Mercury Ion Fluorescent Molecular Sensors Based On Polyamide Receptors

Fluorescent molecular sensing has attracted much attention over the years for its manyinherent merits including high specificity and high sensitivity. This technology has beenwidely used for the real-time in situ detection of the molecular events both in the chemicaland the biological systems.In this work, the design, synthesis, and photophysical properties of nine novel polyamidereceptor based Hg²⁺ ion fluorescent molecular sensors are presented. Moreover, sensingproperties of the amphiphilic ICT sensors AS1-3 in SDS micelle are also investigated.The results indicate that polyamide receptors derived from o-hydroxyaniline or o-phenyl-enediamine could be used to specifically bind Hg²⁺ ion in aqueous solution by an amidedeprotonation mechanism. In addition, their Hg²⁺ ion binding strength and chelatingstoichiometry could be tuned with the number of the amide arms as well as the electrondonating ability of the aromatic nitrogen atoms.Structure modification of this kind of polyamide receptors is very convenient andflexible. Thus, sensors with "off-on" or two wavelength ratiometric signal could be easilydesigned to meet different applications. Comparison of the photophysical properties of thetwo regioisomeric sensors RS1-2 discloses that we should pay much attention to thefluorophore-receptor connecting fashion to get a high performance sensor molecule. SensorS3, with a detecting limit down to 2ppb, shows several favorable sensing properties, andcould be used as a highly efficient Hg²⁺ ion annunciator for drinking water.Micelle significantly modulates both the binding event and signal transformation of theamphiphilic ICT sensors AS1-3. The potential advantages are 4-folds: (1) SDS substantiallyincreases the sensitivity; (2) SDS initiates spectra features which facilitate Hg²⁺ ion analysis:the original "on-off" response of AS2 toward Hg²⁺ ion is transformed into a self-calibratedtwo-wavelength ratiometric signal; (3) thermo-reversible tuning of the dynamic detectionrange is realized; and (4) highly specific Hg²⁺ ion identification could be achieved by usingthe SDS-induced short-wavelength fingerprint emission of AS2-Hg²⁺ complex.