Mesoporous Silica Based Fluorescent Molecular Imprinting Sensor Arrays: Preparation, Characterization And Application

In this dissertation an alternative route to conventional sensor arrays based on molecularly imprinted mesoporous silica is presented.We take advantage of imprinting effect to develop fluorescent imprinting sensor an'ays.A fluorescence turn-on sensor array for metal ions and a fluorescent indicator-displacement sensor array for saccharides are prepared respectively.The design,preparation and application of such fluorescent imprinting sensor arrays have been studied in detail, and are summarized as follows:(1) A simple twisted intramolecular charge transfer(TICT) chromogenic probe for rapid and selective detection of Hg²⁺ and Cu²⁺ was developed.The probe was composed of an electron-acceptor 4-fluoro moiety and an electron-donor 7-mercapto-2,1,3-benzoxadiazole species where the S together with the 1-N provided the soft binding unit.Upon Hg²⁺ and Cu²⁺ complexation,remarkable but different absorbance spectra shifts were obtained in CH₃CN-H₂O mixed buffer solution at pH 7.6,which can be easily used for naked-eye detection.The probe formed a stable 2:1 complex with Cu²⁺,and both 2:1 and 3:1 complexes with Hg²⁺.While alkali-,alkaline earth- and other heavy and transition metal(HTM) ions such as Na⁺,Mg²⁺,Mn²⁺, Co²⁺,Ni²⁺,Ag⁺,Zn²⁺,Pb²⁺ and Cd²⁺ did not cause any significant spectral changes of the probe.This finding is not only a supplement to the detecting methods for Hg²⁺ and Cu²⁺,but also adds new merits to the chemistry of 4,7-substituted 2,1,3-benzoxadiazoles.The initial purpose of this work was to develop a fluorescent molecular imprinting sensor array for mercury speciation.However,the synthesized 4-fluo-7-mercapto-2,1,3-benzoxadiazole reacted with itself under basic condition and formed a mercapto-2,1,3-benzoxadiazole derivative.It showed selective colorimetfic response toward Hg²⁺ and Cu²⁺ which made it a selective chromogenic probe for Hg²⁺ and Cu²⁺.(2) An ion imprinted mesoporous silica based fluorescence turn-on sensor array for discrimination of metal ions was developed.A novel fluorescent functional monomer containing an 8-hydroxyquinoline(8-HQ) moiety in combination with one-pot co-condensation method was employed to prepare fluorescent ion imprinted mesoporous silica.The imprinted materials for Zn²⁺ and Cd²⁺ as well as a control blank non-imprinted material(NIM) were synthesized.With the covalently anchored organic fluorophore in the inorganic mesoporous silica matrix,the binding of metal ions to the imprinting site was directly transformed into fluorescence signals.Both the imprinted materials displayed faster binding kinetics toward metal ions than NIM. Apparent binding constants(adsorption constants) for the materials with the metal ions in water were determined by a Langmuir-type analysis of the spectrofluorimetric titration data.The sensor array composed of the three materials allows discriminating the two template metal ions(Zn²⁺ and Cd²⁺) plus three non-template metal ions(Mg²⁺, Ca²⁺ and Al³⁺) at two different concentrations.This work proves that using a simple fluorescent receptor can provide a pattern based fluorescent sensing system by taking advantage of the imprinting effect.(3) A fluorescent indicator-displacement molecular imprinting sensor array based on phenylboronic acid functionalized mesoporous silica was developed for discriminating saccharides.D-Fructose imprinted material(FrulM),D-xylose imprinted material(XylIM) together with a control blank nonimprinted material (NIM) were synthesized as the elements of the imprinting sensor array. Spectrofluorimetric titrations of the three materials with eight selected saccharides were carded out and Stem-Volmer quenching constants(Ksv) of NIM,FruIM and XylIM with the eight selected saccharides were obtained to investigate the interaction of the materials with saccharides.The present approach couples molecular imprinting technique to indicator-displacement strategy with the use of one conventional saccharide receptor(phenylboronic acid) and one commercially available fluorescent dye(Alizarin Red S.,ARS) as the indicator,and allows identifying two template saccharides(D-fructose and D-xylose) plus eight non-template saccharides (D-arabinose,o-glucose,D-galactose,D-mannose,L-sorbose,D-ribose,L-rhamnose and sucrose).The principal component analysis(PCA) plot shows a clear discrimination of the ten tested saccharides at 100 mM and the first principal component possesses 94.8%of the variation.Besides,the developed saccharide imprinted sensor array is successfully applied to discriminating three brands of orange juice beverage.