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All vertebrate cells generally self-regulate for sustaining homeostasis and cell functions. As a major regulatory mechanism, regulatory volume decrease (RVD) occurs in hypotonicity-induced cell swelling, and then shrinking by the efflux of intracellular osmolytes and water, in which the ions K+, Cl−, and Ca2+ play a key role in the RVD process. We observed that these pivotal ions could result in novel RVD behaviors under repeatedly hypotonic stimulation. However, there is a lack of valid means for assessing the effect of pivotal ions on RVD. In this work, we proposed an effective measurement process based on a quartz crystal microbalance (QCM) combined with cell function of RVD for revealing acute variations in cell volume regulation induced by the pivotal ions. A QCM sensor was implemented by adhering MCF-7 cells to a poly-l-lysine-modified gold chip and cyclic stimulation with hypotonic NaCl medium, in which a frequency shift (Δf) showed the superior feasibility of the technique in exhibiting RVD behaviors. With the increase in the number of cycles, the RVD values decreased progressively under three stimulation cycles with hypotonic NaCl alone. Compared with the first cycle, the RVD level in the second and third cycles declined by 60.7±1.7% and 82.1±1.6% (n=3), respectively; conversely, it recovered in NaCl-KCl solution, but was significantly enhanced by 52.2±0.8% in NaCl-CaCl2 solution. Moreover, the inhibition of chloride channels to block Cl− efflux also decreased the RVD level by 56.2±3.0%. The results indicate that these ions (K+, Cl−, Ca2+) are all able to affect the function of RVD, among which intracellular Cl− depletion reduced RVD during measurement, but which recovered with K+ supplement, and Ca2+ enhanced RVD due to activation of ion channels. Therefore, this work provides a comprehensive assessment of cellular behavior and offers an innovative method for gaining insight into cellular functions and mechanisms. [ABSTRACT FROM AUTHOR]

In this study, Fe3O4 nanoparticles are prepared by the co‐precipitation method. γ‐Fe2O3 and α‐Fe2O3 nanoparticles are obtained by calcining Fe3O4 nanoparticles for 6 h at 200 and 600 °C. The physicochemical properties of the prepared nanoparticles are investigated by field‐emission scanning electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller, and Barrett–Joyner–Halenda methods. The gas sensors based on a quartz crystal microbalance (QCM) coated with Fe3O4, γ‐Fe2O3, and α‐Fe2O3 nanoparticles are fabricated and analyzed. The as‐fabricated QCM sensors displayed a high capability for detecting SO2 at room temperature. Among the sensors, the γ‐Fe2O3 nanoparticles coated QCM sensor exhibited the best response. Moreover, the sensor shows good repeatability and long‐term stability. The correlation between the phase composition of the iron oxide nanoparticles and SO2 sensing performance is also discussed in detail. [ABSTRACT FROM AUTHOR]

Collagen is a major structural protein, and abnormalities in collagen structure can lead to several connective tissue diseases such as osteoporosis. We report the preparation of a collagen sensor using a synthetic peptide as proof of concept for detecting the collagen like peptides. The synthetic peptide 9-fluorenylmethyloxycarbonyl (Fmoc)-(prolyl-prolyl-glycine) 7 -OH was coupled to thiazolidine, which gets adsorbed on metal surfaces. Fmoc-(prolyl-prolyl-glycine) 7 -thiazolidine was immobilized on the surface of a quartz crystal microbalance (QCM) electrode used as a sensor probe. The collagen model peptide (prolyl-prolyl-glycine) 10 could be detected, and the model peptide was directly adsorbed onto the surface of the electrode and was not removed by washing with hot water. Additionally, it was proved that the sensitivity of the probe could be enhanced to nanogram order by immobilizing the blocking reagent, Fmoc-prolyl-prolyl-glycine, within the gap of sensor probes on the electrode. The detectable mass of the model peptide decreased as the probe gap became narrower because of self-association of the probes. Moreover, the sensitivity of sensor probes also decreases as the gap between the probes becomes wider. Therefore, the optimum distance between the immobilized probes was determined from the simulation based on the experimental values. The association rate of the model peptide with sensor probes could be quantitatively determined when the distance between the probes was optimum, and this result suggested that most sensor probes could form a triple helical structure with the model peptide. [Display omitted] • Biosensor using synthetic peptide for future development of diagnosis of collagen-related diseases. • Sensitivity of QCM sensor could be enhanced by immobilizing the blocking reagent. • Optimum probe distance determined from simulation based on experimental values. • Most sensor probes formed triple helical structure with the collagen model peptide. [ABSTRACT FROM AUTHOR]

A sensor based on a gold Quartz Crystal Microbalance (QCM) modified with nanoscale zero-valent iron nanoparticles (nZVI) anchored to reduced graphene oxide (rGO) was developed. An automated measurement microsystem was employed using QCM (modified and unmodified) as an arsine detector device. The QCM measurements of frequency changes are associated with total As concentration (III/V) in the samples. The gold surface QCM modification with nZVI/rGO improved the sensitivity in total As determination. The limit of detection (LOD) was 0.0062 ng mL − 1 for QCM-Au/nZVI/rGO, 100 times higher than the unmodified QCM-Au sensor. Moreover, studies of adsorption energy and electron density of As with QCM-Au/nZVI/rGO and QCM-Au systems were performed. For this purpose, Density Functional Theory (DFT) methodology was used employing arsine adsorption on magnetite nanoparticles supported on graphene, and also on Au as models. This theoretical-experimental research allows us to acquire knowledge of the interaction of Au/nZVI/rGO with As and confirms the experimental results. • A sensor based on a gold Quartz Crystal Microbalance (QCM) modified with nanoscale zero-valent iron nanoparticles (nZVI) anchored to reduced graphene oxide (rGO) was developed. • Density Functional Theory (DFT) methodology was used employing arsine adsorption on magnetite nanoparticles supported on Graphene and also on Au as models. • The gold surface QCM modification with nZVI/rGO improved the sensitivity in total As determination. • This theoretical-experimental research allows to acquire knowledge of the interaction of Au/nZVI/rGO with As and confirms the experimental results. [ABSTRACT FROM AUTHOR]

In this work, two detection methods of solid-phase extraction–high-performance liquid chromatography (SPE-HPLC) and quartz crystal microbalance (QCM) were established, based on a surface molecularly imprinted polymer material (MIP). The material can be used as a selective solid-phase extraction filler and as a coating for sensitive quartz crystal microbalances by virtue of the polyhydroxy structure of grafted silicon spheres together with the network structure from cross-linked polymerization. The adsorption properties of the prepared MIP were analysed by dynamic and static adsorption tests, and the experimental conditions for SPE-HPLC and QCM analysis were optimized. Under the optimal conditions, the linear range of MIP-SPE-HPLC for the detection of carbaryl was 0.5–60 μg L−1 (R2 = 0.99913), and the detection limit was 0.0573 μg L−1. The proposed QCM sensor displayed a linear relationship between the frequency shift and the concentration of carbaryl ranging from 5 to 80 μg L−1 with a low detection limit of 0.6845 μg L−1 (signal-to-noise ratio, S/N = 3). Through a series of experiments, it was shown that the prepared MIP has good adsorption and selectivity for carbaryl, and the MIP-based HPLC and QCM sensor can be applied to the detection of actual food samples. [ABSTRACT FROM AUTHOR]

In this work, a quartz crystal microbalance (QCM) sensor has been fabricated using immunoassay for sensitive determination of Bifidobacterium bifidum. Au nanoparticle has been used for amplifying sandwich assays. The proposed immunosensor exhibited a linear detection range between 103 and 105 CFU/mL with a limit of detection of 2.1 × 102 CFU/mL. The proposed immunosensor exhibited good selectivity for B. bifidum sensing with low cross reactivity for other foodborne pathogens such as Lactobacillus acidophilus, Listeria monocytogenes, and Escherichia coli. In addition, the proposed immunosensor has been successfully used for B. bifidum detection in feces samples and food samples. The frequency decreases of 12, 17, and 10 Hz were observed from the milk samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli. The frequency decreases of 8, 15, and 7 Hz were observed from the feces samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli.

This article describes the enantiomeric discrimination properties of new chiral calix[4]arene derivatives bearing (S)-/(R)-1-phenylethylamine moieties (5a and 5b, respectively) towards the 1-phenylethylamine enantiomers on QCM surface. Initial experiments demonstrated that the 5b coated QCM sensor was the most effective sensing material for enantiomeric discrimination of (R)-/(S)-1-phenylethylamine by exhibiting much more sensing ability towards (R)-enantiomer than (S)-enantiomer. Sensitivity, detection limit and time constant of the 5b coated QCM sensor has been were calculated as 0.082 Hz/µM, 2.7 µM, and 319.2 s, respectively. Additionally, effects of calixarene content and different coating technique on enantiomeric discrimination, and Langmuir and Freundlich isotherms of the sensing results also were studied. As a result, it has been demonstrated that the coating of QCM sensor with a chiral calix[4]arene (5b) having (S)-1-phenylethylamine moieties provides substantially enantiomeric discrimination of 1-phenylethylamine enantiomers. [ABSTRACT FROM AUTHOR]

We describe the synthesis of new chiral calix[4]arene derivatives having (R)-1-phenylethylamine, (S)-1-phenylethylamine, (R)-2-phenylglycinol, and (S)-2-phenylglycinol moieties, and chiral recognition studies for enantiomers of some selected α-amino acid derivatives such as alanine, phenylalanine, serine, and tryptophan using a quartz crystal microbalance (QCM). Initial experiments indicated that the highest selective chiral recognition factor was 1.42 for alanine enantiomers. The sensitivity, limit of detection, and time constant for l-alanine were calculated as 0.028 Hz/μM, 60.9 μM, and 36.2 s, respectively. The results indicated that real-time, sensitive, selective, and effective chiral recognition of alanine enantiomers was achieved with a QCM sensor coated with a chiral calix[4]arene derivative having (R)-2-phenylglycinol moieties. [ABSTRACT FROM AUTHOR]

Abstract Stereo-regulated siloxane film was prepared from the Schiff base of 3- (aminopropyl)triethoxysilane(APTES) and organic compounds having keto group by condensation reaction. The organic compounds such as benzaldehyde, acetophenone, heptaldehyde and camphor were chosen for making various sizes of pores in polymer films. The film was coated on quartz crystal microbalance (QCM) surface for the detection of aliphatic amine vapors such as methylamine, ethylamine, diethylamine, triethylamine, tert-butylamine and ammonia. The structures, morphology and surface roughness of films were studied by FTIR, FESEM and AFM respectively. It was noticed that, the film prepared from camphor has the highest sensitivity for the detection of amines which was due to the bulky globular structure of the camphor molecule by producing reasonable pores of desired size. The polymer film obtained from camphor and APTES was highest sensitivity and fast response towards the detection of organic amine vapors. The linearity of detection was measured up to 250 ppm and the sensitivity of the sensor was found to be 1.20–2.59 Hz/ppm. Graphical abstract Schematic of formation of bulky Schiff base film on QCM surface. Image 1031 Highlights • Stereo-regulated siloxane film is prepared from the Schiff base of APTES and keto group compounds. • Siloxane polymers with camphor shows the highest sensitivity for the detection of amines. • The polymer film shows high sensitivity, fast response for aliphatic amine detection. • Aliphatic amine vapor detection has linearity up to 250 ppm with sensitivity 1.20–2.59 Hz/ppm. [ABSTRACT FROM AUTHOR]

Abstract A quartz crystal microbalance (QCM) sensor for detecting cytochrome c based on an oriented surface epitope imprinted polymer was fabricated in this paper. By using the palmitic acid-modified epitope of cytochrome c as the template and the 3-aminopropyltriethoxysilane as the monomer, we prepared a new oriented surface epitope imprinted polymer by the reverse microemulsion polymerization. The prepared oriented imprinted polymer had better imprinting effect than the non-oriented imprinted polymer. And compared to previous studies, this polymerization method is simple and could be carried out at room temperature in the presence of oxygen, under regular atmospheric conditions. Then, by combining the advantages of molecularly imprinted polymers and QCM sensors, we used the prepared polymer to establish a QCM sensor. The described sensor showed good sensitivity and selectivity towards cytochrome c. The linear range was from 0.005 μg mL−1 to 0.050 μg mL−1 and the detection limit was 3.6 ng mL−1 which is lower than most of previous works. Besides, it could be used for real sample analysis and had satisfactory reproducibility and accuracy. This work proposed a new way of fabricating oriented surface epitope imprinted polymers-based QCM sensors for selectively detecting proteins at very low concentrations. Graphical abstract fx1 Highlights • A new quartz crystal microbalance sensor was successfully modified by an oriented surface epitope imprinted polymer. • Compared to previous studies, the preparation of the polymer was simpler, easier and without harsh environment. • This oriented imprinted polymer had better imprinting effect than the non-oriented one. • This protocol introduced the hydrolysis of tetraethoxysilane into oriented epitope imprinting for the first time. • This sensor had lower detection limit than most of the previous studies and is promising for real sample analysis. [ABSTRACT FROM AUTHOR]

Quartz crystal microbalance (QCM) sensor array was developed for multi-purpose human respiration assessment. The sensor system was designed to provide feedback for human respiration. Thorough optimization of measurement conditions: air flow, temperature in the QCM chamber, frequency measurement rate, and electrode position regarding to the gas flow—was performed. As shown, acquisition of respiratory parameters (rate and respiratory pattern) could be achieved even with a single electrode used in the system. The prototype system contains eight available QCM channels that can be potentially used for selective responses to certain breath chemicals. At present, the prototype machine is ready for the assessment of respiratory functions in larger populations in order to gain statistical validation. To the best of our knowledge, the developed prototype is the only respiratory assessment system based on surface modified QCM sensors.

A strategy for rapid detection of metolcarb was reported based on molecularly imprinted quartz crystal microbalance (QCM) sensor. The molecularly imprinted ploymer (MIP) was prepared and used as the molecular recognition element of the QCM sensor. The adsorption properties of the prepared MIP were evaluated by static and dynamic adsorption test and Scatchard analysis, demonstrating high affinity and homogeneous imprinting sites towards metolcarb. Through a series of evaluation experiments, the proposed MIP-QCM sensor displayed a linear relationship between frequency shift and the concentration of metolcarb ranging from 5 μg L −1 to 70 μg L −1 with a low detection limit of 2.309 μg L −1 (S/N = 3). The proposed sensor exhibited high selectivity towards target metolcarb compared with its structural analogs, and was applied to different food samples with satisfactory recoveries (85.4–95.5%). The above results were in accordance with those obtained by high-performance liquid chromatography, indicating that the prepared MIP-QCM sensor has high accuracy and precision for metolcarb analysis in food matrix. [ABSTRACT FROM AUTHOR]

In recent times, there is an intense need for a reliable non‐invasive diabetes prediction system. Some of the researches in this field suggest that acetone gas in breath has a good correlation to blood glucose levels. Hence, acetone is emerging as a promising bio‐marker in diabetes prediction. In this study, acetone levels are measured using quartz crystal microbalance sensor that has wide‐scale application as a bio‐sensor. It is a piezoelectric sensor which is used to detect and quantify mass variations. The resonant frequency of the sensor changes when there is a deposition of mass on the surface of the crystal. The shift in resonant frequency is directly proportional to the change in the mass concentration. To estimate the performance of this sensor, it is required to understand the sensor's electrical characteristics such as its conductance gain and admittance. This study studies these characteristics and evaluates the behaviour of the sensor in the presence of various acetone concentrations in breath sample for healthy, type 1 and type 2 diabetic subjects. [ABSTRACT FROM AUTHOR]

In this paper, a method for the rapid detection of diethylstilbestrol (DES) using quartz crystal microbalance (QCM) with gold nanoparticles (AuNPs) amplification was developed and this method was used on the arrayed langasite crystal microbalance (LCM) to realize the high-throughput detection of DES. A sensitive membrane which can recognize DES specifically was prepared on the surface of gold electrode through the molecular self-assembly technique. Gold nanoparticles (AuNPs) were coupled with anti-DES antibodies to amplify the signal of QCM. DES was detected through competitive immunoassay. At the same time, five gold electrodes were plated on a single langasite crystal in order to prepare an arrayed LCM sensor. The reliability and efficiency of the arrayed sensor were studied. The QCM sensor exhibits a linear detection range from 16 to 500 ng/mL and a detection limit of 13 ng/mL. The recovery rate of DES in the milk samples was 98.0–104.8%. By using structural analogs, the QCM sensor platform was demonstrated to be specific for the detection of DES. The arrayed LCM sensor was developed successfully and it could detect DES with arrayed method. [ABSTRACT FROM AUTHOR]

A simple quartz crystal microbalance (QCM) sensor based on a sol-gel molecularly imprinted polymer (MIP) film as the recognition element was developed for patulin (PAT) detection. The high adsorption capacity of the proposed MIP for PAT was demonstrated by Scatchard equation analysis. Through the evaluation, based on the QCM frequency change, the developed sensor exhibited a linear concentration range of PAT from 7.5 × 10 −3 μg mL −1 to 6 × 10 −2 μg mL −1 with a lower detection limit of 3.1 × 10 −3 μg mL −1 (S/N = 3). The sensor showed good selective affinity for PAT (selectivity coefficient = 3.82) as well as good reproducibility and long-term stability. The developed sensor was tested on its ability to detect PAT in real samples through a spiking and recovery study with the recoveries ranging from 76.9% to 91.3% (RSDs < 8.4%). The good agreement results of the established MIP-QCM sensor and HPLC–MS method indicated that the developed method could accurately detect PAT in practical food samples. [ABSTRACT FROM AUTHOR]

In this work, a novel water compatible molecularly imprinted polymer was synthesized in bead shape by the precipitation polymerization technique. Immobilization of such imprinted beads on the surface of quartz crystal microbalance (QCM) was made through Au-S links using the “surface-grafting to” approach. The imprinted beads revealed a superiority in terms of recapture ability of analyte in the large concentration range and sensitivity as compared to traditionally imprinted monolith films. The piezoelectric analysis of target analyte (5,6-dihydrouracil) with imprinted polymer beads was found to be highly selective and sensitive, without any cross-reactivity and false-positives, in real samples. A perfect linearity between the frequency shift and the analyte concentration was observed in the range 0.03–1.75 μM, with detection limits varying between 0.003–0.006 μM ( S/N = 3) [cf., imprinted film modified QCM: 0.04–1.32 μM, limit of detection 0.01 μM ( S/N = 3)]. The endogenous 5,6-dihydrouracil level was also obtained in the blood plasma sample which may help exploring concerned dihydropyrimidine dehydrogenase activity, on the basis of concentration ratio [dihydrouracil]/[uracil] in cancer patients undergoing chemotherapy with 5-fluorouracil supplementation. [ABSTRACT FROM AUTHOR]

Citrinin (CIT) is difficult to measure since only trace levels are present in commercial food products. In this study, a novel three-dimensional (3D) molecularly imprinted quartz crystal microbalance (QCM) sensor for trace CIT detection was constructed by electro-polymerizing o -aminothiophenol on Au nanoparticles@mesoporous carbon CMK-3 (AuNPs@CMK-3) functional composite modified Au electrode surface. Herein, AuNPs@CMK-3 functional composite acted as signal amplifier since the 3D structure and large specific surface area of AuNPs@CMK-3 functional composite were beneficial to increase the amount of effective imprinted sites and subsequently improve the sensitivity of the sensor. The preparation process of the QCM sensor was characterized by scanning electron microscope, transmission electron microscope, cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimal conditions, the proposed sensor showed a linear frequency shift to the concentration of target CIT ranging from 6.0 × 10 −9 to 2.0 × 10 −7 mol L −1 with a low detection limit of 1.8 × 10 −9 mol L −1 (S/N = 3). The sensitive sensor exhibited excellent selective recognition, anti-interference capability, reproducibility and long-term stability, and was successfully applied to analyze trace CIT in cereal samples with satisfactory recoveries, suggesting the proposed sensor is promising for the detection of CIT at trace levels in foods. [ABSTRACT FROM AUTHOR]

A novel approach to synthesize molecularly imprinted polymer (MIP) nanoparticles using a MIL-101 support (a type of metal–organic framework) is reported herein for the first time; the sample is referred as MIL@MIP. The nanoparticles were well distributed within the polymer film, and exhibit an octahedral shape, satisfied thermal stability, and a high specific surface area (SSA) of 1579.43 m 2 g −1 . The adsorption behavior of MIL@MIP toward metolcarb in aqueous solution was subsequently examined. The synthesized MIL@MIP displayed satisfactory high transfer mass rates and a high selective adsorption affinity for metolcarb. Based on these results, a quartz crystal microbalance (QCM) sensor based on MIL@MIP was subsequently constructed and examined for the sensitive detection of metolcarb. Under optimal conditions, the detection limit of the system assessed in pear juice was 0.0689 mg L −1 within a linear concentration range of 0.1–0.9 mg L −1 . MIL@MIP–QCM system combines the advantages of MIL-101 and molecularly imprinted technology (MIT), thereby achieving high detection sensitivity and selectivity. The current findings suggest the potential of MIL@MIP for detecting trace level pesticides and veterinary drugs for food safety and environmental control. [ABSTRACT FROM AUTHOR]

In black tea manufacturing, the fermentation process plays a significant role to determine the quality of finished tea. During this process, complex chain of biochemical reactions takes place and green tea leaves transform from grassy to sweet floral aroma. Monitoring and detection of optimum fermentation time are necessary, as both under and over fermented tea produce inferior grades of tea. This paper presents a method of real-time monitoring to detect the optimum fermentation time of black tea using an electronic nose consisting of eight quartz crystal microbalance (QCM) sensors. The sensor is coated with glucose derivative coating materials viz. maltose (MAL), maltodextrin (MDEX), β-cyclodextrin (β-CD), d -glucose ( d -GLU) and polyethylene glycols (PEG) with different molecular weights, 200, 1500, 4000, and 6000. Optimum fermentation times were determined for twelve black tea samples, and the results show good agreement with the estimations of the ultra-violet-visible (UV) spectrophotometer based reference method. [ABSTRACT FROM AUTHOR]

The adsorption of vapors of marker substances, the main pollutants diffusing into air from polymeric household products, is studied. An array of eight quartz crystal microbalance (QCM) sensors is assembled; it ensures the minimum effect of water vapors on the results of microweighing, the maximum sensitivity to one or several classes of organic compounds, and the identification of phenol/formaldehyde and acetone in mixtures with the aim to estimate the level of emissions of phenol, formaldehyde, toluene, and acetone from polymeric household products. A classification of samples of nonfood polymers by the degree of hazard is proposed taking into account the total concentration of easily volatile organic compounds and the presence of phenol/formaldehyde and acetone. The accuracy of the detection of phenol emissions by polymers is confirmed by a standard spectrophotometry method. The use of the sensor array allowed the reduction of the cost and time of analysis and the obtaining of information on the concentrations of other easily volatiles in one measurement. [ABSTRACT FROM AUTHOR]

Geraniol is one of the important qualities determining volatile components of black tea. This paper presents a quartz crystal microbalance sensor to detect geraniol from black tea aroma. The sensor is developed using β-cyclodextrin (β-CD). β-CD is a flavor encapsulating material with toroidal bucket-like structure, whose inside-cavity is hydrophobic and the outside is hydrophilic and it is found to be a suitable coating material for detecting geraniol. Extensive experiments have been carried out with the β-CD sensor and it is observed that the sensor offers better sensitivity for geraniol in comparison with other important constituents of black tea such as linalool, linalool oxide, methyl salicylate, and trans-2-hexenal. Experiments with ten Darjeeling orthodox black tea samples have been carried out with the developed sensor and a correlation factor of 0.9925 has been obtained with the corresponding gas chromatography mass spectrometry analysis. [ABSTRACT FROM PUBLISHER]

It is usually considered that the resonance frequency of quartz crystal resonator is only related to dynamic inductance L1 and dynamic capacitance C1, and load resonance frequency has connection with L1, C1 and static capacitance C0. Hence, the dynamic resistance cannot be measured by frequency. The deduction show that all the frequencies relates to L1, C1, C0 and dynamic resistance R1. Then, a method for measuring the total equivalent parameters of quartz crystal resonator based on zero phase frequency is proposed in this Letter. The simulation results of advanced design system (ADS) verify the validity of this proposal in theory. After that, the phase‐frequency‐curves of a quartz crystal resonator with 10 and 5 MHz are measured, which can obtain equivalent parameters of through data processing. The results show that this method has calculated parameters essentially in agreement with nominal parameters. This method does not have reciprocating debugging process, and the test process is simple as well. In addition, the approximate calculation is not used in this method, and it could be widely extent to the field of sensors, such as quartz crystal microbalance sensors, temperature sensors and so on. [ABSTRACT FROM AUTHOR]

A molecularly imprinted quartz crystal microbalance (QCM) sensor for ractopamine (RAC) detection was developed by electrodepositing a poly-o-aminothiophenol membrane on an Au electrode surface modified by self-assembled Au nanoparticles (AuNPs). The modified electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. This molecularly imprinted QCM sensor showed good frequency response in RAC binding measurements and the introduction of AuNPs demonstrated performance improvements. Frequency shifts were found to be proportional to concentration of RAC in the range of 2.5×10−6 to 1.5×10−4 molL−1 with a detection limit of 1.17×10−6 molL−1 (S/N=3). The sensor showed a good selective affinity for RAC (selectivity coefficient >3) compared with similar molecules and good reproducibility and long-term stability. This research has combined the advantages of high specific surface area of AuNPs, high selectivity from molecularly imprinted electrodeposited membrane and high sensitivity from quartz crystal microgravimetry. In addition, the modified electrode sensor was successfully applied to determine RAC residues in spiked swine feed samples with satisfactory recoveries ranging from 87.7 to 95.2%. [ABSTRACT FROM AUTHOR]

• A NH 2 -TiO 2 /MUA/AuE-QCM sensor was developed based on amidated nano-titanium film. • The short analysis time of the sensor was helpful for trace phosphoprotein detection. • The QCM-sensor was simple and had excellent sensitivity, selectivity and accuracy. • An "all-in-one" NH 2 -TiO 2 /MUA-sensing system was created without tedious pretreatment. A novel quartz crystal microbalance (QCM) sensor for trace-phosphoprotein ultrafast detection was constructed based on the bridge interactions between the NH 2 -TiO 2 sites enriched on Au-electrode and phosphate groups. Herein, 11-mercaptoundecanoic acid (MUA) modified by Au-S bond acted as carrier for immobilizing NH 2 -TiO 2. Functionalized NH 2 -TiO 2 to absorb phosphoproteins. Under the optimal conditions, the proposed sensor showed a linear frequency shift to the concentration of α-casein ranging from 1.0 × 10−3 to 1.0 mg mL−1 with a low detection limit of 5.3 × 10−6 mg mL−1 (S/N = 3), and the limit of quantitation was 0.001 mg mL−1. Compared with traditional Ti4+-IMAC/MOAC-system, the analysis process of NH 2 -TiO 2 /MUA/AuE-QCM sensor was simpler and faster which could complete within 5 min. Additionally, the constructed biosensor was successfully used for the non-fat milk and chicken egg white. This proposed sensor presents a great prospective strategy for the evaluation of the nutrition in different foods. [ABSTRACT FROM AUTHOR]

• The gas-sensing system with EC-coated QCM sensors was developed. • The developed sensor has better selectivity and sensitivity for d -limonene aromas. • The early infestation citrus can be nondestructively and rapidly detected by the sensor. D-limonene is one of the main olefin gas compounds released from citrus and its relative content changes most obviously with the infection time of Bactrocera dorsalis (Hendel). Thus, it is necessary to detect d -limonene content released from citrus, which may lead to detect the presence of early infestation by B. dorsalis in citrus. In this study, a gas-sensing system based on quartz crystal microbalance (QCM) sensors coated with ethyl cellulose (EC) was developed to detect d -limonene aromas emanating from Australian citrus. There was a linear relationship between the frequency shift and d -limonene concentrations ranging from 60 mg m−3 to 6000 mg m−3 with a determination coefficient (R2) of 0.9899, and the limit of detection for d -limonene in pure gas was 300 mg m−3. It has also been observed that the QCM sensor has better selectivity towards d -limonene aroma. Additionally, the sensor was found to be repeatable with an average R value of 96.31 %, and the lifetime of the sensor can be extended at least to one month with an acceptable drift (3.40 %) in their sensing characteristics. Furthermore, it was confirmed that there was high consistency between the QCM sensor's response and the GC–MS for d -limonene aroma. The six VOCs contributing the most to differentiating citrus infested with B. dorsalis were identified. The gas-sensing system based on QCM sensors has potential feasibility for the rapid detection of the presence of B. dorsalis infestations in postharvest citrus. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of an amino morpholine-based the new schiff base calix[4]arene (compound 5), it's coating on Quartz Crystal Microbalance (QCM) crystal as a self-assembled monolayer (SAM), and real-time detection of erythromycin (ERY) in aqueous media. The characterization of the QCM sensor has been succeeded with atomic force microscopy and contact angle measurements. Initial experiments revealed that the frequency response decreased quickly as expected and reached equilibrium within 5 min which means that there was a good interaction between the compound 5 coated QCM sensor surface and ERY molecules. The QCM sensor showed a linear response towards ERY solutions in different concentrations ranging from 10 to 200 μM, with the sensitivity (S) and limit of detection (LOD) being 0.66 Hz/μM and 4.80 μM, respectively. Furthermore, the adsorption behavior and mechanism of ERY onto the QCM sensor were applied for this sensing system and the adsorption data exhibited a good correlation with the Langmuir adsorption isotherm in terms of R 2 and Δm max. The QCM sensor was shown outstanding selective performance to ERY among some biologic molecules such as amino acid, drug, hormone, vitamin. Thus, real-time, sensitive, selective and effective recognition of ERY was performed by a calixarene derivative coated QCM sensor. Image 1 • Calixarene based film was prepared onto the QCM surface by self-assembled monolayer to detect ERY. • Real time detection of ERY by calixarene-based QCM was accomplished for the first time. • Molecular recognition of ERY as sensitive, selective and effective was achieved. [ABSTRACT FROM AUTHOR]

Interferences in human plasma immunoassay are severe challenge that affects the sensitivity and reproducibility of the assay. The clotting factor fibrinogen is a negatively charged protein and is one of the most common sources of interference in immunoassays, and its removal increases the sensitivity and reproducibility. Here, we present a highly sensitive and reproducible method for the detection of prostate specific antigen (PSA) in human plasma immunoassays. Protamine sulfate, a highly positively charged protein, was used to precipitate fibrinogen via ionic interaction to improve the sensitivity and reproducibility of human plasma immunoassay. In a sandwich ELISA for PSA using plasma and protamine-treated plasma samples, the limit of detection was improved from 413 pg/mL in plasma to 235 pg/mL in protamine-treated plasma samples, and the coefficient of variation known as a measure of reproducibility was significantly lowered by protamine treatment. The use of protamine sulfate in human plasma immunoassays for detection of PSA using quartz crystal microbalance (QCM) biosensors resulted in increased sensitivity and reproducibility by about 2-fold and 3-fold, respectively, relative to when not using protamine sulfate. Based on these results, protamine sulfate was the best choice to increase the sensitivity and reproducibility in immunoassays using plasma samples. We have demonstrated that the sensitivity and reproducibility of PSA detection in protamine-treated plasma samples were significantly improved compared with untreated plasma samples in the sandwich ELISA and the QCM sensor assays. Image 1 • A highly sensitive and reproducible human plasma PSA immunoassay was developed. • Protamine sulfate increased the sensitivity and reproducibility of human plasma PSA sandwich ELISA. • The effect of protamine sulfate on human plasma PSA immunoassay was also confirmed by QCM biosensor. [ABSTRACT FROM AUTHOR]

This work reports on the results of investigation of quarts crystal microbalance sensors coated with polybutyl methacrylate and polyvinyl formal/ethylal to wide range of volatile organic compounds. Polymer film coated sensors showed a high sensitivity and an excellent selectivity towards these compounds. Good linearity of the concentration dependence has been obtained in almost all the concentration range of volatile compounds. The detection limit of several analytes was less than 100 ppm. [ABSTRACT FROM AUTHOR]

Fabrication of metal-organic framework (MOF) thin films over macroscopic surface areas is a subject of great interest for gas sensor application platforms such as optics and microelectronics. However, a direct synthesis of MOF films at ambient conditions, in particular pillared-layer MOF films due to their anisotropic structures, remains a significant challenge. Herein, we demonstrate for the first time a facile construction of dense and continuous pillared-layer MOF thin films on a centimeter scale via an aluminum-doped zinc oxide template and hydroxy double salt (HDS) intermediates at room temperature. A series of Cu(II)-based pillared MOFs with different 1,4-benzenedicarboxylic acid (bdc) ligands were explored for optimizing MOF film formation for CO 2 sensor applications. Nonpolar ligands with lower water solubility preferentially formed crystalline pillared MOF structures from HDS intermediates. A Cu 2 (ndc) 2 (dabco) (ndc = 1,4-naphthalene-bdc; dabco = 1,4-diazabicyclo[2.2.2]octane) MOF demonstrated the most dense and uniform film growth with micrometer thickness over one square centimeter area. This synthetic approach for growing Cu 2 (ndc) 2 (dabco) MOF thin films was successfully translated toward two sensing platforms: a quartz crystal microbalance and an optical fiber sensor. These Cu 2 (ndc) 2 (dabco) MOF-coated sensors displayed sensitivity toward CO 2 and response/recovery time on the scale of seconds, even at moderate humidity levels. This work provides a road map for producing continuous and anisotropic crystalline MOF thin films over a centimeter scale area on various substrates, which will greatly facilitate their utilization in MOF-based sensor devices, among other applications.

In this work, a quartz crystal microbalance (QCM) sensor has been fabricated using immunoassay for sensitive determination of Bifidobacterium bifidum . Au nanoparticle has been used for amplifying sandwich assays. The proposed immunosensor exhibited a linear detection range between 10 3 and 10 5 CFU/mL with a limit of detection of 2.1 × 10 2 CFU/mL. The proposed immunosensor exhibited good selectivity for B. bifidum sensing with low cross reactivity for other foodborne pathogens such as Lactobacillus acidophilus, Listeria monocytogenes , and Escherichia coli . In addition, the proposed immunosensor has been successfully used for B. bifidum detection in feces samples and food samples. The frequency decreases of 12, 17, and 10 Hz were observed from the milk samples consisting of the mixtures of L. acidophilus, L. monocytogenes , and E. coli . The frequency decreases of 8, 15, and 7 Hz were observed from the feces samples consisting of the mixtures of L. acidophilus, L. monocytogenes , and E. coli ., (Copyright © 2020 Hou, Zhao, Chen, Li, Lin, Chen, Zhu, Wu, Lian, Huang and Li.)

This paper describes the synthesis of new chiral calix [4]arene derivative having (R)-2-phenylglycinol moiety (compound 6), and its chiral recognition studies for ascorbic acid (AA) enantiomers by using Quartz Crystal Microbalance (QCM). Initial experiments indicated that the outstanding selective chiral recognition (α) was observed as 2.61 for l -enantiomer of AA. The sensitivity (S) and the limit of detection (LOD) values for L -AA were calculated as 0.0226 Hz/μM and 0.63 μM, respectively. Furthermore, the sorption behavior and mechanism of AA onto compound 6 film were evaluated and the sorption data exhibited a good correlation with the Freundlich isotherm models. The maximum uptake of L -AA by the sensor was found as 5895.76 mg/g. In conclusion, chiral recognition of AA enantiomers as real-time, sensitive, selective and effective was performed by a calixarene derivative coated QCM sensor. Image 1 • Chiral detection of AA enantiomers by calixarene-based QCM was performed for the first time. • Enantiomeric detection of AA as real-time, sensitive, selective and effective was accomplished. • It was produced a QCM sensor to be durable and easily recoverable with distilled water. • Calixarene coating onto QCM surface was found to be a useful approach to detect AA. [ABSTRACT FROM AUTHOR]

Quartz crystal microbalance (QCM) sensor array was developed for multi-purpose human respiration assessment. The sensor system was designed to provide feedback for human respiration. Thorough optimization of measurement conditions: air flow, temperature in the QCM chamber, frequency measurement rate, and electrode position regarding to the gas flow-was performed. As shown, acquisition of respiratory parameters (rate and respiratory pattern) could be achieved even with a single electrode used in the system. The prototype system contains eight available QCM channels that can be potentially used for selective responses to certain breath chemicals. At present, the prototype machine is ready for the assessment of respiratory functions in larger populations in order to gain statistical validation. To the best of our knowledge, the developed prototype is the only respiratory assessment system based on surface modified QCM sensors.