New Nanoparticle Characterization Techniques by Differential Mobility Analysis

Nanoparticles are being used increasingly in new fields for new applications. Thoroughcharacterization of particle properties such as size, aggregation, and mass are key to understanding particle behavior. In this dissertation I discuss a variety of new measurement approaches using the aerosol-based technique: differential mobility analysis (DMAS). This technique consists of the combination (hyphenation) of several components, the primary being an ion mobility chamber for the spatial separation of nanoparticles. The specific aerosol source and detector used is flexible and allows for wide applicability of the technique. The applications discussed here relate to a variety of everyday scenarios. Medicinal protein particles are studied to improve the health outcomes associated with this growing class of medicine. Nanoparticle catalysts are studied to improve the activity and repeatability, analogous to how a catalytic converter is used in cars to reduce combustion emissions. Detailed size measurements are made for gold nanoparticles, a class of particles that have been used for cancer treatments and as carrier particles, for example to transport medicine to a particular location within the body. Finally, determination of nanoparticle size is studied by comparing results from different instruments, as determining size in the nanometer scale is more complicated than an analogous measurement of a macroscopic sphere (for example, measuring the length with a ruler and comparing the result to the length derived from the mass of a sphere with a known density). In the second chapter, I demonstrate protein aggregation kinetics measurements by DMAS and asymmetrical flow field flow fractionation. Thermal aggregation was conducted in traditional formulation buffers and good agreement was determined between the two techniques. These are potential alternative instruments to the gold standard, size exclusion chromatography, used by the biopharmaceutical industry. In the third chapter, I demonstrate a calibration technique for mass distribution measurements by DMAS using inductively coupled plasma mass spectrometry for detection. Determination of the total mass of a sprayed ionic standard was sufficient to calibrate measurements of monodisperse gold nanoparticles of various shapes. A disagreement was determined between the ionic standard and a polydisperse distribution of titania coated with small gold nanoparticles. A multiple charge correction was applied that significantly improved the agreement, though the issue remained. In the fourth chapter, comparison measurements are presented for monodisperse gold nanoparticles made in two operational modes of DMAS: step voltage mode and scan voltage mode. The step voltage mode remains at each voltage for a certain dwell time (on the order of 30 s), while the scan voltage mode continuously changes voltages. Good agreement was determined for the two approaches when calibrated using a nanoparticle size standard. Additionally, the scan voltage mode data were analyzed with an alternative calibration method: a direct measurement of the sheath volumetric flow rate. The data from the two scan voltage mode calibrations bracket the measurement made in step voltage mode. This agreement suggests that scan voltage mode measurements for certification of nanoparticle size standards could be used in the future if a few additional uncertainty terms are explored. In the fifth chapter, traceable measurements with quantitative uncertainty analyses are compared for a size standard. The measurement by DMAS is compared to atomic force microscopy, scanning electron microscopy, and electro-gravitational aerosol balance. The measurement by DMAS was bracketed by the other techniques, with microscopy measuring a slightly smaller size and electro-gravitational aerosol balance measuring a slightly larger size. The measurements all agreed within 3%, but some of the differences exceeded the 95% confidence intervals of the measurements. These differences may be significant if these techniques are used to develop future size standards