Ternary System Based on Fluorophore–Surfactant AssembliesCu²⁺ for Highly Sensitive and Selective Detection of Arginine in Aqueous Solution

A new cationic dansyl derivative-based (DIlSD) fluorescence probe was designed and synthesized. Its combination with anionic surfactant SDS assemblies shows enhanced fluorescence intensity and blue-shifted maximum wavelength. Its fluorescence can be slightly quenched by Cu²⁺; however, the fluorescence quenching efficiency by Cu²⁺ is highly increased upon titration of arginine (Arg). As a result, the ternary system containing the cationic fluorophore, anionic surfactant, and Cu²⁺ functions as a highly sensitive and selective sensor to Arg. The optimized sensor system displays a detection limit of 170 nM, representing the highest sensitivity to Arg in total aqueous solution by a fluorescent sensor. Control experiments reveal that the imidazolium groups in the fluorophore, the anionic surfactant, and Cu²⁺ all play important roles in the process of sensing Arg. The electrostatic interaction between the cationic fluorophore and anionic surfactants facilitates the binding of imidazolium rings with Cu²⁺, the surfactant surface-anchored Cu²⁺ is responsible for further binding of Arg, and the electrostatic interaction between anionic surfactants and positively charged amino acids accounts for the selective responses to Arg

Protein Binding-Induced Surfactant Aggregation Variation: A New Strategy of Developing Fluorescent Aqueous Sensor for Proteins

Novel strategies of developing fluorescent sensors for proteins are highly demanded. In this work, we particularly synthesized a cholesterol-derivatized pyrene probe. Its fluorescence emission is effectively tuned by the aggregation state of a cationic surfactant dodecyltrimethylammonium bromide (DTAB). The used probe/DTAB assemblies exhibit highly sensitive ratiometric responses to pepsin and ovalbumin egg (o-egg) with detection limits of 4.8 and 18.9 nM, respectively. The fluorescence changes indicate the protein–surfactant interaction leads to further aggregation of DTAB assemblies. The results from Tyndall effect and dynamic light scattering verify this assumption. The responses to pepsin and o-egg are due to their strong electrostatic or hydrophobic interaction with DTAB assemblies at pH 7.4. The present noncovalent supramolecular sensor represents a novel and simple strategy for sensing proteins, which is based on the encapsulated fluorophore probing the aggregation variation of the 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⁺