Quartz Crystal Resonant Sensor Research Articles

Swelling characteristics and application of two-dimensional materials on hydrophilic quartz crystal resonant dew point sensor

The two-dimensional (2D) water adsorbing material is used as a sensitive layer for the hydrophilic quartz crystal resonant (QCR) dew point sensor, and its own swelling characteristics determine the accuracy of the sensor's recognition of the saturation status of the water vapor. In order to reveal the mechanism relationship between the swelling characteristics of materials and the measurement accuracy of hydrophilic QCR dew point sensors using different 2D materials, we used montmorillonite (MTT), graphene oxide (GO) and molybdenum disulfide (MoS2) coated QCR sensors to test dew point measurement performance in different humidity environment, and then the rate of swelling and intensity of swelling of the three materials were measured by integration of quartz crystal microbalance with dissipation (QCM-D) and ellipsometer. The results showed that MTT had an outstanding swelling rate and intensity with logrithmatic thickness changing curve, especially in the high humidity environment with sudden strength changes. This characteristic makes MTT the most suitable sensitive material for the hydrophilic QCR dew point sensor surface modification among the three 2D materials. Through this study, it implied that the rate of swelling and intensity of swelling are the two major parameters that determines whether a 2D material is suitable for being used as the sensitivity layer of a hydrophilic QCR dew point sensor.

Quartz crystal sensor using direct digital synthesis for dew point measurement

Considering that the quartz crystal resonant (QCR) sensor with the oscillation circuit as a driver will stop oscillation when it encounters a large damping medium. A QCR sensor excitation method based on direct digital synthesis (DDS) was presented in this paper. Meanwhile, a fast frequency tracking algorithm based on variable step size and variable interval was designed. The designed excitation and frequency measurement method was integrated into a complete frequency excitation and tracking system by microprocessor and the system was applied to the dew point sensor. Firstly, the accuracy and reliability of the frequency tracking system was validated, the frequency identification results has a relative error of 0.97 Hz compared with the Agilent 4294A impedance analyzer. Secondly, the sensor was tested in the range of 0–20 °C dew point temperature (DP), and the dew point was identified by judging the frequency shift. The maximum error was 0.3 °C DP compared with the MICHELL S4000 dew point meter. The results showed that the dew point resonant sensor based on the frequency excitation and tracking system has fast and accurate characteristics in dew point identification and measurement, and can overcome the disadvantage of stop oscillation when it encounters a large damping medium.

Novel quartz crystal microbalance based biosensor for detection of oral epithelial cell–microparticle interaction in real-time

Recent applications of quartz crystal resonant sensor technology to monitor cell adhesion and specific ligand interaction processes has triggered the development of a new category of quartz crystal microbalance (QCM) based biosensors. In this study human oral epithelial cells (H376) were cultured on quartz sensors and their response to microspheres investigated in situ using the QCM technique. The results demonstrated that this novel biosensor was able to follow cell–microsphere interactions in real-time and under conditions of flow as would occur in the oral cavity. Unique frequency profiles generated in response to the microspheres were postulated to be due to phases of mass addition and altered cellular rigidity. Supporting microscopic evidence demonstrated that the unique frequency responses obtained to these interactions were in part due to binding between the cell surface and the microspheres. Furthermore, a cellular uptake process, in response to microsphere loading was identified and this, by influencing the rigidity of the cellular cytoskeleton, was also detectable through the frequency responses obtained.

α-Lipoic acid and glutathione protect against the prooxidant activity of SOD/catalase mimetic manganese salen derivatives

Manganese(III) N, N′-ethylenebis(salicylideneiminato) chloride (Mn-salen chloride) and manganese(III) N, N′-ethylenebis(3-methoxysalicylideneiminato) chloride (Mn-(3,3′-MeO)salen chloride) are in vitro superoxide dismutase and catalase mimetics. They protect against free radical-related disease in animals, but Mn-salen can also be a potent prooxidant, damaging free DNA. Mn-salen protects human fibroblast DNA against hydrogen peroxide damage, however, damage to free DNA was confirmed by the comet assay. The DNA-damaging activity was dramatically reduced by co-administration with glutathione with the combination being less damaging to free DNA than either molecule alone. α-Lipoic acid, an antioxidant disulfide commonly used as a dietary supplement, also prevented Mn-salen prooxidant activity. Mn-(3,3′-MeO)salen protected fibroblasts against hydrogen peroxide as efficiently as Mn-salen and showed little damaging activity against free DNA. Protection was invested by both complexes in the presence and in the absence of EDTA, a potential competing chelator. Stabilities of the complexes with respect to decomposition and inactivation were studied by spectroscopic and electrochemical techniques. The complexes’ binding to, and cleavage of, DNA was measured using a quartz crystal resonant sensor. Mn-salen was shown to bind strongly to DNA, prior to cleaving it; Mn-(3,3′-MeO)salen bound weakly and left DNA intact. Co-administration of either glutathione or α-lipoic acid appears to inhibit binding by Mn-salen thus preventing DNA-cleavage.

Observation of Transient Alkali Metal Inclusion in Oxacalix[3]arenes

Oxacalix[3]arenes exhibit transient binding to Na+, K+ and Ca2+, with a strong preference for Na+, as determined by a quartz crystal resonant sensor technique. Computational models for the behaviour indicate that the preference for Na+ is due to the depth to which that cation is drawn into the macrocycle's central cavity.

Development of novel liquid phase qcrs sensor technology

This paper discusses the development of novel liquid phase quartz crystal resonant sensor technologies for label free, real-time detection of pharmaceutical applications. New crystal oscillator technologies are introduced alongside crystal mounting and flow cell designs circumventing more traditional approaches to yield greater robustness, reliability and sensitivity. Data for standardised long-term experiments is presented and analysed with respect to reproducibility and stability and comparisons made with surface plasmon resonance.

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

To investigate the use of quartz crystal resonant sensor (QCRS) technology to determine the adhesion of Staphylococcus epidermidis to fibronectin-coated surfaces. 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. QCRS technology was shown to be a rapid, sensitive and non-destructive method for measuring the adhesion of bacteria to surfaces. 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.

Characterisation of small molecule binding to DNA using a quartz crystal resonant sensor

A new development in quartz crystal resonant sensor (QCRS) technology allows real-time analysis of binding by small molecules to DNA and has been tested using superoxide dismutase mimics.

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.

Vitamin C induced decomposition of lipid hydroperoxides: direct evidence of genotoxin-DNA binding detected by QCRS.

We report direct evidence for human DNA-binding to precursors of mutagenic lesion-inducing compounds, produced form the vitamin C induced decomposition of lipid hydroperoxides, using a quartz crystal resonant sensor assay.

Investigation on the creep characteristics of a quartz crystal resonant force sensor

In this paper the creep behaviour of a combinatory quartz resonant force sensor is discussed and a method for decreasing this behaviour is analysed. A viscoelastic model of the sensor which considers the viscoelastic characteristics of the adhesive used to glue the sensing element and other components is introduced to analyse the creep behaviour of the sensor. The result indicates that the features of the adhesive can bring about remarkable effects on the creep behaviour of the sensor. Among the feature parameters for the applied adhesive the glass transition temperature is the most important one. The adhesive must have a glass transition temperature much higher than its working temperature so as to reduce the creep error of the sensors. These conclusions result in the design and development of a new adhesive, which can be used over a wide temperature range.