Electrosynthesis of polythiophene nanowires via mesoporous silica thin film templates

Early electrosynthesized polythiophene nanowires were prepared employing a mesoporous silica template, which was also electrochemically produced. A cathodic potential step was applied to a fluorine doped tin oxide conducting glass electrode in a cationic surfactant and silicate reagent medium to deposit highly ordered mesoporous silica films. To evaluate the pores order and, consequently, optimal deposition potential, the electrochemical response of the electrodes was studied using ferrocene as redox probe. The modified electrodes were used to accomplish polythiophene electrodeposits employing 0.6 mM thiophene and 0.1 M tetrabutylammonium hexafluorophosphate in anhydrous CH₃CN as working solution. Transmission electron microscope images of the deposits revealed the presence of polythiophene nanowires of about 6 nm in diameter arranged normal to the electrode surface. The unprecedented small size and arrangement of the obtained nanowires place this work as the first study that successfully accomplished the formation of nanoscale electrochemically synthesized conducting polymer nanowires.     

Advanced selective optical sensors based on periodically organized mesoporous hybrid silica thin films

Mesoporous thin films functionalized with silylated [small beta]-diketone compounds with symmetry mesostructure dependent on the probe quantity were used as fast uranyl species sensors with high selectivity and sensitivity.     

Mesoporous silica thin film mechanized with a DNAzyme-based molecular switch for electrochemical biosensing

A novel electroanalytical strategy for copper and ascorbic acid detection was developed by using a nanostructured electrode surface mechanized with a DNAzyme-based molecular gate. This sensing interface was constructed by first electrodeposition of a mesoporous silica thin film on Au electrodes and further assembly of a Cu(II)-specific DNAzyme. The biosensing assay was based on the Cu(II) and ascorbic acid responsible activation of the DNAzyme, which acted as a molecular switch able to control the diffusion of the Fe(CN)₆^{3 −/4 −} electrochemical probe through the nanochannels of the mesoporous film.     

An electrochemical sensor for p-aminophenol based on the mesoporous silica modified carbon paste electrode

A mesoporous silica was synthesised and used to modify the surface of carbon paste electrode (CPE). The electrochemical behaviours of p-aminophenol were investigated. Compared to the unmodified CPE, the mesoporous silica-modified CPE obviously lowers the oxidation potential of p-aminophenol, and remarkably increases its oxidation peak current. The effects of pH value, amount of mesoporous silica, accumulation potential and time were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for p-aminophenol. The linear range is from 0.025?mg?L^?1 to 3?mg?L^?1, and the limit of detection is 0.01?mg?L^?1 after 2-min accumulation. Finally, the method was successfully used to determine p-aminophenol in water samples.     

Label-free electrical determination of trypsin activity by a silicon-on-insulator based thin film resistor.

A silicon-on-insulator (SOI) based thin film resistor is employed for the label-free determination of enzymatic activity. We demonstrate that enzymes, which cleave biological polyelectrolyte substrates, can be detected by the sensor. As an application, we consider the serine endopeptidase trypsin, which cleaves poly-L-lysine (PLL). We show that PLL adsorbs quasi-irreversibly to the sensor and is digested by trypsin directly at the sensor surface. The created PLL fragments are released into the bulk solution due to kinetic reasons. This results in a measurable change of the surface potential allowing for the determination of trypsin concentrations down to 50 ng mL(-1). Chymotrypsin is a similar endopeptidase with a different specificity, which cleaves PLL with a lower efficiency as compared to trypsin. The activity of trypsin is analyzed quantitatively employing a kinetic model for enzyme-catalyzed surface reactions. Moreover, we have demonstrated the specific inactivation of trypsin by a serine protease inhibitor, which covalently binds to the active site of the enzyme.     

Label-free DNA electrochemical sensor based on a PNA-functionalized conductive polymer

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probe is presented. PNA were attached covalently onto a quinone-based electroactive polymer. Changes in flexibility of the PNA probe strand upon hybridization generates electrochemical changes at the polymer-solution interface. A reagentless and direct electrochemical detection was obtained by detection of the electrochemical changes using square wave voltammetry (SWV). An increase in the peak current of quinone was observed upon hybridization of probe on the target, whereas no change is observed with non-complementary sequence. In addition, the biosensor is highly selective to effectively discriminate a single mismatch on the target sequence. The sensitivity is also presented and discussed.     

Preparation of nano-sized Pt metal particles by photo-assisted deposition (PAD) on transparent Ti-containing mesoporous silica thin film

We have investigated a novel technique for the preparation of nano-sized Pt metals on Ti-containing mesoporous silica (TMS) thin film by photo-assisted deposition (PAD). The transparent TMS thin film was prepared on a quartz plate through sol—gel/spin coating. XRD, UV-Vis and Ti K-edge XAFS measurements revealed the formation of isolated Ti oxide species with a tetrahedral-coordination geometry in the silica framework. Deposition of Pt metal precursor on TMS thin film under UV-light irradiation, followed by reduction with molecular hydrogen, afforded a transparent thin film (Pt/TMS). The formation of highly dispersed nano-sized Pt metals having narrow size distributions was determined by Pd L_III-edge XANES and TEM analysis. The TMS and Pt/TMS thin films have been demonstrated to exhibit a strong hydrophilic property, even before UV irradiation, compared to the common mesoporous silica and TiO₂ thin films. After UV-light irradiation, the contact angle of water droplet on the TMS and Pt/TMS thin films became extremely lower, indicating the appearance of the photo-induced super-hydrophilic property.     

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.     

Transparent electrochemical capacitor based on electrodeposited MnO2 thin film electrodes and gel-type electrolyte

A new concept for a transparent electrochemical capacitor was demonstrated. It includes two MnO₂ electrodes separated with a gel electrolyte, making the whole device less than 1 mm thick and transparent. Preliminary electrochemical experiments revealed a capacitance of 2 mF cm^?2 over more than 200 cycles. The device exhibited only a small absorbance change during repeated cycling.     

Label-free electrochemical detection of nanomolar adenosine based on target-induced aptamer displacement

In this work, a label-free electrochemical sensor based on target-induced displacement is reported with adenosine as the model analyte. The sensing substrate is prepared using a gold electrode modified with a self-assembled monolayer of 1,6-hexanedithiol that mediates the assembly of a gold nanoparticle film, which can increase the surface loading of capture probe and enhance the signal. An aptamer for adenosine is applied to hybridizing with the capture probe, yielding a double-stranded complex of the aptamer and the capture probe on the surface. The interaction of adenosine with the aptamer displaces the aptamer sequence and causes it to dissociate from the interface. This results in a decrease in the amount of aptamer/capture probe duplex form, and, accordingly, the desorption of methylene blue, an electroactive indicator bound to the duplex, from the electrode. Then, the redox current of the indicator can reflect the concentration of the analyte. The fabricated sensor is shown to exhibit high sensitivity, desirable selectivity and a three-decade wide linear range.     

Electro-assisted self-assembly of mesoporous silica thin films: application to electrochemical sensing of glutathione in the presence of copper

Journal of Solid State Electrochemistry - Oxidation of the reduced form of glutathione based on the 1:1 copper(Cu+2)-glutathione(GSH) complexes was found to occur at a decreased overpotential at a...     

Deposition of thin mesoporous silica films on glass substrates from basic solution

Transparent thin (ca. 100 nm) films of silica-surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700-900 m2 g-1) with pore diameter 2.0-2.8 nm.     

Preparation and characterization of mesoporous silica thin films from polyethoxysiloxanes

Tetraethoxysilane (TEOS) and polyethoxysiloxanes (PEOSs; prepared by the acid‐catalyzed hydrolytic polycondensation of TEOS) were subjected to the sol–gel process in the presence of cetyltrimethylammonium bromide (CTAB), respectively. The PEOSs with M_w 700–26,000, as prepared by sol–gel coating of TEOS and PEOS under various conditions, were used. Uniform and crack‐free thin films of thickness 276–613 nm were prepared by spin‐coating of a PEOS solution containing CTAB. When the coating films were sintered at 400 °C, the combustion of ethoxy groups and CTAB took place to provide porous silica thin films. The structure of the thin films was found to be dependent on the molecular weight of PEOS and the molar ratio of CTAB/Si: lamellar or hexagonal phase was observed for M_w less than 15,000 and for CTAB/Si molar ratios greater than 0.10. Honeycomb structures were observed for M_w less than 5000 and for CTAB/Si molar ratios of 0.15. The honeycomb structure was also observed by atomic force microscopy and transmission electron microscope. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2542–2550, 2006     

Immobilization and electrochemistry of cytochrome c on amino-functionalized mesoporous silica thin films

The immobilization and electrochemistry of cytochrome c (cyt c) on amino-functionalized mesoporous silica thin films are described. The functionalized silica films with an Im3m cubic phase structure were deposited on conducting ITO substrate by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Pluronic F127 under acidic conditions. The high specific surface area, large pore size and functional inner surface of mesoporous silica thin films result in a high cyt c loading, and the cyt c immobilization on this silicate framework is stable. After adsorption of cyt c, the ordered cubic structure of mesoporous silica and the redox activity of immobilized cyt c are retained as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM) and cyclic voltammetry. The redox behavior of the cyt c/silica film-modified ITO electrode is a surface-controlled quasi-reversible process for the experimental conditions used in this work and the electron transfer rate constant is calculated is 1.33 s⁻¹. The ITO electrode modified by cyt c/silica film possesses a high stability; even cyt c retains its redox activity following immobilization for several months. Furthermore, the electrocatalytic activities of the modified ITO electrode to hydrogen peroxide and ascorbic acid have been studied. Since these behaviors are quite pronounced, the modified electrode can be used for detection of hydrogen peroxide and ascorbic acid.     

Label-free electrochemical impedance sensing of DNA hybridization based on functionalized graphene sheets

Negative-charge change and conformation transition upon DNA immobilization and hybridization on functionalized graphene sheets were monitored by the EIS technique and adopted as the signal for label-free electrochemical DNA hybridization detection.     

Fabrication of mesoporous metal chalcogenide nanoflake silica thin films and spongy mesoporous CdS and CdSe

Mesoporous silica metal oxide (ZnO and CdO) thin films have been used as metal ion precursors to produce the first examples of mesoporous silica metal sulfide (meso-SiO(2) @ZnS, meso-SiO(2) @CdS) or silica metal selenide (meso-SiO(2) @ZnSe, meso-SiO(2) @CdSe) thin films, in which the pore walls are made up of silica and metal sulfide or metal selenide nanoflakes, respectively. A gentle chemical etching with a dilute HF solution of the meso-SiO(2) @CdS (or meso-SiO(2) @CdSe) produces mesoporous cadmium sulfide (meso-CdS) (or cadmium selenide, meso-CdSe). Surface modified meso-CdS displays bright blue photoluminescence upon excitation with a UV light. The mesoporous silica metal oxides are formed as metal oxide nanoislands over the silica walls through a self-assembly process of a mixture of metal nitrate salt-two surfactants-silica source followed by calcination step. The reactions, between the H(2) S (or H(2) Se) gas and solid precursors, have been carried out at room temperature and monitored using spectroscopy and microscopy techniques. It has been found that these reactions are: 1)?taking place through the diffusion of sulfur or selenium species from the top metal oxide layer to the silica metal oxide interface and 2)?slow and can be stopped at any stage to obtain mesoporous silica metal oxide metal sulfide or silica metal oxide metal selenide intermediate thin films.     

Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film

To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substituted OH with Si(CH₃)₃ groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 °C.     

Chiral nematic assemblies of silver nanoparticles in mesoporous silica thin films

Silver nanoparticles (NPs) have been synthesized inside mesoporous silica films with chiral nematic structure. Circular dichroism measurements of the silver NP-loaded silica films show NP-based optical activity in the vicinity of the surface plasmon resonance. These materials, with an optical response associated with the chiral assembly of metal NPs, may be useful for developing new sensors.     

Single molecule spectroscopy studies of diffusion in mesoporous silica thin films

Single molecule spectroscopy is applied in studies of diffusion and surface adsorption in sol-gel-derived mesoporous silica thin films. Mesoporous films are obtained by spin casting surfactant-templated sols onto glass substrates. Small-angle X-ray diffraction results are consistent with hexagonally ordered mesophases in as-synthesized (i.e., surfactant-containing) films. Upon calcination, a 30% contraction and disordering of these structures occurs. Nile Red is used as a fluorescent probe of both the as-synthesized and calcined films. It is loaded into the samples at subnanomolar levels either prior to spin casting or after calcination. Fluorescence imaging and single-point fluorescence time transients show the dye molecules to be relatively mobile in the as-synthesized samples. In contrast, the molecules appear entrapped at fixed locations in dry calcined films. In calcined films rehydrated under high humidity conditions, the Nile Red molecules again become mobile. Time transients obtained from the as-synthesized and rehydrated samples provide clear evidence for frequent reversible adsorption of the dye to the silica surfaces. Autocorrelations of the time transients provide quantitative data on the mean diffusion coefficients (D = 2.4 x 10(-10) and 2.6 x 10(-10) cm2/s) and mean desorption times (1/k = 25 and 40 s) for the as-synthesized and rehydrated films, respectively. The results prove both water and surfactant play important roles in governing matrix interactions and mass transport.     

介孔硅上芘荧光团在氟离子测定中的应用

龋齿是儿童最常见的疾病之一,适量的氟可以促进牙釉质内形成氟磷灰石,增强牙齿的抗酸和抗龋能力.氟还可以抑制或杀灭致龋变链菌,减少牙菌斑沉积,降低龋齿发生.在牙膏中加入适量的氟是预防龋齿最简便易行的方法,但过量的氟会导致慢性中毒.牙膏是人们的生活必需用品,目前市场上销售的含氟牙膏越来越多,因此准确测定牙膏中氟的含量很有必要.文献报道了一些氟离子测定的分光光度法,包括基于分子识别[1-3]或置换反应[4-7]的方法,这些方法的主要缺点是许多阴离子和阳离子会与氟竞争结合位点,严重干扰氟离子的测定.