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The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly( o -methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10 −4 and 3.56 × 10 −4 g/C for the Li + and (C 2 H 5 ) 4 N + doped films, and is different for the cast POMA film, i.e., 11.3 × 10 −4 for Li + and 6.45 × 10 −4 g/C for (C 2 H 5 ) 4 N + . Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li + or (C 2 H 5 ) 4 N + , are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.

The paraoxon hydrolysis reaction catalyzed by organophosphorus hydrolase (OPH) monolayer at the air-water interface was studied. OPH-paraoxon interactions, occurring at the two-dimensional interface, by close-packed, highly orientated OPH monolayer, were investigated by several different surface chemistry techniques; e.g. surface pressure area isotherms, atomic force microscopy (AFM), and in situ epifluorescence microscopy. The characterization of OPH Langmuir and Langmuir-Blodgett films prepared in both the presence and absence of paraoxon, demonstrated significantly distinctive feature when compared with one another. Continuous growth of the OPH aggregates is a distinct phenomenon associated with hydrolysis, in addition to the pH changes in the local environment of the enzyme macromolecules.

Langmuir–Blodgett (LB) film deposition technique was employed for the immobilization of organophosphorus hydrolase (OPH). OPH enzyme was covalently bonded to a fluorescent probe, fluorescein isothiocyanate (FITC), and used as a biological recognition element. Under optimal experimental conditions, OPH monolayers were deposited onto the surface of silanized quartz slides as LB film and utilized as a bioassay for the detection of paraoxon. Two different methods were employed for detection of paraoxon: the fluorescence quenching of the fluorescence probe (FITC) covalently bonded to OPH and the UV–vis absorption spectrum of the paraoxon hydrolysis product. The UV–vis absorption measurement demonstrated a linear relationship between the absorbance at 400 nm and the concentration of paraoxon solutions over the range of 1.0 × 10−7–1.0 × 10−5 M (0.27–27 ppm). By observing the FITC fluorescence quenching, the concentration of paraoxon can be detected as low as 10−9 M (S/N = 3). The research described herein showed that the LB film bioassay had high sensitivity, rapid response time and good reproducibility.

Layer-by-layer (LbL) assembly has been utilized to fabricate an ultrathin film of polyelectrolytes. The architecture was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. The topography of the films was studied using epifluorescence microscopy imaging. The photoluminescence property of the functionalized QDs improved when sandwiched between the polycation layers. The enhanced optical property of QDs allowed easy monitoring of LbL growth and detection of paraoxon with high sensitivity. The presence of organophosphorus compounds was confirmed through UV−vis and emission spectroscopies.

In this paper, we describe the preparation and characterization of Langmuir and Langmuir-Blodgett (LB) monolayers of the enzyme organophosphorus acid anhydrolase (OPAA). Langmuir films of OPAA were characterized on different subphases, such as phosphate, ammonium carbonate, and bis-tris-propane buffers. Monolayers at the air-water interface were characterized by measuring the surface pressure and surface potential-area isotherms. In situ UV-vis absorption spectra were also recorded from the Langmuir monolayers. The enzyme activity at the air-water interface was tested by the addition of diisopropylfluorophosphate (DFP) to the subphase. LB films of OPAA were transferred to mica substrates to be studied by atomic force microscopy. Finally, a one-layer LB film of OPAA labeled with a fluorescent probe, fluorescein isothiocyanate (FITC), was deposited onto a quartz slide to be tested as sensor for DFP. The clear, pronounced response and the stability of the LB film as a DFP sensor show the potential of this system as a biosensor.

The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophosphorus compound, using the layer-by-layer (LbL) deposition technique. To lift the OPH from the solid substrate, a pair of polyelectrolytes (positively charged chitosan (CS) and negatively charged poly(thiophene-3-acetic acid) (PTAA)) were combined. These species were made charged by altering the pH of the solutions. LbL involved alternate adsorption of the oppositely charged polyions from dilute aqueous solutions onto a hydrophilic quartz slide. This polyion cushion was held together by the electrostatic attraction between CS and PTAA. The growing process was monitored by fluorescence spectroscopy. OPH was then adsorbed onto the five-bilayer CS/PTAA system. This five-bilayer macromolecular structure compared to the solid substrate rendered stability to the enzyme by giving functional integrity in addition to the ability to react with paraoxon solutions. The ultimate goal is to use such a system to detect the presence of organophosphorus compounds with speed and sensitivity using the absorption and fluorescence detection methodologies.

An electronic tongue composed of six different sensing units: a bare interdigitated electrode, and interdigitated electrodes coated with stearic acid (SA), a polyaniline oligomer (16-mer), polypyrrole (PPy) and mixtures (1:1, w/w) of 16-mer/SA and PPy/SA, was able to distinguish salt, sweet, bitter and acidic solutions. The films were deposited by the Langmuir–Blodgett (LB) technique onto interdigitated electrodes, and impedance studies were performed over the frequency range 20–10 5 Hz. The sensor is able to distinguish between different brands of mineral water, tea and coffee and can also differentiate tastants below the human detection threshold, proving that conducting polymers are useful sensing materials and transducers for this sort of application.

The composition of the subphase to obtain a stable organophosphorus hydrolase (OPH) monolayer was reexamined. The surface pressure−area (π−A) isotherms show that a subphase at pH 7.6 with 0.5 M KCl...

Photo-cross-linking has received a considerable attention for the design of intelligent materials in biochemical and biomedical applications. In this report, we describe the synthesis and properties of a novel photoreversible poly(ethylene glycol)- (PEG-) based hydrogel system. 9-Anthracenecarboxylic acid was used to modify the hydroxyl groups of an eight-armed PEG polymer (molecular weight 20 000) and the degree of substitution was determined to be 87.4%. The PEG−anthracene macromers (PEG−AN) exhibited high photosensitivity at wavelengths close to visible light (absorption maxima at 366 and 380 nm) and underwent rapid and reversible photo-cross-linking upon exposure to alternating wavelengths of irradiation (365/254 nm) in the absence of photoinitiators or catalysts. Changes in light exposure and wavelength of irradiation reversibly altered the physicochemical properties of the PEG−AN hydrogel, including swellability, absorption spectrum, and topography.

A report is made of Langmuir film of a new semi-amphiphilic alternating N-hexylpyrrole-thiophene AB copolymer (PHPT) that is amenable to transfer as Langmuir–Blodgett (LB) films. PHPT was synthesized by condensation copolymerization via Stille coupling between N-hexyl-2,5-bis(trimethylstannyl)pyrrole and 2,5-dibromothiophene in the presence of Pd(PPh3)2Cl2 as a catalyst in dry DMF and characterized with various analytical techniques. In contrast to homopolymers (e.g. poly(N-alkylpyrrole)s and poly(3-alkylthiophene)s), PHPT formed a reasonably stable monolayer, as inferred through surface pressure and surface potential isotherms, and Brewster angle microscopy (BAM). The dependence of monolayer characteristics on the spreading volume, subphase temperature and compression speeds was also investigated. Electrical characterization revealed the possibility of using PHPT LB films as gas sensors.

In this paper, we report the synthesis and the monolayer behavior (surface pressure and surface potential) of a new amphiphilic coumarin dye, 7-aminocoumarin-4-acetic acid octadecylamide (ACO), at the air−water interface. The spectroscopic characteristics (UV−vis, fluorescence, and fluorescence imaging) of pure and mixed films (1:20, ACO/stearic acid and ACO/oleic acid) at the air−water interface as well as Langmuir−Blodgett (LB) films have been investigated and compared with the spectroscopic characteristics of ACO in solution. These experiments provide evidence of aggregate formation during compression of the monolayer at the air−water interface. Surface pressure dependent in situ fluorescence imaging confirms that the fluorescent quenching of the dye with increasing surface pressure originates as a result of formation of nonfluorescent aggregates. Atomic force microscopy imaging of a pure ACO LB film shows that the size of these aggregates is in the nanometer scale. This work provides information that ...

Surface relief gratings (SRGs) recorded on Langmuir‐Blodgett (LB) films of an azobenzene homopolymer were visualized using micro-Raman imaging. Raman scattering (RS) was achieved using the 780 nm laser line while pre-resonance Raman scattering (pre-RRS) and resonance Raman scattering were achieved using the 633 and 514.5 nm laser lines, respectively. Pre-surface-enhanced resonance Raman scattering (pre-SERRS) and surface-enhanced resonance Raman scattering (SERRS) were collected for the LB films covered with a 6 nm thick silver island film. The SRG could be chemically identified by the spatial variation in the Raman signal scattered by the film due to a concentration gradient. The pre-SERRS provided signals of the same intensity along and across the grooves, indicating that the molecular architecture at the SRG surface is the same at the peaks as in the valleys.

The spectroscopic properties and surface-enhanced spectra of Langmuir-Blodgett (LB) films of methacrylic homopolymer (HPDR13) are presented. It is shown that LB film displays strong fluorescence attributed to the spatial restrictions imposed by its structure. The emission is observed in conjunction with photoisomerization, a process clearly demonstrated by the formation of surface-relief gratings in the LB film [C.R. Mendonça et al., Macromolecules 32 (1999) 1493]. Surface-enhanced Raman scattering (SERS), Surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF) were observed for LB films of HPDR13 deposited onto silver island films. SERS measurements were also carried out on a sample fabricated with one monolayer LB film deposited onto silver islands followed by one overlayer of silver (LB sandwiched between two layers of silver islands). The polymer interacts very weakly with the metal surface (physisorption), and the enhancement effect is determined by the local electric field enhancement. The strong SERS and SERRS signals were suitable for micro-Raman imaging. Line, area mapping and global images of the LB monolayer on silver island are reported. The transfer ratio in the fabrication of the LB suggests a homogeneous coating of the silver islands, thereby the chemical images show the variation of the SERS intensity due to surface enhancement.

We herein report a reexamination of Langmuir and Langmuir−Schaefer films of (5-octadecanoylamino)fluorescein (ODFL) prepared from three different spreading solvents: ethanol (EtOH), CHCl3/EtOH (9:1, v/v), and CHCl3/trifluoroacetic acid (9:1, v/v). It was found that the limiting molecular area of the ODFL monolayer is strongly spreading solvent-dependent, ranging from 15 to 64 A2molecule-1. These results strongly disgree with reported results from Tsukanova et al. (Langmuir 2000, 16, 1167) of the same molecule by using ethanol as spreading solvent. Our study also shows that this fluorescein amphiphile significantly aggregates at the air−water interface. The UV−vis spectra of the monolayer are redshifted about 20 nm compared to that in the solution. Fluorescence quenching was observed from both a pure ODFL monolayer and a monolayer of ODFL mixed with stearic acid. However, fluorescence emission spectra were readily observed from mixed monolayers of ODFL with three synthetic peptide lipid molecules. This st...

The synthesis of a new amphiphilic blend of aniline, between a 16-mer oligoaniline and o -pentadecylaniline (oPA), in molecular films is reported and its morphology and UV/Vis absorption properties are characterized. The blend forms stable Langmuir monolayers at the air/water interface and successful deposition into Langmuir–Blodgett (LB) films was achieved by vertical dipping. By preparing Langmuir monolayers on acidic subphases containing peroxodisulfate, it was straightforward to polymerize the oligomer-monomer mixture. Deposited LB samples exhibited molecularly smooth surfaces, as determined by scanning force microscopy (SFM). The electrooptical properties of mono- and multilayers of 16-mer aniline/oPA mixtures and the polymerized blend were analyzed by UV/Vis spectroscopy.

Stable monolayers of soluble parent polypyrrole (Ppy) and mixed monolayers of cadmium stearate and Ppy were studied for the first time using surface pressure and surface potential isotherms. Ppy was obtained by chemical polymerization of the pyrrole monomer in the presence of dodecylbenzene sulfonic acid and characterized by ultraviolet−visible (UV−vis), Fourier transform infrared (FTIR), and elemental analysis techniques. Pure Ppy monolayers could only be transferred if optimized experimental conditions were employed, but mixed monolayers could be easily transferred in the form of Y-type Langmuir−Blodgett (LB) films, with a uniform layer-by-layer transfer according to UV−vis results. The FTIR spectrum indicated the presence of cadmium stearate along with Ppy. X-ray diffraction patterns showed the presence of cadmium stearate domains. The transferred LB films were characterized by electrical conductivity, cyclic voltammetry, and surface potential measurements.

The effect of pH and type of doping acid on monolayer behavior is investigated for poly(o-ethoxyaniline). Doping during monolayer formation is essential for high-quality Langmuir-Blodgett (LB) films to be obtained. Langmuir films were spread on a variety of subphases, containing trifluoroacetic, hydrochloric, sulfuric or perchloric acids at different concentrations. Doping of the polymer occurs at pH values lower than 3 when spreading of the solution is improved. Pressure-area isotherms display less hysteresis and higher collapse pressures when the polymer is pre-doped and spread on a pH = 1 subphase. Under these conditions monolayers could be transferred from the aqueous subphase onto hydrophilic substrates in the form of Z-type LB films.

Poly(o-ethoxyanilines) (POEA) were synthesized electrochemically and chemically in aqueous acid media. POEA films were readily obtained during the electrochemical deposition on platinum electrodes, while the chemically synthesized material was processed in the form of films either by drop coating or by Langmuir-Blodgett (LB) deposition. The open circuit potential values measured during the chemical synthesis, as well as the color changes observed, are in close agreement with those of the electro-polymerization indicating basically the same changes in oxidation states of the polymer structures. The electrochemical response of all films was investigated by cyclic voltammetry. Two redox processes were observed after stabilization in the electrolyte solution, which are associated with interconversion reactions involving different oxidation and protonation states. Ultra-thin LB films required the shortest time for stabilization. POEA films displayed electrochromism, with color changes from yellow to violet as a function of the potential.

A polyelectrolyte architecture was fabricated that was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. This film was imaged by epifluorescence microscopy. UV−vis and emission spectroscopies were used to monitor the growth of the bilayer film due to the enhanced optical property of QDs. Photoluminescence of the functionalized QDs improved when sandwiched between the polycations layers. The presence of organophosphorus compounds was confirmed through photoluminescence spectroscopy.

The chemical synthesis of a new soluble polyaniline derivative, poly( o -phenetidine), was carried out with monomer excess and the polymer obtained was characterized by elemental analysis, FTIR, UV-vis spectroscopy, gel permeation chromatography, X-ray diffraction and cyclic voltammetry. The poly( o -phenetidine) has chemical and structural properties which are consistent with a pure polymer in the emeraldine oxidation state. Poly( o -phenetidine) Langmuir monolayers were spread from chloroform or dichloromethane solutions on an aqueous solution whose pH was varied from 6 to 2. Because kinetic effects on monolayer compression are extremely important for monolayers from preformed polymers, the influence of the various experimental parameters on the monolayer characteristics was investigated. It is shown that high transfer ratios are obtained in the LB deposition process when Langmuir monolayers are fabricated from very dilute dichloromethane solutions, spread on a low pH subphase, and compressed at a barrier speed of 30 mm min −1 . The monolayer is then transferred onto a solid substrate by vertical dipping. UV—visible spectroscopy and cyclic voltammetry of the deposited LB films reveal essentially the same behavior as cast poly( o -phenetidine) films.

The fabrication of supramolecular structures from the tetraruthenated porphyrin-containing phosphines, {TPyPlRuC 3 (dppb)] 4 }, RuTPyP, is demonstrated with Langmuir and Langmuir-Blodgett films. The surface pressure-molecular area isotherms (π-A) point to an edge-on arrangement for the RuTPyP molecules in the condensed state. Weak aggregation in the Langmuir films was indicated by non-zero surface potentials at large areas per molecule and a slight red shift in the ultraviolet-visible absorption spectrum in comparison to the spectrum in solution. Further aggregation occurs in the Z-type Langmuir-Blodgett films, which was confirmed with ultraviolet-visible spectroscopy of the deposited films. Fourier transform infrared and Raman spectroscopic data for powder and Langmuir-Blodgett films indicate that the RuTPyP molecules are chemically stable in Langmuir-Blodgett films regardless of the contact with water during film fabrication. The nanostructured nature of the Langmuir-Blodgett films was manifested in cyclic voltammetry due to the high sensitivity of the metallic centers in RuTPyP. Electrodes modified with Langmuir-Blodgett films exhibit an anodic peak at 100 mV and a cathodic peak at 7 mV, which is assigned to Rulll/Rull redox processes. Furthermore, Langmuir-Blodgett films from RuTPyP showed electrocatalytic activity for oxidation of benzyl alcohol, illustrated by a large shift of 100 mV in the anodic peak at 400 mV, while electropolymerized and cast films of the same compound displayed smaller and no activities, respectively.

Nanostructured films from two conducting polymers, poly(o-methoxyaniline) (POMA) and poly(3-thiopheneacetic acid) (PTAA), were fabricated with the layer-by-layer (LBL) technique. The electrochemical response of the LBL films differs from that of a POMA cast film, even in a potential range where PTAA is inactive. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated by quartz crystal microbalance measurements. The results show that the transport properties of conducting polymers can be changed by alternation with layers of appropriate materials in LBL films.

Poly( o -alkoxyaniline) Langmuir-Blodgett (LB) films were deposited onto indium tin oxide (ITO) coated glass electrodes using the vertical dipping method. The electrochemical response of multilayer LB films was investigated by cyclic voltammetry which showed, in an acidic aqueous solution, well defined redox processes similar to those observed in films prepared by conventional methods. The film color changed with the applied potential and was related to redox and protonation-deprotonation reactions which lead to changes in the doping level and oxidation state of the poly( o -alkoxyaniline) films.

The recent developments on the main strategies for fabricating Langmuir-Blodgett (LB) films from conducting polymers are presented. Because this is a brief report, we concentrate on our latest results on films produced from parent polyaniline and poly(alkoxyanilines). It is found that the use of a pre-doped polymer on a subphase containing a doping agent enhanced significantly the quality of the Langmuir monolayer. When transferred onto a solid substrate the LB films are already in the doped state as confirmed by UV-Vis spectroscopy. LB films obtained with pre-doped poly(alkoxyanilines) exhibit electrochromism, with color changes from yellow to dark blue as the potential in an electrochemical cell is varied from -0.1 V to 0.7 V (versus SCE). In addition, good quality LB films were obtained with pre-doped, high molecular weight parent polyaniline.

Subphase conditions have been optimized to obtain stable organophosphorous hydrolase (OPH-EC 3.1.8.1) as Langmuir films. The Langmuir film was characterized by surface pressure and surface potential-area isotherms and UV-Vis spectroscopy in situ. The interaction of an organophosphorous compound, namely Paraoxon, with the OPH film was investigated for various surface pressures. The stability of the monolayer and the evidence of the enzyme activity at air-water interface support the use of enzyme LB films as biosensor.

The fabrication of Langmuir and Langmuir-Blodgett (LB) films from high-molecular-weight, doped parent polyaniline is reported. Parent polyaniline was rendered soluble by doping it with functionalized protonic acids (e.g. camphorsulfonic and toluenesulfonic acids) whose counter-ion induces solubility in low boiling point solvents such as chloroform. Condensed monolayers with high collapse pressures (above 30 mN/m) were obtained when an acidic subphase was used. The monolayers could be readily transferred onto hydrophilic substrates in the form of Z-type Langmuir-Blodgett films, and most importantly with transfer ratios close to 1. Interestingly, the films are readily obtained in the doped form and are electroactive.

The complexes [RuCl 3 (dppb)(4-Mepy)](dppb=Ph 2 P(CH 2 ) 4 PPh 2 ) (PP) and [RuCl (etp)(2,2'-bipy)]Cl (etp=PhP(PPhCH 2 ) 2 (PPP) are chloroform soluble and amenable to form Langmuir-Blodgett (LB) films. The morphology of pure and mixed films of these complexes with stearic acid was analyzed using atomic force microscopy (AFM) in air. While complexation with stearic acid led to reasonably uniform LB films of (PP), films from PPP were extremely rough since stearic acid did not help in the transfer process owing to the lack of complexation of stearic acid and PPP molecules.

Langmuir films of parent polypyrrole were investigated using surface pressure and surface potential isotherms, which showed that the films are not true monomolecular layers but multilayer stacks instead. The mean molecular area increased with decreasing subphase temperatures, but it did not change significantly when the compression speed was varied. These Langmuir films could be transferred onto solid substrates in the form of Langmuir-Blodgett (LB) films, with no need to mix the parent polypyrrole with builder materials such as cadmium stearate. Multilayer LB films were characterized by UV-vis, FTIR, surface potential and conductivity measurements.

Doping parent polyaniline (PANI) and its derivatives has been proven essential for obtaining stable Langmuir monolayers that are amenable to transfer onto solid substrates by the Langmuir-Blodgett (LB) technique. The doping process is generally carried out on the Langmuir trough, by spreading the polymer on an acidic subphase. The degree of doping affects the monolayer surface potential as the positive contribution from the double-layer increases with increasing protonation of the polymer molecules. One could then expect that the surface potential should increase with the acidic concentration in the subphase, but instead the potential diminishes for increasing concentration in the range 10−4 − 10.1 M. Interestingly, the results may be discussed in terms of the simple Gouy-Chapman theory, despite the complexity of the macromolecules involved.

The properties of Langmuir films are generally dependent on the pH of the subphase. In a previous work, for instance, we observed that Langmuir films from poly(o-ethoxyaniline) (POEA) suitable for Langmuir-Blodgett deposition were only obtained if spread on an acidic subphase. Because POEA is highly soluble in both undoped and doped states, we have now extended these studies to systematically investigate the effect of doping on the fabrication of Langmuir and LB films. The pressure-area isotherms of the Langmuir films display less hysteresis and higher collapse pressures, when the polymer is doped in solution prior to spreading of the monolayer on an acidic subphase. This procedure leads to stable films that can be readily deposited in the form of LB films.

Multilayer self-assembled (SA) films from poly(3-thiopheneacetic acid) (PTAA) and poly(o-methoxyaniline) (POMA) have been deposited on ITO substrates. The UV-Vis. absorption increased almost linearly with the number of layers. The cyclic voltammetry (CV) results pointed to a different behavior from either POMA or PTAA electrochemical response, probably because of a charge transfer interaction between the carboxyl groups of PTAA and the POMA chains.