Fluorescent Ensemble Based on Bispyrene Fluorophore and Surfactant Assemblies: Sensing and Discriminating Proteins in Aqueous Solution

A particular bispyrene fluorophore (<b>1</b>) with two pyrene moieties covalently linked via a hydrophilic spacer was synthesized. Fluorescence measurements reveal that the fluorescence emission of <b>1</b> could be well modulated by a cationic surfactant, dodecyltrimethylammonium bromide (DTAB). Protein sensing studies illustrate that the selected ensemble based on <b>1</b>/DTAB assemblies exhibits ratiometric responses to nonmetalloproteins and turn-off responses to metalloproteins, which can be used to differentiate the two types of proteins. Moreover, negatively charged nonmetalloproteins can be discriminated from the positively charged ones according to the difference in ratiometric responses. Fluorescence sensing studies with control bispyrenes indicate that the polarity of the spacer connecting two pyrene moieties plays an important role in locating bispyrene fluorophore in DTAB assemblies, which further influences its sensing behaviors to noncovalent interacting proteins. This study sheds light on the influence of the probe structure on the sensing performance of a fluorescent ensemble based on probe and surfactant assemblies

Detection and Identification of Cu²⁺ and Hg²⁺ Based on the Cross-reactive Fluorescence Responses of a Dansyl-Functionalized Film in Different Solvents

A dansyl-functionalized fluorescent film sensor was specially designed and prepared by assembling dansyl on a glass plate surface via a long flexible spacer containing oligo­(oxyethylene) and amine units. The chemical attachment of dansyl moieties on the surface was verified by contact angle, XPS, and fluorescence measurements. Solvent effect examination revealed that the polarity-sensitivity was retained for the surface-confined dansyl moieties. Fluorescence quenching studies in water declared that the dansyl-functionalized SAM possesses a higher sensitivity towards Hg²⁺ and Cu²⁺ than the other tested divalent metal ions including Zn²⁺, Cd²⁺, Co²⁺, and Pb²⁺. Further measurements of the fluorescence responses of the film towards Cu²⁺ and Hg²⁺ in three solvents including water, acetonitrile, and THF evidenced that the present film exhibits cross-reactive responses to these two metal ions. The combined signals from the three solvents provide a recognition pattern for both metal ions at a certain concentration and realize the identification between Hg²⁺ and Cu²⁺. Moreover, using principle component analysis, this method can be extended to identify metal ions that are hard to detect by the film sensor in water such as Co²⁺ and Ni²⁺