Nanoparticle tracking analysis
Nanoparticle tracking analysis (NTA) is a method for visualizing and analyzing particles in liquids that relates the rate of Brownian motion to particle size. The rate of movement is related only to the viscosity and temperature of the liquid; it is not influenced by particle density or refractive index. NTA allows the determination of a size distribution profile of small particles with a diameter of approximately 10–1000 nanometers (nm) in liquid suspension.
The technique is used in conjunction with an
NTA currently operates for particles from about 10 to 1000 nm in diameter, depending on particle type. Analysis of particles at the lowest end of this range is possible only for particles composed of materials with a high refractive index, such gold and silver. The upper size limit is restricted by the limited Brownian motion of large particles; because a large particle moves very slowly, accuracy is diminished. The viscosity of the solvent also influences the movement of particles, and it, too, plays a part in determining the upper size limit for a specific system.
Applications
NTA has been used by commercial, academic, and government laboratories working with
iNTA
Interferometric nanoparticle tracking analysis (iNTA) is the next generation of NTA technology. It is based on interferometric scattering microscopy (iSCAT), which enhances the signal of weak scatterers. In contrast to NTA, iNTA has a superior resolution based on a two-parameter analysis, including the size and the scattering cross-section of the particle.[2]
Comparison to dynamic light scattering
Both dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) measure the Brownian motion of nanoparticles whose speed of motion, or diffusion constant, Dt, is related to particle size through the Stokes–Einstein equation.
where
- Dt is the diffusion constant, a product of diffusion coefficient D and time t
- is Boltzmann's constant,
- T is the absolute temperature,
- η is viscosity
- d is the diameter of the spherical particle.
In NTA this motion is analyzed by video – individual particle positional changes are tracked in two dimensions from which the particle diffusion is determined. Knowing Dt, the particle hydrodynamic diameter can be then determined.
In contrast, DLS does not visualize the particles individually but analyzes, using a digital correlator, the time dependent scattering intensity fluctuations. These fluctuations are caused by interference effects arising from the relative Brownian movements of an ensemble of a large number of particles within a sample. Through analysis of the resultant exponential autocorrelation function, average particle size can be calculated as well as a polydispersity index. For multi-exponential autocorrelation functions arising from polydisperse samples, deconvolution can give limited information about the particle size distribution profile.
History
NTA and related technologies were developed by Bob Carr.
See also
- Dynamic light scattering
- NanoSight Ltd
References
- PMID 20204471.
- S2CID 244124743. Retrieved 27 September 2022.
- ^ Harding, Jill (10 May 2012). "Fast-growing Biotech firm scoops a Queen's Award". Salisbury Journal. Retrieved 27 September 2022.
- ^ A Queen's Award for Enterprise for International Trade 2012 has been awarded to NanoSight. Nanotechnology Now, May 1, 2012.