A Zigbee-Based Wireless Wearable Electronic Nose Using Flexible Printed Sensor Array Panida Lorwongtragool1, Reinhard R. Baumann2,3,*, Enrico Sowade2, Natthapol Watthanawisuth4, Teerakiat Kerdcharoen5,* 1
Faculty of Science and Technology, Rajamangala University of Technology Suvarnabhumi, Nonthaburi, Thailand Department of Digital Printing and Imaging Technology, Institute for Print and Media Technology, Chemnitz University of Technology, Chemnitz, Germany 3 Printed Functionalities, Fraunhofer Institute for Electronic Nano Systems (ENAS), Chemnitz, Germany 4 Nanoelectronic and MEMS Lab National Electronic and Computer Technology Center Pathumthani, Thailand 5 Department of Physics and NANOTEC’s Center of Excellence, Faculty of science, Mahidol University, Bangkok, Thailand *Corresponding author:
[email protected] 2
Abstract A wearable electronic nose (e-nose) has been developed by integrating a low cost chemical sensor array with a wireless communication for applications in healthcare. Its sensing unit was fabricated by a fully inkjet-printing technique, comprising eight different sensor elements manufactured by varying printing patterns and sensing materials. These sensors have shown response to a wide variety of complex odors. A wearable e-nose prototype using Zigbee wireless technology was designed as a compact armband for monitoring the axillary odor released from human body. Preliminary results based on principal component analysis (PCA) could classify different odors released from the human body upon various activities. Keywords: electronic nose, wearable device, inkjet printing, Zigbee, body odor, healthcare monitoring, flexible sensor Introduction Nowadays, the development of wearable systems has advanced rapidly due to their promising applications in the fields of sports, security and healthcare. The key requirements to design the hardware components in wearable devices are usually addressed in terms of compact and flexible, low-weight, low-power and low-cost systems that continuously monitor environmental conditions and communicate with wireless technology [1-3]. Specifically, wearable e-nose can directly collect the data of complex VOCs as emitted from the human body. The approach thus allows monitoring of disorder conditions or health status as well as body hygiene of individuals [4-5]. Moreover, the device offers not only routine monitoring of health status but it is also suitable for home-based point-of-care diagnostics. One significant factor concerning reliability of a wearable e-nose is the design of the sensing unit. In this work, we have manufactured a chemical sensor array based on polymer/CNT nanocomposites using inkjet printing technology. Inkjet printing as direct-writing technology enables the precise deposition of the designed patterns on a desired area. . With the same materials, distinct sensors can be produced by printing in different patterns to achieve the different responses [6-7]. The fabricated chemical sensor array has been installed in the sensing unit of the wearable e-nose and also applied to detect a primary odor source from human body, i.e. the odor around the
c 978-1-4673-4842-3/13/$31.00 2013 IEEE
axillary skin. A Zigbee module based on wireless technology was used as an appropriate platform to transfer the data from the wearable e-nose to a computer due to a compact and low-cost component. This work proposes a novel system of wearable e-nose for healthcare application using a sensing unit based on a fully inkjet-printing technique. Preliminary results have showed the success of classify different odors released from the body of volunteer upon various activities. Wearable Electronic Nose System A. Flexible Printed Sensor Array The sensor array comprises eight different elements produced by varying printed patterns and sensing materials is shown in detail in Table 1. These printed chemical gas sensors are based on polymer/multi-walled carbon nanotubes (MWCNTs) nanocomposites. Polyethylene naphthalate (PEN film, Dupont Teonex Q56FA) film was chosen as substrate material due to its flexible property, smooth surface and heat stability. In this work, the ink depositions were performed by the printing systems Dimatix Materials Printer 2831 (DMP) and the Autodrop micro dispensing system (Microdrop Technologies). Silver ink was inkjet-printed as an array of silver interdigitated electrodes (SIDEs) on top of the substrate then followed by printing the sensing layers. We designed two different patterns that are double printed layers (DPLs) and blended single layer (BSL) for obtaining different response layers [6-7]. The structures of the printed thin films are shown in Fig.1. Five repeating printings of the both DPLs and BSL were performed to increase the amount of sensing layers and therefore to improve the efficiency of the sensing responses. TABLE I DETAILS OF AN INDIVIDUAL ELEMENT IN A PRINTED SENSOR ARRAY Sensor No. Sensing Material Printing Pattern 1 PVC/MWCNTs DPLs 2 Cumene-PSMA/MWCNTs DPLs 3 PSE/MWCNTs DPLs 4 PVP/MWCNTs DPLs 5 PVC/MWCNTs BSL 6 Cumene-PSMA/MWCNTs BSL 7 PSE/MWCNTs BSL 8 PVP/MWCNTs BSL * PVC: Polyvinyl chloride Cumene-PSMA: Cumene terminated polystyrene-co-maleic anhydride PSE: Poly(styrene-co-maleic acid) partial isobutyl/methyl mixed ester PVP: Polyvinylpyrrolidon
291
Fig.1 Two different printed architectures for sensing elements: (a) double printed layers and (b) blended single layer
Fig. 3 Prototype of a wearable e-nose, the sensors is based on inkjet printing and the communication is based on Zigbee technology
Fig.2 Three dimensional structure of the designed SIDE array; sensor numbers refer to the sensing material and printed pattern as shown in table 1
Fig.2 shows the three dimensional structure of the designed SIDE array. It consists of eight SIDEs for deposition of eight different thin films as shown in Table 1. The fingers of each SIDE were defined for the width and separation distance of 200 ȝm. The size of the array is about 20 mm x 20 mm. The sensing materials were inkjet-printed on top of each SIDE as square in an area of 3 mm x 3 mm. Silver ink dispensing parameters and further information about the ink formulations and printing systems can be found in our previous work [6-7]. B. Sensor Testing We have tested the fabricated sensor array in a static chamber to observe the electrical responses when exposed to individual volatile organic compounds (VOCs). A measurement circuit was performed using voltage divider method to obtain the resistances of each sensor. The output voltages of eight elements were acquired through an 8-channel analog multiplexer connected to a USB DAQ device. The Ohm’s law was employed to calculate the individual sensor resistances. The period of reference baseline was defined during the first 2 min without exposure to any VOCs (ambient condition). In the second period, the analyte was injected into the static chamber and the output signals were recorded for 7 min to obtain a steady-state condition. The fractional method was applied on the determined sensor resistances to obtain the sensor responses [8]. In this work, the printed gas sensor array was exposed to VOCs of ammonia, acetic acid, acetone and ethanol. C. Monitoring of Axillary Odor The flexible printed sensor array was integrated into the wearable e-nose prototype, which was designed as a compact armband appropriate for monitoring the axillary odor as shown in Fig. 3. Therefore, body odor could be directly collected from the armpit region. The odor data was recorded in terms of sensor resistances as function of the presented VOCs and their concentrations.
292
Based on a preliminary study, we have collected odor data from the armpits (left (L) and right (R) sides) of a volunteer (33 years-old healthy subject) using the constructed wearable device. Body odors were monitored based on the following activities of the volunteer as simulated in three stages: (i) before exercise (normal stage and used as reference), (ii) after exercise and (iii) after exercise and relaxing for a long time. Before the experiment was performed, the reference baseline was obtained by exposing the sensor to the ambient air. Then the volunteer wore the device and the data was collected for 5 min. The experiments in each stage were carried out for three times. The sensors were recovered to the reference baseline after each experiment before the next experiment started (by exposure of the sensor to the ambient air). We have used principal component analysis (PCA) based on the unsupervised learning method to observe the odor progression in every minute. For one state, we obtained 15 data points (5 points x 3 repeating times) on the space of the first two principal components. Results and Discussion According to different printed sensing layers as shown in Table 1, we have found that the sensor responses of the fabricated chemical sensors yield distinguishable patterns when exposed to the VOCs. Fig. 4 shows the electrical responses of the sensors towards ammonia, acetic acid, acetone and ethanol that are mainly presented in the complex volatiles released from axillary skin [9]. Therefore, based on these characteristics the designed wearable e-nose is considered as suitable system to investigate the VOC fingerprints of human odors. The results also demonstrate an advantage of the inkjet-printing technology in order to fabricate the alternative chemical sensors, which provide a unique pattern for each odorant based on using the same sensing materials. They support our previous work about inkjet-printed chemical sensors based on CNT/PSE nanocomposites [6]. The methods to produce the different sensing elements were proposed in the same way, i.e. DPL and BSL. However, in this work we have proven the operation for other polymers and used these elements in the sensing unit of the e-nose for real applications. In addition, we also improved the sensor responses by printing multi-layers to increase the amount of sensing material as suggested in the previous work.
2013 IEEE 5th International Nanoelectronics Conference (INEC)
e-nose can provide a qualitative correlation of the amount of generated VOCs due to the activities in comparison to the reference stage. Acknowledgments This work was supported by Rajamangala University of Technology Suvarnabhumi and Mahidol University. A research career development grant from National Nanotechnology Center to TK is acknowledged (Project No. P-12-01157).
References
Fig. 4 Percent sensor response of eight sensor elements in a static system when exposed to volatiles of ammonia, acetic acid, acetone and ethanol with a concentration of 200 ppm
The sensing unit of this prototype is based on a flexible substrate, thereby posing an advantage for wearable device. Moreover, this feature could be considered as an important step to enable roll-to-roll processing in order to scale up the productivity in the future. Fig. 5 shows the classification of the armpit odors under the simulated activities using PCA technique. The results can be observed by the variations of principal component scores of all three stages. Odor progression after exercise was monitored and it was found that the data groups were moved out from a normal stage (reference). In addition, we can observe recovering of underarm odor after relaxing of the volunteer. This result provides a straightforward understanding about the relationship between the observed signals and changing of the human odors related to different activities. In other words, the wearable e-nose could be used to evaluate unusual odors of body resulted of health status, i.e., the level of skin hygiene and unusual odors from ailments or stress.
[1] T. Yilmaz, R. Foster, Y. Hao, “Detecting Vital Signs with WearableWireless Sensors” Sensors 2010, 10, pp.10837-10862. [2] A. D. Wilson and M. Baietto, “Advances in Electronic-Nose Technologies Developed for Biomedical Applications”, Sensors 2011, 11, pp.1105-1176. [3] Winston H. Wu, A. A.T. Bui, M. A. Batalin, L. K. Au, J. D. Binney, W. J. Kaiser, “MEDIC: Medical embedded device for individualized care”, Artificial Intelligence in Medicine 2008 42, pp.137—152. [4] A. D. Wilson (2011). Future Applications of Electronic-Nose Technologies in Healthcare and Biomedicine, Wide Spectra of Quality Control, Isin Akyar (Ed.), ISBN: 978-953-307-683-6, InTech. [5] C. Wongchoosuk, M. Lutz, T. Kerdcharoen, “Detection and Classification of Human Body Odor Using an Electronic Nose”, Sensors, 9, 2009, pp.7234-7249. [6] P. Lorwongtragool, T. Kerdcharoen, R. R. Baumann, " All Inkjet-Printed Chemical Gas Sensors Based on CNT/Polymer Nanocomposites: Comparison between Double Printed Layers and Blended Single Layer" in Proceedings of 9th ECTI-CON2012, May 2012, Hua Hin, THAILAND. [7] P. Lorwongtragool, E.Sowade, T. Kerdcharoen, R. R. Baumann, "Inkjet printing of chemiresistive sensors for the detection of volatile organic compounds" in Proceedings of NIP28 – 28th International Conference on Digital Printing Technologies / Digital Fabrication September 9-13, 2012, Quebec, Canada. [8] T.C. Pearce, S.S. Schiffman, H.T. Nagle, and J.W. Gardner, Handbook of Machine Olfaction; Electronic Nose Technology, Wiley-VCH, 2002. [9] S. K. Pandey, K.-H. Kim, “Human body-odor components and their determination”, Trends in Analytical Chemistry, 30 (5), 2011, p.784-796.
Fig. 5 PCA scores plot of underarm odor in different activities
Conclusions The Zigbee-based wireless wearable e-nose was developed using a sensing unit based on a flexible, inkjet-printed sensor array. Eight different sensor elements can respond and generate fingerprints of various VOCs due to different printed patterns and various sensing materials. Classifications based on PCA of armpit odors of the volunteer using the wearable
2013 IEEE 5th International Nanoelectronics Conference (INEC)
293
