Fig. 6. Single nanoparticle detection and size identification.

a Normalized FCS correlation functions of Alexa 647, quantum dots (QDs), plastic nanoparticles (NPs) covered with organic dyes. Corresponding hydrodynamic diameters (D_h) are depicted in top panel. Hydrodynamic diameter data of Alexa 647 is adopted from ref. ⁶⁹., that of QDs from ref. ⁷⁰, those of NPs from supplier test report. Alexa 647 molecules were excited at 1 mW laser power, whereas QDs and NPs are excited at 100 μW. b Retrieved diffusion time (τ_d) of emitters as a function of their D_h. Black line corresponds to linear fit following Stokes–Einstein diffusion law. c Brightness values of single Alexa 647 molecules and nanoparticles (CRM) retrieved from FCS correlation function analysis. Error bars denote standard deviation of FCS experiment. d Fluorescence decays of analyzed emitters. Black lines correspond to fluorescence decay fits. Owing to long lifetime of QDs, repetition rate of laser pulse emission is set to 5 MHz.