Thin-film electrochemical sensor for diphenylamine detection using molecularly imprinted polymers

This work reports on the development of a new voltammetric sensor for diphenylamine based on the use of a miniaturized gold electrode modified with a molecularly imprinted polymer recognition element. Molecularly imprinted particles were synthesized ex situ and further entrapped into a poly(3,4-ethylenedioxythiophene) polymer membrane, which was electropolymerized on the surface of the gold electrode. The thickness of the polymer layer was optimized in order to get an adequate diffusion of the target analyte and in turn to achieve an adequate charge transfer at the electrode surface. The resulting modified electrodes showed a selective response to diphenylamine and a high sensitivity compared with the bare gold electrode and the electrode modified with poly(3,4-ethylenedioxythiophene) and non-imprinted polymer particles. The sensor showed a linear range from 4.95 to 115 μM diphenylamine, a limit of detection of 3.9 μM and a good selectivity in the presence of other structurally related molecules. This sensor was successfully applied to the quantification of diphenylamine in spiked apple juice samples.     

Molecularly imprinted polymer coated on stainless steel fiber for solid-phase microextraction of chloroacetanilide herbicides in soybean and corn

A molecularly imprinted polymer (MIP) with metolachlor as template was firstly coated on stainless steel fiber through chemical bonding strategy to solve the fragility problem of silica fiber substrate for solid-phase microextraction. The surface pretreatment of stainless steel fiber and the polymerization conditions were investigated systematically to enhance the preparation feasibility and MIP coating performance, and then a porous and highly cross-linked MIP coating with 14.8-μm thickness was obtained with over 200 times re-usability which was supported by non-fragile stainless steel fiber adoption. The MIP coating possessed specific selectivities to metolachlor, its metabolites and other chloroacetanilide herbicides with the factors of 1.1–4.6. Good extraction capacities of metolachlor, propisochlor and butachlor were found with MIP coating under quick adsorption and desorption kinetics, and the detection limits of 3.0, 9.6 and 38 μg L⁻¹ were achieved, respectively. Moreover, the MIP-coated stainless steel fiber was evaluated for trace metolachlor, propisochlor and butachlor extraction in the spiked soybean and corn samples, and the enrichment factors of 54–60, 27–31 and 15–20 were obtained, respectively.     

Synergetic effect of sol–gel silica coating and physical/chemical pre-treatment on the oxidation behavior of Ti-6Al-4V alloy

The Ti-6Al-4V alloy was treated in concentrated phosphoric acid solution and by powder blasting, respectively, subsequently coated by silica using sol–gel dip-coating technique. A barrier layer of titanium pyrophosphate (TiP₂O₇) was synthesized at the Ti-6Al-4V substrate surface after the heat treatment. XRD and SEM/EDS analysis revealed that an amorphous silica coating was formed on the alloy. The isothermal and cyclic oxidation behavior of the treated alloy with silica coating and the corresponding bare alloy was investigated at 600 °C in static air to investigate the synergetic effect of the SiO₂ coating and surface treatment on the oxidation resistance of the alloy by thermogravimetry. The average parabolic rate constants of the treated specimens with silica coating were greatly reduced. The stratified oxide layer formed on the bare alloy, while thinner oxide layer formed on the treated alloys with silica coating. The oxidation resistance of the present alloy was improved. The effect of silica coating on the microhardness of the substrate was investigated.     

Improvement of interfacial adhesion of biodegradable polymers coated on metal surface by nanocoupling

A method of securing the adhesion of biodegradable polymer coating was investigated for drug-eluting metal stents, using surface-initiated ring-opening polymerization (SI-ROP) of L-lactide. Introduction of oligolactide on the stainless steel (SS) surface was successful and the thickness of the oligolactide grafts remained on the nanometer scale, as determined by ellipsometry. The presence of an oligolactide graft was also identified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). On top of the grafts, poly(D,L-lactide-co-glycolide) (PLGA) coating was carried out on different substrates such as SS control, plasma-treated SS, and lactide-grafted (referred to as a nanocoupled) SS using electrospraying. When the adhesion forces were measured with a scratch tester, the nanocoupled SS showed the strongest interfacial adhesion between polymer coating layer and metal substrate. The outcome of the peel-off test was also consistent with the result of the scratch test. When degradation behavior of the polymer coating in vitro was examined for up to 4 weeks in a continuous fluid flow, the SEM images demonstrated that polymer degradation was obvious due to hydration and swelling of the polymer matrix. Although the matrix completely disappeared after 4 weeks for SS control and plasma-treated substrates, the nanocoupled SS was persistent with some polymer matrix. In addition, the release profiles of SRL-loaded PLGA coating appeared slightly different between control and nanocoupled groups. This work suggested that the concept of nanocoupling remarkably improved the interfacial adhesion stability between metal surface and polymer layer and controlled drug release, and showed the feasibility of drug-eluting stents.     

An electropolymerized aniline-based fiber coating for solid phase microextraction of phenols from water

An aniline-based polymer was electrochemically prepared and applied as a new fiber coating for solid phase microextraction (SPME) of some priority phenols from water samples. The polyaniline (PANI) film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The efficiency of new coating was investigated using a laboratory-made SPME device and gas chromatography with flame ionization detection for the extraction of some phenols from the headspace of aqueous samples. The scanning electron microscopy (SEM) images showed the homogeneity and the porous surface structure of the film. The results obtained proved the ability of this polymer as a suitable SPME fiber coating for trapping the selected phenols. Influential parameters affecting the extraction process were optimized and an extraction time of 50 min at 50 °C gave maximum efficiency, when the aqueous sample was saturated with NaCl and adjusted at pH 2. This new coating can be prepared easily in a reproducible manner and it is rather inexpensive and stable against most of organic solvents. The PANI thickness can be precisely controlled by the number of CV cycles. At the optimum conditions, the R.S.D. for a double distilled water spiked with phenol and chlorophenols at ppb level were 4.8-17% (n = 3) and detection limits for the studied compounds were between 0.69 and 3.7 ng ml⁻¹, except for phenol and 4-chlorophenol. The optimized method was successfully applied to some real-life water samples.     

Mg0.9Ti0.1Ni0.85Co0.15合金的石墨粉及镍粉球磨表面包覆性能

选用非晶态的Mg0.9Ti0.1Ni0.85Co0.15合金粉末与石墨粉及镍粉进行球磨表面包覆。SEM分析结果表明,己包覆石墨和镍粉的合金表面上吸附着一层小的颗粒,形成薄层将原来的合金表面包覆起来。使用XPS分析了合金表面元素。结果表明,包覆石墨粉后,合金表面碳元素的质量分数和原子分数均增加,Mg的质量分数从22.74%减小至22.23%,原子分数从36.43%减小到32.94%,从而减小了Mg在碱液中的腐蚀几率,提高合金的抗腐蚀性能;包覆镍粉后,合金表面Ni的质量分数由59.89%增加到60.04%,原子分数由40.63%增加到41.02%,形成合金表面富Ni的保护层,提高了合金的抗腐蚀性能。充放电循环测试表明,循环30周后,包覆石墨粉的合金电极容量保持率为32.05%,包覆镍粉的合金电极容量保持率为41.26%,而未包覆的电极容量保持率仅为17.88%。合金电极极化曲线测试结果表明,石墨或镍粉的包覆提高了Mg0.9Ti0.1Ni0.85Co0.15合金电极的循环稳定性和在KOH碱液中的抗腐蚀性能。     

辉光放电光谱法分析镀锌钢板

介绍了利用辉光放电光谱法分析不同种类的热镀锌板和电镀锌板的镀层定量分析；在锌铁合金化热镀锌板上界面定量计算方法的设计；锌铁合金化热镀锌板表面问题的发现。试验结果表明，辉光放电光谱法是配合镀锌板产品质量控制、研究开发的一种有效的分析手段。     

Surface functionalization of polystyrene to bind with FMRF peptides for novel biocompatibility

<正>A generic method was described to change surface biocompatibihty by introducing reactive functional groups onto surfaces of polymeric substrates and covalently binding them with biomolecules.A block copolymer with protected carboxylic acid functionality,poly(styrene-b-tert-butyl acrylate)(PS-PtBA),was spin coated from solutions in toluene on a bioinert polystyrene(PS) substrate to form a bilayer structure:a surface layer of the poly(tert-butyl acrylate)(PtBA) blocks that order at the air-polymer interface and a bottom layer of the PS blocks that entangle with the PS substrate.The thickness of the PtBA layer and the area density of tert-butyl ester groups of PtBA increased linearly with the concentration of the spin coating solution until a 2 nm saturated monolayer coverage of PtBA was achieved at the concentration of 0.4%W/W.The protected carboxylic acid groups were generated by exposing the tert-butyl ester groups of PtBA to trifluoroacetic acid (TFA) for bioconjugation with FMRF peptides via amide bonds.The yield of the bioconjugation reaction for the saturated surface was calculated to be 37.1%based on X-ray photoelectron spectroscopy(XPS) measurements.The success of each functionalization step was demonstrated and characterized by XPS and contact angle measurements.This polymer functionalization/modification concept can be virtually applied to any polymeric substrate by choosing appropriate functional block copolymers and biomolecules to attain novel biocompatibility.     

One-pot electrosynthesis of polyglycine-like thin film on platinum electrodes as transducer for solid state pH measurements

The anodic oxidation of concentrated glycine based aqueous electrolyte on smooth platinum electrode leads to a strongly grafted polyglycine-like coating on the surface in an irreversible way. Due to the proton affinity towards amino groups of polyglycine (PG), the electrodeposited thin film was used as receptor for solid potentiometric pH sensor. In order to reach local pH measurement, we developed miniaturized microelectrodes on glass substrate thanks to photolithography process. We used silver chloride on silver as the reference electrode. The couple (silver chloride, PG based platinum electrode) of microelectrodes gives linear potentiometric response vs. pH in the range [2-12], reversibly and with a sensitivity of 52.4 mV/pH (for 1 mm electrode size). PG based pH electrode is compared to other organic polymer based pH receptor such as linear polyethylenimine (L-PEI), polyaniline (PANI) and glass membrane.     

Near-Surface Structure of Plasma Polymer Films Affects Surface Behavior in Water and its Interaction with Proteins

Using low pressure plasma polymerization, nano-scaled oxygen-rich plasma polymer films (CO) were deposited onto pristine silicon wafers as well as on nitrogen-containing plasma polymer (CN) model surfaces. We investigate the influence of the nature of the substrate as well as a potential sub-surface effect emerging from the buried CO/CN interface, just nanometers below the surface. X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry revealed two important phenomena that occurred during the deposition of the terminal CO layer: (1) a strong degree of oxidation, already for 1 nm nominal thickness, and (2) a gradual transition in chemical composition between the two layers, clearly indicating that effectively a vertical chemical gradient results, even when a two-step coating process was applied. Such terminal gradient film structures were used to study film stability in aqueous environments. Molecular rearrangements were scrutinized in the top-surface in contact with water and we found that the top-surface chemistry and wetting properties of the oxygen-rich termination layer matched those of thick CO reference coatings. Nevertheless, the adsorption of green fluorescent protein (GFP) was observed to be sensitive to the CO terminal layer thickness. Namely, an enhanced protein adsorption was observed for 1–2 nm thick CO layers on CN, whereas a significantly reduced protein adsorption was seen on ≥?3 nm thick CO terminal layers. We conclude that both, surface and sub-surface conditions significantly affect protein adsorption as opposed to the traditional consideration of surface properties alone.     

Preparation of Polymer Particles Coated with Hydroxyapatite

Polymer particles coated with hydroxyapatite were prepared by treating Pd0 immobilized polystyrene-co-acrylic acid particles in aqueous CaCl2 and NaH2PO2 solutions. Hydroxyapatite coating took place at neutral to alkaline pH conditions, and the homogeneous growth of the hydroxyapatite layer on the surface of polymer particles was observed at relatively low temperature (30-50 degrees C). The thickness of the hydroxyapatite layer increased with reaction time. Copyright 1999 Academic Press.     

CaP/壳聚糖复合膜层的电化学共沉积研究

用电化学共沉积方法在医用钛合金表面成功制备了CaP/壳聚糖复合膜层,并用XRD,SEM,FTIR漫反射光谱和XPS等对复合膜层化学组成及结构进行表征.结果表明,加入壳聚糖可使钙磷沉积层结构发生显著变化,将壳聚糖掺入钙磷沉积层,形成CaP/壳聚糖复合物和杂化物.力学实验表明,在钛基底表面未进行表面预处理条件下,CaP/壳聚糖复合膜层与钛基底的结合力高达2.6MPa,比单一CaP电化学沉积层与基底的结合力提高约4倍.文中还对壳聚糖参与表面电沉积反应机理进行了讨论.     

The structure and properties of polymer-metallic coating interphase

The structure of the surface layer in polymers (LDPE and PET) decorated with a thin metal (gold and platinum) layer was studied after their deformation under different conditions. It was found that relatively thick coatings debonded from the polymer substrate during tensile drawing. Debonding was observed at low tensile strains (below 20–30%). During the further drawing of a polymer, a regular microrelief typical of deformable “rigid coating on a soft substrate” systems appeared on its surface. This phenomenon is explained by the fact that the debonding metal coating uncovers not the surface of the pure polymer but a certain modified layer, which has a higher elastic modulus than the pure polymer. The formation of this layer is associated with the inclusion of metal atoms into the polymer during the metal decoration by plasma immersion ion deposition. As a result of this inclusion, a modified layer, which has a higher glass transition temperature, a higher elastic modulus, and other mechanical properties, is formed between the coating and the polymer.     

Preparation of an ion-exchangeable polymer bead wrapped with bilayer membrane structures for high performance liquid chromatography

We synthesized a chromatographic packing material that has a non-covalently attached dihexadecyl phosphate (DHP) bilayer membrane structure on a CA08S, a nonporous-type cationic polymer bead with a diameter ranging from 11 to 14 μm. Confocal fluorescence microscopic and differential scanning calorimetric analyses of the DHP-CA08S complex revealed that the DHP bilayer membrane structures were formed on the surface of the CA08S polymer beads. When the functionality of the DHP-CA08S complex was evaluated in the ion-exchange HPLC of proteins, the retention behavior of the proteins on the DHP-CA08S complex column totally mirrored the anionic property of the DHP bilayer membrane surface, not the cationic property of the CA08S bead. Methylene blue (MB) was eluted from the DHP-CA08S complex column in the isocratic elution mode, but not at all from a CK08S column, a styrene-divinylbenzene based cation-exchange polymer. When the column temperature was elevated from 50 to 60 °C, the peak shape of MB on the DHP-CA08S complex column became fairly sharp without a change in its peak area, which mirrored the characteristic phase transition of the DHP bilayer membrane formed on the DHP-CA08S complex.     

Electroosmotic flow suppression in capillary electrophoresis: chemisorption of trimethoxy silane-modified polydimethylacrylamide

Adsorbed polymers are widely used to suppress electroosmotic flow (EOF) in capillary electrophoresis (CE). Polymeric coatings, physisorbed onto the surface of the capillary wall, are often unstable under harsh conditions. This can be attributed to the reversible nature of the coating which becomes apparent when the adsorbed layer competes with a second species in the electrophoresis buffer solution for attachment/interaction with the capillary surface. In an effort to overcome the problem of coating instability, trimethoxysilane-modified polydimethylacrylamide was synthesized. This copolymer rapidly adsorbs on the wall from ultradilute aqueous solutions. After incubation at a temperature of 60 degrees C silyl groups, which extend from the polymer backbone, form condensation bonds with the silanols on the capillary surface. This enables subsequent formation of strong covalent bonds between the copolymer and the capillary wall. In this research, we establish that physisorption of polymer chains to the surface is essential for close alignment of surface and polymer silane groups which facilitates the formation of covalent bonds.     

Stimuli-responsive properties of N-isopropylacrylamide-based ultrathin hydrogel films prepared by photo-cross-linking

To develop stimuli-responsive ultrathin polymer films on a solid substrate, a novel photo-cross-linkable polymer with both temperature- and pH-responsive properties was prepared. The photoreactive 4-aminobenzophenone (BP) was introduced onto the side groups of poly(N-isopropylaclylamide-co-2-carboxyisopropylaclylamide) [poly(NIPAAm-co-CIPAAm)]. This copolymer was designed for highly random sequences of comonomers. After the formation of spin-coated polymer films on a solid substrate, UV-light irradiation started the cross-linking reaction. The spin-coating processes and stability of the polymer films were quantitatively monitored by a quartz crystal microbalance (QCM), and the thickness was estimated using an atomic force microscope (AFM). These measurements confirmed the formation of a very plain polymer film, and the film thickness was precisely controlled by the concentration of the polymer solution used for spin coating. Moreover, the obtained films showed a high stability due to the cross-liking reaction and UV irradiation. Cyclic voltammetry using potassium ferricyanide revealed that the ions could permeate the photo-cross-linked ultrathin polymer films. The permeability of the ultrathin hydrogel films was dramatically changed by varying the pH and temperature of the aqueous media. These observations suggest that the preparation of isopropylacrylamide-based stimuli-responsive ultrathin hydrogel films is possible.     

Surface properties and swelling behaviour of hyperbranched polyester films in aqueous media

Thin films of hydroxyl (POH) and carboxyl (PCOOH) terminated aromatic hyperbranched polyesters (HBPs) were prepared by spin coating on silicon wafers and subsequently annealed above their glass transition temperature (T_g). The surface properties and the swelling behaviour of these films in aqueous buffer solutions were studied as a function of annealing time using contact angle measurements and ellipsometry. Non-annealed films were hydrophilic with surface free energies of 51 mJ/m² for POH and 49 mJ/m² for PCOOH, respectively. The swelling behaviour of the polymer films in buffer solution with pH 7.4 was described in terms of changes of the thickness and effective refractive index of the swollen layer. Under identical conditions a lower water uptake was found for hydroxyl terminated HBPs (POH) which were annealed more then 2 h. The lower water uptake correlates with the surface properties of the films. The annealed films were less hydrophilic. Their surface free energy was 38 mJ/m² independent of the annealing. Films of carboxyl terminated HBPs (PCOOH) showed similar surface properties after annealing. However, these films were unstable under the same conditions in aqueous solutions. Stable PCOOH films were obtained by additional covalent binding to the substrate using an epoxy silane as a coupling agent.     

Weatherability and wear resistance characteristics of plasma fluoropolymer coatings deposited on an elastomer substrate

The weathering characteristics of thin film formed from plasma polymerisation of perfluoro(methylcyclohexane) on an EPDM substrate under cold plasma process operated at 13.56 MHz was investigated using an ATLAS Ci 3000 Xenon weatherometer. The effects of weathering conditions on the chemical composition of the substrate and the coating were examined using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-ray photoelectron spectroscopy (XPS). The wear behaviour was examined using scanning electron microscopy (SEM). The change in the surface morphological behaviour of the coating indicates that the mending line of the patch-wise coating deposition or the fissure/crack line of the coating is particularly sensitive to the initiation of decomposition. FTIR and XPS spectroscopic investigations confirm that under humid and UV conditions, elimination of fluorine and introduction of new oxygen-containing functional groups play predominant role in the decomposition of the coating. Plausible mechanisms of degradation for the elastomer and the coating have been proposed. The coated substrate shows superior abrasion resistance characteristics with respect to the neat elastomer. The adhesion between the substrate and the plasma polymer coating appears to be excellent and remains strong after weathering.     

Interface of nanoparticle-coated electropolished stents

Nanostructures entail a high potential for improving implant surfaces, for instance, in stent applications. The electrophoretic deposition of laser-generated colloidal nanoparticles is an appropriate tool for creating large-area nanostructures on surfaces. Until now, the bonding and characteristics of the interface between deposited nanoparticles and the substrate surface has not been known. It is investigated using X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy to characterize an electropolished NiTi stent surface coated by laser-generated Au and Ti nanoparticles. The deposition of elemental Au and Ti nanoparticles is observed on the total 3D surface. Ti-coated samples are composed of Ti oxide and Ti carbide because of nanoparticle fabrication and the coating process carried out in 2-propanol. The interface between nanoparticles and the electropolished surface consists of a smooth, monotone elemental depth profile. The interface depth is higher for the Ti nanoparticle coating than for the Au nanoparticle coating. This smooth depth gradient of Ti across the coating-substrate intersection and the thicker interface layer indicate the hard bonding of Ti-based nanoparticles on the surface. Accordingly, electron microscopy reveals nanoparticles adsorbed on the surface without any sorption-blocking intermediate layer. The physicomechanical stability of the bond may benefit from such smooth depth gradients and direct, ligand-free contact. This would potentially increase the coating stability during stent application.     

Benzophenone-initiated grafting photopolymerization of acrylic acid on the surface of polyethylene from the monomer aqueous solution without its deaeration

The photoinduced grafting polymerization of a functional monomer (acrylic acid) is performed on the surface of a polymeric material (polyethylene film) from a nondeaerated aqueous solution of the monomer with the use of a water-insoluble photoinitiator (benzophenone). According to the developed method, the photoinitiator is first deposited on the surface of the polyethylene film from solution in a volatile solvent; then, the surface of the film is covered with a layer of the nondeaerated aqueous solution of the monomer, over which a quartz plate or the second polyethylene film is placed, and the resulting sandwich is exposed to UV radiation. This method is highly efficient when the thickness of the monomer-solution layer is less than 100 ??m. Owing to the small thickness of the monomer solution layer and the absence of the inflow of atmospheric oxygen, molecular oxygen that is initially contained in the monomer solution is rapidly consumed in photooxidation reactions occurring on the surface of the substrate polymer; therefore, molecular oxygen insignificantly affects the efficiency of grafting polymerization.