Challenges at Submicron Particle Characterisation: A Case Study Using Nanoparticle Tracking Analysis (NTA)

Nanoparticle tracking analysis (NTA) is an emerging technique for the analysis of particles in the submicron range of 50–1000 nm. It tracks the Brownian motion of individual particles and calculates the diffusion coefficient and subsequently the hydrodynamic diameter based on the Stokes-Einstein equation. In this study, we provide guidance on the capabilities and limitations using NTA for particle analysis.

We have used polystyrene (PS) particle size standards to evaluate various experimental parameters such as the influence of particle concentration, measurement temperature, and neutral density (ND) filter on sizing and counting. We have also used bimodal samples in different ratios to assess the resolution power of NTA as well as trimodal samples to evaluate two different analysis algorithms.

Within the working range of 10⁶–10⁹ particles/mL, lower particle concentrations of monomodal samples lead to an increase in the detected particle size but allow for more accurate particle concentration measurements. The measurement temperature in the range of 21 °C to 29 °C causes a trend of increasing particle size up to 8 % with increasing temperature. The use of a neutral density filter increases the accuracy of particle size measurements for larger particles, e.g., 800 nm PS beads. The analysis of bimodal or trimodal samples is challenging due to variations in the readout depending on instrument settings and experimental parameters.

In this study, we have addressed several experimental parameters that affect the measurements, and we aim to provide guidance to the scientific community using NTA analysis.