Time-Gated Luminescence Imaging for Background Free in vivo Tracking of Single Circulating Tumor Cells

Fluorescence imaging is severely limited by background and autofluorescence of tissues for in vivo detection of circulating tumor cells (CTCs). Time-gated luminescence (TGL) imaging in combination with luminescent probes that possess hundreds of microsecond emission lifetimes can be used to effectively suppress this background, which has predominantly nanosecond lifetimes. This work demonstrated the feasibility of TGL imaging using luminescent probes for in vivo real time imaging and tracking of single CTCs circulating freely in the blood vessels with higher accuracy given by substantially higher signal to background noise. The luminescent probe used in this work was a commercial Eu3+ chelate (EuC) nanospheres with super long lifetime of near 800 μs, which enabled TGL imaging to achieve background free detection with ~5 times higher signal to noise ratio (SNR) versus steady state. Phantom and in vivo mouse studies indicated that EuC labeled tumor cells moving in medium or bloodstream at the speed of 1~2 mm/s could be captured in real time.