Single Nanoparticle Trapping Studies of Size Dependent Chemistry and Optical Properties

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In this project, funded by the Macromolecular, Supramolecular, and Nanochemistry Program of the Division of Chemistry, Professor Scott Anderson of the University of Utah will develop new techniques for studying single, isolated nanoparticles. The approach will measure the optical properties and surface chemical reactions of trapped nanoparticles while simultaneously allowing the particle mass-to-charge ratio to be measured with precision of one part per million, via measurement of the particle motional frequency in the trap. By also determining the absolute charge state, the absolute mass will be measured. These new capabilities will allow, for the first time, correlations between particle size, charge state, and optical and chemical properties to be studied with high precision. The techniques will initially be applied to semiconductor quantum dots, allowing measurements of spectral properties, including fluorescence lifetimes, to be correlated with particle size, composition, charge state, and the nature of the charging species. Experiments directed at extending the technique to study surface chemistry of non-fluorescent nanoparticles will also be carried out. In these experiments, two particles are trapped simultaneously, and the mass/charge ratio of the non-fluorescent particle is inferred by its effects on the motion of a co-trapped fluorescent particle. Nanoparticles in the 1-10 nanometer diameter range have electronic properties that depend strongly on size. Such particles are used extensively in applications ranging from fluorescent tags for biosensing, to heterogeneous catalysts, to nanomaterials, and in each application, the effects of electronic properties on optical or chemical properties is critical. Because nanoparticles generally are produced with significant size distributions, it is difficult to unravel size-property relationships in any detail. Professor Anderson, along with a graduate student and undergraduate student, will develop a single nanoparticle trapping approach to studying optical properties of semiconductor nanoparticles (quantum dots), with simultaneous high precision mass measurement. The techniques will be extended to metal and other nanoparticles. Prof. Anderson will continue his efforts at recruiting minority students, and will continue to host high school and undergraduate students for research that expose them to sophisticated physical and mathematical concepts.