2017 F. Ross Hallett Memorial Graduate Scholarship in Biophysics

Citation: Dr. Paul Garrett

Award Presentation: Mrs. Barbara Hallett

Seminar Title: 

Atomic Force Microscopy Imaging and Particle Size Determination of Soft Phytoglycogen Nanoparticles

Abstract:

Phytoglycogen nanoparticles, extracted and purified from sweet corn, are a promising sustainable nanomaterial with many applications in the personal care, pharmaceutical and nutraceutical industries. These applications rely on the size of the nanoparticle as well as exceptional properties that emerge from its highly branched structure and unique interaction with water. We have used atomic force microscopy (AFM) imaging to resolve a large discrepancy in the nanoparticle radius measured using dynamic light scattering (DLS) and small angle neutron scattering (SANS), and have calculated the effect of hydration on the nanoparticle size. The AFM measurements are challenging because of the “stickiness” and deformability of the soft nanoparticles. By significantly reducing the interaction between the AFM tip and the “sticky” nanoparticles, we were able to obtain high quality images in both air and water. We found that the particles adsorbed onto hydrophilic surfaces are highly deformed, forming pancake-like objects. By measuring the distribution of the volume of isolated particles in air, we calculated the corresponding distribution of the average effective spherical radius of the particles. By comparing the volumes of nanoparticle aggregates measured in air and water, we determined the effect of hydration on individual nanoparticles. The values of the radius of phytoglycogen nanoparticles measured using AFM in both air and water are in excellent agreement with the value determined using SANS. The much larger particle radius determined using DLS indicates that the diffusion of the nanoparticles is significantly slower than expected. Our AFM measurements of the soft phytoglycogen nanoparticles illustrate the distinct advantages of AFM over other imaging techniques for visualizing nanoscopic objects in a liquid environment.