Colorimetric and fluorometric dual-modal probes for cyanide detection based on the doubly activated Michael acceptor and their bioimaging applications

Abstract

In this study, we synthesized CTB and CB probes based on doubly activated Michael acceptors to selectively detect cyanide (CN(-)) anions through a one-step condensation reaction of coumarinyl acrylaldehyde with the corresponding derivatives of malonyl urea (thiourea). Through the conjugated addition of CN(-) to the β-site of the Michael acceptor, both probes displayed colorimetric and fluorometric dual-modal responses that were highly reactive and selective. CTB generates an active fluorescent response, whereas CB displays a ratiometric fluorescent response. The fluorescent signal of the probes reached its maximum given only 1 CN(-) equivalent and the signal change was linearly proportional to CN(-) concentrations ranging from 0 to 5 μM with the detection limits 18 and 23 nM, respectively. The reaction rate of the probes is highly dependent on the methylene acidity of malonyl urea derivatives. Thus, the response rate of CTB to CN(-) is 1.2-fold faster than that of CB, and the response rate of CB to CN(-) is 1.2-fold faster than that of the previously examined CM. We then verified the highly reactive nature of the β-site of the probes through density functional reactivity theory calculations. In addition, according to proof-of-concept experiments, these probes may be applied to analyze CN(-) contaminated water and biomimetic samples. Finally, cell cytotoxicity and bioimaging studies revealed that the probes were cell-permeable and could be used to detect CN(-) with low cytotoxicity.

Keywords: Bioimaging; Cyanide detection; Fluorescent probe; Malonyl urea (thiourea); Michael acceptor.