Rapid and Quantitative Measurement of Single Quantum Dots in a Sheath Flow Cuvette.

Semiconducting quantum dots (QDs) are finding a wide range of biomedical applications due to their intense fluorescence brightness and long-term photostability. Here, we report precise quantification of the fluorescence intensity of single QDs on a laboratory-built high-sensitivity flow cytometer (HSFCM). The nearly uniform illumination of the particles at the intense portions of the radiation field resulted in narrowly distributed signals with high signal-to-noise ratios. By analysis of thousands of QDs individually in as little time as 1 min, intrinsic polydispersity was quickly revealed in a statistically robust manner. Applications of this technique in QD quality assessment, study of metal ion influence, and evaluation of aggregation upon biomolecule coupling are presented. Moreover, an accurate measurement of the QD particle concentration was achieved via single-particle enumeration. HSFCM is believed to provide a powerful characterization tool for QD synthesis and application development.