SIZE AND DENSITY MEASUREMENT OF CORE-SHELL SILICON NANOPARTICLES BY ANALYTICAL ULTRACENTRIFUGATION
Kanokwan Nontapot, Vinayak Rastogi, Jeffrey Fagan, and Vytas Reipa
Si nanoparticles in the size range below 5 nm have received considerable attention due to their unique size-dependent physicochemical properties.† Quantum confinement of electrons and holes in such structures makes them efficient light emitters as opposed to bulk Si and allows emission color tuning with the NP size. Multiple biomedical applications of Si NPís are motivated by the biocompatibility of the base material. However, despite the availability of multiple Si nanoparticle synthesis methods, the reproducible preparation of well-characterized Si nanoparticle remains a considerable challenge, in particular for particles smaller than 2 nm in diameter. In this study, the capabilities of analytical ultracentrifugation (AUC) in characterizing the ultra-small Si nanoparticles size and shell structure have been explored. Sedimentation coefficients were determined by numerically fitting particle absorbance profiles to a Lammís equation, measured in several solvents, covering a range of viscosity and density. These results have allowed us to solve for the particle size distribution and an effective density of the particle core. The results from AUC will be compared with particle size estimates from high resolution transmission electron microscopy, size exclusion chromatography and dynamic light scattering.