Thin film characterization and vapor sensing properties of a novel perylenediimide material

A novel N,N′-(glycine tert-butylester)-3,4,9,10-perylenediimide was chosen for the study of Langmuir–Blodgett (LB) thin film characterization and the sensing properties against selected volatile organic vapors. Different number of LB film layer was deposited onto a glass and quartz crystal substrate. The thin film fabrication process was monitored with UV–vis and quartz crystal microbalance (QCM) measurement techniques. The results indicated that absorbance increased linearly with the number of the layers on film. A similar linear relationship between frequency shift and number of the layers was observed by the QCM measurement. It can be concluded that high quality and uniform LB films were produced by using this novel perylenediimide material. Chloroform, toluene, benzene, ethyl alcohol and isopropyl alcohol vapors were selected to test this material's applicability in room temperature as a vapor sensor. This novel material showed a fast, large and reproducible response to chloroform and isopropyl alcohol vapor.     

Investigations of prussian blue films using surface plasmon resonance

A fiber-optic based surface plasmon resonance (SPR) instrument is used to characterize electrodeposited prussian blue (PB) films. PB films are deposited potentiostatically or galvanostatically onto the gold sensing surface. When reduced to prussian white (PW), the film undergoes a reversible refractive index change that is observed using SPR. The strong absorbance of PB films within the sensing region of the instrument inhibits quantitative characterization of these films; however qualitative characterization has been achieved. The PB coated SPR probe can be used as an optical transducer of electrochemical phenomena. A PB film is deposited on the gold SPR sensing surface; the probe is submerged in 0.1 M KNO₃ in a tube terminated with a porous vycor frit. The isolated PB half-cell and a AgCl-coated Ag wire are placed in a beaker containing 0.1 M KNO₃ and connected by a variable battery. Addition of chloride to the bulk solution changes the potential of the AgCl wire, which induces a change in the PB film that can be observed using SPR. A change in chloride concentration of 40 μM can be detected using this system.     

Polyaniline–TiO2 nano-composite-based trimethylamine QCM sensor and its thermal behavior studies

Inorganic/organic composites are very attractive due to synergetic behavior and a wide range of potential use. A polyaniline–TiO₂ nano-composite, obtained by combination of chemical polymerization and a sol–gel method, was deposited on the electrode of quartz crystal to implement a quartz crystal microbalance (QCM) chemical sensor. The morphology of the composite film was studied by scanning electron microscopy (SEM) measurements. The coated quartz crystal and a non-coated quartz crystal were mounted in a sealed chamber, and their frequency difference was monitored. When analyte vapor was injected into the chamber, gas absorption decreased the frequency of the coated quartz crystal and thereby caused an increase of the frequency difference between the two crystals. The frequency difference change response towards trimethylamine was evident and could be recovered by N₂ purgation easily. The calibration curve towards trimethylamine, its long-term stability and selectivity were investigated. The thermal behavior of the sensing characteristics was compared with that of a polyaniline QCM sensor. Fourier transform infrared (FTIR) spectra of polyaniline and polyaniline–TiO₂ nano-composite and QCM data under various conditions were used to study the effect of thermal treatment.     

The influence of the surface morphologies of Langmuir Blodgett (LB) thin films of porphyrins on their gas sensing properties

In this work, 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine (OEP) in its free base form and metalated with iron (III) chloride (FeOEP), magnesium(II) (MgOEP) and cobalt(II) (CoOEP) have been used to fabricate Langmuir-Blodgett (LB) thin films. Using the surface pressure-surface area (Π-A) isotherm graphs optimum conditions for thin film deposition have been determined and by changing the deposition parameters various thin films have been deposited. Quartz Crystal Microbalance (QCM) system was used to investigate their gas sensing performances during exposure to Volatile Organic Compounds (VOCs) including chloroform, benzene and toluene. The surface properties have been investigated using Atomic Force Microscopy (AFM) and analyzed together with the QCM results to understand the effect of the surface properties on gas sensing mechanism. It is observed that larger surface area leads to higher response in gas sensing applications in terms of resonance frequency change.     

Effect of soft-hard segment structure on vapor responsiveness of polyurethane conducting composite thin films loaded with multi-walled carbon nanotubes

A series of multi-walled carbon nanotubes/polyurethane (MWNTs/PU) composite conducting dispersoids were prepared via an in situ coupling reaction among linear hydroxyl-terminated polymer diols, 1,6-hexamethylene diisocyanate (HDI) and various chain extenders. The composite conducting thin films were formed by spin-coating and depositing the dispersoids onto comb-like electrode substrates. The resulting structure and the dispersion quality of MWNTs in the dispersoids were examined by means of FTIR, XRD, TEM, SEM and UV-vis analyses. The response of the as-prepared films toward some volatile organic solvent vapors such as benzene, anhydrous ether, acetone and chloroform was evaluated. The experimental results indicated that the composite conducting films constructed by hydroxyl-terminated poly(butadiene-co-acrylonitrile), trimethylolpropane, and MWNTs-OH bear better vapor responsiveness. The dispersion behavior of MWNTs in the dispersoids, types of MWNTs and soft-hard segmental compositions are believed to be closely related with the sensing properties of the films. In particular, the chemical linkage of MWNT-OH with HDI in the PU matrix is expected to improve the dispersivity and further to enhance the sensing properties of the composite sensors. The vapor sensing properties well reveal that these materials have a possibility as a candidate of volatile organic solvent vapor sensors.     

采用聚吡咯修饰的QCM型三甲胺气体传感器

三甲胺是评估肉类食品新鲜度的重要指标之一,并且临床上也比较值得关注,因而三甲胺的检测具有十分重要的意义,为此,我们采用乳聚法制备了聚吡咯材料,并将其涂敷在晶振电极表面后制得敏感石英晶体微天平(QCM).根据敏感QCM和参比QCM间的频率差变化来实现气体的检测.在室温条件下,该气体传感器对三甲胺气体具有较明显的响应.实验从灵敏度、重现性、选择性和稳定性等方面出发,对该传感器的的性能进行了评价.结果表明,虽然传感器的制备方法简单,但它的性能优异.     

Site-directed antibody immobilization on gold substrate for surface plasmon resonance sensors

A simple method for the site-directed immobilization of antibodies on gold substrates has been developed for surface plasmon resonance (SPR) applications. A freshly prepared gold surface on a glass slide was modified with Protein A via homobifunctional cross linker dithiobissuccinimide propionate (DSP) to achieve uniform, stable, and sterically accessible antibody coating. The density of the immobilized antibodies bound to Protein A was examined as a function of the protein concentration, buffer pH, buffer type and reaction time. The suggested scheme was also employed for the modification of gold-coated substrates for quartz crystal microbalance (QCM) applications. The modified gold surface was stable for several weeks and the reproducibility was satisfactory. The current fabrication technique could be applied to construct other immunosensors or biochips.     

Comparison of surface plasmon resonance spectroscopy and quartz crystal microbalance for human IgE quantification

Surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) have been known independently as surface sensitive analytical devices capable of label-free and in situ bioassays. In this study a SPR device and a 10 MHz QCM sensor are employed for the study of human IgE and anti-human IgE-binding reactions upon immobilizing the latter on the gold electrodes. The SPR and QCM response curves to the antibody immobilization and antigen binding are similar in shape but different in time scale, reflecting different resonation principles. Through optimization of the anti-human IgE coating, both the SPR and QCM sensors could detect IgE in a linear range from 5 to 300 IU/ml. Although the intrinsic sensitivity of the SPR device is five times of the 10 MHz QCM, the IgE detection sensitivity of the two methods is, however, different only in a factor of 2. The acceptable QCM sensitivity for the IgE detection is attributed to the fact that QCM measures the sum of molar mass of a protein layer and the entrapped water. Although both the devices use open, stand still liquid cell, and all the measurements are performed at room temperature, the SPR reproducibility and reliability are better than QCM, as the QCM frequency is more sensitive to temperature fluctuations, press changes and mechanical disturbances.     

Formaldehyde sensors based on nanofibrous polyethyleneimine/bacterial cellulose membranes coated quartz crystal microbalance

A novel formaldehyde sensor based on nanofibrous polyethyleneimine (PEI)/bacterial cellulose (BC) membranes coated quartz crystal microbalance (QCM) has been successfully fabricated. The nanoporous three-dimensional PEI/BC membranes are composed of nanofibers with diameter of 30-60 nm. The sensor showed high sensitivity with good linearity and exhibited a good reversibility and repeatability towards formaldehyde in the concentration range of 1-100 ppm at room temperature. Moreover, the results showed that the sensing properties were mainly affected by the content of PEI component in nanofibrous membranes, concentration of formaldehyde and relative humidity. Additionally, the nanofibrous PEI/BC membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors. The simple and feasible method to prepare and coat the PEI/BC sensing membranes on QCM makes it promising for mass production at a low cost.     

Thin polymer film based rapid surface acoustic wave humidity sensors

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) thin films, deposited on the surface of glass slides, were studied using transmission FTIR spectroscopy upon varying relative humidity (RH) from 2 to 70%. The obtained data revealed fast dynamics of water vapor adsorption-desorption with responses on the order of several seconds. Based on the fast FTIR signal intensity changes versus RH, it was proposed that a similar rapid response can be achieved for PVA and PVP coated SAW devices due to changes in mass-loading and film viscoelastic properties upon absorption of water vapor in the films. Sub-micron thickness films were spin-coated onto the surface of LiNbO₃ SAW substrates. Both PVA and PVP based humidity sensors revealed prompt reversible response to variations in humidity, although PVP-based device demonstrated better sensor parameters with total insertion loss variation of about 50 dB over the studied RH range and response time 1.5 s for the humidity step 5-95% (recovery time - 2.5 s), representing one of the fastest SAW-based humidity sensors reported to date.     

三氯甲烷在金属有机框架膜上的吸附过程监测

采用石英晶体微天平（QCM）技术动态监测三氯甲烷在[Cu（C24H22N4O3）]·CH2Cl2金属有机框架膜（Cu—MOFs）上的吸附动力学．吸附与解吸过程中膜质量的变化由QCM的频率变化实时传感测量,结果表明,吸附过程符合假二级动力学模型,其中在三氯甲烷蒸气压条件下的吸附速率常数为在1．01×10^5PaNz存在下速率常数的1．4-2．1倍,半数以上的吸附量相对于气相浓度稀释呈现可逆吸附特征。吸附等温线符合Langmuir等温式,在蒸气压与1．01×10^5PaN2存在条件下（25℃）,三氯甲烷在厚度为0．337μm Cu—MOFs上吸附的平衡常数分别为6．47与3．93L／g,最大吸附量分别为27．2与24．7μg／cm^2。     

Mixed self-assembled lipopolymers with spacer lipids enhancing sensitivity of lipid-derivative QCMs for odor sensors

An odor sensing system using a quartz crystal microbalance (QCM) sensor array and pattern recognition technique has been for years a main research topic in our group. For the general field of artificial olfaction using acoustic-wave based sensors such as QCMs it is vital to search for novel sensing materials. Here we present recent results of our ongoing study on application of pegylated lipids as coatings for QCM odor-sensors. The method presented herein is based on self-assembling of lipids and lipid-derivatives on the QCM surfaces. The disulphide-terminated lipids and lipopolymers are co-chemisorbed onto gold electrodes of QCM sensors by simple immersion in ethanolic solutions. This creates porous supports onto which additional layers of lipopolymers are physisorbed. The method allows for fabrication of lipopolymeric QCM odor-sensors with enhanced sensitivity to odorants, capable of very good discrimination among odorant samples—according to the functional group of an odorant.     

LPG sensing properties of ZnO films prepared by spray pyrolysis method: Effect of molarity of precursor solution

Nanocrystalline ZnO films were deposited onto glass substrates by spray pyrolysis of zinc nitrate solutions and used as a liquid petroleum gas (LPG) sensor. The dependence of the LPG sensing properties on the molar concentration of zinc nitrate solutions was investigated. The ZnO films were oriented along (0 0 2) with the hexagonal crystal structure. The grain size and grain density increased with an increase in molar concentration of zinc nitrate solutions. The gas sensing properties for LPG of the ZnO films for LPG with different grain sizes were measured at different temperatures. The maximum sensitivity of 43% at the operation temperature of 673 K was found for the ZnO film prepared by spraying a 0.1 M solution. The ZnO thin films exhibited good sensitivity and rapid response–recovery characteristics to LPG. Further, it has been shown the gas sensitivity of the ZnO gas sensor depends upon its grain size.     

Mimicking the sense of olfaction: A conducting-polymer-based electronic nose

Abstract— We describe herein the construction of a simple, low-power, broadly responsive vapor sensor. Carbon-black-organic-polymer composites have been shown to swell reversibly upon exposure to vapors. Thin films of carbon-black-organic-polymer composites have been deposited across two metallic leads, with swelling-induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor-sensing elements have been constructed, with each element containing a different organic polymer as the insulating phase. The differing gas-solid partition coefficients for the various polymers of the sensor array produce a pattern of resistance changes that can be used to classify vapors and vapor mixtures. This type of sensor array has been shown to resolve all organic vapors that have been analyzed, and can even resolve H²O from D²O.     

Surface plasmon resonance study on the optical sensing properties of nanometric polyimide films to volatile organic vapours

The optical sensing properties of nanometric polyimide films towards ethanol and methanol vapours have been investigated by surface plasmon resonance technique. To this purpose polyimide sensing layers have been deposited onto gold/glass substrates by glow-discharge-induced vapour deposition polymerization technique. The sensible layer shows reversible and stable responses to different concentrations of methanol and ethanol vapours. A linear dependence between the change in reflectivity and the vapours concentration is observed being the sensitivity to both vapours similar, however, the response is larger in presence of ethanol vapours. Numerical fitting routines on surface plasmon resonance curves indicate that optical changes are motivated by an absorption process of the analyte. This produces a detectable increase of the real refractive index and a swelling process in the polyimide layer.     

基于分子筛薄膜探测神经类毒气的传感器研究

采用ZSM-5分子筛材料对神经类毒剂沙林的相似物甲基磷酸二甲脂(DMMP)气体进行了测试。分子筛材料因为具有选择性吸附分子的能力常被用来作为气体敏感材料,但因为其神经类气体极性较强,被吸附后难于解吸附,因此,分子筛材料很少用于检测神经类气体。利用合成的ZSM-5纳米分子筛作为吸附神经类气体DMMP的敏感材料,将其涂布在2个石英晶体微天平(QCM)上进行差频测试,以减小外界的干扰,并提出了用交变电场进行极性分子解吸附的新方法。DMMP气体的探测最小体积分数达到1×10-6,响应时间和解吸附时间分别小于20 s和90 s。     

Self-assembly of polyelectrolytic multilayer thin films of polyelectrolytes on quartz crystal microbalance for detecting low humidity

Low-humidity sensors were made by layer-by-layer (LBL) self-assembly of poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA) or poly(styrenesulfonic acid) sodium salt (PSS) and poly(allylamine hydrochloride) (PAH) into multilayer thin films on a gold electrode of quartz crystal microbalance (QCM). The thin films were characterized by QCM and atomic force microscopy (AFM). The effects of maleic acid (MA) in PSSMA, the number of layers and the ionic strength on the low-humidity sensing properties (sensitivity) were compared with those of PSS. The sensitivity of the PSSMA/PAH multilayer thin film exceeded that of the PSS/PAH multilayer thin film when the multilayered thin films of polyelectrolytes were prepared from solutions without NaCl. The sensitivity of both PSSMA/PAH and PSS/PAH multilayered thin films was increased by increasing the number of layers and by adding salt to the deposition solution. The PSS/PAH multilayered thin film that was prepared from the solutions with NaCl had the highest sensitivity (1.923 −ΔHz/Δppm_v at 27.5 ppm_v) and a short response time. Spin-coating was also adopted to fabricate PSS-based low-humidity sensors for comparison.     

Composites of carboxylate-capped TiO2 nanoparticles and carbon black as chemiresistive vapor sensors

Titanium (IV) dioxide (TiO₂) nanoparticles (NPs) with a 1-5 nm diameter were synthesized by a sol-gel method, functionalized with carboxylate ligands, and combined with carbon black (CB) to produce chemiresistive chemical vapor sensor films. The TiO₂ acted as an inorganic support phase for the swellable, organic capping groups of the NPs, and the CB imparted electrical conductivity to the film. Such sensor composite films exhibited a reproducible, reversible change in relative differential resistance upon exposure to a series of organic test vapors. The response of such chemiresistive composites was comparable to, but generally somewhat smaller than, that of thiol-capped Au NPs. For a given analyte, the resistance response and signal-to-noise ratio of the capped TiO₂-NP/CB composites varied with the identity of the capping ligand. Hence, an array of TiO₂-NP/CB composites, with each film having a compositionally different carboxylate capping ligand, provided good vapor discrimination and quantification when exposed to a series of organic vapors. Principal components analysis of the relative differential resistance response of the sensor array revealed a clear clustering of the response for each analyte tested. This approach expands the options for composite-based chemiresistive vapor sensing, from use of organic monomeric or polymeric sorbent phases, to use of electrically insulating capped inorganic NPs as the nonconductive phase of chemiresistive composite vapor sensors.     

Oil thermal annealed nano‐structured indium tin oxide thin films for display applications

Indium tin oxide‐coated thin films (200 nm) are deposited on glass substrates by using R.f. sputtering technique. Here, we investigate the influence of new technique of treatment, which is called as “oil thermal annealing” on the nano‐structured indium tin oxide thin films at fixed temperature (150 °C) which improves adhesion strength, electrical conductivity and optical properties (transmittance) of the films. Oil thermal annealing is used to reduce inherent defects that may be introduced during the prepared thin film and cooling processes. Proposed technique is highly suitable for liquid crystal displays, solar cells and organic light emitting diodes, and many other display‐related applications.     

Cycle performance of sol–gel optical sensor based on localized surface plasmon resonance of silver particles

Silver particles generated by the evaporation–condensation method were deposited on the sol–gel derived silica film or the silica glass substrate to form SPR sensors, and their SPR sensing property was examined. When the sensing measurement was repeated, deposited silver particles gradually came off, and optical absorbance was decreased. To avoid these phenomena, silver particles were overcoated with silica thin film prepared by sonogel method. As a result, by adjusting the silica concentration of starting sol or the thickness of sono-silica overcoating, cycle performance of the sensor was improved.