Application of electrochemical impedance spectroscopy for monitoring allergen-antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (Phi = 16 nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.

Silica supported submicron SiO2@Y2SiO5 : Eu3+ and SiO2@Y2SiO5 : Ce3+/Tb3+ spherical particles with a core-shell structure: Sol-gel synthesis and characterization

X-1-y(2)SiO(5):Eu3+ and X-1-Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol-gel process, followed by surface reaction at high temperature (1000 degrees C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time-resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X-1-Y2SiO5 layers have been successfully coated on the sur- face Of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 rim: D-5(0)-F-7(2)), green (Tb3+, 542nm: D-5(4)-F-7(5)), or blue (Ce3+, 450nm: 5d-4f) luminescence, respectively. Pl, excitation, emission, and time-resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles.

Study on charge transfer reactions at multilayers of polyoxometalates clusters and poly(allylamine hydrochloride) (Grotthuss-018)

Multilayers of anionic phosphotungstic acid (PTA) clusters and positively charged protonated poly(allylamine hydrochloride) (PAH) were assembled by layer-by-layer self-assembled method on Au electrode modified by 3-mercaptopropionic acid (3-MPA). The effect of the charge of the surface of the multilayer assembly on the kinetics of the charge transfer reaction was studied by using the redox probes [Fe(CN)(6)](3-)/(4-) [Ru(NH3)(6)](2+/3+). The cyclic voltammetry experiments showed that the peak currents and peak-to-peak potential differences changed after assembling different layers on the electrode surface indicating that the charge of the surface has a significant effect on the kinetics of the studied charge transfer reactions. These reactions were studied in more detail by electrochemical impedance spectroscopy. When [Fe(CN)(6)](3-/-) was used as the redox label, multilayers that terminated with negatively charged PTA showed a high charge transfer resistance but multilayers that terminated with positively charged PAH showed lower charge transfer resistance. With [Ru(NH3)(6)](2+/3+) as the redox label, the charge transfer resistance at multilayers that terminated with positively charged PAH was much higher than at the multilayer terminated by the negatively charged PTA.

Sol-gel fabrication and photoluminescence properties of SiO2@Gd2O3 : Eu3+ core-shell particles

A uniform nanolayer of europium-doped Gd2O3 was coated on the surface of preformed submicron silica spheres by a Pechini sol-gel process. The resulted SiO2@Gd2O3:Eu3+ core-shell structured phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays. The XRD results show that the Gd2O3:Eu3+ layers start to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. The core-shell phosphors possess perfect spherical shape with narrow size distribution (average size: 640 nm) and non-agglomeration. The thickness of the Gd2O3:Eu3+ shells on the SiO2 cores can be adjusted by changing the deposition cycles (70 nm for three deposition cycles). Under short UV excitation, the obtained SiO2@Gd2O3:Eu3+ particles show a strong red emission with D-5(0)-F-7(2) (610 nm) of Eu3+ as the most prominent group.The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (similar to 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4 : Eu3+ phosphor via sol-gel process

Europium-doped nanocrystalline GdVO4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO2@Gd0.95Eu0.05VO4 core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd0.95Eu0.05VO4 layers begin to crystallize on the SiO2 spheres after annealing at 600 C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd0.95Eu0.05VO4 shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by D-5(0)-F-7(2) transition of Eu3+ (618 nm, red).

Complex aggregates of silica microspheres by the use of a polymer template

Evaporation of a droplet of silica microsphere suspension on a polystyrene and poly(methyl methacrylate) blend film with isolated holes in its surface has been exploited as a means of particles self-assembly. During the retraction of the contact line of the droplet, spontaneous dewetting combined with the strong capillary force pack the silica microspheres into the holes in the polymer surface. Complex aggregates of colloids are formed after being exposed to acetone vapor. The morphology evolution of the underlying polymer film by exposure to acetone solvent vapor is responsible for the complex aggregates of colloids formation.

Macroporous fluoropolymeric films templated by silica colloidal assembly: A possible route to super-hydrophobic surfaces

A super-hydrophobic surface was obtained on a three-dimensional (313) polyvinylidene fluoride (PVDF) macroporous film. The porous films were fabricated through self-assembled silica colloidal templates. The apparent water contact angle of the surface can be tuned from 106 degrees to 153 degrees through altering the sintering temperature and the diameter of the colloidal templates. A composite structure of micro-cavities and nanoholes on the PVDF surface was responsible for the super-hydrophobicity. The wettability of the porous surfaces was described by the use of the Cassie-Baxter model and Wenzel's equation.

Luminescence and energy transfer of organically modified silica xerogels (OMSX) doped and undoped with Eu3+ and Tb3+

Organically modified silica xerogels (OMSX) and Eu3+ (Tb3+)-doped OMSX were prepared by the reaction of (3-aminopropyl) triethoxysilane (APS) with 3-isocyanatepropyltriethoxysilane (ICPTES) followed by the subsequent hydrolysis and condensation in the presence of Eu3+ (Tb3+) via sol-gel method, which were characterized by FT-IR, XRD, fluorescence excitation and emission spectra. The as-formed OMSX shows a strong blue emission with the maximum excitation and emission wavelength at 351 and 420 nm, respectively. Due to the spectral overlap between the emission band of OMSX and f-f absorption lines of Eu3+ and Tb3+ in the UV-blue region, an energy transfer was observed from OMSX host to Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. Excitation at 350-360 nm resulted in a very weak emission around 420 nm from OMSX host and strong emission of Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. The emission spectra of Eu3+ and Tb3+ consist of D-5(0)-F-7(J) (J = 0, 1, 2, 3, 4) and D-5(4)-F-7(J) (J = 6, 5, 4, 3), respectively. Furthermore, the predicted structure of OMSX/Eu3+ and OMSX/Tb3+ is presented.

Patterning and optical properties rhodamine B-doped organic-inorganic silica films fabricated by sol-gel soft lithography

Rhodamine B (RB)-doped organic-inorganic silica films and their patterning were fabricated by a sol-gel process combined with a soft lithography. The resulted film samples were characterized by atomic force microscope (AFM), optical microscope and UV/Vis absorption and photoluminescence excitation and emission spectra. The effects of the concentration of the RB dye and heat treatment temperature on the optical properties of the hybrid silica films have been studied. Four kinds of patterning structures with film line widths of 5, 10, 20 and 50 mum have been obtained by micromolding in capillaries by a soft lithography technique. The RB-doped hybrid silica films present a red color, with an excitation and emission bands around 564 and 585 mum, respectively. With increasing the RB concentration, the emission intensity of the RB-doped hybrid silica films increases and the emission maximum presents a red shift. The emission intensity of the films decreases with increasing the heat treatment temperatures.

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

Facilitated ion transfer reactions of 20 amino acids with di.benzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, Ile, Phe, Trp, Met, Ala, Gly, Cys, Gln (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (beta(0)), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attributed to the vicinal effect arising from steric hindrance introduced by their side group and the steric bulk effect by lipophilic stabilization.

Electrochemical recognition of alkali metal ions at the micro-water 1,2-dichloroethane interface using a calix[4]arene derivative

In this paper, a calix[4]arene derivative, 5,11,17,23-butyl-25,26,27,28-tetra-(ethanoxycarbonyl)-methoxy-calix[4]arene (L), is investigated as a host to recognize alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) at the interface between two immiscible electrolyte solutions (ITIES). Well-defined cyclic voltammograms are obtained at the micro- and nano-water \ 1,2-dichloroethane (W \ DCE) interfaces supported at micro- and nano-pipets.

Electrochemiluminescence sensor using tris(2,2 '-bipyridyl)ruthenium(II) immobilized in Eastman-AQ55D-silica composite thin-films

An electrochemiluminescence (ECL) sensor with good long-term stability and fast response time has been developed. The sensor was based on the immobilization of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) into the Eastman-AQ55D-silica composite thin films on a glassy carbon electrode. The ECL and electrochemistry of Ru(bpy)(3)(2+) immobilized in the composite thin films have been investigated, and the modified electrode was used for the ECL detection of oxalate, tripropylamine (TPA) and chlorpromazine (CPZ) in a flow injection analysis system and showed high sensitivity. Because of the strong electrostatic interaction and low hydrophobicity of Eastman-AQ55D, the sensor showed no loss of response over 2 months of dry storage. In use, the electrode showed only a 5% decrease in response over 100 potential cycles. The detection limit was 1 mumol l(-1) for oxalate and 0.1 mumol l(-1) for both TPA and CPZ (S/N = 3), respectively. The linear range extended from 50 mumol l(-1) to 5 mmol l(-1) for oxalate, from 20 mumol l(-1) to 1 mmol l(-1) for TPA, and from 1 mumol l(-1) to 200 mumol l(-1) for CPZ.