 nm) laser
beam is passed through a prism-edged optical flat (Fig.
13.2
), the refractive index of
which is such that the beam refracts at the interface between the flat and a liquid
layer placed above it. Due to the refraction, the beam compresses to a low profile,
intense illumination region in which nanoparticles present in the liquid film can be
easily visualized via a long-working distance, 20
magnification microscope
objective fitted to an otherwise conventional microscope (Fig.
13.3
)[
15
].
