Fingerprint Pattern Recognition Fluorescence Chemical Sensors And Arrays Controlled By Supramolecular Assemblies

Human’s life and security have been seriously threatened by environmental pollution, terrorism and food contamination for the recent decades. Surfactants can self-assemble into microheterogenous supramolecular structures and have been used to modulate the photophysical properties and sensing behaviors of fluorescent molecule sensors due to their abilities of encapsulating fluorophores. Compared to typically fluorescent chemosensors of fluorophore-spacer-receptor (F-S-R) types, fluorescent sensors based on supramolecular assemblies avoid the necessity of covalently binding the fluorophores and the ligand, where the communication between these two components can be realized in the surfactant assemblies when the recognition process occurs. The strategy of non-covalent interaction using supramolecular assemblies can not only reduce the dependence on organic synthesis, but also improve the sensitivity of sensors. Thus, supramolecular assemblies have drawn great attention for fabricating fluorescence sensors. Meanwhile, supramolecular assemblies as sensor platform also have many advantages:1) enhancing the fluorescence quantum yield;2) realizing the water detection of liposoluble fluorescence sensors;3) reducing the weak effects of hydration on sensitivity and enhancing the binding capacity of analytes and F-S-R types sensors in water environment;4) improving the sensitivity of sensors. Therefore, in view of supramolecular assemblies possessing these advantages in construction of fluorescent sensors and that they are currently scarcely used in fingerprint recognition, it is necessary to develop a fluorescent sensors or sensor arrays based on supramolecular assemblies for capability of fingerprint identification.On the basis of progress in the study of fluorescent sensors or sensor arrays based on supramolecular assemblies and the research foundation of our lab, the objectives of the present dissertation is to combine the advantages of supramolecular assemblies and pattern recognition in the sensing studying and to develop single fluorescent sensors and sensor arrays with discriminative powers.In the first part of my research work, a cationic bis-pyrene derivative was prepared and its assemblies with anionic surfactant to function as fluorescent sensor platforms for heavy metal ions in aqueous solution were evaluated. Optical spectroscopy measurements illustrated that both UV-vis absorption and fluorescence emission spectra of bis-pyrene could be well enhanced in the assemblies with the anionic surfactant, SDS. Moreover, fluorescence quenching studies revealed that the sensitivity of bis-pyrene/SDS assemblies is highly dependent on the concentration of SDS. The optimized sensor platform exhibited not only a high sensitivity towards both Cu2+and Co2+in aqueous solution with detection limits smaller than100nM but also a high selectivity towards these two metal ions over a series of divalent metal ions. The high sensitivity was demonstrated to be due to the electrostatic interaction between the metal cations and the anionic surfactants, which dramatically increases the local concentration of metal ions in the near vicinity of pyrene moieties. Moreover, the metal ion target could be identified by addition of glycine to the quenched system. Furthermore, the recovery of Cu2+-quenched fluorescence could be utilized to provide a turn-on fluorescence sensor for neutral amino acids.In the second part, we synthesized two more cationic bis-pyrene fluorophores (S2and S3) with different spacer length and combined with S1to construct a fluorescent sensor array. Fluorescent spectroscopy measurements illustrated that their sensing behaviors could be modulated by anionic surfactant sodium dodecyl sulphate (SDS). The relative spatial location of the two pyrene moieties of the encapsulated bis-pyrene fluorophore would be greatly affected and leads to multiple fluorescence variation modes. This could be due to the stronger electrostatic interaction between trivalent lanthanide ions and SDS aggregates, which produces more pronounced conformation variation of the surfactant assemblies. The three-element sensor array could provide six-signal patterns to lanthanide ions, where the fluorescence responses at both monomer and excimer wavelengths of each sensor system are combined. As a result, the present sensor array possesses great cross-reactive responses to six lanthanide ions (Eu3+, Er3+, Nd3+, La3+, Ho3+and Pr3+) and the discrimination among these Ln3+can be achieved by PCA.