Determining Nanoparticle Size in Real Time by Small-Angle X-ray Scattering in a Microscale Flow System

Abstract

Precise in situ measurements are becoming more important as we seek to identify and harness the unique properties of novel nanomaterials, yet key challenges remain in determining structures with current analytical approaches. We report here an in situ multitechnique approach that permits the real-time measurement of the sizes of nanoparticles in flowing solutions. A series of ligand-stabilized Au nanoparticle standards (dCORE = 0.8−5 nm) was analyzed by simultaneous small-angle X-ray scattering (SAXS) and UV−vis spectroscopy in a microscale flow system. A specially designed observation cell provided access to both measurements at an identical location in the flow system and allowed for the correlation of SAXS and TEM analyses. Comparison of flow-based UV−vis data to those obtained ex situ provided a bridge between in situ SAXS and ex situ TEM measurements. Average core size from both techniques matched closely for each sample, while polydispersity values from SAXS measurements were smaller than those from TEM. By correlating in situ and ex situ measurements for well-defined nanoparticle standards, these experiments form the basis of a powerful approach to assess nanoparticle core size within flowing microscale systems.