Lighting up early metastases by phosphorescence imaging

Tumour metastasis is a main barrier in fully recovery of cancer, in most cases, metastasis has already occurred before the detection of cancer. Until now, the detection limit of tumour sizes is still ~1 mm in mouse models, thus, it is difficult to track tumour metastasis in the early stage by current imaging techniques and related others. Herein, we demonstrated a novel way to detect early tumour metastasis by utilizing background-negligible phosphorescence imaging at room-temperature, putting the detection limits ahead to the stage of tumour metastatic niches. Ultra-bright phosphorescence nanoparticles (NPs) with good biocompatibility and long lifetime (49 ms) were prepared by the simply enveloping process, which achieved high signal to background ratio (SBR) of 2278 ± 242 in subcutaneous imaging. This is the highest one among phosphorescent nanoparticles of organic molecules reported, partially assuring the detection of early metastases from orthotopic liver tumours to lungs with high sensitivity. Finally, the metastatic niches in lungs before the formation of secondary tumours, as confirmed by immunohistochemistry, which appeared after tumour implantation in liver for three days, can be detected by phosphorescent NPs with SBR of 62 ± 23, far ahead of other reported imaging methods under the same conditions, thus providing an efficient approach to early diagnosis of cancer.