Circulating tumor cells (CTCs) served as an important biomarker for tumor 
recurrence and prediction of prognosis. However, selective capture and 
quantification of CTCs from whole blood was still full of challenge due to the 
extremely scare number of CTCs. Moreover, how to keep a high cell viability 
after capture remained to be solved. Here, we described a ratiometric 
fluorescent probe for the efficient capture and accurate determination of CTCs 
by conjugating graphitic carbon nitride quantum dots (g-CNQDs) with gold 
nanoclusters (AuNCs) and further linking with anti-EpCAM antibody to acquire the 
CTC-specific immune probe. In this probe, AuNCs protected by albumin V bovine 
played the role as the fluorophore reference and anti-EpCAM-attached g-CNQDs 
acted as both the response signal and specific recognition element for sensing 
CTCs. In the presence of CTCs, the quenched fluorescence of the immune probe at 
500 nm was recovered due to the detachment of anti-EpCAM from the probe, whereas 
the intensity at 650 nm was essentially unchanged. This strategy realized the 
highly sensitive detection of CTCs in whole blood down to one CTC. Furthermore, 
it was demonstrated that the designed probe allowed capturing living CTCs with 
minimal cell damage. The subsequent reculture of captured cells for 
proliferation revealed that after a 7 day proliferation, almost 28 MCF-7 cells 
were obtained from one target cell. The immune probe was successfully applied 
into capture and detection of CTCs from clinical cancer patients. Our data 
suggested the good potential of fluorescent probe for the clinical diagnosis of 
cancers.