The analysis of nanoparticles is becoming increasingly important in a broad range of sectors including the pharmaceutical industry where nanoparticles are being used as drug delivery vehicles.
Nanoparticle delivery systems may be used to protect drugs from being metabolised by enzymes and to help control their rate of release leading to fewer doses being necessary thus reducing adverse side effects and toxicity.
This is starting to enable delicate biological drugs to be accurately delivered and opens up the potential for using siRNA (small interfering RNA) as therapeutic agents.
Liposomes are one of the best-known examples of nanoparticle delivery systems.
New research using single-walled carbon nanotubes and other 'smart' nanoparticles shows potential.
The size of such particles is becoming increasingly recognised as an important factor in treatment efficacy as a particle's size can affect its circulation and residence time in the blood, as well as the rate of absorption into cells.
Another area where the study of nanoparticles has become important is in the development of artificial joints.
When these wear, metallic, plastic or ceramic particles can build up that cause inflammatory and immune responses, potentially causing the replacement joint to be rejected.
As the industrial use of nanoparticles increases, investigating their toxicity is becoming increasingly important.
Particle size can play a key role in a particles biological activity, with the size being crucial on a particles ability to infiltrate cells.
This has led to an increased need to fully characterise particle size distributions and not just the average size data that some techniques provide.
Two of the most widely used nanoparticle sizing methods are photon correlation spectroscopy (PCS), also referred to as dynamic light scattering (DLS), and electron microscopy (EM), usually known as scanning electron microscopy (SEM).
PCS examines the light scattered from particles detecting the rate of change of interference resulting from particle Brownian motion.
Rather than giving the particle size based on a particle-by-particle calculation, it produces an average figure.
It is a strong technique for looking at samples with a very narrow range of particle sizes (mono-dispersed) but has problems with samples that contain a range of particle sizes (poly-dispersed) with larger particles biasing the average size value produced.
EM is a very exact method of measuring dry particles but often may require significant sample preparation prior to inspection and measurement.
NanoSight's nanoparticle tracking analysis (NTA) method offers a unique way of visualising and analysing particles in liquids that relates a particle's Brownian motion to its size.
Particle movement rate is related to the size of the particle and the viscosity of the liquid through which it is moving, as well as the temperature.
Interestingly, particle density does not influence its rate of movement.
Compared to other light-scattering techniques, NTA enables higher-resolution particle size distribution profiles to be obtained.
It is often claimed that a new instrumental technique is the 'most easy to use' and 'produces the best results in the shortest time' but in the case of using Nanoparticle Tracking Analysis (NTA), this really is the case.
NTA enables individual particles from 10 to 1,000nm to be sized to give particle-by-particle size distribution data rather than the average size data generated by PCS.
The upper size limit is restricted by Brownian motion limitations.
Large particles of one micron in size move relatively slowly and reduce the accuracy of the technique.
The viscosity of the solvent used also plays a role in determining the upper size limit as it influences the movement of the particles.
The lower size limit is dictated by a particles ability to scatter sufficient light to be detectable with analysis of 10nm particles only possible with particles having high refractive indices such as gold and silver.
Care has to be taken when diluting a sample as this may sometimes lead to particle aggregation.
Accurate and reproducible analyses are obtained from recording short video clips lasting only a few seconds to produce particle number and concentration data.
Given the close to real-time nature of the technique, particle-particle interaction information is accessible as is information about sample aggregation and dissolution.
All particle types can be measured and in any solvent type as long as they do not have the same refractive index.
NTA allows the user a simple and direct qualitative view of the sample under analysis (perhaps to validate data obtained from other techniques such as PCS) and from which an independent quantitative estimation of sample size, size distribution and concentration can be immediately obtained.
Hardware requirements NTA employs a specially designed flow cell that is mounted on a conventional optical microscope equipped with a CCD camera capable of operating at 30 frames per second.
