Resistive Water Sensors Based on PEDOT:PSS‑g‑PEGME Copolymerand Laser Treatment for Water Ingress Monitoring SystemsSeongin Hong,† Jung Joon Lee,† Srinivas Gandla, Junwoo Park, Haewon Cho, and Sunkook Kim*

School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon 440-745, Republic of Korea

*S Supporting Information

ABSTRACT: Water sensors are a type of level sensor thatcan be used in various applications requiring the sensing ofwater levels, such as in dams, nuclear power plants, waterpipes, water tanks, and dehumidifiers. In particular, watersensors in water ingress monitoring systems (WIMS) protectlives and property from disasters caused by water leakage andflooding. Here, a resistive water sensor for WIMS thatincorporates poly(3,4-ethylenedioxythinophene):poly(styrenesulfonate) (PEDOT:PSS) grafted with poly(ethylene glycol)methyl ether (PEGME) (PEDOT:PSS-g-PEGME copolymer)as high-conductivity electrodes and laser-treated PEDOT:PSS-g-PEGME copolymer as the low-conductivity resistivecomponent is reported. The configuration of the water sensor is modeled as two parallel resistors (Rlaser treated PEDOT:PSS||Rwater) when water comes into contact with the sensor surface. The two-resistor configuration exhibits a better performance incomparison with single-resistor configurations comprising only PEDOT:PSS-g-PEGME copolymer or laser-treatedPEDOT:PSS-g-PEMGE copolymer. Moreover, PEDOT:PSS-g-PEGME copolymer is applied to the sensor to improve thestability of PEDOT:PSS in water. We demonstrate that the sensor can detect the water level in real time with high sensitivityand accuracy, and thus has potential in applications for monitoring water-related hazards.

KEYWORDS: resistive water sensor, water ingress monitoring systems, PEDOT:PSS, water resistance, laser treatment

Unlike humidity or moisture sensors, the use andapplication of water sensors have not received much

attention. Water sensors are a type of level sensing device thatdetects the water level in various environments.1−5 Watersensing is required in places where water leakage may occur,for example, in dams,6,7 nuclear power plants,8 water pipes,9

water tanks,6 and dehumidifiers.10 In particular, passengerships or bulk carriers require not only water ingress detectionsystems and water ingress alarm monitoring systems (WIDSand WIAS) but also water level detection systems (WLDS) toprotect against water leaks, which can result in fatal injuriesand massive monetary losses.11 For instance, the sinking of thepassenger ship MV Sewol on April 16, 2014 occurred due toseawater inflow through an opening on the side of the ship. Inthe ferry disaster, only 172 out of a total of 476 passengerswere rescued, amounting to a survival rate of only 36.1%.12−14

Due to the lack of accurate and timely flood detection, theinitial response and reporting of the disaster were delayed.Moreover, the flooding was first reported by a high schoolstudent on the ship and not by the crew members. Therefore,water ingress monitoring systems (WIMS) require highlysensitive and accurate real-time monitoring performance toalert the vessel traffic service (VTS), crew, and passengers.There are several types of water sensors, such as ultrasonic

sensors,15,16 float switches,17,18 and resistive water sensors,19

which differ in their operation principles. Ultrasonic sensors

measure the distance to the water surface by sending andreceiving ultrasonic sound waves. However, ultrasonic sensorsare noncontact detectors that can mistake other objects forwater. Float switches with mercury switches are suitable for useonly to detect the water level within water tanks and not onships because float switches can only detect water levelsexceeding the fixed threshold levels of the switches. Mean-while, resistive water sensors are one of the simplest and mostsuitable types of water sensors for WIMS because theresistance of a resistive water sensor decreases with the waterlevel between the two contacts of the device. Thus, whenleaked water comes into contact with the resistive water sensor,the electrical conductivity of the sensor increases with thewater level. The WIMS will then sound the alarm and informthe VTS, crew, and passengers of the level of the leaked water.Poly(3,4-ethylenedioxythinophene):poly(styrene sulfonate)

(PEDOT:PSS) is an effective material for high-performanceresistive water sensors in WIMS. PEDOT:PSS, a conductingpolymer, is a promising electrically conductive material forflexible and transparent electrodes owing to its highconductivity, flexibility, and optical transparency. In addition,because of its low cost and the ease of large-area fabrication

Received: September 29, 2019Accepted: December 2, 2019Published: December 2, 2019

Article

pubs.acs.org/acssensorsCite This: ACS Sens. XXXX, XXX, XXX−XXX

© XXXX American Chemical Society A DOI: 10.1021/acssensors.9b01917ACS Sens. XXXX, XXX, XXX−XXX

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through simple solution coating, PEDOT:PSS is particularlysuitable for advanced flexible and transparent electronics andsensors.20−27 Despite these attractive characteristics, PE-DOT:PSS coated by solution processes face limitations inintegration and patterning. To overcome these limitations,laser treatment is applied to pattern the PEDOT:PSS intoresistive and conductive regions integrated within the samelayer by patterning with high and low laser power, respectively.In this paper, we present, for the first time, resistive water

sensors based on laser-treated PEDOT:PSS-g-PEGME copoly-mer for real-time monitoring in WIMS. The sensors detect andtransmit the floodwater level in real time. Additionally, wepropose a laser treatment method to integrate the conductiveand resistive regions of PEDOT:PSS-g-PEGME copolymer inthe same layer. Using this method, we fabricate resistive watersensors consisting of two high-conductivity PEDOT:PSS-g-PEGME copolymer electrodes connected by low-conductivitylaser-treated PEDOT:PSS-g-PEGME copolymer, as shown inFigure 2. More related details will be described later. As aresult, water level-dependent resistive sensors with highsensitivity and accuracy are achieved, enabling real-timemonitoring of unexpected flooding in disaster monitoringapplications, such as WIMS and circuit breakers for preventingelectric shocks from water contact.

■ EXPERIMENTAL SECTIONMaterials. PEDOT:PSS solution (Clevios PH 1000) was

purchased from Heraeus Ltd. Dimethyl sulfoxide (DMSO) andpoly(ethylene glycol) methyl ether (PEGME, average Mn 550) wereobtained from Sigma-Aldrich. Isopropyl alcohol (IPA) was obtainedfrom Duksan Pure Chemical, South Korea. All materials were usedwithout further purification.

Fabrication of Resistive Water Sensor Using PEDOT:PSS-g-PEGME Copolymer. DMSO (5 wt %), IPA (20 wt %), and PEGME(PSS/PEGME weight ratio = 1:0.5) were added to PEDOT:PSSsolution. The mixture was stirred for over 30 min at roomtemperature (25 °C) before being spin-coated on poly(ethyleneterephthalate) (PET) film at 1500 rpm for 60 s and thermallyannealed at 150 °C for 15 min in air. Finally, the PEDOT:PSS-g-PEGME copolymer on the PET film was patterned by infrared ray(IR) laser (wavelength = 1054 nm) to fabricate the resistive watersensor.

Characterization and Measurements of the Resistive WaterSensor. The transmittance, elemental composition, and surfacemorphology of PEDOT:PSS-g-PEGME copolymer on the PET filmwith and without IR laser treatment were measured using aultraviolet−visible−near-infrared (UV−vis−NIR) spectrophotometer(Agilent, Cary 5000), X-ray photoelectron spectroscopy (XPS,Thermo UK, K-alpha), and scanning electron microscopy (JEOLJSM-6710F), respectively. The sheet resistance and thickness ofPEDOT:PSS-g-PEGME copolymer on the PET film with and withoutIR laser treatment were measured using a four-point probe meter(Napson, RT-70V/RG-5) and a surface profiler (Alpha step, KLA-Tencor), respectively. The electrical characterization of the resistivewater sensor was performed using a Keithley 4200-SCS Semi-conductor characterization system (Tektronix Co.).

■ RESULTS AND DISCUSSIONFigure 1a illustrates our resistive water sensor system in apassenger ship being flooded by unexpected water ingress.When the floodwater rushes into the ship, the water sensors inthe WIMS detect the floodwater level and report theemergency to the VTS, crew, and passengers by usingmaritime communications and sounding the alarm as a rescuecall to prevent the ship from sinking. Our resistive water sensorbased on laser-treated PEDOT:PSS-g-PEGME copolymer is

Figure 1. Concept and configuration of water ingress monitoring systems (WIMS) utilizing resistive water sensor based on laser-treatedPEDOT:PSS-g-PEGME copolymer. (a) Schematic of the WIMS utilizing resistive water sensors in a passenger ship with unexpected water ingress.(b) Device architecture and equivalent circuit of resistive water sensors. (c) Photographs of laser-treated PEDOT:PSS-g-PEGME copolymer watersensors on the PET film. SKKU symbol reproduced with permission from SKKU.

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composed of two PEDOT:PSS-g-PEGME copolymer electro-des separated by laser-treated PEDOT:PSS-g-PEGME copoly-mer on the PET film, as depicted in Figure 1b. The fabricationprocess is illustrated in detail in Figure 2. The current drivenby the voltage applied to bilateral high-conductivity

PEDOT:PSS-g-PEGME copolymer electrodes flows in thelow-conductivity laser-treated PEDOT:PSS-g-PEGME copoly-mer region. When water comes into contact with the sensor,the conductivity and hence the current varies according to thewater level. Thus, the resistance in the laser-treated region with

Figure 2. Schematic of the fabrication process flow for resistive water sensor. (a) Spin coating of PEDOT:PSS solution on the PET film. (b)PEDOT:PSS-g-PEGME copolymer with water resistance on the PET film. (c) IR laser treatment of PEDOT:PSS-g-PEGME copolymer for resistivewater sensor. (d) Electrical characterization of the resistive water sensor by dipping the sensor in water.

Figure 3. Spectroscopic analysis of PEDOT:PSS-g-PEGME copolymer with IR laser treatment. (a) Optical transmittance of PEDOT:PSS-g-PEGME copolymer on PET with and without IR laser treatment. (b) XPS spectra of sulfur 2p for PEDOT:PSS-g-PEGME copolymer with andwithout IR laser treatment. SEM images of PEDOT:PSS-g-PEGME copolymer without (c) and with (d) IR laser treatment.

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a relatively high resistivity is lowered according to the waterlevel. Figure 1c depicts the images of the prepared resistivewater sensors. The sensors exhibit both excellent opticaltransparency (transmittance of 90%; see Figure 3a) as well ashigh flexibility.The schematic of the fabrication process flow for our

resistive water sensor is illustrated in Figure 2. The thickness ofPEDOT:PSS-g-PEGME copolymer coated on PET was 78 nm.To use PEDOT:PSS as a water sensor, water resistance mustbe secured. However, the pristine PEDOT:PSS film dissolvesin water when exposed to water. Therefore, PEDOT:PSS wasgrafted with PEGME to improve the water resistance ofPEDOT:PSS for water sensor applications.28 Water resistancehere means that PEDOT:PSS retains its original resistanceproperties even when exposed to water. The blue, white, andgreen colors represent PEDOT, PSS, and PEGME, respec-tively, in Figure 2b. PEDOT:PSS-g-PEGME copolymer notonly has water resistance but also chemical resistance for watersensor application because PSS chains are cross-linked to eachother, and a highly hydrophilic sulfonic acid group in PSS issubstituted with PEGME by the esterification reaction betweenPEDOT:PSS and PEGME.28−31 Although the film was coatedon 7 × 7 cm2 PET in this study, because the fabrication of thewater sensor is based on a solution process, it is easy tofabricate water sensors with larger areas by the roll-to-rollprocess.32−34 The pattern of the IR laser treatment is depictedin Figure 2c. The pattern width is 1 mm and the diameter ofthe laser beam is 20 μm. In laser processing, it is essential totreat only the target sample coated on the substrate withoutaffecting the substrate. For this purpose, an IR laser wasselected so that only the copolymer would be processedwithout the substrate reacting to the laser. The IR laser is veryeffective and suitable for processing only the PEDOT:PSS

samples because the 1054 nm laser wavelength is absorbedonly by PEDOT:PSS and not by PET.35−38 The electricalproperties were finally analyzed using an I−V measurementsystem at varying levels of water, into which the resistive watersensor was placed.As depicted in Figure 1b,c, the color of the PEDOT:PSS-g-

PEGME copolymer on PET changed from light blue totransparent after IR laser treatment. This indicates that thePEDOT:PSS-g-PEGME copolymer has been effectivelypatterned by the IR laser. Spectroscopic analysis ofPEDOT:PSS-g-PEGME on PET with and without the IRlaser treatment was performed for further confirmation. Figure3a shows that the transmittance of pristine PET was 92% (at550 nm) and that of PEDOT:PSS-g-PEGME coating (≈78nm) was 86%, which increased to 90% after the IR lasertreatment. This demonstrates the patterning of PEDOT:PSS-g-PEGME copolymer on PET by the IR laser treatment. Thesheet resistances of PEDOT:PSS-g-PEGME copolymer were1.107 (±0.046) kΩ/□ without IR laser treatment and >2MΩ/□ with laser treatment. The difference in resistance ismore than 3 orders of magnitude, which enables the sensing ofwater levels through resistance difference. To confirm theresistance of PEDOT:PSS-g-PEGME copolymer to air orwater, the relative resistance changes of pristine PEDOT:PSSand PEDOT:PSS-g-PEGME copolymer film were measuredover time exposed to air or water (Figure S1). When exposedto air, the resistance of pristine PEDOT:PSS film increased by284% on day 7, while the resistance of PEDOT:PSS-g-PEGMEcopolymer film increased by only 18%. When exposed towater, the pristine PEDOT:PSS film was completely dissolvedin water and disappeared from the substrate only on day 1. Onthe other hand, PEDOT:PSS-g-PEGME copolymer retained itsoriginal film form and its resistance increased by only 23% on

Figure 4. Electrical characteristics of water sensors. (a) I−V curves of PEDOT:PSS-g-PEGME copolymer, laser-treated PEDOT:PSS-g-PEGMEcopolymer, and water sensor (PEDOT:PSS-g-PEGME copolymer + laser-treated PEDOT:PSS-g-PEGME copolymer), respectively. (b) Extractedresistance of PEDOT:PSS-g-PEGME copolymer, laser-treated PEDOT:PSS-g-PEGME copolymer, and water sensor. (c) I−V characteristics ofwater sensor with contacted water level from 0 to 4 cm. (d) Resistance of water sensor with increasing water level from 0 to 4 cm.

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day 7. This result shows that PEDOT:PSS-g-PEGMEcopolymer has excellent stability in air or water compared topristine PEDOT:PSS, which can be fully utilized in watersensor applications. The XPS spectra were analyzed todetermine the compositional changes of PEDOT and PSS.In the graph of Figure 3b, the sulfur 2p peak at the bindingenergy of 166.7 eV corresponds to the sulfur in PSS, and thedoublet peaks at the binding energies of 164.0 and 163.0 eVcorrespond to the sulfur in PEDOT.39,40 The PEDOT peakdisappears and only the PSS peak remains in PEDOT:PSS-g-PEGME copolymer after IR laser treatment. BecausePEDOT:PSS absorbs 1054 nm IR radiation,35,36 it can beeffectively etched and patterned by IR at this wavelength. Apeculiarity is that only PEDOT is selectively removed by IRlaser treatment, whereas PSS is not removed. The reason forthe selective etching can be explained by the difference inabsorbance between PEDOT and PSS at the 1054 nmwavelength of the laser used in this study as PEDOT absorbswell at 1054 nm, while PSS does not absorb at all.41,42 As aresult, the PSS remains intact and only the PEDOT part can beselectively etched by this laser. This method is appropriate andconsistent with the purpose of inducing resistance differencesbecause the main contribution to conductivity in PEDOT:PSSoriginates from PEDOT. This result demonstrates a new lasertreatment method that selectively etches only PEDOT whileleaving PSS unaffected, instead of etching both PEDOT andPSS. Figure 3c,d shows that the particle size is approximately100 nm and the surface is smoothened by IR laser treatment.In Figure 3d, individual particles are still visible. These particlescan be assumed to be the particles of the remaining PSS afterthe PEDOT has been removed.

To investigate the I−V characteristics of the water sensors,the output currents of a sample coated with only conductivePEDOT:PSS-g-PEGME copolymer, another sample coatedwith only resistive PEDOT:PSS-g-PEGME copolymer, and athird conductive + resistive PEDOT:PSS-g-PEGME copolymercoated sample (our sensor) are measured. The results aredepicted in Figure 4a. All samples exhibit the typical Ohmicresistor behavior of the electrical current being proportional tothe applied voltage. The reciprocals of the slopes in Figure 4agive the resistance of the devices according to Ohm’s law R =V/I, where R is the resistance, V is the applied voltage, and I isthe current. Figure 4b depicts the resistance (R) of the devicesextracted from Figure 4a. The conductive PEDOT:PSS-g-PEGME copolymer (i.e., nonlaser-treated) device exhibits thelowest resistance due to its high electrical conductivityproperty,43,44 while the resistive PEDOT:PSS (i.e., laser-treated) device exhibits the highest resistance resulting fromthe removal of PEDOT by the laser treatment. The watersensor composed of conductive PEDOT:PSS-g-PEGME andresistive PEDOT:PSS-g-PEGME exhibits the most suitableresistance for detecting water levels compared to the other twosamples (only conductive PEDOT:PSS sample and onlyresistive PEDOT:PSS sample), for which it is difficult tomeasure the conductivity increase from the increasing waterlevel. If the sensor (only PEDOT:PSS) has too highconductivity, it is difficult to distinguish the increase inconductivity by the water level from its initial conductivity, orif the sensor (only laser-treated PEDOT:PSS) has too lowconductivity, it is difficult to integrate with the microcontrollerand operate the system due to its high contact resistance.Figure 4c depicts the I−V curves of the resistive water sensors

Figure 5. Real-time monitoring performance of resistive water sensors. (a) Time-resolved current characteristics of water sensor under variouswater levels for 250 s at 1 V applied voltage. (b) Statistical results of the extracted current as a function of water level for applied voltage of 1 V. (c)Image of water sensor integrated with Arduino for WIMS. Arduino logo reproduced with permission from Arduino. (d) Response performance ofWIMS with water sensor with increasing water level in real time (manual dipping rate ∼1.8 cm/s up to 4 cm).

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with increasing water levels from 0 to 4 cm. The currentsgradually increase with the water level. When the sensor comesinto contact with water, the current primarily flows through thewater rather than the PEDOT:PSS-g-PEGME copolymer.Moreover, the I−V behavior of the water sensor with wateras the current flow path instead of PEDOT:PSS-g-PEGMEcopolymer is very Ohmic, as can be seen from the flatresistance curves plotted against the applied voltage depicted inFigure 4d.To demonstrate the real-time monitoring performance of

the water sensors, the output current was measured in real timefor 250 s at the applied voltage of 1 V under various waterlevels, as illustrated in Figure 5a. The currents are clearlydependent on the level of water in contact with the watersensor. The relationship between laser-treated PEDOT:PSS-g-PEGME copolymer and water as the resistive components inthe water sensor can be explained by the parallel resistormodel, as expressed in eq 1

R R RR RR R

total laser treated PEDOT:PSS water

laser treated PEDOT:PSS water

laser treated PEDOT:PSS water

= ∥

=×+ (1)

In the parallel resistor network, the currents flows differently inPEDOT:PSS and water despite the same voltage across them.When the water level on the sensor increases, Rwater decreases.However, because Rlaser treated PEDOT:PSS is much larger thanRwater, the effect of decreasing Rwater reduces Rtotal. In otherwords, Rtotal with increasing water level continuously decreasesafter the water has initially come into contact with the watersensor, as shown in Figures 4d and 5a. Additionally, the totalcurrent flowing through the water sensor with two parallelresistors (Rlaser treated PEDOT:PSS||Rwater) is slightly larger than thatof single resistor (Rwater). Figure 5b shows the statistical resultsof current as functions of the water level extracted from Figure5a at an applied voltage of 1 V for 250 s. Table S1 shows thestatistical results extracted from Figure 5a, where the measureddata were 250 points for each water level. The currentincreases linearly with the water level.Figure 5c depicts our water sensor integrated with an

Arduino UNO-based microcontroller for the target applicationof WIMS. The current output of the sensor with varying waterlevels in contact with the sensor is calibrated using the data inFigure 5a. The output current can be directly sent to themicrocontroller, which has been programmed to sound thealarm and inform the VTS, crew, and passengers of the waterlevel if water enters the ship due to unexpected conditions,such as collisions or hull corrosion. The WIMS with theincreasing water level in contact with the water sensor wasmonitored in real time. The results are depicted in Figure 5d.The calibrated current in Figure 5d exhibits the responseperformance of the sensor with increasing water level intowhich the sensor was dipped rapidly by hand, up to a waterdepth of 4 cm. The current increases in real time withincreasing water levels. As expected, water rather than laser-treated PEDOT:PSS-g-PEGME copolymer serves as theprimary current path in the sensor after the water has comeinto contact with the sensor surface, even after integration withthe microcontroller.

■ CONCLUSIONSWe proposed a novel resistive water sensor based on laser-treated PEDOT:PSS-g-PEGME copolymer for WIMS. The

design of the resistive water sensor comprises high-conductivity PEDOT:PSS-g-PEGME and low-conductivitylaser-treated PEDOT:PSS-g-PEGME. The configuration ofthe water sensor modeled as two parallel resistors(Rlaser treated PEDOT:PSS||Rwater) exhibited a slightly higher totalcurrent flow than that of the configuration comprising only asingle resistor (Rwater). Moreover, PEDOT:PSS-g-PEGMEcopolymer was applied to the water sensor to enhance itsstability in water. The water sensor could achieve highsensitivity and accurate performance in real time for detectingrapid water flooding in passenger ships or bulk carriers causedby unexpected conditions.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acssensors.9b01917.

Relative resistance changes of pristine PEDOT:PSS andPEDOT:PSS-g-PEGME copolymer film over timeexposed to air or water; statistical data of result extractedfrom Figure 5a (PDF)

■ AUTHOR INFORMATIONCorresponding Author*E-mail: seonkuk@skku.edu.ORCIDJung Joon Lee: 0000-0003-0835-7381Srinivas Gandla: 0000-0002-4586-1483Sunkook Kim: 0000-0003-1747-4539Author Contributions†S.H. and J.J.L. contributed equally to this work.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis research was supported by the National ResearchF ound a t i o n o f Ko r e a (NRF ) (G r a n t s NRF -2018R1A2B2003558, 2018R1D1A1B07048232, and2019R1I1A1A01059217 funded by the Ministry of Education).

■ REFERENCES(1) Authier, M.; Laflamme, B.; Brochu, C. Resistive Water Sensor forHot Tub Spa Heating Element. U.S. Patent US6476363 2002.(2) Doumit, J.; Lynch, R. J., Jr Early Warning Water Leak DetectionSystem. U.S. Patent US65268072003.(3) Kaya, M.; Sahay, P.; Wang, C. Reproducibly reversible fiber loopringdown water sensor embedded in concrete and grout for watermonitoring. Sens. Actuators, B 2013, 176, 803−810.(4) Seyfried, M.; Grant, L.; Du, E.; Humes, K. Dielectric loss andcalibration of the Hydra Probe soil water sensor. Vadose Zone J. 2005,4, 1070−1079.(5) Seyfried, M.; Murdock, M. Response of a new soil water sensorto variable soil, water content, and temperature. Soil Sci. Soc. Am. J.2001, 65, 28−34.(6) Reza, S. K.; Tariq, S. A. M.; Reza, S. M. In Microcontroller BasedAutomated Water Level Sensing and Controlling: Design andImplementation Issue, Proceedings of the World Congress onEngineering and Computer Science, 2010; pp 20−22.(7) Jaeger, K. L.; Olden, J. Electrical resistance sensor arrays as ameans to quantify longitudinal connectivity of rivers. River Res. Appl.2012, 28, 1843−1852.(8) Hashim, M.; Yoshikawa, H.; Matsuoka, T.; Yang, M. InReliability Monitor for PWR Safety System Using FMEA and Go-flow

ACS Sensors Article

DOI: 10.1021/acssensors.9b01917ACS Sens. XXXX, XXX, XXX−XXX

F

Methodology: Application of Risk Monitor for Nuclear Power Plants,2013 21st International Conference on Nuclear Engineering;American Society of Mechanical Engineers Digital Collection, 2014.(9) Yang, Y. J.; Haught, R. C.; Hall, J.; Goodrich, J. A.; Hasan, J. InAdaptive monitoring to enhance water sensor capabilities for chemical andbiological contaminant detection in drinking water systems, Optics andPhotonics in Global Homeland Security II, International Society forOptics and Photonics, 2006; 62030K.(10) Hanson, R. T. Water Leak Detection SystemElectr. Eng. 2017.(11) Kato, A.; Sinde, R.; Shubi, K. Design of an automated riverwater level monitoring system by using Global System for mobilecommunications. Int. J. Comput. Sci. Inf. Secur. 2015.(12) Wu, B.; Yan, X.; Wang, Y.; Wei, X. In Maritime EmergencySimulation System (MESS)-A Virtual Decision Support Platform forEmergency Response of Maritime Accidents, 2014 4th InternationalConference On Simulation And Modeling Methodologies, Tech-nologies And Applications (SIMULTECH); IEEE, 2014; pp 155−162.(13) Lee, K.-M.; Jung, K. Factors Influencing the Response toInfectious Diseases: Focusing on the Case of SARS and MERS inSouth Korea. Int. J. Environ. Res. Public Health 2019, 16, No. 1432.(14) Moura, R.; Beer, M.; Patelli, E.; Lewis, J. Learning from majoraccidents: Graphical representation and analysis of multi-attributeevents to enhance risk communication. Saf. Sci. 2017, 99, 58−70.(15) Rodriguez, A.; Sanchez-Arcilla, A.; Redondo, J.; Mosso, C.Macroturbulence measurements with electromagnetic and ultrasonicsensors: a comparison under high-turbulent flows. Exp. Fluids 1999,27, 31−42.(16) Fattorelli, S.; Lenzi, M.; Marchi, L.; Keller, H. An experimentalstation for the automatic recording of water and sediment discharge ina small alpine watershed. Hydrol. Sci. J. 1988, 33, 607−617.(17) Tanumihardja, W. A.; Gunawan, E. In On the Application ofIoT: Monitoring of Troughs Water Level Using WSN, 2015 IEEEConference on Wireless Sensors (ICWiSe); IEEE, 2015; pp 58−62.(18) Timpong, S.; Itoh, K.; Toyosawa, Y. Geotechnical CentrifugeModelling of Slope Failure Induced by Ground Water Table Change.In Landslides and Climate Change; Taylor and Francis Group: London,2007; pp 107−112.(19) Mendoza-Payan, J. G.; Gallardo, S. F.; Marquez-Lucero, A.Design for an ultrafast water distributed sensor employing polyvinyl-amine cross-linked with Cu (II). Sens. Actuators, B 2009, 142, 130−140.(20) Sun, K.; Li, P.; Xia, Y.; Chang, J.; Ouyang, J. Transparentconductive oxide-free perovskite solar cells with PEDOT: PSS astransparent electrode. ACS Appl. Mater. Interfaces 2015, 7, 15314−15320.(21) Sun, K.; Zhang, S.; Li, P.; Xia, Y.; Zhang, X.; Du, D.; Isikgor, F.H.; Ouyang, J. Review on application of PEDOTs and PEDOT: PSSin energy conversion and storage devices. J. Mater. Sci.: Mater.Electron. 2015, 26, 4438−4462.(22) Wu, F.; Li, P.; Sun, K.; Zhou, Y.; Chen, W.; Fu, J.; Li, M.; Lu,S.; Wei, D.; Tang, X.; et al. Conductivity enhancement of PEDOT:PSS via addition of chloroplatinic acid and its mechanism. Adv.Electron. Mater. 2017, 3, No. 1700047.(23) Xia, Y.; Sun, K.; Ouyang, J. Solution-processed metallicconducting polymer films as transparent electrode of optoelectronicdevices. Adv. Mater. 2012, 24, 2436−2440.(24) Lee, J. J.; Yoo, D.; Park, C.; Kim, J. H.; Choi, H. H. Behavior oftoxic gas sensor based on conducting polypyrrole. Macromol. Symp.2015, 354, 280−286.(25) Lee, J. J.; Yoo, D.; Park, C.; Choi, H. H.; Kim, J. H. All organic-based solar cell and thermoelectric generator hybrid device systemusing highly conductive PEDOT: PSS film as organic thermoelectricgenerator. Sol. Energy 2016, 134, 479−483.(26) Kang, T.-G.; Park, J.-K.; Kim, B.-H.; Lee, J. J.; Choi, H. H.; Lee,H.-J.; Yook, J.-G. Microwave characterization of conducting polymerPEDOT: PSS film using a microstrip line for humidity sensorapplication. Measurement 2019, 137, 272−277.

(27) Heo, J. S.; Eom, J.; Kim, Y. H.; Park, S. K. Recent Progress ofTextile-Based Wearable Electronics: A Comprehensive Review ofMaterials, Devices, and Applications. Small 2018, 14, No. 1703034.(28) Lee, J. J.; Lee, S. H.; Kim, F. S.; Choi, H. H.; Kim, J. H.Simultaneous enhancement of the efficiency and stability of organicsolar cells using PEDOT: PSS grafted with a PEGME buffer layer.Org. Electron. 2015, 26, 191−199.(29) Gu, S.; He, G.; Wu, X.; Guo, Y.; Liu, H.; Peng, L.; Xiao, G.Preparation and characteristics of crosslinked sulfonated poly(phthalazinone ether sulfone ketone) with poly (vinyl alcohol) forproton exchange membrane. J. Membr. Sci. 2008, 312, 48−58.(30) Subramanian, C.; Giotto, M.; Weiss, R.; Shaw, M. T. Chemicalcross-linking of highly sulfonated polystyrene electrospun fibers.Macromolecules 2012, 45, 3104−3111.(31) Mikhailenko, S. D.; Wang, K.; Kaliaguine, S.; Xing, P.;Robertson, G. P.; Guiver, M. D. Proton conducting membranes basedon cross-linked sulfonated poly (ether ether ketone)(SPEEK). J.Membr. Sci. 2004, 233, 93−99.(32) Kim, G.-E.; Shin, D.-K.; Lee, J.-Y.; Park, J. Effect of surfacemorphology of slot-die heads on roll-to-roll coatings of fine PEDOT:PSS stripes. Org. Electron. 2019, 66, 116−125.(33) Zucca, A.; Yamagishi, K.; Fujie, T.; Takeoka, S.; Mattoli, V.;Greco, F. Roll to roll processing of ultraconformable conductingpolymer nanosheets. J. Mater. Chem. C 2015, 3, 6539−6548.(34) Santos, G. H.; Gavim, A. A.; Silva, R. F.; Rodrigues, P. C.;Kamikawachi, R. C.; de Deus, J. F.; Macedo, A. G. Roll-to-rollprocessed PEDOT: PSS thin films: application in flexible electro-chromic devices. J. Mater. Sci.: Mater. Electron. 2016, 27, 11072−11079.(35) Cho, W.; Hong, J. K.; Lee, J. J.; Kim, S.; Kim, S.; Im, S.; Yoo,D.; Kim, J. H. Synthesis of conductive and transparent PEDOT: P(SS-co-PEGMA) with excellent water-, weather-, and chemical-stabilities for organic solar cells. RSC Adv. 2016, 6, 63296−63303.(36) Cho, A.; Kim, S.; Kim, S.; Cho, W.; Park, C.; Kim, F. S.; Kim, J.H. Influence of imidazole-based acidity control of PEDOT: PSS on itselectrical properties and environmental stability. J. Polym. Sci., Part B:Polym. Phys. 2016, 54, 1530−1536.(37) Rehim, M. H. A.; Youssef, A. M.; Al-Said, H.; Turky, G.;Aboaly, M. Polyaniline and modified titanate nanowires layer-by-layerplastic electrode for flexible electronic device applications. RSC Adv.2016, 6, 94556−94563.(38) Heo, S.-Y.; Choi, H.-J.; Park, B.-J.; Um, J.-H.; Jung, H.-J.; Jeong,J.-R.; Yoon, S.-G. Effect of protective layer on enhanced trans-mittance, mechanical durability, anti-fingerprint, and antibacterialactivity of the silver nanoparticles deposited on flexible substrate. Sens.Actuators, A 2015, 221, 131−138.(39) Yoo, D.; Son, W.; Kim, S.; Lee, J. J.; Lee, S. H.; Choi, H. H.;Kim, J. H. Gradual thickness-dependent enhancement of thethermoelectric properties of PEDOT: PSS nanofilms. RSC Adv.2014, 4, 58924−58929.(40) Mengistie, D. A.; Ibrahem, M. A.; Wang, P.-C.; Chu, C.-W.Highly conductive PEDOT: PSS treated with formic acid for ITO-freepolymer solar cells. ACS Appl. Mater. Interfaces 2014, 6, 2292−2299.(41) Cristovan, F. H.; Nascimento, C. M.; Bell, M. J. V.; Laureto, E.;Duarte, J. L.; Dias, I. F.; Cruz, W. O.; Marletta, A. Synthesis andoptical characterization of poly (styrene sulfonate) films doped withNd (III). Chem. Phys. 2006, 326, 514−520.(42) Bhargav, R.; Bhardwaj, D.; Patra, A.; Chand, S.; et al. Poly(Styrene Sulfonate) Free Poly (3, 4-Ethylenedioxythiophene) as aRobust and Solution-Processable Hole Transport Layer for OrganicSolar Cells. ChemistrySelect 2016, 1, 1347−1352.(43) Espinosa, N.; Hosel, M.; Angmo, D.; Krebs, F. C. Solar cellswith one-day energy payback for the factories of the future. EnergyEnviron. Sci. 2012, 5, 5117−5132.(44) Sim, H. J.; Choi, C.; Lee, D. Y.; Kim, H.; Yun, J.-H.; Kim, J. M.;Kang, T. M.; Ovalle, R.; Baughman, R. H.; Kee, C. W.; et al.Biomolecule based fiber supercapacitor for implantable device. NanoEnergy 2018, 47, 385−392.

ACS Sensors Article

DOI: 10.1021/acssensors.9b01917ACS Sens. XXXX, XXX, XXX−XXX

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