Most cancer deaths are caused by recurrent or metastatic tumors. Conventional therapies target rapidly dividing tumor cells, but are unable to eradicate the highly chemoresistant tumor initiating cells (TICs), ultimately responsible for relapse and spreading of the tumors in other parts of the body. A team of researchers at the Center for Self-assembly and Complexity, within the Institute for Basic Science (IBS) developed the first fluorescent sensor to visualize TICs. Functional in lung, central nervous system, melanoma, breast, renal, ovarian, colon, and prostate cancer cell cultures, this could become a useful tool for biopsy-free post-treatment assessment and anti-TIC drug development. The study was conducted in POSTECH (Pohang, South Korea), in collaboration with the Agency for Science Technology and Research (A*STAR, Singapore), and is published in Angewandte Chemie International Edition.