Preparation And Study Of Novel Rhodamine Fluorescent Probes With Their Sensing Capability Toward Mercury Ion And Cysteine

As an effective detecting method, fluorescence molecular probe works based on monitoring fluorescence spectral changes when interaction occurs between the sensing unit and specific analyte, so that the content of analyte can be indicated. As compared with the traditional analytical instruments, such as atomic absorption spectroscopy(AAS), atomic emission spectrometry(AES) and inductively coupled plasma mass spectroscopy(ICP-MS), the fluorescence molecule probe exhibit significant advantages including easily handling, fast response, higher sensitivity, superior selectivity, real-time and in situ analysis property. Therefore, this sensing method is widespread used in chemical, environmental and biological analysis. Designing and fabricating novel fluorescence probes with better performance are becoming the research hotspot in both organic chemistry and analytical chemistry. Among the fluorescent probes, rhodamine derivative fluorochromes play as star molecules for their high extinction coefficient, wide absorption band and high fluorescence quantum yield. Moreover, when encounting with specific analyte, not only obvious changes of absorption and fluorescence spectra occurs, but also accompanying distinct color changes which could enable the probe with naked-eye detection. In this text, we carried out studies focusing on the designing and synthesizing of turn on fluorescence probe upon rhodamine derivatives, the main achievements are as follows: 1. Detcting of Hg2+ by naked eye on the basis of ion-promoted hydrolytic reactionWe designed and synthesized fluorescence probe rhodamine-oxaldehyde by using rhodamine B as the host molecule. In mixed solution of C2H5OH/H2 O, the dissolved probe molecule showed colorless and no fluorescence and adsorption du to the closedspirolactam. With increasing amount of Hg2+ introduced, Hg2+-promoted irreversible hydrolysis of the isopropenyl acetate structure, and then rhodmaine B was released to the solution which induced obviously linear increasing fluorescence together with distinct color changes from colorless to pink. The other coexisting ions including alkali and alkaline earth metal ions(K+, Mg2+, and Ca2+), and some transition metal ions(Ni2+, Co2+, Fe2+, Cu2+, Zn2+, Cd2+, Ag+, Pb2+, Cr3+, and Fe3+) could hardly induce any interference. Our probe realized the high selective and sensitive for Hg2+ detection with the LOD(limit of detection) 2.7 n M. 2. Constructing fluorescence probe for detecting Hg2+ based-on the coordination processWe synthesized fluorescence probe for detecting Hg2+ by bridging rhodmaine fluorophore and terephthalaldehyde. In mixed C2H5OH/H2 O solution, the probe chelated with Hg2+ via carbonyl O and imino N atom, which induced the opening of spirolactam in rhodamine framework. Obvious color and fluorescence intensity changes were presented. The probe exhibited fast response and high selectivity with excellent stability in relative wide p H range. We further immobilized the probe molecule onto silica nanospheres to guarantee its reusability. The obtained inorganic-organic hybrid material also exhibited excellent recognition capability to Hg2+ which endowed this system with potential application in constructing multifunctional hybrid material and designing optical sensing devices. 3. Photochemical sensing of cysteine by utilizing upconversion nanoparticles as excitation sourcePure hexagonal β-Na YF4:Yb3+, Er3+ was prepared by solvothermal method with uniform size and distribution. The hydrophobic nanoparticles were transferred into aqueous media by modifying its surface with α-cyclodextrin. Then the sensing probe for cysteine(RHO) was loaded onto the surface of nanoparticles by hydrophobic interaction. Under excited by 980 nm near-infrared light source, the emission of β-Na YF4:Yb3+, Er3+ at green spectral region showed excellent overlap with the excitation spectra of Cys-RHO, a secondary excitation system was constructed based on this prerequisite. Different amount of Cys could be detected by observing the decline of green spectra and the increasing absorption intensity of ring-opened RHO. The NIR excitation light could increase tissue penetration depth, ease the damage to biological tissue and reduced the interferences caused by background fluorescence. For above reasons, the sensing platform based on upconversion would possess potential utilization in bio-assay, bioimaging and fluorescence labeling.