The in vivo detection of rare circulating cells using non invasive fluorescence imaging would provide a key tool to study migration of eg. tumoral or immunological cells. Fluorescence detection is however currently limited by a lack of contrast between the small emission of isolated, fast circulating cells and the strong autofluorescence background of the surrounding tissues. We present the development of near infrared emitting quantum dots (NIR-QDs) with long fluorescence lifetime for sensitive time-gated in vivo imaging of circulating cells. These QDs are composed of low toxicity ZnCuInSe/ZnS materials and made biocompatible using a novel multidentate imidazole zwitterionic block copolymer, ensuring their long term intracellular stability. Cells of interest can thus be labeled ex vivo with QDs, injected intravenously and imaged in the near infrared range. Excitation using a pulsed laser coupled to time-gated detection enables the efficient rejection of short lifetime (≈ ns) autofluorescence background and detection of long lifetime (≈ 150 ns) fluorescence from QD-labeled cells. We demonstrate efficient in vivo imaging of single fast-flowing cells, which opens opportunities for future biological studies.
 M. Tasso et al, “Sulfobetaine-Vinylimidazole block copolymers: a robust quantum dot surface chemistry expanding bioimaging’s horizons”, ACS Nano, 9(11), 2015
 S. Bouccara et al, “Time-gated cell imaging using long lifetime near-infrared-emitting quantum dots for autofluorescence rejection”, J Biomed Optc, 19(5), 2014