| Due to their unique double-sheet structure, hydroxyl groups, positively charged layer, anion exchange capacities, layered double hydroxides (LDHs) can be modified by organic compounds containing functional groups on the layer surface, thereby preparing the functionalized LDHs. LDHs have good biocompatibility and easy degradation, which show a good application prospect in the field of biology and medicine. But LDHs are lack of targeting function. The idea of the paper is that LDHs are connected with various biological target compounds through the surface modification of the LDHs layer to lay the foundation for their application in biological imaging. The study on the surface modification of LDHs has important significance in the theoretical research and the practical application. This paper contains two parts:(1) Surface modification of Zn-Al-CO3-LDH by folic acid (FA). The Zn-Al-CO3-LDH was synthesized by co-precipitation method. A series of intercalated LDHs products and adsorption products were prepared by assemble of Zn-Al-CO3-LDH and organic fluorescent molecules 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS). The products with good fluorescence properties were silylated by (3-Aminopropyl)-trimethoxysilane (APTS) to form peptide bond with FA. In order to prepare for LDHs functional materials with targeting tumor cell used in vivo bio-imaging, FA molecules functioned with targeting tumor cells were indirectly connected to the plate surface. The structures of products were characterized by XRD, FTIR, TEM, NMR. The fluorescence properties of products were studied by fluorescence spectra. The results suggested that we can not successfully prepare for LDHs functional materials with targeting tumor cell used in vivo bio-imaging by the synthesis method, however, the prepared product can identify FA effectively, which can lay the groundwork for the next part of the study.(2) The study on the identification of Zn-Al-CO3-LDH surface-modified by ANTS to FA. The Zn-Al-CO3-LDH was also synthesized by co-precipitation method. The surface-modified product was prepared by assemble of Zn-Al-CO3-LDH and ANTS. It was found that the prepared product Zn-Al-CO3-LDH-ANTS can identify FA effectively, so it was chosen as a novel fluorescent nanosensor for detecting FA in aqueous media. Then the paper systematically investigated the structure stability and the influence factors of Zn-Al-CO3-LDH-ANTS, such as concentration, pH and some interfering substances (sugars organic compounds and metal ions). The results suggested that the fluorescent nanosensor had good structure stability. The fluorescence quenching method was using for determination of FA. A linear relationship between the fluorescence intensity of Zn-Al-CO3-LDH-ANTS and the concentration of FA in the rage of 10.0 to 100.0μmol/L was obtained, with the following linear regression equation:F0-F=38.52+4.230[FA] (μmol/L), R2= 0.9952. The limit of detection was found to be 1.9 μmol/L, which suggested that the fluorescent nanosensor had higher sensitivity. Addtionally, the tolerable concentration ratios of coexisting substances was glucose, fructose, sucrose, K+, over 100 fold for Mg2+,40 fold for Ca2+, Co2+, Ni2+,10 fold for Cu2+,2 fold for Fe3+, there was no interference was observed. The results suggested that the fluorescent nanosensor had higher selectivity. The possible sensing mechanism was proposed by the XPS analysis and theoretical calculations, which called ligand exchange mechanism that the coordination interaction of FA towards Zn2+ of Zn-Al-CO3-LDH was much stronger than that of ANTS, the FA substitution for ANTS resulted in ANTS losing from Zn-Al-CO3-LDH matrix into solution and fluorescence quenching of Zn-Al-CO3-LDH-ANTS.In summary, LDHs can effectively be surface-modified by organic fluorescent dye ANTS.Through the interaction between subject and object, the surface modification can improve the fluorescence performance and structure stability of object. LDHs can also effectively be surface-modified by biological molecule FA functioned with targeting tumor cells to prepare the functionalized LDHs materials. But the experimental conditions remained to be further studied. In addition, it was found that that the Zn-Al-CO3-LDH surface-modified by ANTS can identify FA effectively, so it can be used as a novel fluorescent nanosensor for detecting FA in aqueous media. These results have very important significance for the development of bio-imaging technology and fluorescent nanosensor. |
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