Coated Quartz Crystal Microbalance Research Articles

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.

Metal-Phenolic Film Coated Quartz Crystal Microbalance as a Selective Sensor for Methanol Detection in Alcoholic Beverages.

The facile real-time monitoring of methyl content in fermented beverages is of fundamental significance in the alcohol and restaurant industry, since as little as 4 mL of methanol entering the blood may cause intoxication or blindness. So far, the practical applicability of available methanol sensors, including the piezoresonance analogs, is somewhat limited to laboratory use due to the complexity and bulkiness of the measuring equipment involving multistep procedures. This article introduces a hydrophobic metal-phenolic film-coated quartz crystal microbalance (MPF-QCM) as a novel streamlined detector of methanol in alcoholic drinks. Unlike other QCM-based alcohol sensors, our device operates under saturated vapor pressure conditions, permitting rapid detection of methyl fractions up to seven times below the tolerable levels in spirits (e.g., whisky) while effectively suppressing the cross-sensitivity to interfering chemical compounds such as water, petroleum ether or ammonium hydroxide. Furthermore, the good surface adhesion of metal-phenolic complexes endows the MPF-QCM with superior long-term stability, contributing to the repeatable and reversible physical sorption of the target analytes. These features, combined with the lack of mass flow controllers, valves and connecting pipes delivering the gas mixture, outline the likelihood for future design of a portable MPF-QCM prototype suitable to point-of-use analysis in drinking establishments.

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°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 – 1.24Hz/ppm) and has adequate repeatability and reproducibility. Linear calibration curves were obtained in the concentration range of carvacrol between 5–300 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.

Effect of effluent gas composition on characteristics of graphene oxide film based relative humidity sensor

Nitrogen and synthetic air have been used as standard effluent gases in relative humidity (RH) sensing experiments, especially to characterise the dynamic sensing capabilities of RH sensors utilising graphene oxide (GO) as the sensing material. In the present work, we have used GO coated quartz crystal microbalance (QCM) as a tool to investigate the mass adsorption characteristics of samples subjected to multiple humidification-dehumidification cycles using N2 or synthetic air as the effluent gas. We identified that the residual mass adsorbed and retained by the GO film is on average 71.6% higher when using N2 in the initial humidification-dehumidification cycle and this subsequently impacted the hysteresis characteristics until the GO film saturated. To negate the impact of the effluent gas, the GO-based sample should be treated with multiple humidification and dehumidification cycles using either effluent gas.

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.

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.

Investigation of MOF-derived humidity-proof hierarchical porous carbon frameworks as highly-selective toluene absorbents and sensing materials

Carbon frameworks (CFs) derived from metal-organic frameworks (MOFs) have been produced as adsorbents of toluene. To further obtain optimum hierarchical porous carbon structure of CFs, different treatment temperatures were applied to a typical kind of MOFs (ZIF-8). The adsorption capacity of the toluene of hierarchical porous CFs obtained from ZIF-8 under 1100 °C (CF-1100, adsorption capacity of 208.5 mg/g) was higher than that of other carbonization temperature and MOFs. Impressively, the adsorbent CF-1100 also exhibited strong hydrophobicity, low desorption temperature, and good selectivity to toluene. The adsorption capacity decreased by only 10.4% under wet condition compared with the dry condition, standing on the top of the recently reported adsorbents. The impressive adsorption performance of CF-1100 is attributed to the larger specific surface area (1024 m2/g) and pore volume (0.497 cm3/g), newly generated micropores (pore width is 0.6–0.8 nm) and mesopores (pore width above 10 nm), and carbonaceous structure with higher degree of graphitization. Based on the adequate adsorption performance, CF-1100 coated quartz crystal microbalances as sensor also showed a high sensitivity of 0.4004 Hz/ppm and small relative standard deviations of 1.0745% for toluene sensing. This contribution provides a foundation for optimizing potential adsorbents and sensing materials for air pollution abatement.

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.

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.

Novel alcohol vapour sensor based on the mixed-ligand modified MOF-199 coated quartz crystal microbalance

ABSTRACT Alcohol vapour sensors can be used in many fields, such as food quality monitoring, etc. Herein, we developed an alcohol vapour sensor based on the quartz crystal microbalance (QCM) technology. A modified metal-organic frameworks (MOFs), m-MOF-199 was coated on the QCM electrode surface. The different coating methods, including drop coating, spin coating and electrospray were used for preparing a thin film on the surface of the QCM electrode. MOF-199 was modified by mixed-ligand strategy in which benzotriazole ligand was introduced into the structure of MOF-199 and characterised by FT-IR, XRD, BET and FE-SEM techniques. The smaller dimension of m-MOF199 led to a better thin film and enhanced QCM sensor efficiency. In order to evaluate the QCM sensor, ethanol was used as a model compound. The developed ethanol sensor showed two linear ranges in the concentration between of 0.5–30 mg L−1 and 30–300 mg L−1 with a 0.1 and 0.5 mg L−1, LOD and LOQ, respectively. The relative standard deviation (RSD %) of measurements was less than 10%. The developed sensor could be applied for various applications including food, environmental and bioanalysis.

An innovative approach for in-situ detection of postejaculatory semen coagulation and liquefaction using superhydrophobic soot coated quartz crystal microbalances

At present, the abnormal viscosity of human ejaculate is a crucial parameter often associated with the male factor infertility. However, the existing techniques for seminal viscosity evaluation are prone to fair criticism, as most of them are semi-quantitative or too ineffective in monitoring the processes of semen coagulation and liquefaction. Within this article, we report a novel method for quantitative in-situ assessment of the postejaculatory dynamics and peculiarities of human seminal fluids (viscosity, volume, sperm concentration) using superhydrophobic soot coated quartz crystal microbalances (QCMs). A detailed analysis of the real-time sensor signal of two soot coated 5 MHz QCMs, generated by the raw ejaculates of normozoospermic and mild-moderate oligozoospermic patients, reveals that the QCMs can quantify the seminal viscosity (e.g. as normal, increased or hyperviscous) and detect in a highly repeatable manner the phases of semen coagulation and liquefaction. In addition, these devices seem useful in establishing correlative dependencies among the fluid volume, spermatozoa concentrations and observed signal fluctuations from patient-to-patient and measurement-to-measurement. Our findings open future opportunities for rapid, cost-effective and reliable determination of the basic parameters and reproductive potential of human spermatozoa based on the physicochemical properties of the seminal plasma.

Corrosion inhibition of iron surfaces with phosphatidic acid

Abstract Preventing the corrosion of iron in inaccessible structures requires a coating method that reaches all surface areas and creates a uniform protective layer. An ages old practice to protect iron artefacts is to coat them with animal fat, that is, a mixture of lipids. This “method” is accidentally ingenious: some natural phospholipids found in animal fat have the potential to form a tightly packed self-assembled monolayer on metal oxide surfaces, similar to the surfactant monolayers that have attracted increasing attention lately. Thus, the most primitive corrosion prevention method may point at a way to coat complex iron structures in an industrial environment. Here the ability of phosphatidic acid, a natural lipid, to coat and protect iron surfaces was examined. Iron coated quartz crystal microbalance (QCM) sensors were used for the experiments, to monitor the deposition of the lipid as well as the acidic corrosion (dissolution) of iron in situ, in real time. The sensors were coated by self-assembled monolayers of di-myristoyl phosphatidic acid using the liposome deposition method. In this process, 50-100 nm vesicles formed by the lipid are delivered in an aqueous solution and spontaneously coat the iron surfaces upon contact. QCM and ellipsometry measurements confirmed that continuous bilayer and monolayer surface coatings can be achieved by this method. QCM measurements also confirmed that the layers were corrosion resistant in 0.01M acetic acid solution that would dissolve the thin iron layer in minutes in the absence of the protective coating. XPS results suggested a chemisorption-based mechanism of phosphatidic acid attachment to the iron surface. Hence, liposome deposition of phosphatidic acid offers a suitable solution to coat iron surfaces in inaccessible structures in situ.

Enhanced SO2 sensing characteristics of multi-wall carbon nanotubes based mass-type sensor using two-step purification process

In this work, a room temperature gas sensor based on functional multi-wall carbon nanotubes (MWNTs) coated quartz crystal microbalance (QCM) was developed. The two-step purification process was used to remove amorphous carbon and inactivated catalyst particles, and added functional groups on the sidewall of tubes. The functional MWNTs were then dispersed in deionized water to deposit on the gold electrode of the QCM. The operative MWNTs-coated QCM sensor was tested with toxic hazardous gases such as hydrogen sulfide, hydrogen, nitrogen dioxide, carbon monoxide, and sulfur dioxide. The sensing results expose that the fabricated sensor exhibits good sensitivity with sulfur dioxide gas at room temperature. The sensitivity of the functional MWNTs based sensor presented to be superior to that of the as-grown MWNTs based sensor.

Identification of Bioactive Compounds in Ginger Based on Molecularly Imprinted Polymer Quartz Crystal Microbalance Gas Sensor

Borneol, citral, and geraniol have been investigated as the major bioactive compound commonly found in ginger. In this work, a molecularly imprinted polymer (MIP) coated quartz crystal microbalance (QCM) sensor array has been employed for selective recognition of bioactive compounds in the ginger essential oil. In the experiment, the concentration of these bioactive compounds previously was measured using solid phase micro extraction gas chromatography-mass spectroscopy (SPME-GC/MS). Design of MIPs as the template of target molecules was created using polyacrylic acid (PAA) polymer matrix and three molecular targets (borneol, citral, and geraniol). An array of QCM sensor was prepared using four 9-Mhz AT-cut quartz crystal embedded between vacuum-deposited Au electrodes. For data recording, the headspace system flew the odorant of three varieties of ginger essential oil as positive control odorant and wild ginger essential oil as negative control odorant into the QCM sensor chamber. Then, mass loading in the MIP films caused frequency change of QCM sensor array due to odorant adsorption in a thin layer of MIP. Principal component analysis (PCA) and linear discriminant analysis (LDA) were applied to analyse the QCM response sensor. PCA score plot showed segregation of feature response of ginger essential oil with and without the molecular target in the coordinate of principal components. Meanwhile, LDA was able to discriminate training datasets of 80 ginger samples containing borneol, citral, and borneol with accuracy more than 92.50%.

A Benzimidazole-Containing Covalent Organic Framework-Based QCM Sensor for Exceptional Detection of CEES

Mustard gas poses a substantial concern for homeland security, and the development of sensors for facile, rapid, highly sensitive, and selective detection of a mustard gas simulant is much desirable. Herein, a new benzimidazole-containing covalent organic framework (COF), termed BABE-TFPy COF, was synthesized by the Schiff base condensation of 1-(4,7-bis(4-aminophenyl)-1H-benzoimidazole-2-yl)ethan-1-ol (BABE) with 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPy). By virtue of its crystallinity, high porosity, excellent chemical stability, and abundant accessible benzimidazole sites, an unprecedented COF coated quartz crystal microbalance (QCM) sensor was judiciously fabricated for the detection of various volatile organic compounds (VOCs). Remarkably, the resultant BABE-TFPy COF coated QCM sensor exhibited significantly higher sensitivity to 2-chloroethyl ethyl sulfide (CEES), a typical hazardous mustard gas simulant, than those of the other common VOCs. Moreover, the frequency changes of the COF coated QCM sensor were linearly related to the concentrations of CEES vapor within the range of 5.6–19.7 ppm, and derived a strikingly low detection limit of 0.96 ppm (signal-to-noise ratio = 3), rendering it an extraordinary QCM sensor for the detection of CEES. The enthalpy change indicated by the temperature-varying microgravimetric experiment, along with the Gaussian theoretical calculation, highly suggests a dual-hydrogen bonding formed between the BABE-TFPy COF and the CEES molecule accounts for such an exceptional recognition of CEES.

Selective chiral recognition of alanine enantiomers by chiral calix[4]arene coated quartz crystal microbalance sensors.

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.

Adsorption-Desorption Control of Fibronectin in Real Time at the Liquid/Polymer Interface on a Quartz Crystal Microbalance by Thermoresponsivity.

The cell manipulation technique using thermoresponsive polymers is currently attracting much attention for applications in the medical field. To achieve arbitrary and accurate cell control, it is necessary to intensely research fibronectin behavior. A smart surface, which has thermoresponsive wettability and which can adsorb or desorb fibronectin repeatedly without the presence of cells, was fabricated by an electrospinning method. The fabricated coating changed its structure as the temperature was changed, and this transformation could substitute for the pulling force generated by the cytoskeletal contraction of cells. Moreover, a coated quartz crystal microbalance was able to detect the fibronectin behavior as frequency shifts, which could be used in the estimation of the mass shift with the aid of suitable equations. This coating and measurement system can contribute greatly not only to the development in the medical field centered on biomaterial manipulation technologies, but also to the improvement of medical instruments.

Glycoprotein imprinted RGO-starch nanocomposite modified EQCM sensor for sensitive and specific detection of transferrin

In this paper an electrochemical sensor for transferrin was developed by anchoring molecularly imprinted polymers (MIPs) on surface of gold coated quartz crystal microbalance (EQCM) using starch nanoparticles (Starch NP) - reduced graphene oxide (RGO) nanocomposite as polymeric format for first time. The nano MIP sensor was developed by electrodeposition of Starch NP-RGO nanocomposite on EQCM electrode in presence of template transferrin. Due to the location of imprinted sites on surface and high specific surface area, analyte molecules have good accessibility and high binding affinity to template molecule thus yielding highly sensitive and efficient signal. Under optimized conditions, the change in frequency of modified electrode coated quartz crystal electrode showed linear dynamic ranges (1–10μM) using EQCM method. The limit of detection 20ppb (EQCM) without any cross reactivity and matrix effect indicates high sensitivity and selectivity for transferrin. The sensor was appreciably selective to transferrin in presence of possible interferrents. The relative standard deviation for determination was 5.23%. On the basis of speediness and sensitivity, the sensor is reusable and shows a great improvement in selectivity and adsorption capacity over other sensors.