Light Scattering in the Nano World
Geofrey Wyatt, President, Wyatt Technology Corp. - January 20, 2016
Nanoparticles play an ever-larger role in a range of industrial and commercial products as well as in the study of molecular and particle aggregation phenomena. Advanced applications of nanotechnology have the potential to enable the precise location of cancerous tumors and prevent undesirable microbial growth and contamination in medical devices and consumer products such as textiles. But the analysis of nanoparticles can still be a highly challenging task. Whereas the physical properties of bulk materials remain constant regardless of their size, the size of nanoparticles often dictates their physical and chemical properties. It is essential, therefore, to be able to characterize nanoparticles in order to successfully commercialize them and understand their potential environmental, health and safety risks.
One significant challenge encountered in nanoparticle engineering is their sensitivity to small differences between seemingly similar particles. Slight variations in surrounding media can cause particles to aggregate, change size and react with their environment to oxidize or absorb contaminants. Understanding the time dependence of nanoparticle properties is vital for storage, environmental and health impacts, as well as for manufacturing and product stability. In addition, the regulations governing the use of Engineered Nanoparticles (ENPs) are not fully defined yet. A comprehensive approach to analysis is long overdue.
Methods for the analysis of nanoparticles have been available since the 1980s and light scattering offers one of the most versatile sets of characterization tools. The three most common variations of analytical light scattering include: multi-angle, dynamic and electrophoretic (MALS, DLS and ELS, respectively), which can all be used to characterize different properties of liquid-borne nanoparticles. Quantum dots and liposomes lend themselves particularly well to these light scattering techniques to enable the determination of size and size distributions, shape or conformation, and propensity for aggregation or flocculation.
Depending on the material, MALS and/or DLS may be used in determining nanoparticle size; the combination of sizes derived from MALS and DLS can give insight into the shape of a nanoparticle. MALS can also assess the structure of core-shell nanoparticles. Both MALS and DLS contribute to nanotechnology characterization and nowhere is this more evident than when these technologies are coupled to asymmetric-flow field-flow fractionation (A4F—a system analogous to a size exclusion chromatography separation, although this one optimized for particles) in order to assess high-resolution size and shape distributions of the particle ensembles. Recent investigations have been carried out to explore new applications of MALS to derive the size and structure distributions of a variety of nanoparticle structures using A4F-MALS.
In the environmental field, light scattering coupled to A4F has been employed successfully to characterize metallic and titanium dioxide nanoparticles that are used by scientists to trace seepage through aquifers, the accumulation of cosmetic constituents in wastewater, or leeching from food packaging into streams and rivers.
Nanomedicine covers a wide range of applications from standard drugs delivered in very small particles for enhanced bioavailability to magnetic nanoparticles used for diagnostic purposes. A4F-MALS already plays an important role in these applications since particle size determinations are a critical factor in making sure these particles go where they are supposed to and, if necessary, permeate vascular and cellular membranes. In contrast to A4F-MALS, standard sizing techniques such as TEM sample only a very small fraction of the particles that may not be representative. Light scattering techniques such as DLS or A4F-MALS sample a much larger ensemble. A4F-MALS, in particular, excels at providing well-resolved size distributions and can add additional insight as to the shape and structure information unavailable from most other analytical techniques.
The light scattering toolbox comprising MALS, DLS and ELS is an essential kit for scientists and engineers working in nanoparticle characterization. The development of reference materials for nanotechnology characterization and new studies into harnessing the power of combined analytical technologies such as AF4-MALS will undoubtedly contribute even more to the continued rapid evolution of nanotechnology in the years to come.
As published in Laboratory Equipment: Light Scattering in the Nano World