Facile Access to Far-Red Fluorescent Probes with Through-Space Charge-Transfer Effects for In Vivo Two-Photon Microscopy of the Mouse Cerebrovascular System.

Much effort has been devoted to the generation of fluorescent probes by synthetic approaches. In this study, we developed a facile strategy to construct far-red fluorescent probes based on through-space charge transfer within complexes of acceptors and donors and their "twist+twist" interactions. Owing to their rare two-photon excitation property, the complexes could be used for in vivo imaging of the mouse cerebrovascular system.

A new fluorescent probe for neutral to alkaline pH and imaging application in live cells.

A new pH-sensitive fluorescent probe NAP-MDA was designed and synthesized. NAP-MDA consists of 1,8-naphthalimide as fluorophore, morpholine and N,N-dimethylethylenediamine as pH-responsive groups. Due to the photoinduced electron transfer (PET) mechanism, the fluorescence of 1, 8-naphthalimide was thoroughly quenched under alkaline condition (pH > 10.0), however, NAP-MDA displayed increasing fluorescence as the rise of acidity. Notably, NAP-MDA possessed an excellent linear dependence with neutral to alkaline pH (7.2-9.4), with a pKa of 8.38. NAP-MDA had good photostability and reversibility. Meanwhile, the probe was selective to pH without interference from common reactive species, temperature and viscosity. Fluorescent testing strips were fabricated with NAP-MDA and were successfully utilized to visualize the different pH with a handhold UV lamp. Confocal fluorescence imaging in live cells demonstrated that NAP-MDA mainly fluoresced in lysosomes, and could be applied for quantification of the pH within live cells.