Photoluminescent organic-inorganic composite films layer-by-layer self-assembled from the rare-earth-containing polyoxometalate Na-9[EuW10O36] and poly(allylamine hydrochloride)

Photoluminescent organic-inorganic composite films incorporating the rare-earth-containing polyoxometalate Na-9[EuW10O36] (EW) and poly(allylamine hydrochloride) (PAH) have been prepared by the layer-by-layer self-assembly method. UV-vis spectroscopy and ellipsometry were used to follow the fabrication process of the EW/PAH composite films. The experimental results show that the deposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayer thickness of ca. 2.1 nm was determined by ellipsometry. In addition, scanning electron microscopy and atomic force microscopy images of the EW/PAH composite films indicate that the film surface is relatively uniform and smooth. The photoluminescent properties of these films were investigated by fluorescence spectroscopy.

Study on photochemical fluorescence enhancement of terbium-fleroxacin complex

The sensitized fluorescence intensity of terbium ion can be notably enhanced when the Tb3+-fleroxacin complex is exposed to 365 nm light. By the measurements of fluorescence spectra, phosphorescence spectra, fluorescence quantum yield and fluorescence lifetime of the system, it is proved that irradiation makes the complex undergo a photochemical reaction and produces a new terbium complex which is more favorable to intramolecular energy transfer. The mechanism of the photochemical fluorescence enhancement was discussed.

Self-assembled gold nanoparticles on functionalized gold (111) studied by scanning tunneling microscopy

Nanogold colloidal solutions are prepared by the reduction of HAuClO4 with sodium citrate and sodium borohydride. 4-Aminothiophenol (ATP) self-assembled monolayers (SAMs) are formed on gold(lll) surface, on which gold nanoparticles are immobilized and a sub-monolayer of the particles appears. This sub-monolayer of gold nanoparticles is characterized with scanning tunneling microscopy (STM), and a dual energy barrier tunneling model is proposed to explain the imageability of the gold nanoparticles by STM. This model can also be used to construct multiple energy barrier structure on solid/liquid interface and to evaluate the electron transport ability of some organic monolayers with the aid of electrochemical method.

Nanostructure and mechanical measurement of highly oriented lamellae of melt-drawn HDPE by scanning probe microscopy

Scanning probe microscopy was used to simultaneously determine the molecular chain structure and intrinsic mechanical properties, including anisotropic elastic modulus and friction, for lamellae of highly oriented high-density polyethylene (HDPE) obtained by the melt-drawn method. The molecular-scale image of the highly oriented lamellae by friction force microscopy (FFM) clearly shows that the molecular chains are aligned parallel to the drawing direction, and the periodicities along and perpendicular to the drawing direction are 0.26 and 0.50 nm, respectively. The results indicate that the exposed planes of the lamellae resulting from the melt-drawn method are (200), which is consistent with results of transmission electron microscopy and electron diffraction. Because of the high degree of anisotropy in the sample, coming from alignment of the molecular chains along the drawing direction, the measured friction force, F, determined by FFM is strongly dependent on the angle, theta, between the scanning direction and the chain axis. The force increases as theta is increased from 0 degrees (i.e., parallel to the chain axis) to 90 degrees (i.e., perpendicular to the chain axis). The structural anisotropy was also found to strongly influence the measurements of the transverse chain modulus of the polymer by the nanoindentation technique. The measured value of 13.8 GPa with transverse modulus was larger than the value 4.3 GPa determined by wide-angle X-ray diffraction, which we attributed to anisotropic deformation of the lamellae during nanoindentation measurements that was not accounted for by the elastic treatment we adopted from Oliver and Pharr. The present approach using scanning probe microscopy has the advantage that direct correlations between the nanostructure, nanotribology, and nanomechanical properties of oriented samples can be determined simultaneously and simply.

The LB films of dansyl chloride labeled octadecylamine and its fluorescence lifetime

Octadecylamine was derivatized with dansyl chloride (5-dimethylaminonaphthalene-1-sulfonyl chloride) In order to simplify and understand the LB films of fluorescent probe labeling proteins. its monolayer and multilayers in the absence and presence of stearic acid were deposited by LB technique. Fluorescence spectra and lifetimes of the fluorescent products were studied to elucidate the microenvironment of molecules in the LB films.

Fluorescence analysis of phospholipase A(2) isolated from Chinese agkistrodon blomhoffii Ussurensis venom

The general and synchronous spectra of phospholipase A(2) (PLA(2)) isolated from Chinese agkistrodon blomhoffii Ussurensis snake venom were studied. The chromophores of PLA(2) were mainly contributed by tyrosine and tryptophane residues when the intervals between the excitation wavelength and the emssion waveleagth (Delta lambda) were 20nm and 75nm, respectively. The pH of buffers could change the fluorescence intensities of PLA(2) by changing the charge distribution of its amino acid chain. Ca2+ can not only increase the emission fluorescence intensity of PLA(2) but also improve the reaction rate of PLA(2) with its corresponding substrate DPPC.

Luminescent properties of organic-inorganic hybrid monoliths containing rare-earth complexes

Transparent organic-inorganic hybrid monoliths containing rare-earth complexes (Eu(TTA)(3)Phen, Tb(Sal)(3)) were prepared via the sol-gel technique. It could be observed by transmission electron microscopy that the fluorescent particles are distributed in the matrix at the microscopic level. The matrix is composed of organic-inorganic semiinterpenetrating networks, i.e., PHEMA-SiO2 system. The fluorescence emission spectra of samples are similar to those from corresponding powdered Eu(III) and Tb(III) complexes, and the half-widths of the strongest bands are less than 10 nm, which indicates that the monolith exhibits high fluorescence intensity and color purity. Furthermore, the fluorescence spectra exhibit no obvious change with decreasing nanoparticle size of the rare-earth complex. The fluorescence lifetimes of samples are longer than pure Eu(III), Tb(III) complexes, respectively. Samples irradiated with an UV lamp (365 nm) are still transparent but become bright red and green in color due to fluorescence of Eu(III) and Tb(III) complexes. (C) 2000 Elsevier Science B.V. All rights reserved.

Laser-time-resolved fluorescence spectroscopy in immunoassays

This paper described a laser-excited time-resolved fluoroimmunoassay set. It made lanthanide ion to couple the anhydrde of diethylenetriaminepentaacetic acid (DTPAA) for labeling antibodies. The experiment used polystyrene tap coated with HCV antigen as the solid phase and a chelate of the rare earth metal europium as fluorescent label. A nitrogen laser beam was used to excite the Eu3+ chelates and after 60 ys delay time,the emission fluorescence was measured. Background fluorescence of short lifetimes caused by serum components and Raman scattering can be eliminated by set the delay rime. In the system condition, fluorescent spectra and fluorescent lifetimes of Eu3+ beta-naphthoyltrifluroacetone (NTA) chelates were measured. The fluorescent lifetime value is 650 mu s. The maximum emssion wavelength is 613 nm. The linear range of europium ion concentration is 1 x 10(-7)- 1 x 10(-11) g.mL(-1) and the detection limit is 1 x 10(-13) g.mL(-1). The relative standard deviation of determination ( n = 12) for samples at 0.01 ng.mL(-1) magnitude is 6.4%. Laser-TRFIA was also found to be suitable for diagnosis of HCV. The sensitvity and specificity were comparable to enzyme immunoassay. The result was obtained with laser-TRFIA for 29 human correlated well with enzyme immunoassay.

Synthesis and properties of three novel series of monomers containing para-methoxyazobenzene as the mesogenic group

Three novel series of monomers, namely n-1-bromo-[4-(4-methoxyphenylazo)phenyloxy]-alkanes (Bn, n = 3, 6, 10), n-[4-(4-methoxyphenylazo) phenyloxy]alkyloxy-4-methoxybenzene (Cn, n = 3, 6, 10) and n-[4-(4-methoxyphenylazo)phenyloxyl]alkyloxy-[4-methoxy-2,5-bis-(chloromethyl)] benzene (Dn, n = 3, 6, 10) were synthesized and characterized with FTIR, H-1 NMR, UV-visible and fluorescence spectroscopy. Their thermal behaviour was studied by different scanning calorimetry and polarizing optical microscopy. The results show that B3, B6 and C6 exhibit monotropic nematic liquid crystalline behaviour.

Self-assembled monolayer of polyoxometalate on gold surfaces: Quartz crystal microbalance, electrochemistry, and in-situ scanning tunneling microscopy study

A new kind of inorganic self-assembled monolayer (SAM) was prepared by spontaneous adsorption of polyoxometalate anion, AsMo11VO404-, onto a gold surface from acidic aqueous solution. The adsorption process, structure, and electrochemical properties of the AsMo11VO404- SAM were investigated by quartz crystal microbalance (QCM), electrochemistry, and scanning tunneling microscopy (STM). The QCM data suggested that the self-assembling process could be described in terms of the Langmuir adsorption model, providing the value of the free energy of adsorption at -20 KJ mol(-1). The maximum surface coverage of the AsMo11VO404- SAM on gold surface was determined from the QCM data to be 1.7 x 10(-10) mol cm(-2), corresponding to a close-packed monolayer of AsMo11VO404- anion. The analysis of the voltammograms of the AsMo11VO404- SAM on gold electrode showed three pairs of reversible peaks with an equal surface coverage of 1.78 x 10(-10) mol cm(-2) for each of the peaks, and the value was agreed well with the QCM data. In-situ STM image demonstrated that the AsMo11VO404- SAM was very uniform and no aggregates or multilayer could be observed. Furthermore, the high-resolution STM images revealed that the AsMo11VO404- SAM on Au(lll) surface was composed of square unit cells with a lattice space of 10-11 Angstrom at +0.7 V (vs Ag\AgCl). The value was quite close to the diameter of AsMo11VO404- anion obtained from X-ray crystallographic study. The surface coverage of the AsMo11VO404- SAM on gold electrode estimated from the STM image was around 1.8 x 10(-10) mol cm(-2), which was consistent with the QCM and electrochemical results.

Protein structural characterization by scanning tunneling microscopy with electrochemistry

The structure characterization of proteins or enzymes by STM on electrochemically prepared HOPG surface studied in this laboratory is reviewed. The serial structures of Hb were observed. The differences between the denaturation and inactivation of HRP were investigated by in situ and ex situ STM. The structural variation of Hb in an organic solvent was imaged while protein denaturation was easily observed in a polar solvent.

Fabrication of nanometer-sized electrodes and tips for scanning electrochemical microscopy

A novel method for fabrication of nanometer-sized electrodes and tips suitable for scanning electrochemical microscopy (SECM) is reported. A fine etched Pt wire is coated with polyimide, which was produced by polymerization on the Pt surface initiated by heat. This method can prepare electrodes with effective radii varying from a few to hundreds of nanometers. Scanning electron microscopy, cyclic voltammetry, and SECM were used to characterize these electrodes. Well-defined steady-state voltammograms could be obtained in aqueous or in 1,2-dichloroethane solutions. Ibis method produced the nanoelectrodes with exposed Pit on the apex, and they can also be employed as the nanotips for SECM investigations. Different sizes of Pt nanotips made by this method were employed to evaluate the kinetics of the redox reaction of Ru(NH3)6(3+) on the surface of a large Pt electrode by SECM, and the standard rate constant kappa (o) of this system was calculated from the best fit of the SECM approach curve. This result is similar to the values obtained by analysis of the obtained voltammetric data.

Investigation of the model compounds at 4-aminobenzoic acid modified glassy carbon electrode by scanning electrochemical microscopy

In this paper, we studied the reactions of both potassium ferricyanide and hexaammineruthenium(III) chloride at a 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) by scanning electrochemical microscopy (SECM) in different pH solutions. The surface of the modified electrode has carboxyl groups, the dissociation of which are strongly dependent upon the solution pH values. The rate constant kb of the oxidation of ferrocyanide on the modified electrode can be obtained by fitting the experimental tip current-distance (I-T-d) curves with the theoretical values. The surface pK(a) of the 4-ABA modified GCE was estimated from the plot of standard rate constant k(o) versus the solution pH and is equal to 3.2, which is in good agreement with the reported result. The SECM approach curves for Ru(NH3)(6)(3+) both on the bare and the modified electrodes show similar diffusion control processes. These results can be explained by the electrostatic interactions between the modified electrode surface and the model compounds with different charges. (C) 2001 Elsevier Science BN. All rights reserved.

Study of elastic modulus and yield strength of polymer thin films using atomic force microscopy

Nanometer-scale elastic moduli and yield strengths of polycarbonate (PC) and polystyrene (PS) thin films were measured with atomic force microscopy (AFM) indentation measurements. By analysis of the AFM indentation force curves with the method by Oliver and Pharr, Young's moduli of PC and PS thin films could be obtained as 2.2 +/- 0.1 and 2.6 +/- 0.1 GPa, respectively, which agree well with the literature values. By fitting Johnson's conical spherical cavity model to the measured plastic zone sizes, we obtained yield strengths of 141.2 MPa for PC thin films and 178.7 MPa for PS thin films, which are similar to2 times the values expected from the literature. We propose that it is due to the AFM indentation being asymmetric, which was not accounted for in Johnson's model. A correction factor, epsilon, of similar to0.72 was introduced to rescale the plastic zone size, whereupon good agreement between theory and experiment was achieved.