Comparative studies on the absorption and fluorescence responses of hemicyanine to HSO3-, CN-, HS- and ClO.

A fluorescent probe Hcy-Im bearing an indolium-hemicyanine structure was designed and synthesized to compare its responses to four anions, namely HSO3-, CN-, HS- and ClO-. The results disclosed that Hcy-Im reacted with all these four anions in 5% DMSO-PBS buffer with different speeds and spectral changes. Hcy-Im responded to HSO3- markedly quicker than CN- and HS-, and it responded to CN- a little quicker than HS- while the response to ClO- was much slower than the other three anions. The detection limits for these four anions were calculated to be 0.15 μM, 1.32 μM, 2.07 μM and 2.29 μM, respectively. The characteristic conjugated CN+ and CC bonds in Hcy-Im were responsible for the responses towards these four anions via a Michael addition-rearrangement reaction, a 1, 2-addition reaction or an oxidation reaction. These different sensing mechanisms were verified by 1HNMR and HRMS. Thus, it could be inferred that hemicyanine-based fluorescent probe could detect HSO3- sensitively and selectively while the interference of HSO3- should not be neglected when it was used for the detection of CN-, HS- and ClO-. Moreover, as HSO3-, HS- and ClO- are anions endogenously generated in human bodies, enough attention should be paid to the presence of physiological level of these three anions in certain tissues when hemicyanine-based fluorescent probe is applied for the detection of biorelevant analytes in biological samples.