Time-Gated Imaging on Live Cancer Cells Using Silicon Quantum Dot Nanoparticles with Long-Lived Fluorescence

In this work we demonstrate time-gated confocal fluorescence imaging on live cancer cells immunostained by antibody-conjugated silicon quantum dot nanoparticles (SiQD-NPs) and organic dyes, for simultaneous detection of two biological targets and removal of background autofluorescence. With almost all radiative recombinations occurring through oxide-related defect states located on the SiQD surface, the SiQD-NPs have very long photoluminescence lifetimes of about 25 μs, in contrast to the nanosecond-range lifetimes of other commonly used biological fluorophores. This drastic lifetime difference enables a time-gated imaging method here, in which the time-resolved photon distribution of each pixel of a fluorescence image is measured by using a time-correlated single-photon counting technique. Then, by integrating the photon histogram of each pixel over respective time windows, the long-lived component of the fluorescence image comprising only the fluorescence emitted from the SiQD-NPs is separated from all ...