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Detection and discrimination of volatile organic compounds using a single film bulk acoustic wave resonator with temperature modulation as a multiparameter virtual sensor array Guang Zeng, Chen Wu, Ye Chang, Cheng Zhou, Bingbin Chen, Menglun Zhang, Jiuyan Li, Xuexin Duan, Qingrui Yang, and Wei Pang ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.8b01678 • Publication Date (Web): 27 May 2019 Downloaded from http://pubs.acs.org on May 28, 2019
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ACS Sensors
Detection and discrimination of volatile organic compounds using a single film bulk acoustic wave resonator with temperature modulation as a multiparameter virtual sensor array Guang Zenga,1, Chen Wub,a,1, Ye Changa, Cheng Zhoua, Bingbin Chenc, Menglun Zhanga, Jiuyan Lib, Xuexin Duana, Qingrui Yanga,*, Wei Panga,* a
State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China b
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China
c
School of Electronic and Information Engineering, Tianjin University, Tianjin 300072, China
KEYWORDS: gas sensing, single-chip film bulk acoustic wave resonator (FBAR), multiparameter virtual sensor array (VSA), temperature modulation, e-nose system
ABSTRACT: This paper describes the detection and discrimination of volatile organic compounds (VOCs) using an enose system based on a multiparameter virtual sensor array (VSA), which consists of a single-chip temperaturecompensated film bulk acoustic wave resonator (TC-FBAR) coated with 20-bilayer self-assembled PSS / PDDA thin films. The high-frequency and microscale FBAR multiparameter VSA was realized by temperature modulation, which can greatly reduce the cost and complexity compared to those of a traditional e-nose system and can allow it to operate at different temperatures. The discrimination effect depends on the synergy of temperature modulation and the sensing material. For proof-of-concept validation purposes, the TC-FBAR was exposed to six different VOC vapors at six different gas partial pressures by real-time VOC static detection and dynamic detection. The resulting frequency shifts and impedance responses were measured at different temperatures and evaluated using principal component analysis (PCA) and linear discriminant analysis (LDA), which revealed that all analytes can be distinguished and classified with more than 97% accuracy. To the best of our knowledge, this report is the first on an FBAR multiparameter VSA based on temperature modulation, and the proposed novel VSA shows great potential as a compact and promising e-nose system integrated in commercial electronic products.
Volatile organic compounds (VOCs) are categorized as hazardous materials that have short-term and long-term negative effects on the environment and human health. Moreover, some exhaled VOCs are effective biomarkers that could be used for the simple detection of diseases; for instance, VOCs such as toluene, isoprene, and acetic acid can be used as biomarkers for detecting lung cancer1-3. Thus, monitoring VOCs is extremely crucial in the fields of environmental monitoring4, chemical warfare5, explosive detection6, and clinical diagnostics7. Over the past few decades, many types of commercial portable devices that can quantitatively detect VOCs have been developed. Most of them are dependent on concentration detection, which leads to the problem of distinguishing an individual gas in a mixture of various VOCs. To meet the specific needs of gas detection systems, gas sensors need not only to sensitively detect the concentration of a single VOC but also to effectively distinguish different VOCs. One of the most useful methods for gas discrimination is the electronic nose (e-nose) system8-11, which consists of an array of gas sensors, each of which is functionalized with
a special chemically or biologically sensitive layer for target analyte detection12-18. Thus, extracting multidimensional features from signals generated by a multi-sensor array (MSA) enables the use of pattern recognition techniques19-23 to identify and discriminate unknown vapors. However, e-nose systems may face many issues, such as complicated sensing circuits, complex modification processes and high breakdown possibilities, since the whole e-nose system does not work if any of the component devices fail24, which makes reducing the cost, size and power consumption of these sensors and increasing their stability difficult. To overcome the drawbacks of traditional MSAs, a new mechanism called the virtual sensor array (VSA) has been developed using an individual sensor based on an e-nose system, in which the individual sensor can produce multidimensional sensing features similar to those achieved by an MSA. Single-chip VSA features a greatly reduced number of sensors, which is beneficial for minimizing the malfunction of the whole e-nose system and integrating it into a miniaturized platform. The key element for form-
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ing a VSA is achieving variant response modes in a single device. One way is to use the intrinsically different modes of special sensors, such as the multimode photonic vapor sensor inspired by Morpho butterflies25-27 and the quartz crystal microbalance (QCM) based on its multiple highorder resonances28-31. In this method, the sensitivity of the device is limited by the lowest sensitivity of different modes; as a result, the sensitivity of this kind of device cannot be very high. Another way is to use a single mode of sensors to create a diversity of responses. The most extensively reported method is temperature modulation; for example, the response of field-effect transistor (FET) devices is different under different temperatures, which can be used to discriminate various analytes32,33. However, these VSAs often require high temperature operation, which far exceeds the tolerable temperature of commercial electronic products. To enable the use of the VSA in our daily life, we need to develop an easily obtainable VSA with good performance that is compatible with most electronic products. Considering that the film bulk acoustic resonator (FBAR) has been commercialized for many years, it offers excellent portability and compatibility with electronic products. In addition, FBAR sensors are known for providing a simple sensing method based on the measurements of resonator frequency shifts and have been widely used as portable electronic gas sensors34,35. Hence, in this work, we are motivated to develop a single-chip VSA system based on the ultrahigh-frequency FBAR. In order to improve the gas sensing characteristics of this system, self-assembled poly (sodium 4styrenesulfonate) (PSS) / poly (diallyldimethylammonium chloride) (PDDA) thin films are adopted as a gas-sensitive layer36. Since the physical adsorption properties of this sensing film would be affected by the temperature, the temperature modulation is chosen to enable a variety of responses by a single sensor. However, the conventional FBAR is also sensitive to the temperature, which is evaluated by the temperature coefficient of frequency (TCF). For the sake of diminishing the TCF of FBARs, the silicon dioxide (SiO2) thin film with a positive temperature coefficient of velocity is introduced as a temperaturecompensated layer to balance the negative temperature coefficient of conventional FBAR. Thus, a temperaturecompensated FBAR is designed to reduce the effect of temperature fluctuation on the sensor. Although zero temperature drift FBAR is the most ideal device for our work, it is difficult to fabricate such device in practice. As a compromise, the low temperature drift FBAR is selected as the core device of this VSA system so as to minimize the interference to the effective sensing signal caused by the high TCF of conventional FBAR as much as possible. For proof-of-concept validation purposes, a prototype temperature-modulated VSA based on the single-chip TCFBAR is designed and fabricated in this study. The temperature modulation is realized by adding a programmable heater under the FBAR chip. And the temperature cycled operation (TCO)37 is employed to control the heater to make the VSA work in the temperature range from 20 °C to 200 °C, which is promising for integration into
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mobile phones, watches and other electronic products. This heating method would ensure the stability of the operating temperature of the FBAR. In the experiment, four different power cycles (0 w, 0.1 w, 0.2 w, 0.3 w) was simply used to form four different temperatures for the VSA, which was utilized to discriminate six different VOC vapors at six different gas partial pressures. And two parameters of the FBAR, the frequency and the impedance, was measured to provide more dimensional information about the analytes, which would play an important role in the statistical data analysis. The change in temperature affects the adsorption and desorption of VOC molecules on the surface of the device, which can be reflected by the different frequency shifts and impedance change. Additionally, in consideration of a fixed period of VOC delivery system, we change the heating method from single power to multiple powers in a cycle, which makes the use of proposed VSA in the discrimination of VOCs more convenient and less power consuming. The results show that the temperature-modulated TC-FBAR VSA sensor exhibits an excellent capability to discriminate similar VOCs, making this VSA a promising candidate as a novel alternative e-nose system.
EXPERIMENTAL SECTION Reagents and materials. PSS (Mw=70,000) and PDDA (Mw
