Quartz Crystal Surface Research Articles

Practical limits of the quartz crystal microbalance and surface plasmon resonance for elucidating salt or ion partitioning into membrane polymers

Determining the partitioning of sodium chloride into polyamide (PA) reverse osmosis membranes used for seawater desalination is indispensable for optimizing the salt retention of the membranes. Furthermore, the recent quest for ion-selective membranes requires physico-chemical characterization techniques capable of elucidating partitioning phenomena of ions into membrane polymers in general. Quartz-crystal microbalance with dissipation monitoring (QCM-D) has been explored for this purpose as it has in theory a sensitivity in the range of pg/cm2 and is an accessible and apparently simple method to use. However, it is a technique that intrinsically lacks an internal reference, and it is affected by liquid bulk changes. As the conventional applications of QCM-D are of biophysical nature where changes in solute concentrations are in the nano to micromolar range, we investigated systematically in how far QCM-D yields reliable results for determining salt partitioning coefficients at concentrations relevant for the industrial-scale. We could clearly demonstrate that QCM-D possibly detects salt absorption only at salt concentrations higher than that in seawater (0.6 M). Furthermore, the variation in the liquid bulk response was so significant that it overlapped with a possibly perceived response due to salt absorption. Therefore, we concluded that salt partitioning coefficients derived from QCM-D data have a low confidence and, in any case, should always be reported accompanied by the raw data. We corroborated these findings with multi-parameter surface plasmon resonance (MP-SPR) which widely confirmed the trends observed with QCM-D.

Sensing volatile organic compounds with CVD graphene: insights from quartz crystal microbalance and surface plasmon resonance studies

This study explores the sensing capabilities of chemical vapor deposition (CVD)-grown graphene in detecting volatile organic compounds (VOCs) through quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. Two distinct sensing devices were developed, each tailored for QCM and SPR transducing mechanisms, utilizing CVD graphene as the sensing element. The sensors demonstrated consistent and reproducible responses when exposed to various concentrations of dichloromethane, chloroform, carbon tetrachloride, benzene, toluene, and m-xylene. Notably, both sensors exhibited unparalleled sensitivity to dichloromethane, with the graphene-coated SPR sensor displaying a sensitivity value of 294 × 10−3 ppm−1 and a limit of detection (LOD) value of 10.62 ppm. Additionally, the SPR sensor showcased remarkably swift response and recovery times, both under 3 sec. Results indicate that the adsorption of VOC molecules on the CVD graphene surface increases with the rising dipole moments and vapor pressure values of the molecules. The utilization of CVD graphene in both sensing approaches demonstrates good reproducibility in detecting ultralow concentrations of VOCs at room temperature.

Synthesis and characterization of nitrogen-doped-MWCNT@cobalt oxide for nerve agent simulant detection

Organophosphorus nerve agents are toxic compounds that disrupt neuromuscular transmission by inhibiting the neurotransmitter enzyme, acetylcholinesterase, leading to rapid death. A hybrid composite was synthesized using a hydrothermal process for the early detection of dimethyl methyl phosphonate (DMMP), a simulant of the G-series nerve agent, sarin. Quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensors were used as detectors. Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs), cobalt oxide (Co3O4), and N-MWCNT@Co3O4 were compared to detect DMMP concentrations of 25–150 ppm. At 25 ppm, the differential frequencies (Δf) of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors were 5.8, 2.3, and 99.5 Hz, respectively. The selectivity results revealed a preference for the DMMP rather than potential interference. The coefficients of determination (R2) of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors for detecting 25–150 ppm DMMP were 0.983, 0.986, and 0.999, respectively. The response times of the N-MWCNT, Co3O4, and N-MWCNT@Co3O4 sensors for detecting 100 ppm DMMP were 25, 27, and 34 s, respectively, while the corresponding recovery times were 85, 105, and 181 s. The repeatability results revealed the reversible adsorption and desorption phenomena for the fixed DMMP concentration of 100 ppm. These unique findings show that synthesized materials can be used to detect organophosphorus nerve agents.

Research on thermal protection of piezoelectric pressure sensor for shock wave pressure measurement in explosion field

PurposeThe purpose of this study is to clarify the mechanism of ambient and transient temperature effects on piezoelectric pressure sensors, and to propose corresponding compensation measures. The temperature of the explosion field has a significant influence on the piezoelectric sensor used to measure the shock wave pressure. For accurate shock wave pressure measurement, based on the actual piezoelectric pressure sensors used in the explosion field, the effects of ambient and transient temperatures on the sensor should be studied.Design/methodology/approachThe compensation method of the ambient temperature is discussed according to the sensor size and material. The theoretical analysis method of the transient temperature is proposed. For the transient temperature conduction problem of the sensor, the finite element simulation method of structure-temperature coupling is used to solve the temperature distribution of the sensor and the change in the contact force on the quartz crystal surface under the step and triangle temperatures. The simulation results are highly consistent with the theory.FindingsBased on the analysis results, a transient temperature control method is proposed, in which 0.5 mm thick lubricating silicone grease is applied to the sensor diaphragm, and 0.2 mm thick fiberglass cloth is wrapped around the sensor side. Simulation experiments are carried out to verify the feasibility of the control method, and the results show that the control method effectively suppresses the output of the thermal parasitic.Originality/valueThe above thermal protection methods can effectively improve the measurement accuracy of shock wave pressure and provide technical support for the evaluation of the power of explosion damage.

Impact of tether length and flexibility on the efficiency of analyte capture by tethered receptors

Molecular tethers that mediate the immobilization of receptors to the sensor surface, carry critical ability to influence sensor outcomes by determining how the receptors are presented to the analyte in the biological medium. An aspect that has however been less explored is the role of flexibility of such tethers in enhancing the efficiency of analyte capture by the receptor, by enhancing its ability to “seek” the analytes in solution. In the enclosed study, we show the length and flexibility of PEG tethers to have a strong influence on the binding of gold nanoparticles (AuNP) or neutravidin (NAv) to tethered amine or biotin receptors respectively. The qualitative similarity in the influence of the tethers, despite the largely dissimilar interactions that drive binding of AuNPs and NAv implies a generic influence at play. The impact of tether length or flexibility is decoupled from that of the density and conformation of tethers, using real-time, quantitative measurements performed using quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) sensors. Substituting neutravidin with neutravidin-conjugated gold nanoparticles accentuated the impact of the tether length, providing additional possibilities to harness the benefits of flexible tethers by increasing the analyte valency. The results emphasize the opportunity to enhance sensor performance by factoring in the influence of tether structure into the design of the sensor interface.

Real-time monitoring of the contractile properties of H9C2 cardiomyocytes by double resonator piezoelectric cytometry.

Testing the mechanical properties of cardiomyocytes plays an important role in the study of the physiological and pathological processes of constant contraction and diastole of the cardiovascular system. However, there is currently no satisfactory and dynamic technology to measure the mechanical properties of cardiomyocytes in a sustained manner, greatly affecting their practical application in clinical diagnosis and treatment evaluation. Herein, a double resonator piezoelectric cytometry (DRPC) technique was employed for dynamic monitoring of H9C2 cardiomyocyte adhesion and the effects of two cardiovascular drugs on the contractile properties of H9C2 cardiomyocytes, i.e., isoprenaline (ISO, a positive inotropic agent) and verapamil (VRP, a negative inotropic agent). Specifically, we used 9 MHz AT and BT-cut bare gold and transparent ITO electrodes and compared their dynamic adhesion to the two electrodes modified with RGD and gelatin respectively versus unmodified to measure the cell generated stress (ΔS) exerted on the quartz crystal surface by a population of cells and the cell viscoelastic index (CVI). We found that the DRPC technique can quantitatively measure the magnitude and direction of the generated forces during the adhesion process of the cells and under the effect of drugs. In conclusion, the technique presented in this study can be used for the simultaneous measurement of cell adhesion, traction force and viscoelasticity of living cells in a noninvasive, dynamic and continuous way, making it an ideal tool for assessing the population contractility of cardiomyocytes and evaluating the efficacy and toxicity of cardiovascular drugs.

Development of a quartz crystal microbalance-based immunosensor for the early detection of mesothelin in cancer

A robust real-time flow injection assay using Quartz Crystal Microbalance (QCM) biosensor has been developed for the detection of mesothelin, an antigen expressed on various malignant tumors including mesothelioma and ovarian cancers. A QCM sensor chip functionalized with self-assembled monolayer of cysteamine used to fabricate a sensitive immunosensor. Mesothelin specific antibody was immobilized on cysteamine modified gold surface of quartz crystal using N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide coupling. Further, ethanolamine was used as a blocking reagent to prevent the non-specific adsorption on antibody functionalized gold surface. Various concentrations of mesothelin was tested and the resonant frequency variation of the crystal was observed by a quartz crystal microbalance until a stable response is obtained. A good correlation between the frequency changes and concentration of mesothelin tested was observed and the QCM biosensor detects mesothelin in the linear range of 100pg/mLto 50 ng/mL. Thus, QCM assay could be a promising technique for early diagnosis of mesothelioma, ovarian and pancreatic adenocarcinoma.

The development of simple microcontroller-based QCM with some treatment on the crystal oscillator surface

The low-cost quartz crystal microbalance (QCM) instrument with the microcontroller as the basis of the embedded system of the frequency counter was implemented. The system uses a quartz crystal transducer from the crystal oscillator component. The frequency shifting was observed and analysed in association with some experimental tests. The experiments such as ethanol evaporation, water vapor in the humidity chamber, and coating the surface with TiO2 particles had been conducted. The developed QCM instrument has shown the ability to measure the frequencies in response to the addition or reduction of mass on the surface of the crystal oscillator. These responses are caused by evaporation, humid condition, and deposited particle on the quartz crystal surface. The QCM was varied into two initial frequencies, 5 and 10 MHz. The 5 MHz system represents the proper “in range” frequency counters, inside a counting limit of the microcontroller up to 5.6 MHz. On the other side, the 10 MHz is an experimental development system. Both types utilise a D flip-flop frequency divider that made a microcontroller-based frequency counter and can count the frequency twice the limit. The more stable 10 MHz have shown promising potential application related to the surface interaction with other material and can hold thicker deposition on its surface with a better stability response than the lower frequency counterpart.

Scanning gel electrochemical microscopy: Combination with quartz crystal microbalance for studying the electrolyte residue

The residue of electrolyte is a main challenge for local electrochemical measurements based on spatially localized contact between the electrolyte and the sample surface, such as scanning droplet cell or scanning electrochemical cell microscopy. By immobilizing electrolyte in the form of gel, scanning gel electrochemical microscopy (SGECM) is expected to overcome this challenge. This work proposes an analytical method for studying the issue of electrolyte residue from gel probes in SGECM. It is based on measuring approach-retract curves of gel probes on a quartz crystal microbalance (QCM), where the resonance frequency is recorded and synchronized with the current response. Verified by SEM observation, the frequency shift after one approach-retract cycle is taken as a measure for systematically compare the extent of electrolyte residue on the Au-coated quartz crystal surface. The results show that the electrolyte residue from freshly prepared gel probes, especially after soaking redox probes, could be reduced to negligible after a few approach-retract cycles. It can also be inhibited by co-electrodeposition of chitosan with tetraethoxysilane for preparing composite gel probe. Electrolyte residue could increase when over-pressing the gel against the sample. The residue of two types of gel probes and microcapillaries is also compared. The combination of QCM with SGECM offers a quality control method for gel probes before quantitative local electrochemical measurements.

Bacteriophage-Based Biosensors: A Platform for Detection of Foodborne Bacterial Pathogens from Food and Environment.

Foodborne microorganisms are an important cause of human illness worldwide. Two-thirds of human foodborne diseases are caused by bacterial pathogens throughout the globe, especially in developing nations. Despite enormous developments in conventional foodborne pathogen detection methods, progress is limited by the assay complexity and a prolonged time-to-result. The specificity and sensitivity of assays for live pathogen detection may also depend on the nature of the samples being analyzed and the immunological or molecular reagents used. Bacteriophage-based biosensors offer several benefits, including specificity to their host organism, the detection of only live pathogens, and resistance to extreme environmental factors such as organic solvents, high temperatures, and a wide pH range. Phage-based biosensors are receiving increasing attention owing to their high degree of accuracy, specificity, and reduced assay times. These characteristics, coupled with their abundant supply, make phages a novel bio-recognition molecule in assay development, including biosensors for the detection of foodborne bacterial pathogens to ensure food safety. This review provides comprehensive information about the different types of phage-based biosensor platforms, such as magnetoelastic sensors, quartz crystal microbalance, and electrochemical and surface plasmon resonance for the detection of several foodborne bacterial pathogens from various representative food matrices and environmental samples.

Research on Dual-Technology Fusion Biosensor Chip Based on RNA Virus Medical Detection.

In recent years, the emergence of COVID-19 and other epidemics caused by RNA(ribonucleic acid)-type genetic viruses has aroused the close attention of governments around the world on emergency response to public safety and health emergencies. In this paper, an electrodeless biosensing detection chip for RNA virus medical detection is designed using quartz crystal microbalance technology and local surface plasmon resonance technology. The plasmonic resonance characteristic in the nanostructures of gold nanorods-quartz substrates with different parameters and the surface potential distribution of the quartz crystal microbalance sensing chip were studied by COMSOL finite element simulation software. The results show that the arrangement structure and spacing of gold nanorod dimers greatly affect the local surface plasmon resonance of nanorods, which in turn affects the detection results of biomolecules. Moreover, high concentrations of “hot spots” are distributed between both ends and the gap of the gold nanorod dimer, which reflects the strong hybridization of the multiple resonance modes of the nanoparticles. In addition, by simulating and calculating the surface potential distribution of the electrode area and non-electrode area of the biosensor chip, it was found that the biosensor chip with these two areas can enhance the piezoelectric effect of the quartz chip. Under the same simulation conditions, the biochip with a completely electrodeless structure showed a better sensing performance. The sensor chip combining QCM and LSPR can reduce the influence of the metal electrode on the quartz wafer to improve the sensitivity and accuracy of detection. Considering the significant influence of the gold nanorod dimer plasma resonance mode and the significant advantages of the electrodeless biosensor chip, an electrodeless biosensor combining these two technologies is proposed for RNA virus detection and screening, which has potential applications in biomolecular measurement and other related fields.

Nano-Sheet-like Morphology of Nitrogen-Doped Graphene-Oxide-Grafted Manganese Oxide and Polypyrrole Composite for Chemical Warfare Agent Simulant Detection.

Chemical warfare agents (CWAs) have inflicted monumental damage to human lives from World War I to modern warfare in the form of armed conflict, terrorist attacks, and civil wars. Is it possible to detect the CWAs early and prevent the loss of human lives? To answer this research question, we synthesized hybrid composite materials to sense CWAs using hydrothermal and thermal reduction processes. The synthesized hybrid composite materials were evaluated with quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensors as detectors. The main findings from this study are: (1) For a low dimethyl methyl phosphonate (DMMP) concentration of 25 ppm, manganese dioxide nitrogen-doped graphene oxide (NGO@MnO2) and NGO@MnO2/Polypyrrole (PPy) showed the sensitivities of 7 and 51 Hz for the QCM sensor and 146 and 98 Hz for the SAW sensor. (2) NGO@MnO2 and NGO@MnO2/PPy showed sensitivities of more than 50-fold in the QCM sensor and 100-fold in the SAW sensor between DMMP and potential interferences. (3) NGO@MnO2 and NGO@MnO2/PPy showed coefficients of determination (R2) of 0.992 and 0.975 for the QCM sensor and 0.979 and 0.989 for the SAW sensor. (4) NGO@MnO2 and NGO@MnO2/PPy showed repeatability of 7.00 ± 0.55 and 47.29 ± 2.69 Hz in the QCM sensor and 656.37 ± 73.96 and 665.83 ± 77.50 Hz in the SAW sensor. Based on these unique findings, we propose NGO@MnO2 and NGO@MnO2/PPy as potential candidate materials that could be used to detect CWAs.

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis.

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met.

Effect of material surface on the formation and dissociation of gas hydrate in restricted space between two parallel substrates

Visual observations of the formation and dissociation of gas hydrate are conducted when reacting CH4-C2H6 gas with a water droplet in restricted space between a silicon wafer and quartz crystal surface, to study the surface effect of materials on hydrate formation and decomposition. It is found that hydrate first appears at the gas–water-quartz triple-phase contact line at 2.95 MPa and 2.2 °C and then grows preferentially around the quartz surface which is more hydrophilic, while hydrate dissociates earlier at the silicon surface which is less hydrophilic either by heating (beginning at 2.90 MPa and 9.2 °C) or depressurization (beginning at 1.03 MPa and −0.4 °C). A three-dimensional model, based on the classical nucleation theory, is established to understand the nucleation mechanism of gas hydrate at a triple-phase contact line. The results obtained indicate that triple-phase contact line is with higher driving force for hydrate nucleation and the hydrate nucleation at the triple-phase contact line on quartz has a lower free energy barrier and smaller critical size of nucleus compared with that on silicon wafer. Furthermore, molecular dynamics simulation is applied to compare the effects of two surfaces with different wettability on methane hydrate dissociation. It is found that methane bubbles will form on the less hydrophilic surface upon hydrate dissociating, which promotes the decomposition of the nearby hydrate. According to the results discussed above, the property of material surface can play a significant role on hydrate formation and dissociation, e.g., hydrate forming preferentially at a more hydrophilic surface while dissociating earlier at a more hydrophobic surface in restricted space.

Mussel-inspired polyethylene glycol coating for constructing antifouling membrane for water purification

HypothesisPolyethylene glycol (PEG) holds considerable potential in the fabrication of antifouling surfaces due to its strong hydration property. However, anchoring PEG polymer as a stable surface coating is still challenging because of its weak surface bonding property. Inspired by the mussel adhesion strategy, it is hypothesized that PEG polymer can be robustly attached onto substrates with the assistance of a “bio-glue” layer. ExperimentsThe “bio-glue” layer composited of Levodopa/polyethyleneimine (LP) is firstly deposited onto substrates, followed by covalently anchoring the poly(ethylene glycol) diglycidyl ether (PEGDE) layer via ring-opening reaction. The antifouling property of as-prepared coating was characterized using several techniques including quartz crystal microbalance (QCM) and surface forces apparatus (SFA). Furthermore, the PEGDE/LP coating was applied in membrane functionalization for oil-in-water (O/W) emulsion separation. FindingsPEGDE/LP coating shows outstanding stability and superior antifouling properties towards various potential foulants. In the O/W emulsion separation process, the PEGDE/LP-coated membrane maintains its super-hydrophilic property under harsh solution conditions and achieves high water flux (∼3000 L m−2 h−1 bar−1) and 90% water flux recovery ratio for separation of O/W emulsions containing different bio-foulants. This coating strategy provides a promising approach for fabricating stable coating with outstanding antifouling properties in various environmental engineering applications.

Graphene Oxide/Silver Nanoparticles Platforms for the Detection and Discrimination of Native and Fibrillar Lysozyme: A Combined QCM and SERS Approach.

We propose a sensing platform based on graphene oxide/silver nanoparticles arrays (GO/AgNPs) for the detection and discrimination of the native and toxic fibrillar forms of an amyloid-prone protein, lysozyme, by means of a combination of Quartz Crystal Microbalance (QCM) and Surface Enhanced Raman Scattering (SERS) measurements. The GO/AgNPs layer system was obtained by Langmuir-Blodgett assembly of the silver nanoparticles followed by controlled adsorption of GO sheets on the AgNPs array. The adsorption of native and fibrillar lysozyme was followed by means of QCM, the measurements provided the kinetics and the mechanism of adsorption as a function of protein concentration as well as the mass and thickness of the adsorbed protein on both nanoplatforms. The morphology of the protein layer was characterized by Confocal Laser Scanning Microscopy experiments on Thioflavine T-stained samples. SERS experiments performed on arrays of bare AgNPs and of GO coated AgNP after native, or fibrillar, lysozyme adsorption allowed for the discrimination of the native form and toxic fibrillar structure of lysozyme. Results from combined QCM/SERS studies indicate a general construction paradigm for an efficient sensing platform with high selectivity and low detection limit for native and amyloid lysozyme.

New Insights on Plasmin Long Term Stability and the Mechanism of Its Activity Inhibition Analyzed by Quartz Crystal Microbalance.

We used the research quartz crystal microbalance (RQCM) to monitor regulatory effects of plasmin and trypsin in the presence of their inhibitor α2-antiplasmin. The gold surface of quartz crystals was modified with a β-casein layer that served as a substrate for protease digestion. The addition of plasmin or trypsin as well as their mixtures with α2-antiplasmin resulted in an increase of resonant frequency, f, and in a decrease of motional resistance, Rm, depending on the molar ratio of protease: antiplasmin. At equimolar concentrations of protease and α2-antiplasmin (5 nM:5 nM) full inhibition of protease activity took place. Monitoring of plasmin activity on an hourly and daily basis revealed a prominent effect of autolysis and decrease of plasmin activity in freshly activated samples. The degree of inhibition as well as plasmin half-life (t1/2 = 2.48 ± 0.28 days) connected with its degradation was determined.

Multifractal analysis of ultrasonically machined surfaces of cylindrical quartz crystals: the effect of the abrasive grits

Since synthetic quartz is essential to produce 3D resonators for numerous applications in precision electronics, in this work the surface topography of cylindrical quartz bars is investigated using the multifractal technique. The cylindrical bars were manufactured with ultrasonic machining using five SiC grits ranging from 6 to 50 μm. The machined surfaces were initially characterized by contact profilometry and scanning electron microscopy (SEM). The multifractality of the machined surfaces was scrutinized using a box-counting method applied to the images obtained with 500X magnification. The multifractal spectrum indicated that the fractal dimension f(α) and the width of the fractal spectrum Δα are dependent on the grit size, but this dependence is not monotonic. The lowest (negative) value for Δf(α) was found for 25 μm grits indicating that for these grits the lower frequency events (grooves with tens μm width occurring along the USM direction) control the surface topography much more than high-frequency events related to brittle microcracking. The abrasive wear due to the continuous slurry recycling in lateral tool-workpiece interfaces contributed to smooth the groove texture as well as the sharpness of microscopic indentations, which remained observed on the surfaces machined with 50 μm grits. The opposite paths observed for the arithmetical mean deviation of the measured profile (Ra) and Δf(α) parameters with the cutting rate measured for each grit size were valuable to differentiate flat-rough and unlevelled-rough topographies in quartz bars.

Streptavidin Coverage on Biotinylated Surfaces.

Biosensors and other biological platform technologies require the functionalization of their surface with receptors to enhance affinity and selectivity. Control over the functionalization density is required to tune the platform’s properties. Streptavidin (SAv) monolayers are widely used to immobilize biotinylated proteins, receptors, and DNA. The SAv density on a surface can be varied easily, but the predictability is dependent on the method by which the SAv is immobilized. In this study we show a method to quantitatively predict the SAv coverage on biotinylated surfaces. The method is validated by measuring the SAv coverage on supported lipid bilayers with a range of biotin contents and two different main phase lipids and by using quartz crystal microbalance and localized surface plasmon resonance. We explore a predictive model of the biotin-dependent SAv coverage without any fit parameters. Model and data allow to predict the SAv coverage based on the biotin coverage, in both the low- and high-density regimes. This is of special importance in applications with multivalent binding where control over surface receptor density is required, but a direct measurement is not possible.

Stability evaluation of environmentally volatile pollutants sensing devices by developing theoretical calculation and mathematical modeling

In this paper, an organic macrocycle based on pillar[5]arene molecule including pyridine units (pyr-P5) was synthesized and its sensing ability was evaluated by integrating its spun thin films into Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) sensing systems. The pyr-P5 mass sensitive-sensor's sensitivity and limit of detection (LOD) performance for benzene, toluene, and m-xylene were calculated to be 2.44, 1.67, and 1.11 Hz ppm−1 and 1.22, 1.79, and 2.70 ppm, respectively. In order to illuminate the swelling characteristics of the pyr-P5 optical sensor, the diffusion coefficients of these vapors were calculated by applying the early-time Fick’s diffusion equation. The nonlinear autoregressive with exogenous input neural network was designed by utilizing experimental data from SPR kinetic results to model the change in photodetector response. The calculated diffusion coefficients using artificial neural network model are approximately equal to real-data diffusion coefficients as verified by very high correlation coefficients.