Lysosome-specific sensing and imaging of pH variations in vitro and in vivo utilizing a near-infrared boron complex

As a focus issue, the study of lysosomal pH has attracted much attention, as it is closely associated with the state of lysosome which plays a vital role in endocytosis and autophagy. In order to investigate lysosomal pH, fluorescence bioimaging is one of the most widely-explored approaches. Unforturnately, it is insufficient in near-infrared (NIR) region, which could minimize photo damages of organisms and maximize tissue penetration in living systems. As a novel family of NIR dyes, hemicyanine has been selected for NIR bioimaging and biosensing owing to its excellent optical properities, easy preparation and good biocompatiability. Employing a classic rhodamine-hemicyanine hybrid, we first designed and synthesized a NIR boron complex (HCy-BIZ-BF2) with lysosome-targeting and pH-sensing properties. It is worth mentioning that after coordinated with boron fluoride, HCy-BIZ-BF2 exhibited improved photostability as well as enlarged Stokes shift, and was subsequently applied to monitoring lysosomal pH in cells stimulated with chloroquine. The further investigation of pH changes in mice illustrated that HCy-BIZ-BF2 performed well in pH detection in living organisms. Therefore, this concept of boron complex derived from hemicynaine is not just in pH detection, but conductive to promising novel NIR bioprobes and precise measurements of physiological parameters in specific physiological processes.