TURN-ON fluorescence detection of cyanide using an ensemble system consisting of a dansyl-based cationic probe and dicyanovinyl derivative

Abstract

An imidazolium-bearing dansyl-based probe (probe 1; D) and three dicynovinyl group-containing substrates with different alkyl chain length (S1, S2 and S3) were prepared. Three binary ensembles, designated DS1, DS2, and DS3, were generated for CN- detection in a buffer solution of HEPES: DMSO (2:8) (pH = 7.4) by combining these probe and substrates. Upon addition of CN-, each ensemble gave a large fluorescence emission enhancement, but showed little response to the addition of other anions, indicating the high selectivity toward CN- detection. DS1 including an octyl pendant-bearing substrate (S1) gave a high association constant (K-a,K-app = 2.38 x 10(8)M(-1)) and a low LOD (200 nM) for CN- sensing in HEPES: DMSO (2:8) (pH = 7.4). Dynamic light scattering (DLS), transmission electron microscopy (TEM) and H-1 NMR studies indicate that the substrate (S1) was associated with cationic probe 1 to form supramolecular self-assemblies following its addition reaction with a nucleophilic CN- .This assembly formation that causes the dansyl fluorophore of probe 1 to reposition from a hydrophilic water to the hydrophobic assembly interiors is likely responsible for a significant increase in the fluorescence intensity of the ensemble system. The other ensemble systems (DS2 and DS3) containing relatively short alkyl chains (pentyl and methyl, respectively) were inferior to the long alkyl chain system (DS1), indicating the importance of the alkyl chain length for highly sensitive CN- detection.