Microtech2010 2010

Electrospray –Differential Mobility Analysis: A Probe for Nanoparticle and Protein Colloidal Stability and Kinetics

D-H. Tsai, S. Guha, L.F. Pease, R.A. Zangmeister, M.J. Tarlov, M.R. Zachariah
University of Maryland and NIST, US

Keywords: nanoparticles, ion mobility, coloidal stability, protein measurement

Abstract:

Here we describe the use of Electrospray (ES)-DMA to determine nanoparticle size distribution, the nature of surface coatings, and their colloidal stability. More specifically we employ Electrospray (ES) - to extract NP’s from solution into the aerosol phase, and pass them to a Differential Mobility Analyzer (DMA). We present examples through a systematic examination of alkylthiol SAM-and DNA functionalized Au-NP’s. Formation of self-assembled monolayers (SAMs) was detected from a change in particle mobility, which could be modeled to extract the surface packing density. Since the ES-DMA system directly samples from a solution, this approach enables one to monitor temporal changes occurring in solution. In a second set of experiments we demonstrate electrospray gas phase ion-mobility analysis as a new method to investigate colloidal aggregation, and the parameters that govern it. Nanoparticle suspensions characterized by ES-DMA were able to monitor the aggregate distribution as a function of time. By sampling at various times, we determine the degree of flocculation and the flocculation rate, which we find to be inversely proportional to the ionic strength and proportional to the residence time. The results are extended to look at protein aggregation and stability. The ES-DMA offers the opportunity to probe the size and aggregate distribution of NP’s and proteins in solution, the nature and stability of molecular coatings, and their colloidal stability.
 
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