Ultrasmall quantum dots for fluorescent bioimaging in vivo and in vitro

Photoluminescent semiconductor quantum dots (QDs) are widely used in many branches of diagnostics and biomedicine. Using ultrasmall QDs for designing fluorescent nanoprobes increases their capacity for penetrating through cell membranes, which allows one to use them for tracking intracellular processes at the molecular level. Obtaining small-size QDs is usually impeded due to the fast kinetics of reactions of their formation and growth in a colloidal medium. We propose a method of synthesizing defectless CdSe QDs with a diameter of 1.5 nm based on the injection reaction in an organic medium, with superfast termination of the growth of QDs at the early stage of their formation. Separation of QDs by means of gel-permeation chromatography allows one to completely remove the excess of cadmium precursors not entering the reaction, which ensures the subsequent obtaining of QDs with a controllable fluorescence wavelength and high quantum yield in the process of depositing protective epitaxial shells of different compositions. The obtained ultrasmall QDs may find application in developing photoluminescent nanoprobes for visualizing intranuclear processes in cells.