Coated Quartz Crystal Microbalance Sensor Research Articles

Nanoscale MOF-74-based QCM gas sensor for CO2 detection at room temperature

CO2 is one of the main components of air, accounting for 0.03–0.04% (300–400 ppm) of the total volume of the atmosphere. CO2 gas is chemically stable and is an inert gas, which makes the means of detecting it extremely limited. To overcome these challenges, in this paper, nanoscale M-MOF-74 (M=Mg, Ni, Zn, Co) was synthesized by a facile method in a two-hour reaction at room temperature, which combined with a quartz crystal microbalance (QCM) sensor-enabled the detection of CO2 gas at room temperature. The CO2 sensing performance of M-MOF-74 coated QCM sensors at room temperature was systematically investigated. The experimental results showed that the Mg-MOF-74 sensor responded to 2000 ppm CO2 at room temperature with 66, and at the same time, had good linearity, high response/recovery (75 s/50 s), and good selectivity to CO2. The electrical parameters and quality factor of the QCM were further verified by impedance analysis. In addition, the potential CO2 adsorption mechanism may be mainly related to the open metal sites in the Mg-MOF-74 material and the synergistic effect of Mg-O bonds. This work confirms that the M-MOF-74 material provides a new avenue for QCM CO2 sensing, and the sensor is expected to be a potential candidate for CO2 detection.

Development of a portable, low-cost QCM sensor-based device for detecting α-pinene in Indian cardamom

One of the key quality indicators for Indian cardamom is α-pinene. To detect α-pinene, linoleic acid, a constituent fatty acid present in rice bran oil, was found responsible for the physisorption of α-pinene through Van der Waals (vdW) interaction. For the analysis and study of the sensing behaviour of α-pinene, a portable gas measuring device incorporating the rice bran oil coated quartz crystal microbalance sensor (RB-QCM) is developed for real-time detection. The sensor offers a good sensitivity (0.367 Hz/ppm) and a rapid response/recovery time (6 s/11 s). The physical adsorption affinity of α-pinene is calculated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. For estimating α-pinene in cardamom samples, the sensor demonstrated a coefficient of 0.98, with the peak area (%) determined by gas chromatography-mass spectrometry (GC–MS). SEM, FTIR, and AFM are used to analyse the structure and morphology of the sensor coating. According to this study, the rice bran oil-coated QCM sensor is a promising method for detecting α-pinene.

Humidity sensing properties and respiratory behavior detection based on chitosan-halloysite nanotubes film coated QCM sensor combined with support vector machine

This work demonstrated an accurate and reliable quartz crystal microbalance (QCM) humidity sensor based on the chitosan-halloysite nanotubes (CS-HNTs) composite that can be used to monitor respiration lines. The hydrophilic polymer chitosan (CS) with halloysite nanotubes (HNTs) was characterized using SEM, TEM, XRD, XPS, FT-IR, and WCA investigations to analyze the microscopic morphology, molecular structure, chemical bond, and hydrophilicity. The experimental results showed that the QCM humidity sensor of CS-HNTs film demonstrated high sensitivity (69.1 Hz/% RH), superior humidity hysteresis (<2.8% RH), excellent long-term stability, repeatability, and outstanding selectivity. The subtle changes in fingertip movements and exhaled air humidity in different modes were detected by the QCM humidity sensor. A respiratory behavior monitoring model based on support vector machines was constructed to accurately determine five breathing modes and apply it to human breath detection and health medical diagnosis.

Chitosan Coating on Quartz Crystal Microbalance Gas Sensor for Isopropyl Alcohol and Acetone Detection

The development of acoustic wave sensors was driven by the presence of modern technology. Quartzcrystal microbalance (QCM) has excellent sensing capabilitiesand has wide range ofapplications. Selection of sensing layer is crucial to ensure the performance of the QCM sensor for volatile organic compound (VOC) detection. Hence, the objective of this paper is to compare the performance of chitosan coated QCM sensor for different analyte gas: isopropyl alcohol (IPA). Finite element simulation was implemented usingCOMSOL Multiphysics to study the resonance frequency shift before and after sensing. Simulation results shows IPA detection shows a higher resonance frequency shift of 62.5 Hzcompared to acetone due to higher molar mass. Experimental work is conducted to validate the simulation results where IPA analyte gas yields in 84.8 Hz which is higher than acetone analyte gas at 41.8 Hz. The functional groups for both sensing layer and analyte gas also affects the gas detection performance. IPA analyte gas possessed hydroxyl groups that favors to hydrogen bond formation with chitosan sensing layer. Thus, the QCM sensor with chitosan as the sensing layer has the potential for VOC sensing of different molar mass and functional groups.

Synthesis and Gas Adsorption Properties of γ ‐Fe 2 O 3 Nanoparticles for Mass‐Type Sensing Application

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.

Identification of an efficient adsorbent for ethanol sensing at room temperature using quartz crystal microbalance

Zeolite coated quartz crystal microbalance (QCM) is proposed as an efficient sensor for the detection of ethanol at room temperature. In this work, three zeolites DaY, ZSM-5, and BEA were investigated in order to determine the most efficient adsorbent for ethanol sensing at room temperature. The sensing performances were found to be mostly influenced by the acid site density and the zeolite's pore size. The BEA coated QCM sensor exhibited the best performances with a high relative frequency shift from 9.0 × 10−7 to 2 × 10−6 for 10 ppm of ethanol. Furthermore, this sensor exhibited fast response and recovery times which makes it a suitable material for the monitoring of ethanol in the air. In addition, the ethanol diffusion order was evaluated using Fickian diffusion law and was found to be the highest for the zeolite BEA. A sensing mechanism was also proposed for the adsorption and desorption of ethanol into zeolites based on unstable protonated dimers, water and diethyle ether resides for the energy-efficient ethanol sensor.

Detection of Carvacrol Content in Oregano Essential Oil by Molecularly Imprinted Polymer Coated Quartz Crystal Microbalance Sensor

The essential oil extracted from the oregano (Origanum vulgare) is rich in phenolic compounds that have strong antioxidant and antibacterial properties. Carvacrol is the major component of oregano essential oil. The current study describes the use of a molecularly imprinted quartz crystal microbalance (QCM) sensor to detect carvacrol in oregano essential oil. For the formation of the sensing film, the surface of a quartz crystal with a silver electrode was modified by simple drop coating with a synthesized polymer solution and thermally polymerized at 95&#x00B0;C in an inert atmosphere. The polymer was synthesized by copolymerization of styrene, methyl methacrylate, acrylonitrile and divinylbenzene in an optimum ratio with template carvacrol. The analytical performance of the sensor has been observed to be reasonably good (sensitivity &#x2013; 1.24Hz/ppm) and has adequate repeatability and reproducibility. Linear calibration curves were obtained in the concentration range of carvacrol between 5&#x2013;300 ppm. The molecularly imprinted polymer structure and surface morphology were analyzed by FTIR spectroscopy, SEM and AFM. Validation of the proposed sensor with oregano essential oil samples has been performed by correlating the frequency deviation of the sensor with the estimations of carvacrol obtained from gas chromatography.

Application of an artificial neural network and QCM sensor coated with γ-Fe2O3 nanoparticles for estimation of SO2 gas sensing characteristics

γ-Fe2O3 nanoparticles (NPs) were synthesized by co-precipitation method and a following annealing treatment at 200 °C in ambient air for 6 hours. A mass-type sensor was prepared by coating γ-Fe2O3 NPs on the active electrode of quartz crystal microbalance (QCM). The obtained results of the γ-Fe2O3 NPs based QCM sensor indicate the high response and good repeatability toward SO2 gas in the range of 2.5 – 20 ppm at room temperature. Moreover, the frequency shift (DF) and change in mass of SO2 adsorption per unit area (Dm) of the γ-Fe2O3 NPs coated QCM sensor have a relationship with the mass density of γ-Fe2O3 NPs and SO2 concentrations. The artificial neural network (ANN) model using Levenberg-Marquardt optimization was used to handle the DF and Dm of the γ-Fe2O3 NPs coated QCM sensor. The results of the model validation proved to be a reliable way between the experiment and prediction values.

Application of an artificial neural network and QCM sensor coated with γ-Fe2O3 nanoparticles for estimation of SO2 gas sensing characteristics

γ-Fe2O3 nanoparticles (NPs) were synthesized by co-precipitation method and a following annealing treatment at 200 °C in ambient air for 6 hours. A mass-type sensor was prepared by coating γ-Fe2O3 NPs on the active electrode of quartz crystal microbalance (QCM). The obtained results of the γ-Fe2O3 NPs based QCM sensor indicate the high response and good repeatability toward SO2 gas in the range of 2.5 – 20 ppm at room temperature. Moreover, the frequency shift (DF) and change in mass of SO2 adsorption per unit area (Dm) of the γ-Fe2O3 NPs coated QCM sensor have a relationship with the mass density of γ-Fe2O3 NPs and SO2 concentrations. The artificial neural network (ANN) model using Levenberg-Marquardt optimization was used to handle the DF and Dm of the γ-Fe2O3 NPs coated QCM sensor. The results of the model validation proved to be a reliable way between the experiment and prediction values.

Highly sensitive formaldehyde sensors based on CuO/ZnO composite nanofibrous mats using porous cellulose acetate fibers as templates

An innovative formaldehyde sensor based on CuO/ZnO composite nanofibrous mats (C-NFMs) coated quartz crystal microbalance (QCM), which is capable of stable determination of formaldehyde gas at ambient temperatures sensitively and selectively, has been successfully fabricated. Triaxial and highly porous C-NFMs with high surface area (126.53 m2 g−1) were synthesized by electrospinning a sol-gel cellulose acetate (CA)/CuAc2/ZnAc2 complex solution and following by calcination process. Benefiting from the unique heterojunction structure, immense pore interconnectivity and large surface area of C-NFMs, the as-developed QCM sensors exhibited an extremely low limit of detection (LOD) down to 26 ppb and a limit of quantification value equals to 87 ppb. Besides, the C-NFMs coated QCM sensors also demonstrated short response times (80s), the long-term stability during 3 weeks as well as good selectivity to formaldehyde over diverse volatile organic compounds. The sorption equilibrium in the adsorption process of QCM coated sensors was well met with the Freundlich model, which certified the heterogeneous adsorption between formaldehyde gas and C-NFMs.

WS[formula omitted] thin film based quartz crystal microbalance gas sensor for dimethyl methylphosphonate detection at room temperature

WS2 thin films were deposited on quartz crystal microbalance (QCM) oscillators via radio frequency magnetron sputtering to detect hazardous gases at room temperature (RT). WS2 coated QCM sensors were tested against various hazardous gases including acetone, toluene, xylene, isopropyl-alcohol, hydrogen cyanide, hydrogen sulfide, ammonia, dimethyl methylphosphonate (DMMP, nerve agent simulant) and 2-Chloroethyl ethyl sulfide (mustard simulant). It was observed that fabricated sensors exhibit superior sensor performance to DMMP gas at RT. Additionally, one of the sensors showed reliable stability, high sensitivity, and a low theoretical limit of detection of 5 ppb. As a result, WS2 coated QCM sensor has a great potential for the monitoring of nerve agent.

Poly(2-Hydroxyethyl methacrylate-co-N,N-dimethylacrylamide)-Coated Quartz Crystal Microbalance Sensor: Membrane Characterization and Proof of Concept.

Application-oriented hydrogel properties can be obtained by modifying the synthesis conditions of the materials. The purpose of this study is to achieve customized properties for sensing applications of hydrogel membranes based on poly(2-hydroxyethyl methacrylate), HEMA and N,N-dimethylacrylamide, DMAa. Copolymer p(HEMA-co-DMAa) hydrogels were prepared by varying the DMAa monomer ratio from 0–100% in 20% increments. Hydrogel membranes were characterized by attenuated infrared spectroscopy. Swelling and sorption were evaluated using cation solutions. Copolymers were also synthesized on the gold surface of quartz crystal microbalances (QCM) as coating membranes. A proof of concept was conducted for approaching the design and development of QCM sensors based on P(DMAa-co-HEMA)-membranes. Results showed that the water and ion adsorption capacity of hydrogel membranes increased with higher DMAa content. Membranes are not selective to a specific location but did show different transport features with each cation. The QCM coated with the selected membrane presented linear relationships between resonance frequency and ions concentration in solution (10–120 ppm). As a consequence, hydrogel membranes obtained are promising for the development of future biosensing devices.

Low-fouling CNT-PEG-hydrogel coated quartz crystal microbalance sensor for saliva glucose detection.

Saliva glucose detection based on a quartz crystal microbalance (QCM) sensor has emerged as a promising tool and a non-invasive diagnostic technique for diabetes. However, the low glucose concentration and strong protein interference in the saliva hinder the QCM sensors from practical applications. In this study, we present a robust and simple anti-fouling CNT-PEG-hydrogel film-coated QCM sensor for the detection of saliva glucose with high sensitivity. The CNT-PEG-hydrogel film consists of two layers; the bottom base PBA-hydrogel film is designed to recognize the glucose while the top CNT-PEG layer is used to restrict protein adsorption and improve the biocompatibility. Our results show that this CNT-PEG-hydrogel film exhibited a 10-fold enhancement on the detection limit compared to the PBA-hydrogel. Meanwhile, the adsorption of proteins on the surface of the CNT-PEG-hydrogel film, including bovine serum albumin (BSA), mucin (MUC), and fibrinogen (FIB), were reduced by 99.1%, 77.8%, and 83.7%, respectively. The CNT-PEG-hydrogel film could detect the typical saliva glucose level (0–50 mg L−1) in 10% saliva with a good responsivity. To sum up, this new tool with low-fouling film featuring high stability, specificity, and selectivity holds great potential for non-invasive monitoring of saliva glucose in human physiological levels.

Complex characterization of human urine using super-nonwettable soot coated quartz crystal microbalance sensors

The laboratory dipstick analysis of human urine is among the frequently ordered medical tests due to the profusion of biomarkers that can be used to indicate the occurrence of health problems. Regrettably, the authenticity of these assays is compromised at low biomarker concentrations or when obtaining quantitative results is mandatory. Here, we reveal the first of its kind super-nonwettable soot coated quartz crystal microbalance (QCM) based biosensors with strong potential for in-situ quantification of human urine. Unlike the existing counterparts, the signal generated by the as-developed devices seems to reverberate the joint effect of a few biochemical components of the urine (pH, protein, urea, creatinine and uric acid) via visible changes in the rate of super-nonwetting to super-wetting state transition of the interfacial soot coating. In turn, the developed QCM sensors are endowed with the ability of recognizing subtle differences (e.g., tenths or units of mmol/L) in the urine’s biochemistry at minimized noise levels, by registering fundamentally distinct resonance responses in terms of quantitative values and course of the signal. Our invention rises additional questions, whose answer is pending, but may inspire the research society for dedicating efforts in future fabrication of facile, time-efficient and flexible platforms for complex urinalysis.

Effect of the phase composition of iron oxide nanorods on SO2 gas sensing performance

α-FeOOH nanorods were synthesized by a facile precipitation method. γ-Fe2O3 and α-Fe2O3 nanorods were then obtained by calcining for 6 h at 200 and 600 °C in ambient air, respectively. A mass-type sensor was developed based on the different iron oxide phase compositions of α-FeOOH, γ-Fe2O3 and α-Fe2O3 coating a quartz crystal microbalance (QCM). The gas sensing properties of three as-prepared sensors were systematically examined for detecting sulphur dioxide gas (SO2) at room temperature. The effect of phase composition of iron oxide nanorods on sensing properties was also discussed. Although as-prepared iron oxides have a similar morphologic structure, the sensor based on γ-Fe2O3 exposes the highest response to SO2. The sensing results show that the γ-Fe2O3 coated QCM sensors had an extremely good performance for SO2 gas in the 2.5–20 ppm range at room temperature.

Dynamic wettability alteration for combined low salinity brine injection and surfactant flooding on silica surface

Experimental results of dynamic contact angle measurements of low salinity brine and combined low salinity water and surfactant flooding (LSW–SF) on silica surface are presented in this study. Dynamic contact angle experiments were carried out for four crude oil samples with low salinity brines and combined low salinity and sodium dodecylbenzene sulfonate (SDBS) solutions. Similar measurements with the same ion strength in presence of different cations, Na+ and Ca2+, for low salinity injections and combined low salinity–SDBS solutions were also carried out to study the change in dynamic contact angles and wetting behavior. The presences of different cations change the initial contact angles in low salinity solution injections and show different dynamic behaviors in presence of different crude oils. The signs and values of the line tension to oil/water interfacial tension ratios have been calculated from the size dependence of the dynamic contact angle measurements on the silica coated quartz crystal microbalance sensors. Analysis indicates positive line tension values for low salinity brine systems and negative values for LSW–SF systems. Injection of surfactant solutions in presence of electrolyte prompts the spreading of the oil droplet over the surface, which is induced by interfacial tension gradient from the top of the oil droplet toward the contact line. The results indicated that spreading time, which is the required time for oil drop to gradually flatten out, is dependent on type of electrolytes and is a function of surface excess concentration of the surfactant.

Molecular Imprinting Polymer-Based QCM Sensor for Detection of α-Pinene

The quartz crystal microbalance (QCM) modified by chitosan/α-pinene, prepared by spin-coating technique has been successfully developed with molecular imprinting polymer (MIP) concept. To remove the template, we carried out two treatments namely heating and vacuum in a desiccator. To find out selectivity of the sensor, the QCM modified with polymer chitosan has been tested with another analyte such as acetone, ethanol, N-amyl alcohol, iso-amyl alcohol. The result shows that chitosan/α-pinene coated QCM sensor can provide a good response as good as sensitivity. The best QCM at heating treatment in a furnace with the decline of frequency is 32 Hz, then the QCM vacuum pumping treatment with decline frequency is 27 Hz.

Polypyrrole-Modified Tin Disulfide Nanoflower-Based Quartz Crystal Microbalance Sensor for Humidity Sensing

In this paper, quartz crystal microbalance (QCM) humidity sensors based on polypyrrole (PPy) modified tin disulfide (SnS2) nanocomposite have been fabricated. The morphology and composition of the PPy/SnS2 nanocomposite film were examined by means of SEM and TEM. The hydrophilicity of the PPy/SnS2 nanocomposite film sensor was verified by the contact angle experiment. The humidity sensing characteristics of the PPy/SnS2 nanocomposite sensor was studied at room temperature. The experimental results illustrated that the PPy/SnS2 nanocomposite coated QCM sensor was very sensitive to humidity and demonstrated high sensitivity, short response time, and excellent repeatability, which was surpassed the pure PPy and pure SnS2. The Langmuir adsorption model is used to explain the humidity sensing mechanism of PPy/SnS2 based QCM sensor. The enhanced humidity sensing properties are attributed to the nanostructure and hydrophilicity of the PPy/SnS2 nanocomposite.

Real-time and selective recognition of erythromycin by self-assembly of calix[4]arene on QCM sensor

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 R2 and Δmmax. 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.

Quartz crystal microbalance-coated cellulose acetate nanofibers overlaid with chitosan for detection of acetic anhydride vapor

Acetic anhydride is one of the most often used reagents in the production of heroin, and the detection of this compound in the air is a methodological challenge. This work aims to devise cellulose acetate (CA) nanofibers overlaid with chitosan (Cs) on a quartz crystal microbalance (QCM) for the detection of acetic anhydride. A base layer of CA nanofibers was coated on QCM via electrospinning and then immersed in Cs solution to fabricate CA nanofibers overlaid with chitosan (CA/Cs nanofibers). On scanning electron microscopy (SEM) images, both CA and CA/Cs nanofibers appeared very smooth and homogenous. The increased nanofiber diameter following chitosan immersion indicated that the chitosan layer covered the CA nanofibers. In addition, coverage was verified by the existence of primary amine groups of Cs in CA/Cs nanofibers on the FTIR spectra. The addition of a chitosan layer on top of CA nanofibers clearly increased the sensory response. The sensitivity of the QCM CA/Cs nanofiber sensor exposed to 10–1000 ppm acetic anhydride vapor was up to 0.234 Hz/ppm, with a lower limit of detection (LOD) of 5 ppm. The sensor also showed a rapid response time (44 s), as well as repeatable and long-term stable behavior, during 5 months of measurements. The as-prepared sensor was also more sensitive to acetic anhydride vapor than to other vapors. A reversible nucleophilic addition interaction between acetic anhydride molecules and the primary amine groups in chitosan was believed to be responsible for the sensing mechanism. The high sensory ability implied that CA/Cs nanofiber coated QCM sensors will be highly suitable for use in the detection of acetic anhydride vapor.