Reactive oxygen species (ROS) and cellular oxidant stress have long been associated with cancer. Unfortunately, the role of HClO in tumor biology is much less clear than for other ROS. Herein, we report a BODIPY-based HClO probe (BClO) with ultrasensitivity, fast response (within 1 s), and high selectivity, in which the pyrrole group at the meso position has an "enhanced PET" effect on the BODIPY fluorophore. The detection limit is as low as 0.56 nM, which is the highest sensitivity achieved to date. BClO can be facilely synthesized by a Michael addition reaction of acryloyl chloride with 2,4-dimethylpyrrole and applied to image the basal HClO in cancer cells for the first time and the time-dependent HClO generation in MCF-7 cells stimulated by elesclomol, an effective experimental ROS-generating anticancer agent.

Mitochondrial polarity strongly influences the intracellular transportation of proteins and interactions between biomacromolecules. The first fluorescent probe capable of the ratiometric imaging of mitochondrial polarity is reported. The probe, termed BOB, has two absorption maxima (λabs = 426 and 561 nm) and two emission maxima--a strong green emission (λem = 467 nm) and a weak red emission (642 nm in methanol)--when excited at 405 nm. However, only the green emission is markedly sensitive to polarity changes, thus providing a ratiometric fluorescence response with a good linear relationship in both extensive and narrow ranges of solution polarity. BOB possesses high specificity to mitochondria (Rr =0.96) that is independent of the mitochondrial membrane potential. The mitochondrial polarity in cancer cells was found to be lower than that of normal cells by ratiometric fluorescence imaging with BOB. The difference in mitochondrial polarity might be used to distinguish cancer cells from normal cells.

The first Golgi-localized cyclooxygenase-2 (COX-2)-specific near-infrared (NIR) fluorescent probe, Niblue-C6-IMC, able to detect cancer cells, was designed. Importantly, Niblue-C6-IMC preferentially labeled the tumors in a mouse tumor model with deep tissue penetration capacity. It may be a promising molecular tool for guiding tumor resection during surgery.