Nanoparticle Tracking Analysis (NTA) is a specialized optical technique designed to visualize and characterize individual particles suspended in a liquid. It addresses the challenge of analyzing materials in the nanoscale range, typically defined as 1 to 1,000 nanometers. NTA provides information about particle populations that traditional measurement methods cannot capture due to the particles’ small size. This approach allows researchers to gain a precise understanding of the size and quantity of these components in a sample.
How Nanoparticle Tracking Analysis Works
The core mechanism of NTA relies on the combination of laser light scattering and the physical phenomenon of Brownian motion. A sample containing nanoparticles in suspension is introduced into a specialized chamber and illuminated by a precisely focused laser beam. This beam creates a thin, intense plane of light within the fluid, similar to how a projector illuminates dust motes in a dark room.
When nanoparticles pass through the illuminated volume, they scatter the laser light, making them visible as bright points of light against a dark background. An optical microscope positioned perpendicularly to the laser beam captures this scattered light. A high-speed camera then records a video of these light points as they move randomly within the field of view.
The software tracks the center of each particle’s scattered light spot from frame to frame, mapping its erratic motion. This movement, known as Brownian motion, is caused by the incessant bombardment of the particles by the surrounding liquid molecules. The speed of this movement is inversely proportional to the particle’s size: smaller nanoparticles move rapidly, while larger particles move more sluggishly.
Key Data Provided by NTA
The analysis of the recorded particle trajectories yields two key metrics: particle size distribution and particle concentration. To determine the size, the software calculates the mean squared displacement for each particle over the video sequence, which provides the diffusion coefficient. This coefficient quantifies the speed of the particle’s movement in the liquid.
The diffusion coefficient is then converted into a hydrodynamic diameter for each individual particle using the Stokes-Einstein equation. This calculation incorporates known variables like the temperature and viscosity of the liquid medium, allowing the system to determine the size as if the particle were a perfect sphere. NTA calculates the size for thousands of particles, generating a detailed particle size distribution.
Particle concentration is determined by counting the total number of tracked particles within the known measurement volume illuminated by the laser beam. The software converts the particle count into an absolute concentration, typically expressed as particles per milliliter. This count-based approach provides a direct measure of how many particles are present.
Scientific and Industrial Applications
The ability to accurately size and count individual nanoparticles in fluid has made NTA a valuable tool across numerous scientific and industrial sectors. In the biomedical field, NTA is widely used for the characterization of extracellular vesicles (EVs), such as exosomes, which are nanosized bubbles released by cells that carry biological cargo. Analyzing the size, concentration, and surface markers of these EVs is important for developing non-invasive disease diagnostics and understanding cell-to-cell communication.
The pharmaceutical industry uses NTA for quality control and development of advanced drug delivery systems. Researchers assess the stability and size distribution of viral vectors used in gene therapies and vaccine production. NTA is also applied to characterize liposomes and polymeric nanoparticles, ensuring these engineered carriers are the correct size to effectively deliver therapeutic agents.
NTA is also valuable in environmental science for monitoring pollutants and microscopic materials in water sources. The technology identifies and quantifies colloids and fine particulate matter, including microplastics. This is crucial for assessing environmental impact and developing water purification strategies.
Distinctions from Other Nanoparticle Methods
NTA offers distinct advantages over established techniques like Dynamic Light Scattering (DLS) and Electron Microscopy (EM). Unlike DLS, which measures the average light scattered by an entire population of particles (an ensemble measurement), NTA tracks and measures each particle individually. This particle-by-particle approach provides much higher resolution, allowing NTA to accurately resolve samples that contain multiple distinct size populations, where DLS often produces a single, averaged size result skewed toward larger particles.
NTA is one of the few techniques that provides a direct, count-based measurement of particle concentration in solution, which DLS cannot do. Compared to Electron Microscopy, NTA analyzes particles in their native, liquid state without the need for drying or staining, which can alter particle morphology and size. While EM offers high-resolution images of particle structure, NTA uniquely provides both the hydrodynamic size and the absolute concentration in a single, rapid measurement.