Amperometric glucose biosensor by means of electrostatic layer-by-layer adsorption onto polyaniline-coated polyester films

An amperometric glucose biosensor was fabricated using polyaniline-coated polyester films. Polyaniline was reacted with camphorsulfonic acid to produce a salt, which was then dissolved in chloroform containing polystyrene. Using this solution, the coating was performed onto polyester films. Glucose oxidase was immobilized onto these films using an electrostatic layer-by-layer adsorption technique. In this method, poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and the evidence of layer-by-layer adsorption was obtained using a quartz crystal microbalance technique. A biosensor was fabricated from these films as a working electrode, and used to measure the glucose concentration accurately.     

Amperometric cholesterol biosensor using layer-by-layer adsorption technique onto electrospun polyaniline nanofibers

An amperometric cholesterol biosensor was fabricated using electrospun polyaniline nanofibers. Polyaniline was dissolved in chloroform with camphorsulfonic acid, and polystyrene was added in this solution. Using this mixed solution, nanofibers were formed and collected by electrospinning. Then cholesterol oxidase was immobilized onto these fibers using an electrostatic layer-by-layer adsorption technique. Poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and evidence of layer-by-layer adsorption was investigated using a quartz crystal microbalance (QCM) technique. A cholesterol biosensor was fabricated from these nanofibers as a working electrode, and it was used to measure the cholesterol concentration.     

Fabricating Water-Insoluble Polyelectrolyte into Multilayers with Layer-by-layer Self-assembly

Summary A water insoluble azo-containing polyelectrolyte (PEAPB6P-AC) was successfully fabricated into multilayer films based on the layer-by-layer adsorption technique by using N, N-dimethylformamide (DMF) as the assembling media. The multilayer growth and structure were studied with UV-vis spectroscopy, and the multilayer surface were imaged with Atomic Force Microscopy and compared with that fabricated in water. The results show that assembling PEAPB6P-AC in DMF can effectively eliminate the hydrophobic aggregation of the azo units and consequently results in a much smoother multilayer surface than that fabricated in water. This improvement to the layer-by-layer adsorption technique, which can avoid some major difficulties faced when assembling hydrophobic polyelectrolytes in aqueous solutions, seems to be a versatile way to fabricate high quality multilayer films when using the hydrophobic even water-insoluble polyelectrolytes as assembling units.     

Decolorization of reactive red 198 using preferentially-oriented metal-organic framework thin films: A structure/property correlation

The aim of this work was to investigate the structure/property correlation in metal-organic framework thin films, in particular MOF-199, toward the decolorization of harmful organic dye reactive red 198. MOF thin films were fabricated on bare and surface-modified TiO₂ substrates using a layer-by-layer deposition technique. Our results indicate that the preferentially-oriented MOF grown on DHBA-functionalized titania sublayer exhibits better photocatalytic activity due to its capability of absorbing a broader range of light. These films also exhibit an orientation-dependent adsorption behavior. While the MOF with oriented crystallites shows bigger adsorption capacity, its initial (kinetic) adsorption was lower when compared to the film grown on bare substrate.     

Study on self-assembly properties of aryl-alkyl hyperbranched polyesters with carboxylic end groups

Summary Carboxylic ended aryl-alkyl hyperbranched polyester poly(5-hydroxyethoxyisophthalic acid) (PHEIA) was synthesized and employed for an electrostatic layer-by-layer self-assembly procedure, in which poly(diallydimethylammonium chloride) (PDAC) was used as the polyanion while PHEIA acted as the polycation. From both aqueous solution and water-THF mixture of PHEIA, self-assembly films have been successfully formed as monitored by UV-Vis spectroscopy and contact angle measuring device. In the self-assembled surface where PHEIA acted as outmost layer, sphere-like particles with uniform diameter was observed by Atom Force Microscope (AFM). This phenomenon should be attributed to the aggregation of PHEIA. Furthermore, the layer-by-layer self-assembly procedure provided a favorable method for adjusting the hydrophilicity of the substrate without much interpenetration between these two polyelectrolyte layers. Received: 31 August 2001/Revised version: 2 October 2001/Accepted: 9 October 2001     

Activated Carbon-Entrapped Microfibrilated Cellulose Films As An Effective Adsorbent For Removing Organic Dye From Aqueous Effluent

Activated carbon-entrapped microfibrilated cellulose (AC/C) films were successfully fabricated by self-assembly of cellulose microfibrils via a simple and environmentally friendly method. The structures and properties of films were characterized by scanning election microscope (SEM) as well as density, turbidity, and mechanical analyses. Cationic brilliant red 5GN (CBR) was selected as a model dye, and the adsorption of CBR in aqueous solution by AC/C films was evaluated. Adsorption kinetics was described by the pseudo-second-order model, and the absorption behaviors were in agreement with a Langmuir isotherm. Thermodynamic analyses indicated that CBR adsorption onto AC/C film was favorable. The adsorption–desorption cycle of AC/C films was repeated three times without significant loss of adsorption capacity. Moreover, AC particles in films showed high stability during adsorption. This work proposes a novel utilization of bulk forms of adsorption particles within cellulose networks to achieve better adsorption applications in water treatment.     

层层自组装法制备碳纳米管薄膜研究进展

综述了近年来通过层层自组装法制备碳纳米管薄膜的一些最新研究进展,重点介绍了通过物理吸附和化学吸附两种方式来制备碳纳米管组装膜,并对如何提高碳纳米管薄膜的电化学稳定性方面进行了论述。     

An effective layer-by-layer adsorption and polymerization method to the fabrication of polyoxometalate-polypyrrole nanoparticle ultrathin films

A layer-by-layer (LbL) adsorption and polymerization method was developed for the controllable preparation of polypyrrole (PPy) nanoparticles within ultrathin films. By repetitive adsorption of pyrrole and subsequent polymerization with 12-molybdophosphoric acid, the polyelectrolyte multilayer films containing PPy nanoparticles were fabricated. UV-visible absorption spectrocopy, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and cyclic voltammograms (CVs) were used to characterize the PPy nanoparticles and their multilayer thin films. UV-visible spectra indicate that the growth of PPy nanoparticles was regular and occurred within the polyelectrolyte films. The size of prepared PPy nanoparticles was found by TEM to increase with the increasing of polymerization cycles. The electrochemistry behavior of the multilayer thin films was studied in detail on ITO. The results suggest that the LbL adsorption and polymerization method developed herein provides an effective way to prepare PPy nanoparticles in the polymer matrix.     

Adsorption study of nonionic surfactants on polyester fibers

An adsorption study of a series of nonionic surfactants on polyester fiber was performed to determine the relative importance of sub-strate affinity in the detergency process. The fiber used in this study was a multifilament polyester yarn. Because of the relatively low surface area/g of the yarn, analytical methods for detecting the depletion of surfactant due to adsorption have to be extremely sensitive. One qualitative technique used was streaming potential measurements. The electrokinetic effect, which the streaming poten-tial measures, depends on the nature of the electrical double layer at the fiber/solution interface. The modification of the streaming potential indicates that the extent of surfactant adsorption onto the fiber surface is very similar for the nonionic surfactants studied. A very sensitive, quantitative analytical technique, which can only be used for surfactants with an appropriate chromophore, is ultraviolet (UV) spectroscopy. The UV study showed that the adsorption of the nonylphenol ethoxylate onto the polyester is Langmuirian with the adsorption plateau occurring at the critical micelle concentra-tion. For alcohol ethoxylates without a UV chromophore, con-venient quantification at the ppm level represents a difficult analyt-ical problem. In this work, total carbon analysis was developed as a sensitive analytical tool for surfactant determination. Agreement between the UV and total carbon data for the nonylphenol ethox-ylate was quite good. The relevance of the data to the detergency process is discussed.     

Multilayer membranes via layer-by-layer deposition of PDDA and DNA with Au nanoparticles as tags for DNA biosensing

A novel Au nanoparticles (Au-NPs)-based protocol for DNA hybridization detection based on assembly of alternating DNA and poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by layer-by-layer (LBL) electrostatic adsorption has been studied. Electrochemical impedance spectroscopy (EIS) and UV-vis absorbance measurements were used to study the film assembly. All the results indicate that the uniform multilayer can be obtained on the polypyrrole (PPy) coated electrode surface and the hybridization reaction can be amplified by the layer-by-layer progress. The hybridization was detected by the reductive signal of Au-NPs and nonspecific adsorption was greatly eliminated by an unrelated DNA sequence to the target DNA. Under optimum conditions, a significant sensitivity enhancement had been obtained, and the detection limit was down to 3.20 × 10⁻¹⁴ M when 6 layers assembled. The DNA biosensor has good stability and reproducibility.     

Growth of ZnO Films with Controlled Morphology by Aqueous Solution Method

A novel method based on utilizing varied ionic strength and specific adsorption was developed to prepare c -oriented zinc oxide (ZnO) films with controlled morphology in aqueous solution. Structure and morphology of the films were investigated by using X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy methods. A layer-by-layer growth manner of ZnO rod crystals was observed. The diameter of the ZnO rods can be controlled through the incorporation of the cost-effective strong electrolyte NaCl. The reason for the variation of ZnO-film morphology is that the enhanced ionic strength because of the addition of NaCl promotes not only the related reactants' concentration but also the specific adsorption of organic groups. Furthermore, acetyleacetone used as an assistant can play an important role in specific adsorption, leading to the formation of pyramid crystals through mild secondary growth.     

Fabrication and mechanical properties of single-wall carbon nanotubes and hyperbranched diazonium salt multilayers

Acidized single-wall carbon nanotubes (SWNTs) were fabricated into multilayers with a hyperbranched azobenzene-containing polymeric diazonium salt (PDAS) using the layer-by-layer adsorption technique. The fabrication process, multilayer thickness variation, multilayer surface morphology and the interaction between SWNTs and PDAS were monitored by UV-Vis absorption spectroscopy, optical ellipsometry, Atomic Force Microscopy, Scanning Electron Microscopy and Raman spectroscopy. Moreover, the nanomechanical properties of the multilayer films were measured by nanoindentation. All results show that SWNTs and PDAS can be fabricated into multilayers based on the cooperation of electrostatic absorption and chemical cross-linkage between SWNTs and PDAS. Further, this cooperation endows the SWNT/PDAS multilayer films with outstanding nanomechanical properties. The hardness and modulus are about 2.0GPa and 10.0GPa, respectively. Finally, the SWNT/PDAS multilayer film can be peeled off to be a free-standing film.     

Immobilization of cholesterol oxidase and potassium ferricyanide on dodecylbenzene sulfonate ion‐doped polypyrrole film

Dodecylbenzene sulfonate (DBS)‐doped polypyrrole (PPY) conducting polymer films were electrochemically deposited onto the indium‐tin‐oxide (ITO)‐coated glass plates in aqueous medium. The enzyme cholesterol oxidase (ChOx) was immobilized on these DBS–PPY films by a physical adsorption technique. These ChOx‐immobilized DBS–PPY films were characterized by ultraviolet–visible and Fourier transform infrared spectroscopy. The enzyme activity studies indicate that ～40% of ChOx leaches out from the ChOx/DBS–PPY film. The ChOx activity in the ChOx/DBS–PPY film was assayed as a function of cholesterol concentration. The results of amperometric measurements conducted on ChOx/DBS–PPY/ITO film show linearity over the range 2–8 mM of cholesterol solution. The ChOx/DBS–PPY/ITO electrodes exhibit a response time of 30 s and are stable for ～3 months at 4 °C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3486–3491, 2001     

Cholesterol biosensor based on electrochemically prepared polyaniline conducting polymer film in presence of a nonionic surfactant

Cholesterol biosensor has been fabricated by covalently coupling cholesterol oxidase (ChOx) via glutaraldehyde onto electrochemically prepared polyaniline film in presence of TritonX-100 [4-(1,1,3,3-tetramethylbutyl) phenyl polyethylene glycol], a non-ionic surfactant onto indium-tin-oxide (ITO) glass substrate. These ChOx/PANI-TX-100/ITO bioelectrodes have been characterized using Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV) and scanning electron microscopy (SEM) techniques. The results of response measurements carried out on ChOx/PANI-TX-100/ITO bioelectrodes using amperometric and photometric techniques, reveal detection limit as 5 mg/dl, linearity from 5 to 400 mg/dl of cholesterol and sensitivity as 131 μA/(mg/dl cm⁻²). These biosensing electrodes are thermally stable up to 65 °C, can be used about 20 times and have a shelf-life of about 10 weeks when stored at 4 °C. Attempts have also been made to utilize the ChOx/PANI-TX-100/ITO bioelectrodes for estimation of free cholesterol concentration in serum samples.     

Electrochemically fabricated polyaniline nanowire-modified electrode for voltammetric detection of DNA hybridization

A novel and sensitive electrochemical DNA biosensor based on electrochemically fabricated polyaniline nanowire and methylene blue for DNA hybridization detection is presented. Nanowires of conducting polymers were directly synthesized through a three-step electrochemical deposition procedure in an aniline-containing electrolyte solution, by using the glassy carbon electrode (GCE) as the working electrode. The morphology of the polyaniline films was examined using a field emission scanning electron microscope (SEM). The diameters of the nanowires range from 80 to 100 nm. The polyaniline nanowires-coated electrode exhibited very good electrochemical conductivity. Oligonucleotides with phosphate groups at the 5′ end were covalently linked onto the amino groups of polyaniline nanowires on the electrode. The hybridization events were monitored with differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. The approach described here can effectively discriminate complementary from non-complementary DNA sequence, with a detection limit of 1.0 × 10⁻¹² mol l⁻¹ of complementary target, suggesting that the polyaniline nanowires hold great promises for sensitive electrochemical biosensor applications.     

Influence of laponite on the drug loading and release performance of LbL polyurethane/poly(acrylic acid) multilayers

A facile way to fabricate clay-based multilayers was introduced. Compared to other works, poly(acrylic acid)–laponite nanocomposites (PAA-Lap) were used as a membrane component instead of Lap alone. Coupled with water-soluble polyurethane (PU), a series of PU/PAA-Lap multilayer films were fabricated via layer-by-layer assembly containing different contents of Lap. The effect of clay content on the loading and release behavior of PU/PAA-Lap multilayers was investigated in various pH solutions with cationic methylene blue as the indicator. It was found that the introduction of Lap can influence the charge density, swelling rate, and pH stability of the film. When the content of Lap in the film was increased to a certain degree, the main adsorption mechanism changed from chemical to physical adsorption, but the releasing mechanism had no change. We hope this method can be used as a model for the fabrication of clay-based polymer drug delivery systems in low-pH environments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47348.     

Layer-by-layer thin films of polyaniline alternated with natural rubber and their potential application as a chemical sensor

Self-assembled films of polyaniline (PAni) alternated with natural rubber (NR) were successfully produced by layer-by-layer self-assembly technique (LbL), by using the latex of natural rubber obtained from the Hevea-brasiliensis tree. The centrifuged NR latex was used without any previous treatment. The influence of pH on the adsorption kinetics and film growth was evaluated. The films presented a typical linear growth, showing a constant adsorption of material in each deposition step. The FTIR spectroscopy study confirmed the presence of rubber chains (cis-1,4-poly-isoprene) on the LbL films. The morphological characterizations showed great roughness and a spherical shape of the NR particles as a predominant characteristic on the film’s surface. Finally, the potential use of the films as a chemical sensor was identified in our tests.     

Preparation of niobium oxide films as a humidity sensor

Niobium oxide films were prepared over a quartz plate by withdrawing it from a solution of niobium penta-isopropoxide (NIP) dissolved in sec-propyl alcohol. The films calcined at 673 K were well controlled in the film thickness either by NIP concentration in the solution or by the withdrawing rate of the quartz plate from the solution. BET surface area of the calcined films was as huge as around 400 m²g₋₁ and was not reduced by cyclic adsorption/desorption of water vapor. A rapid decrease and increase in the electrical resistivity of the calcined films was well associated with the cyclic adsorption/desorption of water vapor. The decrease in the electrical resistivity of the films by water vapor adsorption was more than 10 times sensitive than the decrease caused by the adsorption of ethanol, hydrocarbons, carbon monoxide and carbon dioxide. These results suggest an application of the niobium oxide films as an element of a humidity sensor.

The calcined films were proved by SEM observation to consist of tiny particles possessing a lotofmicropores sized less than 20 A. The decrease in the electrical resistivity of the films, or the increase in the electrical conductivity, was attributed to the water vapor adsorbed in these micropores. In order to identify the charge carriers during water vapor adsorption on the films, changes in the impedance and the phase shift caused by water vapor adsorption were measured using an LCR meter in AC frequency range of 10 Hz to 100 kHz. From a complex impedance plotting, single semicircule was obtained for water vapor adsorption onto the films, suggesting single adsorbed species as a charge carrier. Assuming an equivalent electric circuit for the films adsorbing water vapor, a constant capacitance was calculated under various partial pressures of water vapor, probably suggesting that the charge carriers will be H₃O⁺ on the films.     

Sequentially adsorbed electrostatic multilayers of polyaniline and azo polyelectrolytes

In this study, multilayer films composed of alternate polyaniline (PANI) and azo-polyelectrolyte (PNACN, PPAPE, PNANT or PNATZ) layers were fabricated through the electrostatic layer-by-layer self-assembly scheme. In the electrostatic adsorption process, PANI was used as the polycation and the azo polyelectrolytes were used as the polyanion. The multilayer growth was monitored by UV-vis spectroscopy and optical ellipsometry. The photoresponsive and electrochromic properties of the multilayer films were studied by UV-vis spectroscopy and electrochemical measurement. Results show that the multilayer films exhibit linear increases in both the absorbance and film thickness with the increase of the deposition cycles. The thickness contributed by each individual layer depends on the pH of the PANI and azo-polyelectrolyte dipping solutions. The multilayer films can show photoinduced dichroic properties contributed by the azo-polyelectrolyte layers, but the ability to form surface-relief-grating (SRG) upon Ar⁺ laser irradiation is relatively weak. The multilayer films possess the characteristic absorption bands related to the azo chromophores and PANI. As the location of the PANI bands depends on its oxidation states, the multilayer films can show sensitive electrochromic variation. For instance, the PANI/PNACN multilayer films can undergo a transition from transparent yellow-green through deep green to opaque black when the potential changes from −0.1 to 0.8 V. It is demonstrated that using the azo polyelectrolytes with different hues, enriched spectrum of the colors can be obtained by the electrochemical transitions. The multilayer films containing both photoresponsive and electroactive components can be expected for applications in optics, photonic devices and others.     

Preparation and electrochemical properties of gold nanoparticles containing carbon nanotubes-polyelectrolyte multilayer thin films

Multi-walled carbon nanotubes (MWCNT)/polyelectrolyte (PE) hybrid thin films were fabricated by alternatively depositing negatively charged MWCNT and positively charged (diallyldimethylammonium chloride) (PDDA) via layer-by-layer (LbL) assembly technique. The stepwise growth of the multilayer films of MWCNT and PDDA was characterized by UV–vis spectroscopy. Scanning electron microscopy (SEM) images indicated that the MWCNT were uniformly embedded in the film to form a network and the coverage density of MWCNT increased with layer number. Au nanoparticles (NPs) could be further adsorbed onto the film to form PE/MWCNT/Au NPs composite films. The electron transfer behaviour of multilayer films with different compositions were studied by cyclic voltammetry using [Fe(CN)₆]^3−/4− as an electrochemical probe. The results indicated that the incorporation of MWCNT and Au NPs not only greatly improved the electronic conductivity of pure polyelectrolyte films, but also provided excellent electrocatalytic activity towards the oxidation of nitric oxide (NO).