How Nanoparticle Tracking Analysis Compares to Dynamic Light Scattering for Measuring Particle Size
Nanoparticle Tracking Analysis (NTA) and Dynamic Light Scattering (DLS) are complementary techniques that offer different insights into your samples. DLS will generally measure a wider size range than NTA, but NTA offers greater resolution than DLS (even with Multi-angle Dynamic Light Scattering).
In an ideal scenario, you may want to consider a combination of both systems to take advantage of the complementary information the two techniques can provide.
What is Nanoparticle Tracking Analysis?
NTA provides real time monitoring of the subtle changes in the characteristics of particle populations with all analyses confirmed by visual validation. Measurements take just minutes, allowing time-based changes and aggregation kinetics to be quantified .
NTA makes practical and effective use of the properties of both light scattering and Brownian motion to gather the nanoparticle size distribution of samples in liquid suspension. This is particularly important in making real time measurements such as in the study of protein aggregation, viral vaccines and exosomes/microvesicles.
NTA visualises, measures and characterises virtually all nanoparticles (10 – 2000 nanometres). A monochromatic light source (laser beam) is passed through the sample chamber and picks up the particles in suspension in such a manner that they can be easily magnified. Enhanced by a near-perfect black background, particles appear individually as point-scatterers moving under Brownian motion. Polydisperse and multimodal systems are instantly recognisable and quantifiable , and when engaged in fluorescence mode, suitably labeled particles can be discriminated from the non-labeled background.
A video camera captures a video file of the particles moving under Brownian motion and using the Stokes Einstein equation, calculates individual particle hydrodynamic diameter. The ‘movie’ is stored at a rate of 30 frames per second and results may be outputted to a spreadsheet format.
NTA is a three to five step measurement process . The process of loading the sample into the cell and getting results can take as little as two to three minutes, and you can run batches of samples under the same conditions and directly compare results. Samples are prepared in an appropriate liquid (typically water-based) at a concentrated level of 107 − 109 particles/ml and placed in the sample chamber which has a volume of 0.3 ml.
What is Dynamic Light Scattering?
DLS is the most common method of measurement for particle and molecular size analysis in the nanometer range. Typical applications are emulsions, micelles, polymers, proteins, nanoparticles or colloids.
Based on the Brownian motion of dispersed particles, DLS can be used to determine the size of small particles in suspension or polymers in solution.
The basic principle of DLS is simple: the sample is illuminated by a laser beam and the fluctuations of the scattered light are detected at a known scattering angle by a faster photon detector.
The diffusion of particles moving under Brownian motion is converted to size and a size distribution using the Stokes-Einstein relationship. Non-Invasive Back Scatter technology (NIBS) is incorporated to give the highest sensitivity simultaneously with the highest size and concentration range.Measurement of size as a function of concentration enables the calculation of k D , the DLS interaction parameter. The Microrheology option uses the DLS measurement of tracer particles to probe the structure of dilute polymer and protein solutions.
How do the two compare for measuring particle size?
The technique of Nanoparticle Tracking Analysis utilises the trajectories of individual scattering objects observed under a microscope and their displacement related to each object’s size. Dynamic Light Scattering on the other hand, utilises a technique where the intensity fluctuations in the scattered light are analysed and related to the diffusion of the scattering objects.
In a study published in Pharmaceutical Research, NTA was shown to accurately analyse the size distribution of monodisperse and polydisperse samples . The presence of small amounts of large (1,000 nm) particles generally does not compromise the accuracy of NTA measurements, and a broad range of population ratios can easily be detected and accurately sized. NTA proved to be suitable to characterise drug delivery nanoparticles and protein aggregates, complementing DLS.
DLS measures changes in scattering intensity from a bulk sample, whereas NTA measures observed particle diffusion directly, particle-by-particle. This provides a series of key advantages of the NTA method . NTA can give a wealth of additional information beyond particle size and:
- can detect samples 10 – 1000 times more diluted than DLS
- requires no information about collection angle, wavelength or solvent refractive index
- can give the % by number of aggregated particles directly .
- provides direct measurement without modeling or assumptions
- can offer higher resolution of peaks if you have polydisperse distributions
- can quickly and effectively provide the number weighted size (ie. if you need to show the smallest nanorods)
- allows you to selectively look at only a fluorescently tagged part of the distribution.
Why it’s important to detect size and count of nanoparticles
It’s essential that every effort is made to classify nanoparticles and access their safety, ensuring they’re fit for their purpose. Knowing the size distribution of individual nanoparticles offers a competitive advantage in many industries and fields of research .
NTA instruments offer the best opportunity for gathering accurate data and instruments. For example, the Malvern NanoSight NS300 can automatically track a range of different sized particles simultaneously.
Malvern NanoSight NS300 provides high resolution size distribution, concentration, protein aggregation and viscosity measurements for individual nanoparticles while a fluorescence mode allows differentiation of fluorescing particles. Events such as aggregation and dissolution can be monitored as they occur. The software is specifically designed to meet the needs of both new and experienced users and Standard Operating Procedures (SOPs) can be easily set up. For a more in-depth analysis of results, NS300 can offer customised reporting and full access to raw data.