Photophysical Properties of Some Fluorescent Dyes in SDS Micellar Solutions.

Photophysical properties of fluorescent dyes such as Safranin T, Acridine Orange, Pyronin B and Pyronin Y in SDS micelles were examined by using spectroscopic techniques. Firstly, spherical micelles in deionized water were prepared with Sodium Dodecyl Sulfate (SDS) surfactants and they were transformed into their layered structures (lamellar micelles) by the aid of NaCl (sodium chloride). SEM studies confirmed the transformation of SDS micelles from the spherical structures to the lamellar structures. Secondly, absorption and fluorescence characteristics of the dyes in deionized water and the SDS micelles aqueous solutions were characterized in the presence of various NaCl concentrations at above the critical micelle concentration (CMC). Moreover, the photophysical properties of the dyes in various media were discussed by fluorescence quantum yield and fluorescence lifetime data. The micellar structures called a mimetic membrane system changed the photophysical properties of the dyes compared to those in deionized water.

Merocyanine 540 adsorbed on polyethylenimine-functionalized graphene oxide nanocomposites as a turn-on fluorescent sensor for bovine serum albumin.

Graphene oxide (GO)-based fluorescence sensors are attractive and versatile tools for various sensing applications. Herein, we report the photophysical properties of merocyanine 540 (MC540) in an aqueous dispersion including graphene oxide (GO) and GO chemically functionalized with branched polyethylenimine (PEI), and the application of a novel designed MC540/PEI-GO system for BSA (bovine serum albumin) detection. Initially, the negatively charged GO surface was modified using PEI to form high positively charged PEI-GO nanocomposites via the amine groups of PEI. Later, to form MC540/PEI-GO system, MC540 molecules were assembled on PEI-GO nanocomposites having an attractive surface for negatively charged functional materials. The interaction of MC540 molecules with PEI-GO nanocomposites in aqueous dispersion led to a change in the photophysical properties of the dye. The variations in the photophysical properties of MC540 were spectroscopically characterized and explained. It was determined that the interaction of MC540 with GO sheets and PEI-GO nanocomposites strongly quenched the fluorescence of the dye. However, the quenching effect of the PEI-GO nanocomposites on the fluorescence of MC540 was specifically prevented by the addition of BSA, in which the fluorescence of MC540 was nearly recovered. By using the PEI-GO nanocomposites-based fluorescence platform, BSA has been detected with a LOD (limit of detection) of 7.45 nM, which is one of the best applications among BSA sensors to date. The designed sensor system was easily applied for the detection of BSA in commonly used biological media and clinical injectable fluids. Consequently, we suggest a simple, fast, sensitive and selective BSA sensor designed by assembling MC540 molecules on PEI-GO nanocomposites.

The investigation of the electrical properties of Fe3O4/n-Si heterojunctions in a wide temperature range.

Monodisperse 8nm Fe3O4 nanoparticles (NPs) were synthesized by the thermal decomposition of iron(III) acetylacetonate in oleylamine and then were deposited onto n-type silicon wafer having the Al ohmic contact. Next, the morphology of the Fe3O4 NPs were characterized by using TEM and XRD. The optical properties of Fe3O4 NPs film was studied by UV-Vis spectroscopoy and its band gap was calculated to be 2.16eV. Au circle contacts with 7.85×10(-3)cm(2) area were provided on the Fe3O4 film via evaporation at 10(-5)Torr and the Au/Fe3O4 NPs/n-Si/Al heterojunction device were fabricated. The temperature-dependent junction parameters of Au/Fe3O4/n-Si/Al device including ideality factor, barrier height and series resistance were calculated by using the I-V characteristics in a wide temperature range of 40-300K. The results revealed that the ideality factor and series resistance increased by the decreasing temperature while the barrier height decreases. The Richardson constant of Au/Fe3O4/n-Si/Al device was calculated to be 2.17A/K(2)cm(2) from the I-V characteristics. The temperature dependence of Au/Fe3O4/n-Si/Al heterojunction device showed a double Gaussian distribution, which is caused by the inhomogeneities characteristics of Fe3O4/n-Si heterojunction.

From Dark to Light to Fluorescence Resonance Energy Transfer (FRET): Polarity-Sensitive Aggregation-Induced Emission (AIE)-Active Tetraphenylethene-Fused BODIPY Dyes with a Very Large Pseudo-Stokes Shift.

The work presented herein is devoted to the fabrication of large Stokes shift dyes in both organic and aqueous media by combining dark resonance energy transfer (DRET) and fluorescence resonance energy transfer (FRET) in one donor-acceptor system. In this respect, a series of donor-acceptor architectures of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes substituted by one, two, or three tetraphenylethene (TPE) luminogens were designed and synthesised. The photophysical properties of these three chromophore systems were studied to provide insight into the nature of donor-acceptor interactions in both THF and aqueous media. Because the generation of emissive TPE donor(s) is strongly polarity dependent, due to its aggregation-induced emission (AIE) feature, one might expect the formation of appreciable fluorescence emission intensity with a very large pseudo-Stokes shift in aqueous media when considering FRET process. Interestingly, similar results were also recorded in THF for the chromophore systems, although the TPE fragment(s) of the dyes are non-emissive. The explanation for this photophysical behaviour lies in the DRET. This is the first report on combining two energy-transfer processes, namely, FRET and DRET, in one polarity-sensitive donor-acceptor pair system. The accuracy of the dark-emissive donor property of the TPE luminogen is also presented for the first time as a new feature for AIE phenomena.

Rhodamine 101-graphene oxide composites in aqueous solution: the fluorescence quenching process of rhodamine 101.

The interaction of rhodamine 101 (Rh101) with graphene oxide (GO) in aqueous dispersion was examined using advanced spectroscopic techniques. Rh101-GO composites in water were easily prepared by mixing an aqueous solution of both components since GO sheets interacted with the cationic dyes via π-π and electrostatic cooperative interactions. In the composites, the fluorescence of Rh101, which was a well-known laser dye with a high fluorescence quantum yield, could be efficiently quenched by GO. The quenching mechanism of Rh101 by GO sheets was evaluated by the Stern-Volmer (SV) equation and the time-resolved fluorescence studies. The results revealed that the fluorescence quenching of Rh101 by GO in the aqueous dispersion is due to the static quenching mechanism. The formation of the Rh101-GO composites at various pH values was spectroscopically monitored, and the spectroscopic results revealed that the composites were formed at the pH values studied except in the strong acidic media (pH ≈ 2). The interaction of Rh101 with GO in aqueous solution was spectroscopically followed in the presence of SDS (sodium dodecyl sulphate) at the surfactant concentrations above and below the CMC (critical micelle concentration). The fluorescence studies revealed that the fluorescence of Rh101 in the aqueous solution remarkably increased at the surfactant concentration forming the micelle of SDS.

The effect of poly(vinyl alcohol) on the photophysical properties of pyronin dyes in aqueous solution: a spectroscopic study.

The photophysical properties of pyronin B (PyB) and pyronin Y (PyY) in water and poly(vinyl alcohol) (PVA) aqueous solutions were studied by using absorption, steady-state fluorescence and time-resolved fluorescence spectroscopy techniques at room temperature. The spectroscopic and photophysical properties of pyronin dyes in the concentrated PVA aqueous solution were different than those found in water. The aggregation of the pyronin dyes in the concentrated PVA aqueous solution was prevented with ease while the dye aggregation was generally formed in water with high dye concentration. The decrease in the aggregation tendency of pyronin dyes in the concentrated PVA aqueous solution caused an increase in radiative transitions. The addition of PVA into the aqueous solution induced the enhancement in the fluorescence intensity of the dyes compared to those in water. As a result, the quantum yields of the dyes were improved by the addition of PVA at high loading. The time-resolved fluorescence study revealed that the fluorescence decay of dyes in all solutions were found to be single-exponential and the fluorescence lifetime of pyronin dyes in the concentrated PVA aqueous solution were also higher than those found in water.

Promotion by phosphate of Fe(III)- and Cu(II)-catalyzed autoxidation of fructose.

Although the oxidative destruction of glucose and fructose has been studied by several investigators over the past century, the mechanism by which phosphate promotes these oxidation reactions is not known. A wide range of oxidation products have been used to monitor the oxidation of sugars and free radicals have been shown to be involved. The influence of phosphate concentration on the rate of production of free radicals and several sugar oxidation products has been studied. It was found that fructose is much more susceptible to autoxidation than glucose, galactose, or sucrose. The promotion of sugar oxidation by phosphate was found to be iron dependent. Addition of the iron chelators, diethylenetriaminepentaacetic acid (DTPA) and desferrioxamine completely suppressed the oxidation reactions, even at high concentrations of phosphate. Formaldehyde was positively identified as a product of fructose oxidation by HPLC analysis of its acetylacetone adduct. A mechanism is proposed in which phosphate cleaves the oxo bridges of the iron(III)-fructose complex, based on UV spectral analysis and magnetic susceptibility measurements, and thereby catalyzes the autoxidation of fructose.