479837 Influence of Electrostatic Interactions on Particle Tracking for Microrheology Analysis

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Nur Hamideh1, Leslie M. Shor2 and Yi-Syuan Guo2, (1)University of Connecticut, Storrs, CT, (2)Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT

Influence of Electrostatic Interactions on Particle Tracking for Microrheology Analysis

Nur Hamideha, Yi-Syuan Guoa, Leslie M. Shora,b

a Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT USA

b Center for Environmental Sciences and Engineering, University of Connecticut, Storrs, CT USA

Particle-tracking microrheology can be used to measure solution viscosity in-situ with high spatial resolution. In this technique, thermally-induced Brownian motions of fluorescent nano- or micro-sized spherical particles are tracked using an optical microscope. Viscoelastic drag on the spherical particles reduces the mean squared displacement of particles based on the Stokes-Einstein relation. This technique is increasingly used in biological applications using a range of different viscoelastic solutions, tracer particles, and chamber materials and dimensions. Here we evaluate accuracy of particle-tracking microrheology measurements as a function of charge interactions between tracer particles and the sample chamber. Two kinds of fluorescent tracers were used: 0.5 μm diameter negatively-charged carboxylated polystyrene (PS) beads and 0.2 μm diameter positively-charged aminated PS beads. Experiments were performed in an experimental assembly comprised of two glass microscope slides sealed with silicone grease. Both glass surfaces were pre-treated by applying 25 μL aliquots of four different types of biological solutions (tryptic soy broth, lysogeny broth, yeast extract, and bovine serum albumin), spread with a sterile swab, and allowed to dry. Particle trajectories of 50-80 particles were quantified in 40% glycerol-water solution and 58 μg/mL exopolysaccharide (EPS) solution using a Zeiss Axio Observer.Z1 inverted microscope and 40x objective, then analyzed using Fiji ImageJ and MatLab. Deviations between viscosity measured using particle tracking microrheometry and viscosity measured using traditional bulk-scale viscometry will be presented. These results will give insights into modulation of charge interactions by biological solution surface treatment in particle tracking microrheology.


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