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At least 613 records · Page 34Linked to original sources
PubMed1997

Optimisation of the experimental conditions of a new method, based on a quartz crystal microbalance, for the determination of cyanide.

A new method based on a quartz crystal microbalance was developed for the determination of cyanide. As the sensitivity depends on pH, temperature and nitrogen flow rate, a modified simplex was used to optimise these experimental parameters. Two different versions of the proposed method were optimised. For the first version a sensitivity increase of 1.5 was observed after 27 runs, whereas for the second version a sensitivity increase of 1.7 was observed after 12 runs.

Cyanides↗
PubMed2000

Microclimate monitoring of indoor environments using piezoelectric quartz crystal humidity sensors.

The aim of this paper is to describe indoor microclimate monitoring at two different locations, Sandham Memorial Chapel, in Hampshire, England, and the castle El Alcázar, in Segovia, Spain. Piezoelectric quartz crystal sensors with novel humidity sensitive poly(ethyleneimine) coatings and Pt resistance thermometers were used to measure the relative humidity (RH) and temperature gradients across one of the paintings of the British artist, Stanley Spencer, housed in Sandham Memorial Chapel. The measurement period extended from December 1997 to September 1998. Each coated crystal was set in its own housing from which temperature and RH measuring circuits were connected via a cable to the computer. The 9 month monitoring period incorporated the range in seasons from winter through to autumn. Between December and February the RH at the back of the painting was found to be lower than that at the front. In March and April the reverse was true. Additionally, there were large spikes in the data in some of the months for both RH and temperature, probably caused by direct sunlight falling on the sensors. At the second site monitoring was performed for a shorter period, from December 1997 to early January 1998. It served, however, to show that abrupt changes can occur in the microclimate surrounding the painting. These fluctuations can with time lead to alterations to the paint surface and result eventually in cracking and damage to the art work.

Air Pollution, Indoor↗
PubMed2000

Disposable, low cost, silver-coated, piezoelectric quartz crystal biosensor and electrode protection.

The use of a commercial, silver-coated, piezoelectric quartz crystal as a disposable, low cost and reliable immunosensor is presented. The protection of the silver electrode from undesirable oxidation was achieved by polystyrene or carboxy-poly(vinyl chloride) (PVC-COOH) modification. In addition to serving as protection for the electrode, polymer films provided a substrate for antibody immobilization by either physical adsorption or covalent linkage. Polystyrene modification showed an additional advantage of improvement of surface smoothness. The atomic force microscope (AFM) and scanning electron microscope (SEM) were used to evaluate the morphologies of polymer films obtained by dip or drop coating techniques. It was found that drop coating provided more significant improvement in surface smoothness than dip coating, and the resulting sensor surfaces were more suitable for in situ liquid phase assay. Although PVC-COOH-modified sensors were not suitable for liquid phase assay because of the high surface roughness, the covalent linkages (amide bonds) between antibodies and -COOH groups in the polymer film offered better sensor performance in ex situ assay in terms of a higher antibody binding capacity and better antigen detection sensitivity.

Biosensing Techniques↗
PubMed2001

A quartz crystal resonant sensor (QCRS) study of HSA--drug interactions.

Human serum albumin (HSA) was immobilised on the gold surface of a quartz crystal resonance sensor (QCRS) and exposed to warfarin and diazepam. Distinct decreases in frequency of differing magnitudes were observed upon exposure of the protein to each of the compounds suggesting strongly that a ligand interaction was occurring. Moreover, as sequential exposure in any order was observed to yield distinct repeatable frequency decreases for the ligands indicated, screening for site specific binding may be possible. Identically immobilised bovine serum albumin (BSA) gave no response to either compound.

Animals↗
PubMed2002

Effect of static magnetic field on growth of Escherichia coli and relative response model of series piezoelectric quartz crystal.

The effect of magnetic field on the growth of bacteria was studied with the series piezoelectric quartz crystal (SPQC) sensing technique. The growth situations of Escherichia coli (E. coli) in the absence and presence of different intensities of static magnetic fields were examined and analyzed. The results showed that the growth of E. coli was inhibited due to the presence of magnetic fields. By fitting frequency shift (deltaD) versus time curves according to the frequency shift response equation of SPQC, the relationships between three kinetic growth parameters, i.e., the asymptote A, the maximum specific growth rate mu(m) and lag time lambda, and magnetic field intensity were established. Based on these results, a new response model containing the magnetic field intensity was derived as: delta(f) = 167.7 (7.25 - 7.11B)/[1 + exp[4 x 2.46e(-3.97B)/(7.25 -7.1 IB)] x (4.42 + 16.46B - t) + 2]] The kinetic parameters of bacterial growth obtained from this model are close to those obtained from the logistics popular growth model, in which the concentration of the bacteria was determined by the traditional pour plate count method.

Biosensing Techniques↗
PubMed2002

Determination of 4-aminophenol using the quartz crystal microbalance sensor.

In this paper we report a method for the determination of 4-aminophenol (4-AP) in solution using a quartz crystal microbalance (QCM) sensor. 4-AP reacts with (para-unsubstituted) phenols to form hydrophobic indophenol dye species that precipitate out and adsorb to the surface of the crystal to produce a shift in the crystal resonant frequency. This frequency change, due to in-situ indophenol mass adsorption, can be related to the initial 4-AP concentration. A range of phenols (namely o-cresol, 1-naphthol, resorcinol, catechol and 8-hydroxyquinoline) and their reaction with 4-AP were tested. Ammonium persulfate (APS) and potassium periodate were used as initiators to improve the speed of the reaction and the rate of formation of the precipitate. APS elicited improved signal in terms of response times and frequency shifts compared with KIO4. Of the phenols studied, resorcinol gave the best response time of 6 min for 4-AP determination. The reaction of resorcinol with 4-AP gave extended response times and signal size with decreasing concentration of 4-AP (in the range 2-5 mM).

Aminophenols↗
PubMed2006

Characteristics of the series resonant-frequency shift of a quartz crystal microbalance in electrolyte solutions.

We report the novel characteristics of the series resonant-frequency shift, DeltaF, of a one-face sealed quartz crystal microbalance (QCM) in solutions of monovalent electrolytes and divalent electrolytes. In the present study, we used NaCl, KCl, LiCl, NaNO3 and CH3COONa as monovalent electrolytes, and MgCl2, CaCl2, MgSO4 and Na2SO4 as divalent electrolytes. These experiments reveal that, in all the solutions, the DeltaF values vary linearly with an increase in the square root of the density-viscosity product of the solutions, and the immersion angle dependence of DeltaF appears. Moreover, we have found that the intercept values of DeltaF are dependent only on the cation species, and that the slope values of DeltaF with the viscosity and density of the solutions are related only to the valence of ions. We also suggest that the DeltaF values are independent of anion species, conductivity and permittivity of the solutions.

Crystallization↗
PubMed1987

The fate of instilled pulmonary surfactant in normal and quartz-treated rats.

Naturally prepared radiolabelled pulmonary surfactant can be rapidly cleared from the alveolar surface to the lung tissue after intratracheal instillation into experimental rats. This clearance is both time- and dose-dependent, a large dose (10 mg/animal) becoming associated with lung tissue more rapidly than a smaller more physiological dose (0.75 mg/animal). The data indicate that extracellular dipalmitoyl-phosphatidylcholine, the major component of pulmonary surfactant, is not catabolized at the alveolar surface. Alveolar free cells (mainly macrophages) appear to play a minor role in surfactant clearance. Quartz-induced phospholipidosis does not lead to an alteration in the rate of bulk surfactant clearance from the alveolar surface, although the initial distribution of the removed phospholipid complex may change in relation to the enlarged heterogenous free cell population.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2001

A rapid, non-destructive method for the determination of Staphylococcus epidermidis adhesion to surfaces using quartz crystal resonant sensor technology.

AIMS: To investigate the use of quartz crystal resonant sensor (QCRS) technology to determine the adhesion of Staphylococcus epidermidis to fibronectin-coated surfaces. METHODS AND RESULTS: QCRS sensors (14 MHz) with 4 mm gold electrodes were coated with fibronectin and exposed for 15 min to suspensions of Staph. epidermidis ranging in concentration from 1 x 10(2) to 1 x 10(6) cfu ml(-1). Changes in resonant frequency were recorded and showed a linear relationship with the logarithm of cell concentration over the range tested. CONCLUSIONS: QCRS technology was shown to be a rapid, sensitive and non-destructive method for measuring the adhesion of bacteria to surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: This report demonstrates that QCRS technology has the potential to be used for a range of applications requiring measurement of bacteria on surfaces. In particular, it may be used for the real-time monitoring of bacterial biofilm formation.

Bacterial Adhesion↗
PubMed1986

Desorptivity versus chemical reactivity of polycyclic aromatic hydrocarbons (PAHs) in atmospheric aerosols collected on quartz fiber filters.

Nine polycyclic aromatic hydrocarbons (PAHs) contained in air samples collected on quartz fiber filters inside an urban tunnel and in a nearby mixed commercial residential area in the city of Rio de Janeiro, Brazil, were exposed to scrubbed air (to measure desorption loss) and to particle-free ambient air (to measure chemical reaction losses in the absence of desorption). The exposures were conducted for 5.5 to 9 hour periods at ambient temperature (22-26 degrees C) at face velocities typical of high volume sampling. Under prevailing atmospheric conditions all nine PAHs experienced filter losses which (for most of them) followed first order kinetics. For the ambient samples, in a 6 hour exposure period, the following five PAHs showed filter losses (% in parantheses) attributed exclusively to chemical reaction: benzo(b)fluoranthene (43), benzo(k)fluoranthene (39), benzo(a)pyrene (70), benzo(ghi)perylene (44), and indeno (1,2,3-cd)pyrene (41). The other four showed the following unassigned losses: pyrene (100), fluoranthene (65), crysene (72), and benzo(a)anthracene (71). The results are discussed in the light of possible filter artifacts in PAH sampling and the use of PAH profile signatures for source identification of atmospheric particulate matter in receptor modeling.

Adsorption↗
PubMed1999

POCK model simulations of pulmonary quartz dust retention data in extended inhalation exposures of rats.

In recent years, a physiology-oriented multicompartmental kinetics (POCK) model was developed to simulate pulmonary retention data of biopersistent, noncytotoxic aerosols in long-term inhalation exposures of rats. Experimental data were successfully simulated for submicrometer-sized aerosols like carbon black, diesel soot, and titanium dioxide and for a micrometer-sized xerographic toner aerosol (Stöber et al., 1994, 1995). This article describes for various rat strains successful POCK model simulations of experimental pulmonary retention data of micrometer-sized aerosols of biopersistent cytotoxic SiO2 modifications like quartz and quartzite. In the past, the POCK model was not applied to cytotoxic aerosols and dusts. Cytotoxicity was considered incompatible with the model assumption of a constant macrophage lifetime independent of the macrophage aerosol load. The few relevant experimental retention studies with biopersistent silica found in the open literature showed particulate lung burdens up to some 15 mg per rat lung. Apparently, at these loads, pulmonary burdens could be simulated because the fraction of alveolar macrophages killed by the cytotoxic particles was possibly still small compared to the total number of viable macrophages. Of necessity, however, the classical alveolar clearance in these studies was exclusively performed by alveolar macrophages that were burdened with cytotoxic particles, and the cells appeared to suffer from a substantial initial decrease of their inherent mobility. Thus a sizeable reduction of the alveolar clearance rate coefficient in comparison to nontoxic aerosol was found. The results for the model parameters of several different exposure studies are shown and interpreted in comparison to nontoxic titanium dioxide retention parameters.

Administration, Inhalation↗
PubMed2003

The performance of laboratories analysing alpha-quartz in the Workplace Analysis Scheme for Proficiency (WASP).

The Workplace Analysis Scheme for Proficiency (WASP) is a proficiency testing (PT) scheme for the analysis of occupational hygiene and environmental air samples and is operated in the United Kingdom by the Health and Safety Laboratory (HSL) on behalf of the Health & Safety Executive (HSE). One of the 26 analytes available to laboratories is silica (alpha-quartz) on 25 mm Gelman GLA5000 filters. This paper investigates the performance of laboratories participating in the scheme since the HSL took over the production of the samples in 1998. The average relative standard deviation (RSD) of results obtained by a laboratory is 11.5%. This is reduced to 8.5% when the values from laboratories using indirect analytical methods are excluded. Laboratories using indirect analytical methods accounted for some of the most variable data. For the on-filter analytical methods the data suggested a relationship between relative standard deviation and loading that increased gradually from +/-4% at high analyte levels to +/-10-15% at low levels. The average precision estimate for the on-filter analytical methods was found to be 5.6% RSD for the infrared technique and 6.7% RSD for the X-ray diffraction technique. These figures compare favourably with those reported in the published HSE methods. No significant difference was found between the average result reported by laboratories using on-filter infrared (IR) analysis and the average result reported by laboratories using on-filter X-ray diffraction (XRD) analysis. An ANOVA analysis found the repeatability estimate was just as large as the 'between laboratory' variation for both the XRD and IR on-filter analysis techniques. When a limited number of 'realistic' samples were included in the scheme, XRD analysis was found to perform slightly better than IR analysis. The performance of laboratories in the WASP scheme compares very favourably with other published data from a PT scheme where indirect silica analytical methods are predominately used.

Air Pollutants, Occupational↗
PubMed2002

In vitro selection of N peptide-binding RNA on a quartz-crystal microbalance.

We report here an in vitro selection of a hairpin loop-RNA bound to N Peptide from bacteriophage lambda on a 27 MHz quartz-crystal microbalance (QCM) to study an interaction between an RNA structure and an RNA-binding peptide. The N Peptide was immobilized on a QCM electrode and specific RNAs binding to the peptide were selected from a GNRNA pentaloop-randomized RNA library with in situ monitoring of selection processes using a QCM. After the 5th round selection, the consensus sequences including a GCGCA loop were obtained from the pentaloop library. This RNA sequence was different from a binding site of a native N Protein (boxB RNA).

Base Sequence↗
PubMed2002

Direct monitoring of EcoRII restriction enzyme reactions on a 27 MHz quartz-crystal microbalance.

EcoRII is a type IIe restriction endonuclease characterized by a highly cooperative reaction mechanism that depends on simultaneous binding of the dimeric enzyme molecule to two copies of its recognition site. Gaining insights about reaction property of EcoRII binding to its recognition site and effect of divalent metal ion on DNA cleavage process, a DNA-immobilized quartz crystal microbalance (QCM), which enables real-time monitoring both the binding of enzyme and the cleavage reaction on DNA strands as mass changes, was utilized.

Deoxyribonucleases, Type II Site-Specific↗