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Speaker: Bohdan Yeroshenko 

Title: Measurement of the electrophoretic mobility fluctuation of a single nanoparticle

Abstract: Single nanoparticle experiments allow probing stochastic properties of individual particles, information that is not readily available with conventional ensemble measurements. Our experiments are based on the combination of optical tweezers and electrophoresis in alternating electric fields. At the core, it is the high-speed measurement of the displacement of a single-trapped particle in response to an external electric field. The periodic displacement of the nanoparticle due to the electric field is proportional to the particle’s electrophoretic mobility. Thorough consideration of the noise sources in our system, allowed us to develop a novel data analysis approach. Using this approach, we can separate the signal due to the fluctuations in the forced periodic motion and the other thermal noises. Furthermore, we can now estimate the probability distribution of a single nanoparticle electrophoretic mobility and its power spectral density. We have determined that the electrophoretic mobility of a single 1-micrometer silica particle undergoes significant non-gaussian low-frequency fluctuations. In this talk, I will explain the principles of the experiment, show the experimental data of electrophoretic mobility fluctuations, and discuss the possible origin of these fluctuations and their implications.