Fluorescent sensing of nucleus density assists in identifying tumor cells using an AIE luminogen

•Fluorescent sensing of nucleus density of cells has been realized with an aggregation-induced emission (AIE) luminogen.•The probe used is capable of revealing the distinct differences in nucleus structures between tumor cells and normal cells.•Cancer cells in the malignant pleural effusion and the tissue sections from cancer patients can be illuminated. Nucleus density is an important factor associated with a wide variety of cell behaviors. Mapping nucleus density is essential to study its roles in fundamental biology and pathological conditions, but ideal tools are still lacking. Herein, we report a density-responsive bioprobe (MASPB) for fluorescent sensing of cell nucleus density. MASPB is a small-molecule probe with aggregation-induced emission (AIE) attribute. It can easily penetrate into the nucleus with red fluorescence, whose intensity is correlated to the nuclear condensation. Upon MASPB staining, distinct structures in nucleus between tumor cells and normal cells are clearly revealed. We demonstrated the ability of MASPB to distinguish rare tumor cells from normal cells in malignant pleural effusion samples by virtue of their different cellular distributions, which outshined traditional histochemical stain in contrast and successfully detected tumor cells from all 10 cancer patients. Moreover, the capability of MASPB for fluorescent differentiation of tumor/normal regions in various tissue specimens was also validated. The findings presented herein provide a facile and rapid tool for nucleus density mapping. This could enable a wide range of applications in the fields of basic research and clinical cancer diagnosis.