Elementary charge characterization of quantum dots in solution using laser scanning microscopy

The ability to measure quantum dot properties at the single particle level and in the native liquid environment forms a valuable asset for improving our understanding of quantum dot properties and for realizing improved quantum dot applications. In this work, we succeed in measuring the electrical charge of individual quantum dots in solution with precision exceeding a single elementary charge, e. This is achieved on CdSe/CdS core/shell quantum dots with sizes of 15 nm and 25 nm in a nonpolar liquid, by employing laser scanning microscopy in combination with electrophoresis. Electrophoretic mobilities derived from the amplitudes of the field-induced motion are found to be clustered around values associated with discrete charge numbers, i.e., −2e, −e, 0, e, 2e. This research offers potential for characterizing the size, electric charge, and correlations with optical properties, at the single-quantum dot level, in solution.