1558-1748 (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2019.2927187, IEEE Sensors Journal Abstract— In this paper, a PVA-nanofibers Heat Absorption Monitoring (PVA-HAM) sensor is fabricated by developing the HAM sensor to detect 2,4-Dinitrotoluene (DNT). Polyvinyl Alcohol (PVA) has a high melting point, electrospinning capability, and ability to form the hydrogen bond with DNT. Thus, a thin layer of PVA nanofibers is implemented on the active area of the sensor through electrospinning method which improves the absorption ability and sensitivity of the PVA-HAM sensor due to the formation of the hydrogen bond between PVA and DNT molecules, as well as the huge surface to volume ratio of PVA nanofibers. Uniform nanofibers with the average fiber diameter of 97 nm can be obtained using 9.1 wt% PVA solution and controlling electrospinning conditions. The surface morphology of PVA-HAM sensor demonstrates that the absorption area has increased 3.87 times compared with bare HAM sensor. Experimental results show that the PVA-HAM sensor is able to detect DNT about 13.27 ppb in 80 ms which indicates that the limit of detection has improved 3.77 times than the bare sensor. In addition, the fabricated sensor has high repeatability and reproducibility, and also it has good selectivity to DNT compared with common volatile chemicals. Index Terms— DNT detection, Heat absorption monitoring, MEMS, PVA nanofibers, PVA-HAM sensor. I. INTRODUCTION XPLOSIVE vapor detection is necessary for public security, environment monitoring, human health, and mine exploration fields [1-4]. Because of the variety of explosive mixture which often has low pressure, the detection of traces is a hard task [5]. Land mines contain 2,4- Dinitrotoluene (DNT), which is a nitroaromatic explosive, as an impurity or as the main degradation intermediate of TNT [6]. In addition, DNT contaminates the soil and groundwater extensively around its production and processing facilities, and it causes acute toxicity [7]. Therefore, DNT detection is a crucial procedure. Many electronic devices are focused on the detection of vapor traces, such as optical sensors (based on terahertz spectroscopy, photoluminescence, fluorescence, etc.), mass The paper was submitted for review in December 23, 2018. 1 Department of Electrical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran; fsamaeifar@yahoo.com 2 Department of Electrical Engineering, Malek Ashtar University of Technology, Tehran, Iran; afifi@mut.ac.ir 3 Department of Electrical Engineering, Shahid Sattari Aeronautical University of Science and Technology, Tehran, Iran; h.abd@ssau.ac.ir *Corresponding authors: Fatemeh Samaeifar: fsamaeifar@yahoo.com, Ahmad Afifi: afifi@mut.ac.ir sensors (Surface acoustic wave (SAW)), Quartz Crystal Microbalance (QCM), electrochemical sensors, or Micro- Electro-Mechanical Systems (MEMS) [8-10]. MEMS-oriented sensors are classified into micro-cantilever beams [11-15], film bulk acoustic resonator (FBAR) [16], field asymmetric waveform ion mobility spectrometry (FA- IMS) [17], differential scanning calorimeter (DSC) [18], differential thermal analysis (DTA) [19, 20], and heat absorption monitoring (HAM) [21, 22]. Although MEMS sensors have high sensitivity [16], the surface area of explosive adsorption in these sensors is quite small, so only a few numbers of explosive particles can be trapped on the sensors. Hence, the sensitivity of MEMS sensors improves by increasing the surface area. To enhance the surface area of explosive absorption of MEMS sensors, many techniques have been introduced such as using porous materials [23, 24] or Carbon Nanotube (CNT) network [25]. Our previous work [22] shows that the HAM sensor has high sensitivity, fast detection time, low power loss, good selectivity, high repeatability, and device-to-device reproducibility. Similar to other MEMS sensors, the surface area of explosive adsorption of HAM sensor is relatively small. In this paper, a PVA-nanofibers Heat Absorption Monitoring (PVA-HAM) sensor is implemented by developing the HAM senor to detect ultra-trace of DNT. Polyvinyl Alcohol (PVA) nanofibers, which are sensitive to DNT, are electrospun on the surface of PVA-HAM sensor to increase the DNT adsorption ability of sensor due to the huge surface to volume ratios of PVA nanofibers and the formation of the hydrogen bond between PVA and DNT molecules. The experimental results show that PVA-HAM sensor has higher sensitivity compared with bare HAM sensor. II. CONFIGURATION AND OPERATION PRINCIPLE Regarding the principles [26], the sensor is designed based on suspended-type membrane micro-hotplates (STM). As shown in Fig. 1a, it is comprised of 3 main sections including a frame, thermal isolating tethers, and an active area. On the active area, two interdigit serpentine platinum resistors are placed, one of which is used as a heater and the other one is used as a thermometer. Dimension (length × width) of active area and tethers are 440 µm × 440 µm and 400 µm ×50 µm, respectively. Moreover, the sensor is composed of 5 layers including silicon, silicon oxide, chromium, platinum, and gold Implementation of PVA-nanofibers heat absorption monitoring sensor for ultrasensitive detection of 2,4-dinitrotoluene F. Samaeifar 1 *, A.Afifi 2 *, and H. Abdollahi 3 E