Highly selective "Off-On" fluorescent probe for histidine and its imaging in living cells.

A naphthalimide-based fluorescent probe CP has been synthesized with simple steps. It can selectively and sensitively recognize copper ions (Cu(2+)) in HEPES buffer (50mM, pH 7.2). The fluorescence intensity of CP is linearly proportional to the concentration of Cu(2+) ranging from 0-8.3μM (correlation coefficient R(2)=0.9808). The resulted complex CP@Cu can serve as a turn-on fluorescent probe for the detection of histidine and histidine rich proteins in broad pH application range. Upon the addition of histidine, the fluorescence intensity of CP@Cu exhibits a linear correlation with the concentration of histidine ranging from 0-200μM (correlation coefficient R(2)=0.9912). Moreover, CP@Cu has potential for imaging histidine in vitro experiments and has promise in real sample applications with great validity.