Wireless-electrodeless Quartz Crystal Microbalance Research Articles

Online pH monitoring based on a wireless electrodeless quartz crystal microbalance with dissipation

Online real-time detection is crucial for biochemical and healthcare monitoring. Methods that could conduct the measurements in low-volume analytes are essentially required. A wireless electrodeless quartz crystal microbalance with dissipation (WE-QCM-D) based sensor was proposed to realize real-time pH monitoring in low-volume solutions. The WE-QCM-D pH sensor was fabricated by coating with a pH-sensitive poly (hydroxyethyl methacrylate-co-methacrylic acid) (poly (HEMA-co-MAA)) film and observed the dynamic pH variation in the range from 4 to 9. The sensitivity of the WE-QCM-D pH sensor nearby the pKa was 1.47 V/pH and the maximum response time was around 80 s. The pH sensor performed well in synthetic urines with a measurement deviation less than 1% compared with that measured by a pH meter and reversible responses has been achieved when 140μl buffer solutions at pH 4.18, 5.6 and 7.62 were loaded on the quartz disc that was located in a glass vial. The results indicated that the WE-QCM-D pH sensor could be potentially used for online low volume detections.

Study on micropillar arrangement optimization of wireless-electrodeless quartz crystal microbalance sensor and application to a gas sensor

This paper studies the structural design of the wireless-electrodeless quartz crystal microbalance (QCM) sensor, which has a rectangular AT-cut quartz oscillator installed in the microchannel fabricated by nanoimprint lithography. The quartz oscillator was supported by the micropillars in the microchannel, and by optimizing the micropillar arrangement, it was found that the structural damping could be significantly reduced by performing the finite elemental piezoelectric analysis. This behavior was then confirmed by the experiments using the evaluation chips. By supporting the four corners of the quartz oscillator with the micropillars, the structural damping could be reduced, achieving a high-quality factor (Q-factor) of about 24700. This high Q-factor was also realized in the experiments, and we investigated its application to a hydrogen-gas sensor. We succeeded in detecting hydrogen gas with an extremely low concentration of 10 ppm.

A wireless electrode-free QCM-D in a multi-resonance mode for volatile organic compounds discrimination

Wireless sensor technology is a facile way of realizing low cost and miniaturized device for the detection of the volatile organic compounds (VOCs). A wireless electrodeless quartz crystal microbalance with dissipation (WE-QCM-D) sensor array was developed by using a single sensor working in a multi-resonance mode, which obtained an acoustic spectra of the quartz crystal at four harmonics (6 MHz, 18 MHz, 30 MHz and 42 MHz). Multi-responses (frequency shift, and energy dissipation) of WE-QCM-D sensor array were obtained via a ring-down mode and employed as discrimination factors for VOCs. The gas discrimination capability of the WE-QCM-D sensor array has been tested by coating a 100 μg polyvinylpyrrolidone film on the quartz disc and achieved an optimal recognition rate of 97.5 % with K nearest neighbor algorithm. The results indicate that the single element WE-QCM-D sensor array could be a promising way to realize compact and low-cost VOCs monitoring systems.

A wireless-electrodeless quartz crystal microbalance method for non-enzymatic glucose monitoring

Continuous glucose monitoring (CGM) in vivo is required for tight glycaemic control. Enzyme-free glucose sensors were proposed to solve the problems of daily invasive calibration and short lifespan of the current enzyme based continuous glucose monitors. In this report, a wireless-electrodeless quartz crystal microbalance method that tracks film dissipation was developed and proposed as a basis for a miniaturized implantable glucose monitor. An AT-cut blank quartz disc (14 mm in diameter) was stimulated wirelessly by a planar copper coil and working in the ring-down mode at a fixed frequency point (˜6 MHz). A 600–800 nm (3-acrylamidopropyl) tri-methylammonium chloride modified poly(acrylamide-co-3-acrylamideophenylboronic acid) hydrogel film was coated on the quartz disc for glucose sensing. The viscosity variations of the polymer film induced by the glucose binding were observed by measuring the dissipation change of the sensor. The linear relationship between the dissipation response and the glucose concentration was achieved in the range of ˜0 to 10 mM, with a sensitivity of 2 × 10−5 mM−1 and a response time of around 5 min at 37 °C. Furthermore, the response of the modified film to other interferences including the fructose, galactose, mannose, uric acid was dramatically reduced. The results suggest the wireless-electrodeless quartz crystal microbalance with dissipation system has the potential to be used as a subcutaneously implanted real-time glucose monitor.

A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor

Highly sensitive chemical warfare agents (CWAs) detection is demanded against the usage of the CWAs for war or terrorism aims. A dimethyl methylphosphonate (DMMP), simulant for sarin, monitoring sensor based on a homemade wireless-electrodeless quartz crystal microbalance with dissipation (QCM-D) was developed. With this noncontact configuration, deterioration of the sensing ability cause by the electrodes and drilling on the gas chamber for wire lead was avoided. Nano-structured hollow ball-like indium oxide (In2O3) was synthesized using a facile hydrothermal method and then decorated with cubic gold particles (In2O3-Au). Both of them were applied as the sensing films to detect DMMP. The In2O3-Au based QCM-D sensor exhibited 2.1 Hz/ppm to DMMP range from 5 ppm to 50 ppm, which was 400% higher compared to the undecorated one. Moreover, with the simultaneously monitored dissipation value, desorption processes of DMMP was further investigated and the overshoot that appear in some researches was explained in terms of visco-elastic variations in mechanical stiffness. The results suggest that the wireless-electrodeless QCM-D could be a promising strategy for observation of materials under dynamic conditions.

A Noncontact Dibutyl Phthalate Sensor Based on a Wireless-Electrodeless QCM-D Modified with Nano-Structured Nickel Hydroxide.

Dibutyl phthalate (DBP) is a widely used plasticizer which has been found to be a reproductive and developmental toxicant and ubiquitously existing in the air. A highly sensitive method for DBP monitoring in the environment is urgently needed. A DBP sensor based on a homemade wireless-electrodeless quartz crystal microbalance with dissipation (QCM-D) coated with nano-structured nickel hydroxide is presented. With the noncontact configuration, the sensing system could work at a higher resonance frequency (the 3rd overtone) and the response of the system was even more stable compared with a conventional quartz crystal microbalance (QCM). The sensor achieved a sensitivity of 7.3 Hz/ppb to DBP in a concentration range of 0.4–40 ppb and an ultra-low detection limit of 0.4 ppb of DBP has also been achieved.

RNA Aptamer Binds Heparin-Binding Epidermal Growth Factor-Like Growth Factor with High Affinity and Specificity and Neutralizes Its Activity

Summary Background Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family and is involved in various diseases including cancers. Aptamers are synthetic oligonucleotides (RNA or DNA) that fold into unique three-dimensional structures and specifically bind to their targets with high affinity. We aimed to generate an aptamer with high affinity and specificity for HB-EGF. Methods Recombinant human HB-EGF (rhHB-EGF), comprised of the extracellular EGF-like and heparin-binding domains of HB-EGF, was used as the target. The aptamer against HB-EGF (the anti-HB-EGF aptamer) was obtained by systematic evolution of ligands by exponential enrichment (SELEX). Results After the 10th round of SELEX, aptamers were reverse-transcribed and PCR-amplified. Within obtained forty-six clones, twenty-three were identical (the anti-HB-EGF aptamer). The analysis using wireless-electrodeless quartz crystal microbalance revealed that the anti-HB-EGF aptamer had high affinity for rhHB-EGF (KD value: 12.2 ± 1.1 nmol/L). The dot-blot analysis revealed that the anti-HB-EGF aptamer specifically bound to rhHB-EGF. The analysis using confocal microscopy indicated that the anti-HB-EGF aptamer also bound to membrane-bound HB-EGF. Western-blot assay indicated that the anti-HB-EGF aptamer inhibited the phosphorylation of rhHB-EGF-mediated EGF receptor (EGFR). Conclusion We identified a novel RNA aptamer that bound with high affinity and specificity to rhHB-EGF and potently inhibited the rhHB-EGF-mediated phosphorylation of EGFR. The anti-HB-EGF aptamer may be a promising therapeutic agent for specifically neutralizing HB-EGF signaling.

Aggregation Behavior of Amyloid β1–42 Peptide Studied Using 55 MHz Wireless–Electrodeless Quartz Crystal Microbalance

A homebuilt wireless–electrodeless high frequency quartz crystal microbalance is adopted for long-time monitoring of the aggregation behavior of amyloid β1–42 peptide in a flow-cell system. The monomer amyloid peptides are immobilized on both surfaces of the crystal, and an amyloid-β solution is injected. The monotonic frequency decrease indicates aggregation on the crystal, which yields aggregation rate. Aggregation is observed even at a peptide concentration as low as 550 nM.

Nonspecific-adsorption behavior of polyethylenglycol and bovine serum albumin studied by 55-MHz wireless–electrodeless quartz crystal microbalance

The nonspecific binding ability of polyethylenglycol (PEG) and bovine serum albumin (BSA) on modified and unmodified surfaces is quantitatively studied by a wireless–electrodeless quartz crystal microbalance (WE-QCM). PEG and BSA are important blocking materials in biosensors, but their affinities for proteins and uncoated substrates have not been known quantitatively. The WE-QCM allows quantitative analysis of the adsorption behavior of proteins on the electrodeless surfaces. Affinities of PEG, BSA, human immunoglobulin G (hIgG), and Staphylococcus protein A (SPA) for α -SiO 2(quartz), Au thin film, PEG, and BSA are systematically studied by the homebuilt flow-injection system. PEG shows low affinities for the SiO 2 surface ( K A = 4.2 × 1 0 4 M −1) and the Au surface ( K A = 6.6 × 1 0 4 M −1), but BSA shows higher affinity for the SiO 2 surface ( K A = 1.4 × 1 0 6 M −1). Both PEG and BSA show low affinities for hIgG ( K A ∼ 1.5 × 1 0 5 M −1). However, the number of binding sites of PEG to hIgG is significantly larger than that of BSA, indicating that blocking for hIgG is favorably achieved by BSA, rather than PEG.

Effects of Flow Rate on Sensitivity and Affinity in Flow Injection Biosensor Systems Studied by 55-MHz Wireless Quartz Crystal Microbalance

In this paper, we developed a 55-MHz wireless-electrodeless quartz crystal microbalance (QCM) and systematically studied the effects of flow rate on the sensitivity to the detection of proteins and on the affinity between biomolecules evaluated by the flow injection system. Brownian motion of proteins in liquid suggests a low probability of meeting, and the convection effect plays an important role in the sensitivity and the affinity in the flow cell injection system. The wireless quartz crystal was isolated in the QCM cell, and flow rates between 50 and 1000 microL/min were used for monitoring binding reactions between human immunoglobulin G and Staphylococcus aureus protein A. The sensitivity was significantly increased as the flow rate increased, while the affinity value remained unchanged. However, the affinity value was affected by the reaction time for a large-concentration analyte, indicating the need of a high-sensitivity biosensor system for accurate evaluation of affinity. The electrode effect on the QCM sensitivity was also theoretically investigated, showing that the electrode significantly deteriorates the QCM sensitivity and makes the Sauerbrey equation invalid.

1J4-2 Monitoring of aggregation behavior of amyloid β peptide using wireless-electrodeless quartz-crystal microbalance(Bulk wave devices/Surface wave devices)

1J4-2 Monitoring of aggregation behavior of amyloid β peptide using wireless-electrodeless quartz-crystal microbalance(Bulk wave devices/Surface wave devices)

Concentration dependence of IgG–protein A affinity studied by wireless-electrodeless QCM

The binding affinity between human immunoglobulin G (IgG) and protein A was studied by the homebuilt wireless-electrodeless quartz crystal microbalance (QCM). Protein A was immobilized on the electrodeless AT-cut quartz plate of 0.05 mm thick and its fundamental resonance frequency near 34 MHz was measured by a noncontacting manner using a line antenna. The vibrational analysis was performed to ensure higher sensitivity of the electrodeless QCM. A flow-cell system was fabricated to continuously measure the resonance frequency during the injection sequence of the IgG solutions with concentrations of 1–20,000 ng/mL. The exponential frequency changes were recorded to determine the affinity based on the Langmuir kinetics. The equilibrium constant KA significantly varied between 6×106 and 6×1010 M−1, depending on the IgG concentration, which is attributed to various formations of IgG–protein A complexes.