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.