Interpretation of Quartz Crystal Microbalance Behavior with Viscous Film Using a Mason Equivalent Circuit

In odor sensing based on Quartz Crystal Microbalances (QCMs), the sensing film is crucial for both sensor sensitivity and selectivity. The typical response of the QCM due to sorption is a negative frequency shift. However, in some cases, the sorption causes a positive frequency shift, and then, Sauerbrey’s equation and Kanazawa’s equation cannot be applied to this situation. We model the QCM response with a Mason equivalent circuit. The model approximates a single layer of a uniform viscous coating on the QCM. The simulation of the equation circuit shows the possibility of the positive frequency change when the sorption occurs, which is the situation we find in some of the odor sensing applications. We measured the QCM frequency and resistance using the Vector Network Analyzer (VNWA). The QCMs were coated with glycerol, PEG2000, and PEG20M. To simulate odor exposure, a microdispenser was used to deposit the water. A positive frequency shift was observed in the case of PEG2000, and a negative frequency change was obtained for PEG20M. These results can be explained by the Mason equivalent circuit, with the assumption that when the film is exposed to water, its thickness increases and its viscosity decreases.

Download Full-text

Self-assembly of phthalocyanines on quartz crystal microbalances for QCM liquid sensing applications

Sensors and Actuators B Chemical ◽

10.1016/j.snb.2013.09.034 ◽

2014 ◽

Vol 190 ◽

pp. 651-656 ◽

Cited By ~ 14

Author(s):

Dilek D. Erbahar ◽

Mika Harbeck ◽

Gülay Gümüş ◽

Ilke Gürol ◽

Vefa Ahsen

Keyword(s):

Self Assembly ◽

Quartz Crystal ◽

Sensing Applications ◽

Quartz Crystal Microbalances ◽

Liquid Sensing

Download Full-text

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

Gels ◽

10.3390/gels7040151 ◽

2021 ◽

Vol 7 (4) ◽

pp. 151

Author(s):

Angel Ramon Hernandez-Martinez

Keyword(s):

Quartz Crystal ◽

Gold Surface ◽

Hydroxyethyl Methacrylate ◽

Proof Of Concept ◽

Synthesis Conditions ◽

Hydrogel Membranes ◽

Sensing Applications ◽

Linear Relationships ◽

Membrane Characterization ◽

Quartz Crystal Microbalances

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.

Download Full-text

Polymer–Plasticizer Coatings for BTEX Detection Using Quartz Crystal Microbalance

Sensors ◽

10.3390/s21165667 ◽

2021 ◽

Vol 21 (16) ◽

pp. 5667

Author(s):

Abhijeet Iyer ◽

Veselinka Mitevska ◽

Jonathan Samuelson ◽

Scott Campbell ◽

Venkat R. Bhethanabotla

Keyword(s):

Partition Coefficients ◽

Infinite Dilution ◽

Quartz Crystal ◽

Traditional Approach ◽

Ternary Mixtures ◽

Time Curve ◽

Low Concentrations ◽

Sensitivity And Selectivity ◽

Quartz Crystal Microbalances ◽

The Difference

Sensing films based on polymer–plasticizer coatings have been developed to detect volatile organic compounds (VOCs) in the atmosphere at low concentrations (ppm) using quartz crystal microbalances (QCMs). Of particular interest in this work are the VOCs benzene, ethylbenzene, and toluene which, along with xylene, are collectively referred to as BTEX. The combinations of four glassy polymers with five plasticizers were studied as prospective sensor films for this application, with PEMA-DINCH (5%) and PEMA-DIOA (5%) demonstrating optimal performance. This work shows how the sensitivity and selectivity of a glassy polymer film for BTEX detection can be altered by adding a precise amount and type of plasticizer. To quantify the film saturation dynamics and model the absorption of BTEX analyte molecules into the bulk of the sensing film, a diffusion study was performed in which the frequency–time curve obtained via QCM was correlated with gas-phase analyte composition and the infinite dilution partition coefficients of each constituent. The model was able to quantify the respective concentrations of each analyte from binary and ternary mixtures based on the difference in response time (τ) values using a single polymer–plasticizer film as opposed to the traditional approach of using a sensor array. This work presents a set of polymer–plasticizer coatings that can be used for detecting and quantifying the BTEX in air, and discusses the selection of an optimum film based on τ, infinite dilution partition coefficients, and stability over a period of time.

Download Full-text

Recent Advances in ZnO-Based Carbon Monoxide Sensors: Role of Doping

Sensors ◽

10.3390/s21134425 ◽

2021 ◽

Vol 21 (13) ◽

pp. 4425

Author(s):

Ana María Pineda-Reyes ◽

María R. Herrera-Rivera ◽

Hugo Rojas-Chávez ◽

Heriberto Cruz-Martínez ◽

Dora I. Medina

Keyword(s):

Carbon Monoxide ◽

High Performance ◽

Gas Sensing ◽

Experimental Studies ◽

Electrical Performance ◽

Long Term Stability ◽

Sensing Applications ◽

Recent Advances ◽

Sensitivity And Selectivity ◽

Doped Zno

Monitoring and detecting carbon monoxide (CO) are critical because this gas is toxic and harmful to the ecosystem. In this respect, designing high-performance gas sensors for CO detection is necessary. Zinc oxide-based materials are promising for use as CO sensors, owing to their good sensing response, electrical performance, cost-effectiveness, long-term stability, low power consumption, ease of manufacturing, chemical stability, and non-toxicity. Nevertheless, further progress in gas sensing requires improving the selectivity and sensitivity, and lowering the operating temperature. Recently, different strategies have been implemented to improve the sensitivity and selectivity of ZnO to CO, highlighting the doping of ZnO. Many studies concluded that doped ZnO demonstrates better sensing properties than those of undoped ZnO in detecting CO. Therefore, in this review, we analyze and discuss, in detail, the recent advances in doped ZnO for CO sensing applications. First, experimental studies on ZnO doped with transition metals, boron group elements, and alkaline earth metals as CO sensors are comprehensively reviewed. We then focused on analyzing theoretical and combined experimental–theoretical studies. Finally, we present the conclusions and some perspectives for future investigations in the context of advancements in CO sensing using doped ZnO, which include room-temperature gas sensing.

Download Full-text