(131g) Particle Characterization in Blood Plasma Using Nanoparticle Tracking Analysis

Particles used for drug delivery must overcome many biological barriers to successfully reach their target. One of those challenges is to evade the immune system and circulate through the body until they find their intended target. Many different engineered particles have been used to improve the circulation time of particles such as by adding poly(ethylene glycol) (PEG) ligands, adjusting particle size and shape, and attaching peptides to the surface. Though some of these tactics have resulted in longer circulation times in the blood, there is still significant off site accumulation of the particles in the liver or spleen due to detection by the immune system. It is difficult to determine why off site accumulation occurs and how changes to the particle structure or surface affect it as there are very few tools available to directly study particles in blood.

Particles for drug delivery are typically characterized using dynamic light scattering (DLS). DLS works well with clean, monodisperse samples. However is does not work well to measure particles in blood as the components of blood also scatter light. Characterizing the size of the particles directly in blood plasma, however, is important to determine the extent of protein corona formation on the particles. With DLS, this is typically done by exposing particles to blood plasma followed by washing or dilution with water until DLS measurements can be done to measure the increase in particle size. By washing or diluting the particles, however, the loosely bound proteins of the soft corona are removed and the measurements do not reflect what the particle would experience in vivo. As an alternative, we have developed a method of analyzing particles in blood plasma using nanoparticle tracking analysis (NTA). By using fluorescently labeled particles, particles can be analyzed in complex solutions such as blood plasma. The size of the particle, and thus the size of the protein corona, can be measured in pure blood plasma using this method. In this work, polystyrene particles incubated in blood plasma are measured using NTA in pure blood plasma and in diluted blood plasma and the results are compared to DLS. Surface modification is done to attach PEG ligands of different molecular weights to the particles and the size of the particle is again measured in blood plasma using both DLS and NTA. Measuring the size of the particles by NTA has surprising results with protein coronas on PEGylated particles that are almost 50% of the size of the particle. A dilution study was done comparing the size of the particles measured at different plasma concentrations until the concentration was dilute enough for comparison to DLS measurements. At low plasma concentration, size results are consistent with DLS measurements, however a logarithmic trend is apparent in the particle size with plasma concentration suggesting that by washing a PEGylated particle, most of this soft corona is removed, leaving behind a surface without any protein corona. The use of this characterization method will allow for testing of engineered particles for drug delivery directly in blood plasma to determine the features that improve behavior in the blood.