Assembly of CdS nanoparticles in patterned structures by a novel ion-entrapment process in thermally evaporated fatty acid films

The formation of cadmium sulfide nanoparticle assemblies in a patterned manner on suitable substrates is described. The protocol for realizing such structures comprises the following steps. In the first step, patterned films of a fatty acid are thermally evaporated onto solid supports using suitable masks (e.g., a transmission electron microscope grid). Thereafter, the fatty acid film is immersed in cadmium sulfate solution and Cd2+ ions entrapped in the lipid matrix by electrostatic complexation with the carboxylate ions of the fatty acid molecules. The final step involves reaction of the entrapped Cd2+ ions with Na2S, leading to the in situ generation of cadmium sulfide nanoparticles within the patterned lipid matrix. This approach shows promise for generating patterned nanoparticle assemblies of different chemical compositions.     

Thin films of polyelectrolyte-encapsulated catalase microcrystals for biosensing

Polyelectrolyte (PE)-encapsulated catalase microcrystals were assembled onto gold electrodes by their sequential deposition with oppositely charged PEs, utilizing electrostatic interactions to form enzyme thin films for biosensing. The PE coating around the microcrystals provided a regular surface charge, thus facilitating the stepwise film growth, and it effectively prevented catalase leakage from the assembled films. The encapsulated catalase was shown to retain both its biological and its electrochemical activity. Direct electron transfer between catalase molecules and the gold electrode was achieved without the aid of any electron mediator. In pH 5.0 phosphate buffer solution, the apparent formal potential (E(o)') of catalase was -0.131 V (vs Ag/AgCl). As a H2O2 biosensor, films consisting of one layer of the encapsulated catalase displayed considerably higher (approximately 5-fold) and more stable electrocatalytic responses to the reduction of H2O2 than did corresponding films made of one layer of nonencapsulated catalase or solubilized catalase. An increase in either the number of "precursor" PE layers between the gold electrodes and the catalase microcrystal layers in the film or the number of PE layers encapsulating the catalase microcrystals was found to decrease the electrocatalytic activity of the electrode. At low precursor PE layer numbers (approximately 2) and PE encapsulating layers (approximately 4), the current response was proportional to the H2O2 concentration in the range 3.0 x 10(-6) to 1.0 x 10(-2) M. The overall electroactivity of the multilayer film increased for the first two layers of encapsulated catalase, after which a plateau was observed. This was attributed to the increasing difficulty of electron transfer and substrate diffusion limitations. The current approach of using immobilized PE-encapsulated enzyme microcrystals for biosensing provides a versatile method to prepare high enzyme content films with high and tailored enzyme activities.     

Patterned silver nanoparticle films by an ion complexation process in thermally evaporated fatty acid films

The formation of silver nanoparticle films in a patterned manner on suitable substrates is described. The protocol for realising such structures comprises of the following steps. In the first step, patterned films of a fatty acid are thermally evaporated onto solid supports using suitable masks (e.g. a TEM grid). Thereafter, the fatty acid film is immersed in silver nitrate solution and Ag⁺ ions entrapped in the lipid matrix by electrostatic complexation with the carboxylate ions of the fatty acid molecules. The final step involves the reduction of the Ag⁺ ions in situ thus leading to the formation of silver nanoparticles within the patterned lipid matrix. The process of metal ion incorporation and reduction may be repeated a number of times to increase the nanoparticle density in the lipid matrix. The silver nanoparticle density may also be increased by dissolution of the fatty acid molecules in suitable solvents. The process of Ag⁺ ion entrapment and formation of silver nanoparticles within the patterned lipid matrix has been followed by quartz crystal microgravimetry, UV-VIS spectroscopy, FTIR, SEM and EDX. The process described shows immense potential for extension to assemblies of nanoparticles in more intricate patterns as well as to the growth of semiconductor quantum dots in such patterns.     

Layer by layer composite film of dimyristoyl-phosphatidylcoline and bacteriorhodopsin fabricated by multilayer molecular thin film method using fatty acid and lipid

A composite film of dimyristoyl-phosphatidylcoline (DMPC) and bacteriorhodopsin (BR) was fabricated by multilayer molecular thin film method using fatty acid and lipid on a quartz substrate or a hydrogenated amorphous silicon thin film. FTIR reflection absorption spectrums and UV absorption spectrums of the films were characterized on the detail of surface structure of the films. The spectroscopic data exhibited a specific layer by layer interaction of BR and environmental molecule DMPC above fatty acid. Especially, 4 layer composite LB films DMPC and BR exhibited an entirely different feature of IR reflection absorption spectrum depend on fatty acid species.     

Dye-loaded porous nanocapsules immobilized in a permeable polyvinyl alcohol matrix: a versatile optical sensor platform

In this work we report on a versatile sensor platform based on encapsulated indicator dyes. Dyes are entrapped in hollow nanocapsules with nanometer-thin walls of controlled porosity. The porous nanocapsules retain molecules larger than the pore size but provide ultrafast access to their interior for molecules and ions smaller than the pore size. Dye-loaded nanocapsules are immobilized in a polyvinyl alcohol (PVA) matrix with high solvent permeability and rapid analyte diffusion. This approach provides robust sensing films with fast response and extended lifetime. To demonstrate the performance characteristics of such films, pH-sensitive indicator dyes were entrapped in vesicle-templated nanocapsules prepared by copolymerization of tert-butyl methacrylate, butyl methacrylate, and ethylene glycol dimethacrylate. As pH sensitive dyes, Nile blue A, bromophenol blue, and acid fuchsin were tested. Time-resolved absorbance measurements showed that the rate of the color change is controlled by the rate of diffusion of protons in the hydrogel. The pH-induced color change in a ~400 μm thick film is complete within 40 and 60 s. The porous nanocapsule loaded films showed excellent stability and reproducibility in long-term monitoring experiments. Compartmentalization of the indicator dyes within the nanocapsules increased their stability. The matrix caused a shift in the position of the color change of the dye compared to that in an aqueous buffer solution. The encapsulation/immobilization protocol described in this account is expected to be broadly applicable to a variety of indicator dyes in optical sensor applications.     

Reduced single molecule photobleaching in fumed Langmuir-Blodgett films

An approach for reducing photobleaching of dyes doped into lipid films formed using the Langmuir-Blodgett technique is discussed. Fluorescent lipid analogs are often doped into lipid membranes to characterize microscopic domains present in the films. Dye photobleaching can limit the information from these studies which can be especially problematic for single molecule fluorescence measurements. Here we show that a protective polymer coating grown on the film using a fuming process can reduce dye photobleaching without perturbing the underlying lipid structure. Following the transfer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers to a glass substrate using the Langmuir-Blodgett technique, the films are exposed to vapors of ethyl 2-cyanoacrylate. Polymer formation produces a thin protective barrier on the lipid film that reduces photobleaching of the underlying fluorescent lipid analogs. Single molecule orientation measurements reveal that the molecular structure of the underlying monolayer is unaltered by polymer formation, suggesting that this method is a general, nonperturbative technique for the reduction of photobleaching in fluorescence studies of Langmuir-Blodgett films.     

The influence of pH over topography and spectroscopic properties of silica hybrid materials embedding meso-tetratolylporphyrin

Hybrid porphyrin-silica materials consisting in 5,10,15,20-tetratolyl-21H,23H-porphine, encapsulated in silica matrices were obtained by sol-gel method. The hydrolysis and condensation reactions were performed by using tetraethylorthosilicate as precursor, either in one-step acid or in two steps acid-base catalysis, assisted or not by an ultrasonic field. The porphyrin-silica hybrid materials were monitored and characterized by AFM, FT-IR, fluorescence and UV-vis spectroscopy. As a result of porphyrin entrapping into silica gels, a general phenomenon regarding hyperchromic effects of the Q bands, occurs. UV-vis study revealed that during the sol-gel process, major changes regarding porphyrin ring structure occur, especially at acidic pH, when the dicationic species of porphyrin are formed. During acid-base catalyzed method the dye molecules tend to aggregate by π−π and hydrophobic co-facial interactions of sandwich H-type. In acid catalyzed process, the protonation of the porphyrins prevent the formation of aggregates, due to increased electrostatic repulsion between the molecules.     

Diffusion dynamics of small molecules from mesoporous silicon films by real-time optical interferometry

Time-dependent laser reflectometry measurements are presented as a means to rigorously characterize analyte diffusion dynamics of small molecules from mesoporous silicon (PSi) films for drug delivery and membrane physics applications. Calculations based on inclusion of a spatially and temporally dependent solute concentration profile in a one-dimensional Fickian diffusion flow model are performed to determine the diffusion coefficients for the selected prototypical polar species, sucrose (340 Da), exiting from PSi films. The diffusion properties of the molecules depend on both PSi pore size and film thickness. For films with average pore diameters between 10-30?nm and film thicknesses between 300-900?nm, the sucrose diffusion coefficient can be tuned between approximately 100 and 550?μm2/s. Extensions of the real-time measurement and modeling approach for determining the diffusivity of small molecules that strongly interact with and corrode the internal surfaces of PSi films are also discussed.     

Self-assembled hybrid films of phosphotungstic acid and aminoalkoxysilanes on SiO2/Si surfaces

The present paper describes the influence of the chemical structure of two aminoalkoxysilanes: 3-aminopropyltriethoxysilane (APTS) and N-(3-(trimethoxysilyl)-propyl)-ethylenediamine (TSPEN) on the morphology of thin layer hybrid films with phosphotungstic acid (HPW), a Keggin heteropolyanion. X-ray photoelectron spectroscopy analyses indicated that both silane films showed protonated amine species interacting with the heteropolyanion by electrostatic forces as well as the presence of secondary carbamate anions. The hybrid films have different surface morphology according to atomic force microscopy analyses. The hybrid film with TSPEN forms flatter surfaces than the hybrid film with APTS. This effect is ascribed to higher flexibility and chelating ability of the TSPEN on adsorbed molecules. Ultrasonication effect on surface morphology of the hybrid film with APTS plays a fundamental role on surface roughness delivering enough energy to promote surface diffusion of the HPW heteropolyanions. This diffusion results in agglomerate formation, which corroborates with the assumption of electrostatic bonding between the HPW heteropolyanions and the protonated amine surface. These hybrid films could be used for electrochemical sensor design or to build photochromic and electrochromic multilayers.     

Enzyme-immobilized Langmuir-Blodgett film for a biosensor

A lipid-protein monolayer for a biosensor was prepared utilizing a Langmuir- Blodgett technique. The enzyme glucose oxidase was used as the protein. Three types of lipid were chosen to change the surface charge of the polar group. The enzyme was immobilized on the lipid monolayer by adsorption from the subphase solution onto the lipid monolayer on the air/water interface. It was found that the lipid-enzyme interaction was dominated by electrostatic forces, and the characteristics of the film can be controlled by expansion and recompression of the adsorbed monolayer. Finally, a glucose sensor was fabricated by depositing the film onto a hydrogen peroxide electrode.     

Structural and electrochemical behaviour of sol-gel zirconia films on 316L stainless-steel in simulated body fluid environment

Sol-gel thin film offers a number of advantages that makes it an attractive method for obtaining ceramic coatings on metallic implants. In this study, the feasibility of using a polymeric sol-gel zirconia film on 316L SS substrate was evaluated using potentiodynamic polarization measurements to measure the corrosion resistance in simulated body fluid environment. Fairly uniform, dense and crack-free films were produced by dip-coating the 316L stainless-steel substrate in a precursor solution containing sonocatalysed zirconium propoxide and yttrium acetate, followed by firing at 600 °C in vacuum. The resultant films were characterized by thermal studies (TGA-DTA), XRD, FT-IR and polarization studies.     

Single-molecule studies of diffusion by oligomer-bound dyes in organically modified sol-gel-derived silicate films

Single-molecule fluorescence spectroscopy is used to study dye diffusion within organically modified silicate (ORMOSIL) films. ORMOSIL films are prepared from sols containing tetraethoxysilane and isobutyltrimethoxysilane in 2:1 and 1:9 molar ratios. Nile red and a new silanized form of nile red that can be covalently attached to the silicate matrix are used as fluorescent probe molecules. The number and rate of single molecules diffusing through these films increases dramatically with increasing film organic content. Autocorrelation of the fluorescence images yields a quantitative measure of the relative populations of fixed and diffusing species. Surprisingly, both "free" and silicate-bound nile red exhibit relatively facile translational motions. Single-molecule/single-point fluorescence correlation spectroscopy (FCS) is used to measure the dye diffusion coefficients in submicrometer-scale film regions. The most common diffusion coefficients for "free" and silicate-bound nile red molecules in the 1:9 films are 3.9 x 10(-10) and 1.6 x 10(-10) cm(2)/s, respectively. The unexpectedly rapid diffusion of silicate-bound nile red is attributed to the presence of liquidlike silicate oligomers in the films. A lower bound for the molecular weight of the oligomers is estimated at 2900. Bulk solution-phase FCS experiments performed on "free" and silicate-bound nile red species extracted into chloroform solutions provide valuable support for these conclusions. Comparison of the results derived from experimental and simulated time transients indicates film heterogeneity occurs on sub-100-nm-length scales and likely results from the presence of inorganic- and organic-rich domains.     

聚苯胺薄膜的制备及导电性

采用真空蒸发沉积法,以盐酸掺杂态和本征态聚苯胺粉末为原料,分别在Si(100)和载玻片上沉积了聚苯胺膜。利用傅立叶红外光谱仪(FT-IR)和扫描电镜(SEM)对薄膜进行了表征,并研究了原料颗粒尺寸对成膜质量的影响。电导率测试结果表明,采用该方法沉积的薄膜电导率在10-6S/cm量级,达到了防静电材料电导率的要求。     

Reconstitution of membrane proteins into polymer-supported membranes for probing diffusion and interactions by single molecule techniques

We have established a robust and versatile analytical platform for probing membrane protein function in a defined lipid environment on solid supports. This approach is based on vesicle capturing onto an ultrathin poly(ethylene glycol) (PEG) polymer brush functionalized with fatty acid moieties and subsequent vesicle fusion into a contiguous membrane. In order to ensure efficient formation of these tethered polymer-supported membranes (PSM), very small unilamellar vesicles (VSUV) containing fluorescent lipids or model transmembrane proteins were generated by detergent depletion with cyclodextrin. Thus, very rapid reconstitution of membrane proteins into PSM was possible in a format compatible with microfluidics. Moreover, surfaces could be regenerated with detergent solution and reused multiple times. Lipid and protein diffusion in these membranes was investigated by fluorescence recovery after photobleaching, single molecule tracking, and fluorescence correlation spectroscopy. Full mobility of lipids and a high degree of protein mobility as well as homogeneous diffusion of both were observed. Quantitative ligand binding studies by solid phase detection techniques confirmed functional integrity of a transmembrane receptor reconstituted into these PSM. Colocomotion of individual ligand-receptor complexes was detected, demonstrating the applicability for single molecule fluorescence techniques.     

Single-molecule fluorescence trajectories for investigating molecular transport in thin silica sol-gel films

Single-molecule fluorescence tracking has been used to examine diffusion of small molecules in sol-gel films in order to identify spatial heterogeneity in the structure and molecular diffusivities for different regions of the film. Fluorescence intensity profiles from single molecules are fit to a two-dimensional Gaussian function to determine their x,y positions with subpixel resolution. Scatter plots and histograms of molecular step sizes indicate that the trajectories conform to the predictions of a two-dimensional random walk. The mean-square step size is shown to be an unbiased estimate of the variance of the step-size probability distribution and a valid statistic for determining the diffusion coefficient from a molecular trajectory. The diffusion coefficients measured for different molecules are subjected to an F test, which showed that the sol-gel film exhibits spatial variation in the diffusion coefficient on a micrometer-length scale. The spatial variation in diffusivities is a measure of structural heterogeneity of these films.     

壳聚糖自组装复合修饰血红蛋白的研究

利用静电自组装技术和通过改变溶液的pH值与组装循环数在云母基底上制备了壳聚糖／血红蛋白复合膜,并运用原子力显微镜(AFM)和红外光谱对其结构进行了表征。结果表明,在以去离子水为溶剂的血红蛋白溶液与pH为5．5的壳聚糖醋酸溶液复合制备的三循环膜结构紧密,壳聚糖与血红蛋白相互作用能较好地达到平衡。体现了壳聚糖与血红蛋白之间良好的生物相客性,为临床应用壳聚糖对血红蛋白进行修饰来改进其作为血液替代品的缺陷方面作了一些基础性的探讨。     

Total internal reflection fluorescence-correlation spectroscopy study of molecular transport in thin sol-gel films

Total internal reflection fluorescence correlation spectroscopy is used to measure mass transport rates through thin sol-gel films. Fluctuations in the fluorescence signal derive from molecular statistics due to the small number (approximately 1000) of rhodamine 6G dye molecules in the observation region. Autocorrelation of the fluctuating signal is fit to a model describing diffusion in the evanescent wave excitation. Silica sol-gel films were prepared by dip-coating 27-nm porous silica particles, which were synthesized by a base-catalyzed sol-gel method, onto microscope slides. The measured diffusivities ranged from 1 to 2 orders of magnitude slower than free diffusion and decreased with increasing number of dips used to prepare the film. Scanning electron microscopy (SEM) was used to examine the film structure and showed that increasing the number of dips produced more uniform and well-ordered films. To determine what role the dip-coating process plays in inducing order, deposited films were further dipped into ethanol containing no particles. These films were annealed by this process and become more ordered, as determined by SEM, and show a corresponding reduction in the molecular diffusivity.     

Surface characterization of lipid/chitosan nanoparticles assemblies, using X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry

Chitosan/tripolyphosphate nanoparticles are promising drug delivery systems, which show excellent capacity for protein entrapment and improvement of mucosal peptide absorption. We have recently developed a new drug delivery system consisting of assemblies formed between preformed chitosan nanoparticles and phospholipids (dipalmitoylphosphatidylcholine and dimiristoylphosphatidylglycerol) which are endogenous to the lung. These assemblies are prepared by lipid film hydration with a nanoparticles suspension. The aim of this work was to elucidate the architecture of these structures using sensitive surface analysis techniques such as X-ray photoelectron spectroscopy and static time-of-flight secondary ion mass spectrometry, as well as to determine their physicochemical characteristics. The combination of zeta potential measurements with the results obtained by X-ray photoelectron spectroscopy and static time-of-flight secondary ion mass spectrometry, demonstrated that a complete lipid coating of the nanoparticles can be achieved using a lipid film formed by both dipalmitoylphosphatidylcholine and dimiristoylphosphatidylglycerol, this way conferring to the lipid film a strong negative charge, which favors the interaction with the positively charged nanoparticles. Therefore, the major role of electrostatic interactions as driving forces to control the organisation of the lipid/nanoparticles assemblies was clearly evident. The implications of these findings for the structural organisation of the assemblies, for their in vitro behaviour, as well as for their mechanism of formation are discussed.     

Effects of diffusion on interfacial fracture of gold-chromium hybrid microcircuit films

In this study, the effects of diffusion on gold-chromium film durability was determined from interfacial fracture energy measurements on laboratory samples aged to simulate long term service. The samples were prepared by sputter deposition of gold films and chromium adhesive layers on sapphire substrates. Some films were left in the as-deposited condition while others were given an accelerated age to drive the chromium off the interface and into the gold film. Stressed overlayers and nanoindentation were then used to induce interfacial delamination and blister formation from which interfacial fracture energies were determined using mechanics-based models. These tests showed that the fracture energies for interfacial failure of the as-deposited and annealed films occurred near 1.3 J m^–2 even when diffusion had driven all chromium into solution. These results clearly demonstrate that chromium in solution is as effective in promoting adhesion as continuous chromium adhesive layers.     

Patterning of pH sensitive fluorescent bipyridazine derivatives

A pH sensitive pipeprazine substituted bipyridazine fluorophore, DPP-BPDZ was explored as a pH sensor in solution and thin film state. Greenish highly fluorescent solution of the DPP-BPDZ with fluorescence quantum yield of 0.63 showed fluorescence decrease as the acetic acid concentration of the media was increased. The fluorescence quenching was correlated linearly with the content of acetic acid dose and attributed to the protonation at the terminal piperazine group. An acid sensitive film was fabricated using a transparent polymeric host (PMMA) and the DPP-BPDZ dye molecules as a guest. The resultant bright green fluorescent film (1.4 microm thick) showed exponential decrease of the fluorescence intensity as the pH of the dipping solution was decreased. In the range of pH below 4.5, the film sensitivity to pH was higher than the pH range over 4.5. A patternable film sensor was fabricated by introducing a photo acid generator (PAG) layer on the dye layer. Fluorescence patterns was formed on the film sensor through a photo-mask by relatively weak power of UV light (0.4 mW/cm2). Fluorescent line patterns having 10 microm line width were obtained with high fluorescence contrast between the patterns.