Interference from Proteins and Surfactants on Particle Size Distributions Measured by Nanoparticle Tracking Analysis (NTA)

Purpose

Characterization of submicron protein particles continues to be challenging despite active developments in the field. NTA is a submicron particle enumeration technique, which optically tracks the light scattering signal from suspended particles undergoing Brownian motion. The submicron particle size range NTA can monitor in common protein formulations is not well established. We conducted a comprehensive investigation with several protein formulations along with corresponding placebos using NTA to determine submicron particle size distributions and shed light on potential non-particle origin of size distribution in the range of approximately 50–300 nm.

Methods

NTA and DLS are performed on polystyrene size standards as well as protein and placebo formulations.

Results

Protein formulations filtered through a 20 nm filter, with and without polysorbate-80, show NTA particle counts. As such, particle counts above 20 nm are not expected in these solutions. Several other systems including positive and negative controls were studied using NTA and DLS.

Conclusions

These apparent particles measured by NTA are not observed in DLS measurements and may not correspond to real particles. The intent of this article is to raise awareness about the need to interpret particle counts and size distribution from NTA with caution.