Quartz crystal microbalance

The adsorption of alkyl trimethyl ammonium bromide with alkyl groups from C 10 to C 16 onto solid surfaces (iron and cementite (Fe 3 C)) is investigated with and without NaCl. For the first time the adsorption of these surface active compounds onto model carbon steel compounds are measured directly by the use of a quartz crystal microbalance (QCM). The adsorption increases steeply around the critical micelle concentration (cmc) in bulk which was also determined for the homologous series. The adsorption of the higher homologues shows rather rigid surface structures while a detailed interpretation of the isotherms for the lowest homologues is disturbed by high bulk viscosities. Based on the obtained results, and in comparison with similar adsorbents on hydrophilic oxide surfaces, it is concluded that the surfactant is adsorbed patchwise in similar structures as in bulk. Finally, the possibilities for close-packing of the surfactant film are discussed.

Wheat germ agglutinin (WGA) lectin is a model compound for the interaction between viruses and cells during infection events and thus an interesting analyte for mass-sensitive sensing to study these interaction phenomena. Scanning tunneling microscopy studies reveal that surface molecular imprinting leads to cavities having the dimensions of WGA dimers. These reincorporate WGA from phosphatebuffered saline between 1 and 160 μg/ml. Whereas the quartz crystal microbalance (QCM) frequency for molecularly imprinted polymer (MIP)-coated electrodes decreases, indicating uptake of the analyte, their nonimprinted counterparts yield positive, concentration-dependent frequency shifts characteristic for slip of the analyte on the QCM surface. The MIPs achieve selectivity factors towards bovine serum albumin of roughly 4 at higher protein concentrations. Brunauer-Emmett-Teller analysis reveals that binding is favored by 29 kJ/mol until the adsorption of up to ten monolayers on the MIP, whereas above this range the value is lower. Together with the binding behavior of MIP and nonimprinted polymers, this indicates that the MIP acts as a nucleus for multilayer deposition onto the surface.

Polymeric films can be grown by a sequential, self-limiting surface chemistry process known as molecular layer deposition (MLD). The MLD reactants are typically bifunctional monomers for stepwise condensation polymerization and can yield completely organic films. The MLD of organic-inorganic hybrid polymers can also be accomplished using a bifunctional organic monomer and a multifunctional inorganic monomer. In this work, the growth of a poly(aluminum ethylene glycol) polymer is demonstrated using the sequential exposures of trimethylaluminum (TMA) and ethylene glycol (EG). These hybrid polymers, known as alucones, were grown over a wide range of temperatures from 85 to 175°C. In situ quartz crystal microbalance and ex situ X-ray reflectivity experiments confirmed linear growth of the alucone film versus number of TMA/EG reaction cycles at all temperatures. The alucone growth rates decreased at higher temperatures. Growth rates varied from 4.0 Å per cycle at 85°C to 0.4 Å per cycle at 175°C. In situ Fourier transform infrared spectroscopy was used to monitor the surface reactions during alucone MLD. Ex situ FTIR spectroscopy, X-ray photoelectron spectroscopy, and X-ray reflectivity measurements were also employed to determine the chemical composition, thickness, and density of the alucone films. These ex situ studies revealed that the alucone films grown on Al 2 O 3 ALD surfaces evolved under ambient conditions before reaching a stable state. Alucone films capped with rapid SiO 2 ALD displayed much more stability than alucone films grown on Al 2 O 3 ALD surfaces. These results indicated that H 2 O may facilitate the chemical transformation of the alucone MLD films. The alucone films represent a new class of organic-inorganic hybrid polymers. Modification of this basic alucone MLD chemistry with use of other diols or other bifunctional monomers can produce different alucone polymers with variable properties.

Effects of ultrasound irradiation on DNA polymerase (Klenow fragment, KF) reactions were studied on the template/ primer DNA-immobilized quartz crystal microbalance (QCM). Under ultrasound irradiation, binding of KF to the DNA was suppressed due to the decrease of the binding rate constant (k 1) and the increase of the dissociation rate constant (k-1). The catalytic elongation rate (k cat) was increased, but the stability of the KF/DNA/monomer ternary complex (K m) was decreased by the ultrasound irradiation. Ultrasound effects are discussed in correlation with the conformation changes of domain structures in KF.

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), ζ-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experi-ments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

The adsorbed amount and layer structure of lysozyme, ␤-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and ␤-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though ␤-casein and silica are negatively charged at the pH used. No ␤-casein remained adsorbed after rinsing with a 150 mM buffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. ␤-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and ␤-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/␤-casein layers contain higher amounts of protein compared to those of pure lysozyme or ␤-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and ␤-casein. The protein layers are probably highly interpenetrated with no clear separation between them.

In this work, 2, 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 (˘-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.

The insolubility of single-walled carbon nanotubes (SWNT) in either water or organic solvents has been a limitation for the practical application of this unique material. Recent studies have demonstrated that the suspendability of SWNT can be greatly enhanced by employing appropriate surfactants. Although the efficiency of anionic, cationic, and nonionic surfactants has been demonstrated to different extents, the exact mechanism by which carbon nanotubes and the different surfactants interact is still uncertain. To deepen the understanding of this interfacial phenomenon, we have investigated the effects of chemical modifications of the surface on the extent of nanotube-surfactant interaction. Such changes in the surface chemistry of the SWNT can be achieved by simply varying the pretreatment method, which can be acidic or basic. We have found that intrinsic surface properties such as the PZC (point of zero charge) are greatly affected by the purification method. That is, the electrical charge of the SWNT surface varies with the pH of the surrounding media. However, it has been found that during the adsorption of the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) on SWNT Coulombic forces do not play a central role, but are overcome by the hydrophobic interactions between the surfactant tail and the nanotube walls. Only at pH values far from the PZC do the Coulombic forces become important. The hydrophobic forces between the surfactant tail and the nanotube determine the structure of the surfactant-stabilized nanotubes. In such a structure, each nanotube is covered by a monolayer of surfactant molecules in which the heads form a compact outer surface while the tails remain in contact with the nanotube walls. It is important to note that although the final configuration can be described as a cylindrical micelle with a nanotube in the center, the mechanism of formation of this structure does not proceed by incorporation of a nanotube into a micelle, but rather by a two-step adsorption that ends up in the formation of a surfactant monolayer.

An amperometric lactate biosensor was developed based on a conducting polymer, poly-5,2 0 -5 0 ,2 00 -terthiophene-3 0 -carboxylic acid (pTTCA), and multiwall carbon nanotube (MWNT) composite on a gold electrode. Lactate dehydrogenase (LDH) and the oxidized form of nicotinamide adenine dinucleotide (NAD + ) were subsequently immobilized onto the pTTCA/MWNT composite film. The modified electrode was characterized by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), and electrochemical experiments. The detection signal was amplified by the pTTCA/MWNT assembly onto which a sufficient amount of enzyme was immobilized and stabilized by the covalent bond formation between the amine groups of enzyme and the carboxylic acid groups of the pTTCA/MWNT film. Experimental parameters affecting the sensor responses, such as applied potential, pH, and temperature, were assessed and optimized. Analytical performances and dynamic ranges of the sensor were determined, and the results showed that the sensitivity, stability, and reproducibility of the sensor improved significantly using pTTCA/MWNT composite film. The calibration plot was linear (r 2 = 0.9995) over the range of 5 to 90 lM. The sensitivity was approximately 0.0106 lA/lM, with a detection limit of 1 lM, based on a signal/noise ratio of 3. The applicability of the sensor for the analysis of L-lactate concentration in commercial milk and human serum samples was demonstrated successfully.

Polyelectrolyte multilayers (PEMs) composed of two natural polysaccharides-chitosan (Chi) and alginate (Alg) were deposited by Layer by layer (LbL) assembly on top of biocompatible poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs). Folic acid (FA) or FA grafted poly(ethylene glycol) (PEG-FA) were covalently bounded to the PEMs via carbodiimide chemistry. The assembly of biocompatible PEMs was monitored on planar surfaces by means of the quartz crystal microbalance with dissipation (QCM-D) technique and on top of PLGA NPs by means of f-potential measurements. BSA was used as model protein to characterize protein adsorption on PEMs. QCM-D showed protein deposition could not be observed on the Chi/Alg multilayer, for both Chitosan and Alginate as top layers. Finally, cellular uptake experiments were carried out by co-culture of HepG2 cells in presence of NPs. Flow Cytometry and confocal laser scanning microscopy (CLSM) were used to investigate the influence of the surface chemistry of the NPs on uptake. For the HepG2 cell line significantly less uptake of PLGA NPs coated with Chi/Alg than the bare NPs was observed but the uptake increased after attachment of FA molecules.

This thesis contains a systematic study of the dispersion of pristine HiPco Single Walled Carbon Nanotubes (SWNTs) in a series of organic solvents. A double beamed UV-Vis-NIR absorption spectrometer coupled with an integrating sphere was employed to demonstrate the dispersibility of SWNTs in different solvents. Raman Spectroscopy and Atomic Force Microscopy (AFM) were used to confirm the debundling and exfoliation of SWNTs aggregates. An investigation of the solubility of SWNTs in four chlorinated aromatic solvents demonstrated that the similarity in structure between solvent molecules and nanotube sidewall is not a dominant factor to obtain stable SWNT solutions. A comparative study of the solubility of SWNTs between the aromatic solvents and other reported solvents was then conducted, in terms of the solvent solubility parameters, including Hildebrand and Hansen solubility parameters. Although the established correlation between extinction/absorption coefficients as a function of Hildebrand/Hansen solubility parameters indicated there may be a selective debundling of metallic and semiconducting SWNTs in different solvents, this was not confirmed by a detailed Raman investigation. A further study of the dispersion limit of SWNTs in different solvents as a function of the solvent solubility parameters was carried out. Good agreement with literature is demonstrated here in terms of Hildebrand parameters, but not in terms of the Hansen solubility parameters. It has been demonstrated that the degree of dispersion is critically dependent on sample preparation conditions, in particular sonication. Finally, the effect of sonication parameters and solvent properties ii during the dispersion of SWNTs was investigated. The results indicated that the sonication process is closely dependent on many of the physical parameters of the solvent, including vapour pressure, viscosity, surface tension, density and molecular weight. Longer sonication time and higher sonication power help debundling SWNTs in organic solvents but significantly damage the nanotubes. The choice of solvent should be guided by minimisation of sonication requirements. iii DECLARATION

Using estimates of particulate matter (PM), PM10 and PM2.5 made from the mass size distributions measured regularly using a Quartz Crystal Microbalance (QCM) impactor for the period October 1998-December 2000 at the coastal station Trivandrum, the long-term average values (for 27 months) of PM10 and PM2.5 are estimated. The season wise shares of PM10 and PM2.5 to PM are computed. Results indicate highest contribution of PM10 to PM during local summer/premonsoon while the contribution of PM2.5 to PM peaks during local winter. These shares are lowest during monsoon months. Average values of PM10 and PM2.5 were found to be around 50 and 43 mg m À 3 under ambient conditions. For making an environmental assessment these values are corrected for humidity changes and reduced to a constant RH level of 50%. An order of magnitude estimate is made of the sea salt contribution to the total based on recent measurements during the INDOEX. After these apportionments, it is found that even though the PM10 concentration is well below the standards set by several national environmental agencies, the PM2.5 concentration appears to be quite critical. The findings are discussed.

Thymidylate synthase (TS) and dihydrofolate reductase (DHFR) play essential role in DNA synthesis, repair and cell division by catalyzing two subsequent reactions in thymidylate biosynthesis cycle. The lack of either enzyme leads to thymineless death of the cell, therefore inhibition of the enzyme activity is a common and successful tool in cancer chemotherapy and treatment of other diseases. However, the detailed mechanism of thymidylate synthesis cycle, especially the interactions between cycle enzymes and its role remain unknown.

Quartz crystal microbalance (QCM) modified with graphene has been fabricated using solution drop-coating method and used for the detection of formaldehyde. Measurement was based on frequency shifts due to the adsorption of vapor at the surface of modified electrode. It was found that frequency shifts were linear to the concentrations of analytes in the range of 10 and 100ppm with the correlation coefficients of above 0.996. The influence of humidity on the sensor was also examined. Results showed that the humidity effects were innegligible.

Abstract:  The recovery and identification of latent fingerprints from a crime scene are crucial to many investigations. The cyanoacrylate (superglue) fuming method (CFM), which develops fingerprints by growing a polymer coating over the print residue, is a powerful method but encounters severe limitations when prints are aged or exposed to harsh environmental conditions. We examine the aging process and how the changes that occur to a fingerprint residue over time influence the growth of polymer during development. We identify loss of initiator by erosion and degradation that, when coupled with a loss of water from the print residue, result in a decreased ability to polymerize ethylcyanoacrylate. Then, we present a methodology by which the ability of aged latent fingerprints to polymerize ethylcyanoacrylate is recovered. Two print enhancement agents, acetic acid and ammonia, are demonstrated to improve the growth of polymer from the print ridges by over an order of magnitude, while retaining the integrity of the print structure. Comparison between the two enhancement agents indicate that the enhancement occurs due to ridge coating by the ammonia or acetic acid and pH control of the latent print.

Molybdenum sulfide is deposited by atomic layer deposition (ALD) using molybdenum hexacarbonyl and hydrogen sulfide. Film growth is studied using in-situ quartz crystal microbalance, ex-situ X-ray reflectivity and ellipsometry. Deposition chemistry is further investigated with in-situ Fourier transform infrared spectroscopy. Self-limiting nature of the reaction is observed, typical of ALD. Saturated growth rate of 2.5 Å per cycle at 170 C is obtained. As-deposited films are found amorphous in nature. As-grown films are tested as lithium-ion battery anode under half cell configuration. Electrochemical chargedischarge measurements demonstrate a stable cyclic performance with good capacity retention. Discharge capacity of 851 mAh g À1 is obtained after 50 cycles which corresponds to 77% of capacity retention of the initial capacity.

As part of the preparation process during assembly of thermally activated batteries, the stainless steel piece parts are n o d y cleaned by vapor degreasing w i t h trichloroethylene. Severe restrictions on the use of chlorinated and fluorinated hydrocarbons in recent years prompted the evaluation of a number of aqueous cleaners as a replacement technology for this application. A total of seven commercial aqueous degreasers was evaluated in this study at several dilution ratios and temperatures. One organic cleaner was also examined under ambient conditions. The effectiveness of the cleaner was determined by the use of x-ray phatoelectron spectroscopy (XPS), which is a surface analytical technique that is very sensitive to low levels of surface containinants. A quartz-crystal microbalance (QCM) that is immersed in the cleaning bath was evaluated as a tool for monitoring the bath cleanliiess. The best overall cleaning results were obtained with Micro, Impro-Clean 3800, and Sonicor cleaners. ~-_ _ *Currently with Sandia National Laboratories, Neutmn Generator DepL grease, and wax. These metal parts include the battery case, current collectors, blank end plates, and headers which are metal plates containing glass-to-metal kedthroughs. In the past, these were normally cleaned by vapor degreasing with trichloroethylene, since this provided excellent results. However, severe restrictions as a result of the Montreal Protocol have been imposed on the use of chlorinated and fluorinated hydrocarbons in recent years. These materials have been linked with destruction of the protective ozone layer in the upper atmosphere. The Department of Energy (DOE) has mandated that these haaogemted organic cleaners can no longer be used at any of the facilities within the nuclear-weapon complex, which includes Sandia National Laboratories and, until last year, Martin-Marietta Specialty Components, Inc. (Largo, FL). A number of alternatives were considered. One possibility involved the use of non-halogenated organic solvents. This option would be dBicult to implement because of costs and concerns involving environmental safety and health (ES&H) issues at Sandia and the DOE. The ff aminability and toxicity of such solvents would make them unacceptable. A second alternative considered was supercritical extraction with GO,. This was deemed too costly and time-consuming for a production environment. In addition, the high pressures and large tanks required were ES&H concerns. A third option was the use of aqueous cleaners. On first examination, there did not appear to be any Serious ES&H issues with this technology. It is relatively easy to use and the cost should be reasonable. There are a fair number of commercial aqueous cleaners on the market, with a wide variety of active ingredients. Some of the aqueous cleaners are terpene based, while others contain various proprietay alcohols, activators, and sufiactmts. Inhibitors are usually added to prevent corrosion of metal parts during cleaning. (Compatibility of the cleaner with the parts to be cleaned can be an important issue for some materials.) Many have little or no volatile organic compounds (VOCs), which increases safety by minimizing flammability and personnel-exposue concerns. Many are biodegradable, which facilitates waste disposal. Consequently, they are considered environmentally benign. We decided to pursue the last option, as it appeared to be the most viable one for implementation at Sandia and for the DOE in the long run to address cleaning needs, based on preliminary work at Sandia, Martin-Marietta, and Allied Signal, Kansas City, MO. A total of seven commercial aqueous degreasers was evaluated in our study. A commercial organic solvent was added later in the study, for comparative purposes, l l l y realizing that it was uniikely to be used. To be practical, it was envisioned that parts would be cleaned in ti batch mode, rather than using a once-through technique. S i n c e the con taminants would continue to accrue w i t h repeated use, some means of monitoring the bath would be necessary. The

A piezoelectric quartz crystal where the gold electrode is amalgamated with mercury is proposed as a sensor for sulphur compounds. The sensor is selective towards such compounds in both the vapour phase (particularly SO 2 and H 2 S) and liquid phase. The dependence of its responsiveness to SO 2 on the mercury concentration, amalgamation conditions and experimental procedure is discussed. The sensor is especially stable under continuous-flow conditions. For application to the determination of free and bound sulphur dioxide in wine, a continuous-flow manifold was developed with a view to combine sample treatment and detection on-line. The results thus obtained were favorably compared with those provided by the Ripper recommended method. The reproducibility of analyses of real wine samples was better than 3.5% and recoveries ranged from 98 to 103%.

This work describes the synthesis of a thiolated polyethylene oxide that self-assembles on gold to create a non-fouling surface. Thiolated polyethylene oxide was synthesised by reacting 16-mercaptohexadecanoic acid with polyethylene glycol mono methyl ether. The coverage of the thiolated polyethylene oxide on gold was studied by cyclic voltammetry, and the modified surfaces were characterised by X-ray photoelectron spectroscopy and ellipsometry. Protein resistance was assessed using quartz crystal microbalance. Results showed a non-fouling character produced by the thiolated polyethylene oxide. The synthesised product was used as the passivation layer on nano-patterned surfaces consisting of arrayed nano-spots, fabricated by plasma based colloidal lithography. The specific adsorption of anti-bovine serum albumin in the mercaptohexadecanoic acid spots was verified by atomic force microscopy. #

A nanocrystalline diamond coated thickness shear mode resonator has been fabricated as an alternative to the quartz crystal microbalance. Due to the low temperature phase transition of quartz, the piezoelectric material was replaced with langasite, a piezoelectric with no phase transition up to its melting point. The resulting device shows clear resonant behavior and oscillates in both air and in liquid. The diamond coating shows clear faceting by scanning electron microscopy and sp 3 bonding by Raman spectroscopy.

Quartz crystal microbalance (QCM) sensors coated with molecular imprinted polymers (MIP) have been developed for the determination of thymine. In this method, methacryloylamidoadenine (MA-Ade) have used as a new monomer and thymine template for inspiration of DNA nucleobases interaction. The thymine can be simultaneously hydrogen binding to MA-Ade and fit into the shape-selective cavities. Thus, the interaction between nucleobases has an effect on the binding ability of the QCM sensors. The binding affinity of the thymine imprinted sensors has investigated by using the Langmuir isotherm. The thymine imprinted QCM electrodes have shown homogeneous binding sites for thymine (K a : 1.0 × 10 5 M −1 ) while heterogeneous binding sites for uracil. On the other hand, recognition selectivity of the QCM sensor based on thymine imprinted polymer toward to uracil, ssDNA and ssRNA has been reported in this work.

In this paper, a portable instrument is developed for a qualitative discrimination among different gas samples. The system is able to implement various gas measurement protocols entered by a user, display incoming online samples during an observation, and display classified gas sets from several observations. The system comprises the following: 1) an input unit, which is a quartz sensor array in a cell with microcontroller circuitry for sampling and data transfer; 2) a computational unit, which is a dedicated computer administrated with specially coded software; and 3) an output unit, which consists of relays for controlling gas valves and a liquid crystal display (LCD) for data presentation. The sampling circuitry is programmed using a low-level language, and the computer is programmed using a high-level programming language. The operating system is specifically configured to obtain a dedicated system. The distributed components of the system (the sampler, the display, and the application processes) are automatically started when the system is turned on. The system can easily be moved to a site where a gas observation is required. The system is extensively tested in a laboratory environment for the qualitative and quantitative properties of three industrial gases: acetone, chloroform, and methanol. Reasonably good results are obtained during both tests, e.g., the system successfully classified different species in qualitative tests and different concentration amounts in quantitative tests.

The solubility of nitrogen, oxygen, carbon dioxide and water in poly(lactic acid) (PLA) was measured using a quartz crystal microbalance (QCM). For that purpose an apparatus based on the quartz crystal microbalance technique was built. This apparatus was calibrated with the system carbon dioxide in atactic polystyrene and the determined precision was of 3%. Measurements were performed up to atmospheric pressure and in the temperature region from 293.2 to 313.2 K.

Polymeric films can be grown by a sequential, self-limiting surface chemistry process known as molecular layer deposition (MLD). The MLD reactants are typically bifunctional monomers for stepwise condensation polymerization and can yield completely organic films. The MLD of organic-inorganic hybrid polymers can also be accomplished using a bifunctional organic monomer and a multifunctional inorganic monomer. In this work, the growth of a poly(aluminum ethylene glycol) polymer is demonstrated using the sequential exposures of trimethylaluminum (TMA) and ethylene glycol (EG). These hybrid polymers, known as alucones, were grown over a wide range of temperatures from 85 to 175°C. In situ quartz crystal microbalance and ex situ X-ray reflectivity experiments confirmed linear growth of the alucone film versus number of TMA/EG reaction cycles at all temperatures. The alucone growth rates decreased at higher temperatures. Growth rates varied from 4.0 Å per cycle at 85°C to 0.4 Å per cycle at 175°C. In situ Fourier transform infrared spectroscopy was used to monitor the surface reactions during alucone MLD. Ex situ FTIR spectroscopy, X-ray photoelectron spectroscopy, and X-ray reflectivity measurements were also employed to determine the chemical composition, thickness, and density of the alucone films. These ex situ studies revealed that the alucone films grown on Al 2 O 3 ALD surfaces evolved under ambient conditions before reaching a stable state. Alucone films capped with rapid SiO 2 ALD displayed much more stability than alucone films grown on Al 2 O 3 ALD surfaces. These results indicated that H 2 O may facilitate the chemical transformation of the alucone MLD films. The alucone films represent a new class of organic-inorganic hybrid polymers. Modification of this basic alucone MLD chemistry with use of other diols or other bifunctional monomers can produce different alucone polymers with variable properties.

Studies in flow displacement systems have shown that the reversibility of bacterial adhesion decreases within seconds to minutes after initial contact of a bacterium with a substratum surface. Atomic force microscopy (AFM) has confirmed that the forces mediating bacterial adhesion increase over a similar time span. The interfacial rearrangements between adhering bacteria and substratum surfaces responsible for this bond maturation have never been studied. Quartz crystal microbalance with dissipation (QCM-D) senses the interfacial region in real time and nondisruptively up to 250 nm from the sensor surface. In this paper, QCM-D is combined with real-time observation of bacterial adhesion in a flow displacement system, in order to analyze resident-time-dependent changes in dissipation. Three different Streptococcus salivarius strains showed a nonlinear relation between total dissipation shift (ΔD) and number of adhering bacteria, whereas inert and rigid silica particles demonstrated a linear relation between ΔD and the number of adhering particles. This suggests removal of interfacial water due to residence time dependent deformation of the nonrigid bacterium-substratum interface during bond maturation. Dissipation could be described by an exponentially decaying function, which combined with adhesion data allowed extraction of the dissipation shifts per bacterium upon initial contact (ΔD 0 ), after bond maturation (ΔD ¥ ), as well as a characteristic time constant (τ bm ). All bacterial strains showed significant bond maturation within one minute after their arrival at the substratum surface, which was not observed for silica particles. Dissipation analysis at the level of individually adhering bacteria would have been impossible without the simultaneous real-time analysis of bacterial adhesion numbers.

In situ polymerization of aniline using ammonium peroxydisulphate (APS) as an oxidizing agent in the presence of chitosan (Cs) was used to synthesize Cs/polyaniline (PANI) nanofibers. The structure and morphology of the Cs/PANI nanofibers powder were characterized by using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV-visible spectroscopy and scanning electron microscope (SEM). The surface of the Cs/PANI seems like interconnected nanofibers with diameters of approximately 50 nm. A film of the Cs/PANI nanofibers was built onto a quartz crystal microbalance (QCM) electrode by drop casting and this film was used to develop a sensor to measure the concentration of volatile organic vapors such as amines and alcohols in air. The frequency shifts ( f) of the QCM, due to the vapor adsorption onto the Cs/PANI nanofibers film, were measured and related to the vapors' concentrations. Linear relationships existed between the f (Hz) and the analytes' concentrations. The sensor showed a good sensitivity, reproducibility and reversibility. The influence of different temperatures on the vapor adsorption onto the Cs/PANI nanofibers film was studied. The kinetics of diffusion of the gases and the diffusion coefficients (D), were discussed.

Soluble alkyl- and alkoxyl-substituted regiochemically defined polyterthiophenes are used as active layers in sensing organic thin films transistors (OTFTs). Such active layers have a polycrystalline morphology and the substituent chains bear different associated dipole moments. Volatile organic compounds carrying moieties that are chemically homologous to the selected polymers’ side chains are used as analytes. Both electrical and quartz crystal microbalance sensor responses are evaluated and a rationale for the sensing mechanisms involving weak polar/polar-type interactions is proposed.

This paper discusses the interrelated phenomena of solid electrolyte interphase (SEI) formation and the irreversible charge consumption which occurs during the ®rst cycle of a graphite electrode, as well as their relevance to the cycling stability of lithium-ion batteries. Thus, results from relevant characterization methods, namely, in situ mass spectrometry, in situ infrared spectroscopy, in situ Raman and video microscopy, in situ scanning probe microscopy, in situ quartz crystal microbalance, and differential scanning calorimetry were combined for a more thorough understanding of observations made in cycling experiments. From electrochemical cycling tests, we have learned that a high speci®c charge ($360 Ah/kg of carbon), satisfactory cycle life of the graphite electrodes (1000 deep cycles), and an irreversible charge of <7% during SEI formation can only be obtained when water contamination of the cell is avoided. Under such conditions, a good-quality SEI ®lm is formed on the carbon surface. We conclude that during SEI ®lm formation, at ®rst the carbonate solvent(s) are reduced, forming ethylene gas, organic radicals, oligomers, and polymers. Then a SEI ®lm is precipitated on the surface via a nucleation and growth mechanism. The irreversible charge consumption due to SEI formation is proportional to the BET speci®c surface area of the graphite and rapidly increases with increasing water content in the cell. #

An  immunohistochemical  (IHC)  technique  was  optimised  using  a  monoclonal  antibody  (MAb)  to  detect  Mycoplasma  mycoides  subsp.  mycoides  (Mmm),  the  agent  of  Contagious  Bovine  Pleuropneumonia (CBPP), in sections of lung tissue. A panel of MAbs was produced and screened for Mmm  specificity  and  for  cross-reactivity  against  other  mycoplasmas  belonging  and  not  belonging  to  the  Mycoplasma  mycoides  cluster,  using  in  parallel  indirect  ELISA  (i-ELISA)  and Immunoblotting  (IB).  Based  on  i-ELISA  and  IB  characterization  data,  1  MAb  (clone  3G10E7)  was  selected and its highest affinity vs Mmm was confirmed by the Quartz Crystal Microbalance (QCM) technology. Afterwards, IHC analyses were conducted to compare MAb 3G10E7 vs rabbit Mmm specific  hyperimmune  serum  using  lung  tissue  sections  of  CBPP  infected  and  CBPP  negative  animals. Results suggest that screening of MAbs using in parallel ELISA, IB, and QCM technology enables to select high affinity target specific MAbs. Immunohistochemical results demonstrated that  MAb  3G10E7  improved  IHC  performances,  showing  reduced  background  staining  and  no  cross-reactivity against Mycoplasma bovis, which is responsible of pneumonia in cattle.

Poly(2-hydroxyethyl methacrylate) based thin coatings were electro-synthesized by cyclic voltammetry on Au-coated quartz crystal surfaces to study different solid-liquid interfacial processes. By varying the electrochemical parameters and the presence or not of a crosslinking agent, films were obtained with thicknesses ranging from 5 to 90 nm. Surface characterization was performed by X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. Using quartz crystal microbalance with dissipation monitoring to investigate the relationship between the film thickness and the swelling behavior, it was found that these characteristics can be modulated by varying either the number of voltammetric cycles or the presence of the crosslinker. Cell adhesion and biocompatibility tests indicate that these film coatings were suitable for biomedical applications.

Carcinoma tumor cells express highly glycosylated mucins acting as ligands for selectin adhesion receptors and thus facilitating the metastatic process. Recently, a sulfated galactocerebroside SM4 was detected as solely P-selectin ligand on MC-38 colon carcinoma cells. Here we characterize the functionality of SM4 as selectin ligand using model membrane approaches. SM4 was found concentrated in lipid rafts of MC-38 cells indicating a local clustering that may increase the avidity of P-selectin recognition. To confirm this, SM4 was incorporated at various concentrations into POPC model membranes and lateral clustering was analyzed by fluorescence microscopy and found to be comparable to glycolipids carrying the sLe x epitope. SM4 containing liposomes were used as cell models, binding to immobilized P-selectin. Quartz crystal microbalance data confirmed SM4/P-selectin liposome binding that was inhibited dose-dependently by heparin. Comparable binding characteristics of SM4 and sLe x liposomes underscore the similarity of these epitopes. Thus, clustering of SM4 on tumor cells is a principle for binding P-selectin.

Gas and volatile organic compounds (VOCs) release in soil is known to be linked to microbial activity and can differently affect the life of organisms in soil. Electronic noses (E-noses) are sensing devices composed of sensor arrays able to measure and monitor ...

This review details the methods used in the production of a range of Q-state semiconductor and metal particles in Langmuir᎐Blodgett films, and describes some of the many methods used to characterise the particle-films. Chalcogenide based semiconductor particles can be grown in Langmuir᎐Blodgett films by cycles of immersion in a solution containing the appropriate metal cation and exposure to a chalcogenide gas. The preparation of metal Ž . chalcogenide MX, where X s O, S, Se, Te particles is discussed in terms of mechanistic insights into particle formation and growth. In particular, research investigating the role of the metal ion coordination sphere in the rate of particle formation and the roles of water and chemical capping in particle growth are presented. Various analytical techniques have been used to characterise the films including UVrvisible absorption and grazing angle FTIR spectroscopies, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, surface plasmon resonance and quartz crystal microbalance gravimetry. Methods for manipulating the optical properties of the particle-films, such as the production of core-shell particles and co-existent particles of different composition are presented. The formation of Q-state metal particles by CO or hydrazine reduction is referred to as an analogous technique. Finally, the results of photoelectrochemical and photobleaching measurements, are discussed in light of their potential usage as components in photoactivated devices. ᮊ

In the recent studies, the quantification methods for iodine in different food samples demand sophisticated laboratory equipment. Other methods are not sensitive enough for trace analyses of iodine. In this paper, a simple, fast, easy-to-use, and sensitive technique for the determination of iodine content is described using quartz crystal microbalance. The iodine content is related to the decrease in frequency caused by the deposition of iodine into the gold electrodes. This method, having a detection limit of 0.5 µg/L, showed reproducible results and no significant interferences from common ions.

A ferritin-immobilized electrode based on self-assembled monolayer (SAM)-modified gold electrodes was developed. Various alkane thiols containing functional groups as the terminal group were used for the SAMs. The ferritin-immobilized SAM-modified electrodes were characterized by electrochemical, atomic force microscopy (AFM) and quartz crystal microbalance (QCM) techniques. The results indicated that ferritin was selectively immobilized onto amino terminal alkane thiol-modified electrodes by the electrostatic interaction between ferritin and the terminal functional groups of the SAMs. The ferritin-immobilized modified electrode showed a direct electron transfer reaction between ferritin and the electrode. The electrochemically regulated uptake and release of iron ions for ferritin immobilized on the SAMs was demonstrated. The AFM and QCM results showed that ferritin molecules covered the whole electrode surface at almost a full monolayer level. The results obtained in this work indicate that ferritin has potential for a biomaterial in nanomaterial synthesis for potential magnetic, catalytic and biomedical sensing applications.

The auto-cleavage product from the C-terminal part of the capsid protein of the flock house virus, namely the c 1 peptide, was used as a model peptide to characterize the initial steps of viral membrane penetration. Monolayers at the air-water interface were used to investigate the phase behaviour of ternary lipidpeptide mixtures, whereas solid-supported membranes were used to visualize the lytic activity of the c 1 peptide. 1,2-Dipalmitoyl-sn-glycero-phospatidylcholine/1,2-dipalmitoyl-sn-glycero-phospatidylserine (4:1) membranes were used as negatively charged model membranes. By means of film balance techniques lipid/peptide discrimination was found resulting in a lipid-rich and a peptiderich phase. Quartz crystal microbalance and scanning force microscopy experiments led to the conclusion of a detergent-like mechanism of the c 1 peptide resulting in mixed lipid-peptide micelles with a molar ratio of 2.8:1. A monolayer adsorption with an ongoing lysis of membranes was found with c 1 peptide molecules interacting at membrane defects.

Molecularly imprinted polymers (MIPs) are gaining great interest as tailor-made recognition materials for the development of biomimetic sensors. Various approaches have been adopted to interface MIPs with different transducers, including the use of pre-made imprinted particles and the in situ preparation of thin polymer layers directly on transducer surfaces. In this work we functionalized quartz crystal microbalance (QCM) sensor crystals by coating the sensing surfaces with pre-made molecularly imprinted nanoparticles. The nanoparticles were immobilized on the QCM transducers by physical entrapment in a thin poly(ethylene terephthalate) (PET) layer that was spin-coated on the transducer surface. By controlling the deposition conditions, it was possible to gain a high nanoparticle loading in a stable PET layer, allowing the recognition sites in nanoparticles to be easily accessed by the test analytes. In this work, different sensor surfaces were studied by micro-profilometry and atomic force microscopy and the functionality was evaluated using quartz crystal microbalance with dissipation (QCM-D). The molecular recognition capability of the sensors were also confirmed using radioligand binding analysis by testing their response to the presence of the test compounds, (R)-and (S)-propranolol in aqueous buffer.

The study deals with the adhesion and proliferation of bovine retina pericytes onto surfaces of poly(hydroxymethylsiloxane) (PHMS) modified either by cold plasma or by low-energy ion beams. The surface treatment was able to convert the original polymer matrix into SiO 2like phases for O 2 -plasma or ion-mixed SiC x O y (H z ) phases for ion irradiation, respectively, with different modification levels of the surface free energy (SFE) and related surface wettability. Pericytes exhibited a negligible adhesion and proliferation onto untreated PHMS, an enhanced adhesion but not proliferation on plasma-treated PHMS, and great adhesion and proliferation to full confluence on ion-irradiated PHMS, as measured by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), quartz crystal microbalance, and optical microscopy. On the other hand, the adhesion and proliferation of GP8.39 endothelial cells (EC), which are strongly associated with pericytes in microvasculature, were very scarce onto both untreated and surface-modified PHMS. The surface-selective pericytal response was related to changes of physicochemical properties of PHMS film, from hydrophobic/neutral towards hydrophilic/negatively charged polymer layers, as well as to short-and long-time events of cell-surface interaction. We propose that surface properties can mediate and modulate cellpolymer matrix adhesion through the establishment of stereospecific chemical interactions and/or electrostatic repulsion, which can also explain the different behavior of pericytes compared to EC. D

This review discusses the current state of electrochemical biosensors in the determination of mycotoxins in foods. Mycotoxins are highly toxic secondary metabolites produced by molds. The acute toxicity of these results in serious human and animal health problems, although it has been only since early 1960s when the first studied aflatoxins were found to be carcinogenic. Mycotoxins affect a broad range of agricultural products, most important cereals and cereal-based foods. A majority of countries, mentioning especially the European Union, have established preventive programs to control contamination and strict laws of the permitted levels in foods. Official methods of analysis of mycotoxins normally requires sophisticated instrumentation, e.g. liquid chromatography with fluorescence or mass detectors, combined with extraction procedures for sample preparation. For about sixteen years, the use of simpler and faster analytical procedures based on affinity biosensors has emerged in scientific literature as a very promising alternative, particularly electrochemical (i.e., amperometric, impedance, potentiometric or conductimetric) affinity biosensors due to their simplicity and sensitivity. Typically, electrochemical biosensors for mycotoxins use specific antibodies or aptamers as affinity ligands, although recombinant antibodies, artificial receptors and molecular imprinted polymers show potential utility. This article deals with recent advances in electrochemical affinity biosensors for mycotoxins and covers complete literature from the first reports about sixteen years ago.

Piezoelectric sensors are acoustic sensors that enable the selective and label-free detection of biological events in real time. These sensors generate acoustic waves and utilize measurements of the variation of the wave propagation properties as a signal for probing events at the sensor surface. Quartz crystal microbalance (QCM) devices, the most widespread acoustic resonators, allow the study of viscoelastic properties of matter, the adsorption of molecules, or the motility of living cells. In a tutorial-like approach, this review addresses the physical principles associated with the QCM, as well as the origin and effects of major interfering phenomena. Special attention is paid to the possibilities offered by QCM that go beyond microweighing, and important recent examples are presented.