Fluorescence properties of riboflavin-functionalized mesoporous silica SBA-15 and riboflavin solutions in presence of different metal and organic cations

Riboflavin was covalently linked to mesoporous SBA-15 silica surface via grafting technique. Then fluorescence properties of the system obtained were analyzed in the presence of several metal and organic cations. Both quenching and strengthening of fluorescence as well as significant changes in the maximum fluorescence wavelength were observed. The results were compared with absorption and fluorescence data obtained for riboflavin water solutions.     

Uranyl Soil Extraction and Fluorescence Enhancement by Nanoporous Silica Gel: pH effects

Nanoporous silica gel was employed to extract uranyl from contaminated soil and to enhance the fluorescence intensity and lifetime. The fluorescence lifetime and intensity of uranyl ions absorbed within nanoporous silica gel was measured from pH 1?C13. The results show that the uranyl fluorescence intensity can be enhanced by approximately two orders of magnitude by the silica nanoporous matrix from pH 4?C12 with the greatest enhancement occurring from pH 4?C7. The enhanced fluorescence lifetime can be used in time-gated measurements to help minimize the influence of background environmental fluorophores.     

Turn-off Fluorescence Chemosensor for Iron with Bis(2-aminoethyl)-2-(9-fluorenyl)malonamide Functionlized SBA-15

An bis(2-aminoethyl)-2-(9-fluorenyl)malonamide as fluorophore ligand was immobilized onto mesoporous silica type SBA-15 via post synthesis grafting. The obtained material was characterized by small and wide angle X-ray diffraction, N₂ adsorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis that indicate the successful immobilization of the ligand on the surface of mesoporous silica. The sensing ability of the obtained material was studied by addition of the cations Fe³⁺, Mg²⁺, Cr³⁺, Co²⁺, Ni²⁺, Cu²⁺, Hg²⁺ and Zn²⁺ to water suspensions of the assayed solid. Of all the cations tested addition of Fe³⁺ ion to a suspension of this material resulted in the largest decrease in the fluorescence intensity. Turn-off photoluminescence of this material was remarkably observed for iron ions in comparing of the other cations. A good linearity between the fluorescence intensity of this material and the concentration of Fe³⁺ ion is constructed, which enables it as a fluorescence chemosensor for detecting the Fe³⁺ ion with a suitable detection limit of 1.35?×?10^?5. It can be introduced as a novel fluorescent sensor in aqueous solution for a lot of practical applications in chemical, environmental and biological systems.     

Interactions between imazethapyr and bovine serum albumin: Spectrofluorimetric study

The interaction between imazethapyr (IMA) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. The Stern–Volmer quenching constant (K_SV) at three temperatures was evaluated in order to determine the quenching mechanism. The dependence of fluorescence quenching on viscosity was also evaluated for this purpose. The results showed that IMA quenches the fluorescence intensity of BSA through a static quenching process. The values of the binding constant for the formed BSA–IMA complex and the number of binding sites were found to be 1.51×10⁵ M^?1 and 0.77, respectively, at room temperature. Based on the calculated thermodynamic parameters, the forces that dominate the binding process are hydrogen bonds and van der Waals forces, and the binding process is spontaneous and exothermic. The quenching of protein fluorescence by iodide ion was used to probe the accessibility of tryptophan residues in BSA and the change in accessibility induced by the presence of IMA. According to the obtained results, the BSA–IMA complex is formed in the site where the Trp-134 is located, causing it to become less exposed to the solvent.     

注射用头孢美唑钠与牛血清白蛋白相互作用的研究

荧光光谱法研究了注射用头孢美唑钠（Cefmetazole Sodium for Injection,CS）与牛血清白蛋白（BSA）的作用机制。结果表明,头孢美唑钠对BSA具有荧光猝灭作用,其猝灭方式为静态猝灭,求出了猝灭常数、结合常数及结合位点数。研究了Zn2＋对头孢美唑钠与BSA作用的影响,Zn2＋的加入使得头孢美唑钠与BSA的结合常数与结合位点数减小。     

Adsorption of firefly luciferase at interfaces studied by total internal reflection fluorescence spectroscopy

The adsorption of luciferase onto silica surfaces was studied by total internal reflection fluorescence (TIRF) spectroscopy. Two model surfaces were used: hydrophilic and hydrophobic silica. Luciferase adsorbed differently on these two surfaces. Initial kinetics of luciferase adsorption onto the hydrophilic surface showed that luciferase adsorbs over an adsorption energy barrier of 3 kT The quantum yield of luciferase fluorescence decreased at the hydrophilic silica surface, which indicated that the protein conformation was altered during adsorption. Luciferase adsorption onto the hydrophobic silica surface proceeded with a small adsorption energy barrier and the fluorescence efficiency of adsorbed protein remained unchanged after adsorption. The affinity of luciferase for luciferin was measured using quenching of luciferase fluorescence with luciferin. The binding constant of the adsorbed luciferase-luciferin complex at the hydrophilic silica surface was two orders of magnitude smaller than the respective binding constant in the solution. Adsorbed luciferase showed an absence of ATP-dependent visible luminescence, indicating that the adsorbed enzyme was not active at either of the two silica surfaces.     

山姜素与脱氧核糖核酸的相互识别研究

应用荧光光谱法及紫外-可见光谱法研究了生理条件下(pH 7.4)山姜素(ALP)与DNA分子之间的相互识别。考察了不同温度下(25,32和39 ℃),DNA对山姜素荧光猝灭情况。实验发现, DNA能猝灭山姜素的内源性荧光,随着温度的升高,荧光猝灭常数K_SV逐渐减小(K_SV分别为3.288×103, 2.923×103和2.467×103 L·mol-1),并且DNA对山姜素的猝灭速率常数K_q要大于药物小分子与生物大分子之间的最大扩散所控制的碰撞猝灭常数,得出DNA对山姜素的荧光猝灭是单一的静态猝灭过程。DNA与山姜素相互作用紫外-可见光谱显示,DNA不能使得山姜素的吸收峰发生减色效应和红移现象,而山姜素也不能使溴化乙锭-DNA体系的荧光强度及最大荧光峰位置发生变化,即山姜素不和溴化乙锭竞争与DNA的结合位点。DNA热变性实验发现,解链DNA对山姜素的荧光猝灭程度要大于正常DNA的猝灭程度,由此推断山姜素与DNA不存在嵌插作用。同时,I-离子效应和盐效应表明,山姜素与DNA之间主要以沟槽模式相结合。     

重金属Cu2+增强农药甲萘威对ctDNA作用的光谱法研究

运用荧光光谱和紫外吸收光谱研究了在Cu2 的参与下农药甲萘威与小牛胸腺DNA(ctDNA)的相互作用.实验结果表明,甲萘威可以嵌入小牛胸腺DNA的双链中形成DNA加合物,从而使甲萘威的荧光光谱发生猝灭.通过计算这种猝灭为静态猝灭.当有Cu2 的参与下,甲萘威的猝灭常数增大,结合位点数n也有很大的增加.通过对热力学函数的计算和分析,在有Cu2 参与时,金属离子可能在甲萘威分子与ctD-NA分子间起"离子架桥作用",使甲萘威分子与ctDNA分子间静电相互作用增强,故△H对△G的贡献增大.     

Silica-covered Au nanoresonators for fluorescence modulating of a graphene quantum dot

We synthesize Au@SiO2composite particles with a core-shell structure, and utilize the Au@SiO2nanoparticles to modulate the fluorescence emission of the graphene quantum dot(GQD) through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.     

Fluorescence lifetime imaging of oxygen in living cells

The usefulness of the fluorescent probe ruthenium tris(2,2′-dipyridyl) dichloride hydrate (RTDP) for the quantitative imaging of oxygen in single cells was investigated utilizing fluorescence lifetime imaging. The results indicate that the fluorescence behavior of RTDP in the presence of oxygen can be described by the Stem-Volmer equation. This shows that fluorescence quenching by oxygen is a dynamic quenching process. In addition, it was demonstrated that the fluorescence lifetime of RTDP is insensitive to pH, ion concentration, and cellular contents. This implies that a simple calibration procedure in buffers can be used to quantify oxygen concentrations within cells. First fluorescence imaging experiments on J774 macrophages show a nonuniform fluorescence intensity and a uniform fluorescence lifetime image. This indicates that the RTDP is heterogeneously partitioned throughout the cells, while the oxygen concentration is constant.     

Highly selective fluorescent chemosensor for detecting Hg(II) in water based on pyrene functionalized core–shell structured mesoporous silica

Novel pyrene functionalized mesoporous core–shell structured silica (denoted as SiO₂@mSiO₂/Py-Si) was designed and synthesized as a highly selective fluorescent chemosensor for detecting Hg²⁺ in water. The core–shell structured silica was prepared by a simple sol–gel process through coating SiO₂ nanospheres with a layer of ordered mesoporous silica. The surface of outer mesoporous silica shell was then further functionalized by the fluorescent chromophore alkoxysilane modified pyrene (Py-Si). XRD data confirmed that the hexagonal ordered mesoporous structure was preserved after functionalization. The chemosensing material successfully exhibited a remarkable “turn on” response toward Hg²⁺ over miscellaneous metal ions. A good linear response towards Hg²⁺ in the concentration range of 10^?8–10^?4 M was constructed with R²=0.9913. Most importantly, a satisfactory detection limit of 3.4×10^?9 g mL^?1 (down to ppb level) was obtained, which is 100 times lower than our previous report of covalently grafted Py-OH to the bulk mesoporous silica SBA-15. These results indicated that SiO₂@mSiO₂/Py-Si can be used as a highly selective and sensitive fluorescence sensor for Hg²⁺.     

Effect of Polystyrene Microsphere Surface to Fluorescence Lifetime Under Two-Photon Excitation

Molecular assays such as immunoassays are often performed using solid carriers and fluorescent labels. In such an assay format a question can be raised on how much the fluorescence of the label is influenced by the bio-affinity binding events and the solid carrier surface. Since changes in fluorescence intensity as labels bind to surfaces are notoriously difficult to quantify other approaches are preferred. A good indicator, independent of the fluorescence intensity of the label, is the fluorescence lifetime of the marker fluorophore. Changes in fluorescence lifetime reliably indicate the presence of dynamic quenching, energy transfer or other de-excitation processes. A microsphere based assay system is studied under two-photon excitation. Changes in fluorescence lifetime are studied as labeled protein conjugates bind on microsphere surfaces – both direct on the surface and with a few nanometer distance from the surface. Fluorescence signal is measured from individual polystyrene microspheres and the fluorescence lifetime histogram is simultaneously recorded. The results indicate that self-quenching and quenching by the polystyrene surface are both present in such a system. However, the effect of the surface can be avoided by increasing the distance between the surface and the label. Typical distances achieved by a standard sandwich type of assay, are already sufficient to overcome the surface induced quenching in fluorescence detection.     

Elucidation of Selectivity for Uranyl Ions with an ICT Organosilane-Modified Fluorescent Receptor

A fluorescent receptor, isocyanatopropyl trimethoxysilane grafted 9-amino acridine (AcI), was synthesized and characterized by elemental analysis, FTIR and NMR spectroscopy. Photophysical properties and pH-dependent fluorescence behavior of AcI were investigated and its complex stoichiometry with uranyl ion was elucidated. Change in fluorescence emission of AcI with pH of the solution was observed and pKa value was determined by using integrated emission intensity versus pH. It was found that AcI exhibited fluorescence enhancement, which can be attributed to an internal charge transfer (ICT) mechanism, upon titration with uranyl ions in mixture of ethanol-buffer solution while the fluorescence emission of AcI was not affected by addition of other divalent transition metal ions except mercury (II) ions. On the other hand, the both fluorescence and UV-vis titration measurements revealed unique selectivity for uranyl ions over the interfering mercury (II) ions. The spectrofluorometric titration clarified that uranyl interacted with AcI to form AcI ₂(UO ₂ ^2?+ )₃ (2:3) complex structure with an apparent association constant of K?=?7.41?×?10⁶ M^?2/3. The interference effect of some cations on fluorescence enhancement exhibited by complex was also tested.     

Magnetic nanocomposite spinel and FeCo core-shell and mesoporous systems

The fabrication of condensed silica and mesoporous silica coated spinel CoFe₂O₄ and FeCo alloy magnetic nanocomposites are reported. The encapsulation of well-defined 5 nm thick uniform silica layer on CoFe₂O₄ magnetic nanoparticles was performed. The formation of mesopores in the shell was a consequence of removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the mesoporous silica. The mesoporous silica shells leads to a larger coercivity than that of pure CoFe₂O₄ magnetic nanoparticles due to the decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated by condensed and mesoporous silica. The condensed silica can protect the reactive FeCo alloy from oxidation up to 300 °C. However, saturation magnetization of FeCo nanoparticles coated by silica after 400 °C annealing is dramatically decreased due to the oxidation of the FeCo core. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product could be used in the field of biomedical applications.     

Synthesis and spectroscopic characterization of Kiton Red-620 dye doped silica gel rods

The work was carried out to achieve two different but interdependent objectives; one to synthesis a transparent silica matrix with enough strength and thermal stability, by sol–gel technique, to host an organic dye molecule without quenching its fluorescence and two to find the probability if the said material is suitable for the construction of solid state dye lasers. Crack-free transparent silica gel rods with good mechanical strength, thermal stability and dimensions were successfully synthesized by sol–gel techniques. The rods were doped with Kiton Red-620 dye in different concentration separately. Effect of various synthesis parameters like time, temperature and aging condition was extensively studied to obtain crack-free silica rods doped with dye. Optical properties of prepared rods were studied by FTIR, UV/VIS–NIR and fluorescence spectroscopy. It is observed that Kiton Red-620 dye doped silica gel rods show good fluorescence with sharp peaks in the visible range. Their UV–VIS spectrum indicates the absorption in visible range. Thermal stability of rods were studied by DSC/TGA methods. Eventually it is found that these dye doped silica gel materials explore the possibility for new solid-state dye laser materials.     

壳聚糖包覆的CdTe量子点荧光猝灭法测定吉米沙星

以壳聚糖包覆的CdTe量子点为荧光探针,基于荧光猝灭法建立了吉米沙星定量测定方法。结果表明,体系的荧光强度与吉米沙星浓度在3.46×10-9～3.46×10-7 g.L-1范围内呈良好的线性关系(r=0.999 2),线性回归方程为F0/F=1.063 7+0.016 7c(g.L-1)。对2.77×10-7 g.L-1吉米沙星溶液进行7次平行测定的相对标准偏差为2.7%,基于荧光猝灭法相关理论证明了该相互作用过程为静态猝灭。本方法灵敏度高,检测线性范围宽,为吉米沙星定量测定提供了简便可靠的方法。     

荧光光谱法研究2-硝基苯胺与牛血清白蛋白的相互作用

采用荧光光谱法研究了不同酸度下,2-硝基苯胺与牛血清白蛋白(BSA)间的相互作用。实验结果表明,2-硝基苯胺对BSA的猝灭机制属于静态猝灭过程。经研究得到了不同酸度和不同温度下2-硝基苯胺与BSA反应的结合常数、结合位点数。根据热力学常数确定了二者间的作用力类型为氢键和疏水作用力。同步荧光结果表明,2-二硝基苯胺的存在改变了牛血清白蛋白的分子构象。     

Static and dynamic quenching of luminescent species in polymer media

A method developed for quantitative determination of static and dynamic contributions to luminescence quenching is applied to Ru(II) complexes in polymer matrices (silica gel and polystyrene), quenched by oxygen. This method is based on both intensity and lifetime quenching experiments. The curvature of intensity Stern-Volmer plots is related to the results.     

含油岩屑固体粉末荧光的研究

通过对含油岩屑固体粉末荧光的研究,指出了在固体粉末中含油浓度在一定范围内时,其粉末荧光强度与含油的浓度成线性关系,对二者关系进行线性拟合,其相关系数R=0．9936。当样品中的含油的浓度达到一定程度时,其荧光强度保持一个恒定的值。同时,研究了固体粉末荧光猝灭现象以及猝灭机制。指出含油岩屑粉末的荧光猝灭,主要是生荧团分子之间形成络合物以及由于激发光谱和发射光谱重叠所引起的交叉弛豫所致。最后比较了固体粉末中荧光浓度猝灭与溶液中浓度猝灭。这些对于研究和开发对含油岩屑直接进行荧光检测的录井技术具有重要的指导意义。     

四苯基卟吩激发—重态衰变的“外部重原子效应”的研究

考查了在有芳烃卤代物RX(如氯苯、溴苯和碘苯)存在时,四苯基卟吩TPP的荧光衰变现象。基于荧光衰变动力学分析,发现:在RX和TPP之间生成复合物是引起重原子效应的一个基本步骤。荧光衰变的动力学参数则进一步表明:可观察的外部重原子效应主要是由于发生分子间电荷转移相互作用而引起的。