Dendrimeric Morphology and Mechanical Modulus of Soft Phytoglycogen Nanoparticles Revealed by AFM Force Spectroscopy

Phytoglycogen is a naturally occurring glucose polymer that is produced in the form of highly branched, compact nanoparticles by sweet corn. The deformability, unique hydration and inherent safety of the particles makes them desirable for applications in personal care, nutrition and biomedicine. We have used atomic force microscopy (AFM) force spectroscopy to measure the size, morphology, and stiffness of the phytoglycogen nanoparticles in both water and air. For measurements in water, we were successful in covalently bonding isolated phytoglycogen particles to gold using an intermediate layer of 4-mercaptophenylboronic acid. We used the Quantitative Imaging mode of our JPK AFM to collect high resolution force-distance maps of a large number of individual phytoglycogen particles, which revealed the inner dendrimeric morphology of the particles at the largest applied forces and allowed us to quantify the increase in the elastic modulus in going from the outer to the inner regions of the particles. We also observed large increases in the modulus for dry particles in air, quantifying the effect of hydration on the mechanical stiffness of the particles.