Au Nanocomposite Based Chemiresistive Ammonia Sensor for Health

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An Au nanocomposite based chemiresistive ammonia sensor for health monitoring Sadanand Pandey, and Karuna Kar Nanda ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.5b00013 • Publication Date (Web): 15 Oct 2015 Downloaded from http://pubs.acs.org on October 17, 2015

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An Au nanocomposite based chemiresistive ammonia sensor for health monitoring Sadanand Pandey1,2* and Karuna K. Nanda1 1

Materials Research Centre, Indian Institute of Science, Bangalore 560012, India. 2 Department of Applied Chemistry, University of Johannesburg, 37 Nind Street, Doornfontein, Johannesburg 2028, South Africa

ABSTRACT We have developed a fast and highly sensitive chemiresistive sensor based on the nanocomposite of polysaccharide (guar gum) and gold nanoparticles for the room temperature detection of ammonia in the range of 0.1 parts-per-quadrillion (ppq) to 75000 parts-per-million (ppm). Sensor response, selectivity and stability studies reveal excellent sensing of the nanocomposite. The room temperature operation under ambient and the wide range sensing indicates that the composites can be explored for environmental as well as biomedical applications. We have first time quantified the ammonia level released from the urine and blood serum of human beings using the resisitive sensor. The urine ammonia level was found to be ~24000 ppm and is higher for patients with renal problems. This demonstrated the utility of the sensor for health monitoring.

KEYWORDS: Nanocomposites, Ammonia sensor, Gold nanoparticle, Blood urea nitrogen, Urine, chemiresistive sensor

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Ammonia is one of the most harmful environmental pollutants. Not only chemical processing plants, but also our body releases ammonia that is high for patients with congestive heart failure, heart attack, kidney failure/disorder, gastrointestinal bleeding, urinary tract obstruction, etc.1-3 In this regard, early and accurate ammonia detection is essential. Chemiresistive sensors based on three-terminal transistors and two-terminal resistive sensors for ammonia detection have attracted significant attention.4-6 The sensing is based on the conductance change of the sensor when exposed to ammonia vapour. Though there are several reports on chemiresistive sensing, we summarize few important results in Table. 1.

2,7-24

It may be noted that the sensors can be

useful for ammonia detection either in parts-per-trillion (ppt) range 17-19 or few thousands of partper million (ppm) range.22-25 The sensing from ppt to ppm level by a single sensor is very rare. In the literature, several reports are found for ammonia sensing using Ag, Al, Pt, Ni, etc. however, to the best of our knowledge, we obtain only one report based on NanoPANI-Au composite material as chemiresistive ammonia sensor.26 So, "not much investigation is found on Au which is a known a good catalyst" or "Need to improve the sensing performance". Hence, it can be a motivation for this work. Breath ammonia level is of the order of few ppm and can be investigated spectroscopically.2 Body fluids such as blood and urine is expected to have very high ammonia level. Therefore, detection of ammonia at few thousands of ppm is of paramount importance for health monitoring and to the best of our knowledge, no quantification analysis of ammonia level in urine is available. Here, we report for the first time a rapid and highly sensitive chemiresistive sensor for the room temperature detection of ammonia levels in a wide range from 0.1 parts-perquadrillion (ppq) to 75000 ppm or higher. The sensor is based on the nanocomposite (abbreviated as GG/Au nanocomposite) of polysaccharide (guar gum, GG) and gold (Au) nanoparticles. Sensor response, temporal response, reversibility, selectivity and stability studies reveal excellent ammonia sensing of the nanocomposite. Moreover, for the first time, we quantify the ammonia level in urine. The ammonia level is found to be few thousand ppm and is higher for patients with renal problems. This demonstrates that the chemiresistive sensor can be used for the health monitoring. In addition, the sensor can also be used in environmental monitoring, chemical processing plants, and gas detection for counter-terrorism because of the remarkable low as well as high detection limit along with the simplicity of the operation. *[Appropriate place for Table.1] 2 ACS Paragon Plus Environment

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EXPERIMENTAL SECTION Chemicals and Biofluid Chloroauric acid (HAuCl4) was obtained from Aldrich and GG from Merck, India. Aqueous solutions were prepared using De-ionized (DI) water from a Milli-Q Plus system (Millipore Co.). The urine and blood serum samples were collected from male and female patients of different age groups through our Institute (IISc, Bangalore) health centre and stored at -80 °C until used. The clinical tested values were obtained by using Roche Cobas C111. Synthesis and characterization of GG/Au nanocomposites The synthesis procedure and the characterization of Au nanoparticles in GG have been reported in Ref. 25. For the synthesis of Au nanoparticles in GG, a 1% w/v of GG is added with aqueous solution of HAuCl4 (10 mM). The pH of the solution at the beginning of the experiment was kept at 8 and the reaction temperature was 80 oC. In order to make the double loading, aqueous solution of HAuCl4 (20 mM) are used, keeping all the conditions same. Fabrication and characterization of the sensor device Nanocomposite films based on Au nanoparticles and GG were formed on cover slip (1cm x 1cm) by drop casting method followed by dring in air. Electrodes were prepared using silver paste and are connected to source-measurement-unit which are used for measuring the electrical properties of the sensing film. A Keithley meter was used to serve as both DC voltage source and current meter. The measurements were performed in a very simple home-made testing chamber (approximate volume of ~800 cm3) as shown in Figure 1c. The distance between aqueous ammonia solution and sensor film is kept 1 cm. In the sensing experiment, the ammonia vapours of different concentration (Supplemetary information, method of preparation of samples) evolves spontaneously from aqueous solution were introduced into the testing chamber manually at the humidity of ~48% and temperature of 20-250C. The detected concentration of the ammonia vapours inside the testing chamber was evaluated by the change in current at constant voltage of 20 V. The response time (tres) and recovery time (trec), defined as the time required to reach 90% of the final equilibrium value, was also evaluated. The sensor response, defined as the relative variation in conductance due to the introduction of analyte ∆G/Go, ∆G= G − Go, where Go is the conductance in dried air and G is that in the dried air mixed with ammonia vapor

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variation of current with time (temporal response) has been monitored for the sensing study. All the results were obtained from the same sensor device in the static state and the dry air 3 ACS Paragon Plus Environment

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background. Finally, the sensing properties of the GG/Au nanocomposites are tested against increasing ammonia concentration in the range of 0.1 ppq–100000 ppm by monitoring the changes in current through DC current-voltage (I-V) measurement using Keithley 237. The method for the detection of urea level in human urine is same as the detection of ammonia vapor evolved from aqueous ammonia solution, experimentally. The level of urea in human urine as well as UUN can be quantified by using the calibration curve for ammonia and the equations 1 and 2. The topographical image of the sensing film was taken in an optical profilometer Zeta 20 instrument. Structural configuration analysis was performed using a Perkin–Elmer PE 1600 FTIR spectrophotometer (USA) in the range of 4000–800 cm-1. Presence of Au nanoparticles within the polymer network of GG/Au nanocomposites was confirmed by using JEOL JEM2100F and field emission electron transmission microscope (TEM). Preparation of ammonia stock solution for sensing study Concentrated ammonia (~25%) solution with an assay of 99.9% was purchased from Merck (Germany). The different ammonia concentration was prepared by diluting in DI water. However for the selectivity study of the sensor, ammonia concentration of 100000 ppm was used and compared with analytical reagent (AR) graded various volatile organic compounds (VOCs) without any dilution. The concentration measurement is based on the current against concentration plot. This calibration plot was used as the reference for determination of amount of urea in urine samples.

RESULTS AND DISCUSSION Our sensor is based on the nanocomposite film of GG/Au and the configuration used is shown in Figure 2a. The digital photograph and scanning electron microscopy image of the film with electrical leads is shown in (Figure 1a,b). Au nanoparticles are found to be spherical in shapes with the average particle size of ∼6.5 nm obtained using transmission electron microscopy analysis. The sensing films are prepared by using drop-casted techniques are in the range of 0.25 to 0.35 mm thick. Conductivity of a GG thin film and that of the composite films was found to be 8.45x10-9 and 2.56x10-6 Ω-1cm-1, respectively. This clearly indicates that the conductivity of the films is enhanced by the loading of Au nanoparticles in GG. This can be due to the formation of electron conducting channel by the presence of Au nanoparticles in the film. The ammonia sensing 4 ACS Paragon Plus Environment

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experiments are carried out using a static testing chamber as shown in Figure 1c. In this context, it is worthy to note that the static system is better suited for environmental as well as health monitoring. Figure 1d shows the room temperature I-V characteristics of a sensing film at different ammonia concentrations (1 ppq, 1 ppt, 1 ppb and 1 ppm). Here, the ammonia is generated from aqueous ammonia as NH4OH NH3+H2O and the current increases with increase in ammonia concentration which has been exploited for ammonia sensing. *[Appropriate place for Figure.1] Temporal response for different ammonia concentrations is shown in Figure 2b ranging from 0.1 ppq to 100 ppm. The response at higher range of concentrations (10000-100000 ppm) is shown in the inset. The change in current with increase in the ammonia concentration follows a linear behaviour as shown in Figure 2c. It increases with the increase in ammonia concentration as shown in Figure 2c. Figure 2d shows the response/recovery time which increases with increasing the ammonia concentration. The response ∆G/Go of the film at different ammonia concentration are shown in Figure 2e. It can be noted that the sensor response increases linearly with the increase in ammonia concentration and saturates beyond 30000 ppm. The sensor response ∆G/Go for 0.1 ppq is found to be ~26 which is extremely high and sensitive. This means that the low detection limit of the sensor is at the level of ppq. Response, current and sensitivity are included separately from 0.1ppq to 10ppq in (Fig.S1a,b,c) for better clarification.The highest detection limit is 75000 ppm when the loading of Au nanoparticles in the film is doubled (Figure 3a,b). *[Appropriate place for Figure.2] Lastly, the stability of the sensor towards ammonia sensing has been studied over a period of 6 months (Figure 3c). It is observed that the sensor response ∆G/Go of the sensor at 1 ppm concentration of ammonia decreases by 6% in 6 months and then remains stable revealing a remarkable stability of the sensor. Overall, the sensor response is excellent and very fast. It may be noted that the sensor recovers automatically in the ambient at room temperature without any external stimulus like UV irradiation or Joule heating. As the concentrated ammonia is diluted with water to obtain different concentration, we have investigated the response of the sensor with DI water. It is worthy to mention here that water vapour alone is hardly contributing to the sensing of ammonia (Figure S2a) and hence, different water vapour content in the analyte sample has negligible effect on the sensor response. 5 ACS Paragon Plus Environment

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We have also studied the ammonia sensing under the variation of humidity from 22 to 72% at room temperature condition by keeping the other parameters constant (100 ppm ammonia concentration, distance of the film and the analyte, temperature). It follows that there is an increase in the sensor response ∆G/Go with relative humidity. The change in the sensor response ∆G/Go is only about 7.1% in the range of 22 to 72 %RH. Thus, the sensor can work efficiently within the range 22 to 72%RH (figure.3d). *[Appropriate place for Figure.3] Sensing mechanism In order to investigate the mechanism associated with ammonia sensing, temporal response of the analyte in different environments (ambient, nitrogen and oxygen) has been performed (Figure 4a). Nitrogen and oxygen environments are created by purging the chamber with using pure and dry gases. It is found that the sensor does not respond in nitrogen environment and the performance of the sensor is similar both in ambient and oxygen environments. This suggests that the measured current is the outcome of the interaction of ammonia with the sensor in presence of oxygen rather the influence of physisorbed water to the film. It is observed that neither GG nor Au film exclusively is responsible for the ammonia sensing. However in the composite, it is suspected that oxygen chemisorption is facilitated at the interface of GG and Au NPs. It plausibly be due to the breaking of the H-bonding of –OH groups in GG in the presence of Au NPs. Hence, oxygen adsorption takes place by H-bonding with –OH groups. The oxygen adsorption in the film facilitates the ammonia sensing by the change in the conductivity of the sensor. The oxygen adsorption in the film decreases its electrical conductivity by withdrawing electron from the film (Figure 4b). However, upon exposure to ammonia vapor, electrical conductivity increases by reverting back electron to the film as ammonia removes adsorbed oxygen from the surface (Figure 4c) [24]. It is reported in the literature28-30 that ammonia reacts with adsorbed oxygen giving nitrous oxide (or nitrogen) and water at room temperature: 2NH3 + 5O- 2NO + 3H2O + 5e-.

Importantly, almost no response is observed in nitrogen

environment. This mechanism is similar to sensing in metal oxide semiconductors where the ammonia reacts with adsorbed oxygen causing the successful detection. Overall, the presence of oxygen is essential for ammonia sensing and is available from the ambient. Moreover, a film composed of GG alone or Au film (Figure not provided) is found futile in ammonia sensing under identical experimental condition suggesting the combined effect of GG and Au. 6 ACS Paragon Plus Environment

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It can be noted from Table 1 that the performance of GG/Au sensor in terms of sensitivity and is far superior as compared to our previously reported GG/Ag sensor

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context, we would like to note that the average size of Au nanoparticles (~6.5 nm) is smaller as compared to Ag nanoparticles (~8.5 nm) and the density (4.7x1011 #/cm2) of Au nanoparticles in the GG/Au film is also very high. This is believed to be the reason for the superior performance of GG/Au film. *[ Appropriate place for Figure.4] In order to further explore the mechanism, ammonia of 100 ppm was exposed to the GG/Au film and FTIR spectroscopy studies before and after exposure were carried out. Spectrum of unexposed GG/Au film as shown in Figure 5a, mainly reveals water absorption bands with O– H stretching vibrations at 3000–3500 cm-1. Bands corresponding to aliphatic C-H stretching and C=O stretching carboxylate group of typical saccharides appears at 2917 and 1641 cm−1, respectively. The polysaccharide displays other peaks at 1010 and 869 cm-1, due to the bending vibration of the O-H and C-H bond, respectively. Interestingly, the spectrum remains identical after the ammonia exposure (Figure 5a, Table S1). We have also performed the TEM characterization of sensing film before and after ammonia exposure. No change in shape, morphology or crystallinity is observed (Fig. 5b). The topographical images taken in an optical profilometer before and after the ammonia exposure show identical features as shown in Figure 5c,d with nearly identical root-mean-square roughness (~0.07 µm) of the film. Over all, GG/Au film retains its structure/morphology even after the ammonia exposure suggesting that the sensor film can be used several times. *[Appropriate place for Figure.5] Selectivity is one of the important criteria for a useful sensor. In this regard, various volatile organic compounds (VOCs) such as cyclohexane, n-butyl acetate, o-xylene, acetone, acetonitrile, diethylether, ethanol, iso-propyl alcohol, methanol, tetrahydrofuran, and organic sulphides (hydrogen sulphide, mercaptoacetic acid ) have been studied as analytes. It can be noted from (Figure. 6a,b) that all the other analytes except sulphides show almost negligible response (Fig.S2b). As ammonia is known to be a strong reducing agent over all these VOCs, we believe that ammonia efficiently donates electron to the adsorbed oxygen and enhances the


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sensor response. However, the interference of sulphides cannot be ignored in ammonia detection though the response to sulfides is low as compared ammonia. *[Appropriate place for Figure.6]

Urea determination in human urine Urine is found to be sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultative anaerobic Gram negative rods and cocci.31 In the process of elimination from the body, urine can acquire strong odours due to bacterial action by the release of ammonia from the urea. In order to estimate urea concentration in urine, samples from 42 males and females patients were collected and used for the sensing experiments and then corresponding temporal responses are obtained for these samples under identical conditions. The concentration of ammonia for these samples is found out from the calibration curve for known concentrations of ammonia. The urea concentration is evaluated using the following relation where urea is completely converted into ammonia. The relationship between the concentrations of urea and ammonia is given by 2x [A] (mg/dL) = [U] (mg/dL)

(1)

where [U]= urea concentration and [A] = ammonia concentration. As the molecular weight of urea is 60 and that of urea nitrogen is 28, the conversion factors between urine urea nitrogen (UUN) and urea are given by Urea [mg/dL] = UUN [mg/dL] * 60/28

(2)

The same conversion is valid for blood urea nitrogen (BUN) in case of human serum. The temporal responses of urine samples from three volunteers are shown in Figure S2c. Each sample is examined at least three times and the average result is presented here. The average amount of ammonia is detected to be 2400 mg/dL (24000 ppm) which indicates the urea present in human urine is ~1200 mg/dL (12000 ppm) which is in agreement with reported value.31 The accuracy is found to be better than 97% over the entire range. Overall, the chemiresistive sensor based urea quantification method reported here has high accuracy over a wide concentration range. As a whole, the presence of ascorbic acid and glucose which are present in human urine sample does not interfere in the detection of urea or UUN. It shows good selectivity of the sensor towards urea quantification from urine sample. The reliability of the ammonia quantification from urine has further been evaluated by measuring the current for 8 ACS Paragon Plus Environment

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24000 ppm of ammonia and comparing with the urine sample (Figure S2d). Almost similar current is obtained for both the analytes as can be seen from Figure S2d. This demonstrates that the quantification of ammonia/urea is possible through a chemiresistive sensor. We have also examined the UUN and urea in urine samples of different age groups as shown in Figure S3a,b. It is observed that the average urea level and UUN are found to be in the range of 474-733 and 221-342 mg/dL, respectively for the age group 0-20 and 21-50 years. On the other hand, the average value of urea and UUN are 1312 and 628 mg/dL, respectively for 5190 years of age group. Our observation is that the urea and UUN in the urine is very high for 5190 years of age group and is believed to be due to some abnormality, diseases or reduce efficiency of the kidney. In order to establish the quantification of urea by using chemiresistive sensor, we compare the value of urea in urine samples obtained using our sensor (measured values) with the clinical tested values as shown in Figure S3c. It is interesting to note a linear relation between them with a slope of ~1.0 and a correlation coefficient (R2=0.99) indicating the high accuracy and preciseness of our sensor.

Urea in blood serum There are several methods such as conductometry, amperometry, potentiometry, fiber-optic sensor, colorimetric, photometric, mass spectrometry etc. for urea determination.32-35 Roche Cobas C111 is based on the principle of photometric determination and is widely used. Clinical values of BUN were obtained by using this instrument and compared with values obtained using our chemiresistive sensors. It may be noted that samples were diluted several times for measuring BUN/UUN. In order to estimate urea concentration of blood serum, samples from 33 male and female patients were collected and then corresponding temporal responses are obtained for these samples under identical conditions. The average amount of ammonia detection is 616 mg/dL (6160 ppm). This indicates that the urea present in blood serum is approximately 30 mg/dL (300 ppm) which is in agreement with reported values32. A typical temporal response for three volunteers serum samples are illustrated in Figure S4a-c (Supplementary Information). Different serum samples obtained from 6-72 years old different patients have been analysed for urea and BUN by using our sensor and the histogram is shown in Figure 7a,b. It was observed that normal average range of urea and BUN are between 27-48 and 13-22 mg/dL, 9 ACS Paragon Plus Environment

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respectively irrespective of the ages. The higher urea levels above this range are due to diabetic or kidney disorder. *[Appropriate place for Figure.7] In order to compare the significance of our method for urea/BUN detection, we compare our measured values with the clinical tested values for twenty serum samples (Figure 7c,d). Interestingly, a linear relation is obtained and R2 of 0.90, a slope of 0.821 and an intercept of 0.026 are obtained when the data are fitted into a straight line. Similarly, R2 of 0.90, a slope of 0.821 and an intercept of 0.0123 are obtained from BUN data (Figure 7d). As the intercept is close to zero for both the cases, the sensor value can be retrieved by multiplying the clinical value with the respective slopes. It is worthy to mention here that the method proposed here does not require any additional reagents such as urease to facilitate the measurement or any external reference. In addition, there is no pre-requisite sample preparation step for the analysis which takes not more than 3 minutes per sample on an average. Furthermore, the sensor proposed here can be used for several investigations. Overall, the method is convenient and environment friendly for laboratory measurements and can not only be used for biomedical applications but also for environmental monitoring as well chemical reaction studies. 24

Reproducibility of sensor The reproducibility of the sensor has been tested for aqueous ammonia, serum as well as urine samples. The relative standard deviation (RSD) of the sensor response with different ammonia concentrations (fig.2c,e) and the comparison of the measured value of

urea and BUN

concentrations with the clinical tested values (fig.7c,d) are found to be less than 3% for three successive measurements. The maximum RSD of sensor response with double loading of Au nanoparticles (fig.3a,b) is ~2.2%. This study confirms excellent reproducibility of the ammonia sensor for detecting ammonia vapour from aqueous ammonia/serum/urine samples.

CONCLUSIONS We have developed a highly sensitive chemiresistive sensor based on GG/Au nanocomposite for environmental and biomedical diagnosis.

The sensing is based on the

conductance change of the sensor when exposed to ammonia vapour. The sensor shows an 10 ACS Paragon Plus Environment

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excellent low as well high detection limit of 0.1 ppq and 30000 ppm, respectively at room temperature at a very fast response/recovery time of few seconds to few minutes. The high detection limit can be enahnced to 75000 ppm by simply increasing the loading of Au nanoparticles. We have explored the real life application of our sensor for the detection of the ammonia vapour released from the biofluid (urine/serum) which is first of its kind and shown that the chemirestive sensor can suitably be calibrated for the diagnosis of various diseases. We have also shown that the urea concentration in human urine and blood serum can easily be quantified. The same technique can in principle be applicable to measure ammonia/urea in other biological fluids, such as plasma, sweat, saliva, cerebrospinal liquids, etc. One of the biggest advantages of the sensor is the room temperature operation under ambient in the wide range and do not required any external stimulus for response or recovery of a sensor. The response, stability, spontaneity, selectivity and reproducibility make this sensor excellent as compared to the sensors reported in the literature. The films are stable over 6 months and can be used many times without affecting the sensing efficiency. Hence, the application of these films is promising as simple, robust, cost-effective for ultra trace to extremely higher detection of ammonia in clinical samples.

ASSOCIATED CONTENT Supporting Information Available: Preparation of NH3 solution of different concentration, Additional figures of response time curve of the film in presence of water, ammonia; selectivity study of the sensor; temporal response for volunteers` urine and serum samples. Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author: [email protected]; [email protected] (Dr. Sadanand Pandey) Ph.; +27-11-5596644 Notes: The authors declare no competing financial interest.


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ACKNOWLEDGEMENTS The authors SP is thankful to University Grant Commission (UGC), India and National research foundation (NRF), South Africa for its generous financial support. The authors also acknowledge financial assistance of Robert Bosch Center for Cyber Physical Systems, and Indian institute of science for Lab facilities, Dr. Gopal Goswami for help and support. I would like to give thanks to Mr. Hari for sulphide sensing study. Dr. Nagabhusan (CMO) for permitting and Mr. Rajesh (Pathologist) for helping us to analyze the body fluid of different patients in IISc health centre, We also thank R.V metropolis diagnostic & health care centre Pvt. Ltd, Bangalore (India) for examining the urine samples.

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(10) Llobet, E. et al. Fabrication of highly sensitive tungsten oxide ammonia sensors. Electrochem. Soc. 2000, 147, 776-779. (11) Chen, T.-Y. et al. Ammonia sensing properties of a Pt/AlGaN/GaN Schottky diode. IEEE Trans. Electron Devices 2011, 58, 1541-1547. (12) Chabukswar, V.V.; Pethkar, S.; Athawale, A.A. Acrylic acid doped polyaniline as an ammonia sensor. Sens. Actuators 2011, B 77, 657-663. (13) Ghosh, R.; Midya, A.; Santra, S.; Ray, S.K.; Guha, P.K. Chemically reduced graphene oxide for ammonia detection at room temperature. Appl. Mater. Interfaces 2013, 5, 7599−7603. (14) Xing, W.; Hu, J.; Kung, S.-C.; Donavan, K.C.; Yan, W.; Wu, R.; Penner, R.M. A chemically-responsive nanojunction within a silver nanowire. Nano Lett. 2012, 12, 1729−1735. (15) Yavari, F.; Castillo, E.; Gullapalli, H.; Ajayan, P.M.; Koratkar, N.

High sensitivity

detection of NO2 and NH3 in air using chemical vapor deposition grown graphene. Appl. Phys. Lett. 2012, 100, 203120. (16) Zan, H.W.; Dai, M.Z.; Hsu, T.Y.; Lin, H.C.; Meng, H.F.; Yang, Y.S. Ammonia gas sensor based on pentacene organic field-effect transistor. IEEE Sensor Journal 2012, 12, 504-601. (17) Chen, G. et al. Enhanced gas sensing in pristine carbon nanotubes under continuous ultraviolet light illumination. Sci. Rep. 2012, 2, 343. (18) Dai, M-J. et al. Highly sensitive ammonia sensor with organic vertical nanojunctions for noninvasive detection of hepatic injury. Anal.Chem. 2013, 85, 3110−3117. (19) Field, C.R.; In, H.J.; Begue, N.J.; Pehrsson, P.E. Vapor detection performance of vertically aligned, ordered arrays of silicon nanowires with a porous electrode. Anal. Chem. 2011, 83, 4724−4728. (20) Gong, J.; Li, Y.H.; Hu, Z.S.; Zhou, Z.Z.; Deng, Y.L. Ultrasensitive NH3 gas sensor from polyaniline nanograin enchased TiO2 fibers. J. Phys. Chem C 2010, 114, 9970−9974. (21) Chen,

S.;

Sun,

G.

High

sensitivity

ammonia

sensor

using

a

hierarchical

polyaniline/poly(ethylene-co-glycidyl methacrylate) nanofibrous composite membrane. Appl. Mater. Interfaces 2013, 5, 6473−6477.


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(22) Krutovertsev, S.A.; Sorokin, S.I.; Zorin, A.V.; Letuchy, Ya. A.; Antonova, Yu. O. Polymer film-based sensors for ammonia detection. Sens. Actuators B 1992, 7, 492–494. (23) Penza, M.; Milella, E.; Musion, F.; Alba, M.B.; Cassano, G.; Quirini, A. AC and DC measurements on Langmuir-Blodgett polypyrrole films for selective NH3 gas detection. Mater. Sci. Eng. C 1998, 5, 255–258. (24) Pandey, S.; Goswami, G.K.; Nanda, K.K. Nanocomposite based flexible ultrasensitive resistive gas sensor for chemical reactions studies. Sci. Rep. 2013, 3, 2082. (25) Pandey, S.; Goswami, G.K.; Nanda, K.K. Green synthesis of polysaccharide/gold nanoparticle nanocomposite: An efficient ammonia sensor. Carbohydr Polym. 2013, 94, 229-234. (26) Venditti, I.; Fratoddi, I.; Russo, V.; Bearzotti. A. A nanostructured composite based on polyaniline and gold nanoparticles: synthesis and gas sensing properties. Nanotechnology 2013, 155503. (27) Wang Z.H. Nanobelts, nanowires and nanodiskeltes of semiconducting oxides-From materials to nanodevices. Adv. Mater. 2003, 15, 432-436. (28) Ebbing, D.; Gammon, S.D. General Chemistry, 10th ed.; Brooks Cole publisher: US, 2012, ISBN-13: 978-1285051376 (29) Duo, W.; Dam-Johnsen, K.; Ostergaard, K. Kinetics of the gas-phase reaction between nitric oxide, ammonia and oxygen. Can. J. Chem. Eng. 1992, 70, 1014-1020. (30) Tulliani, J.-M.; Cavalieri, A.; Mussob, S.; Sardellad, E.; Geobaldo, F. Room temperature ammonia sensors based on zinc oxide and functionalized graphite and multi-walled carbon nanotubes. Sens. Actuat. B 2011, 152, 144. (31) Stevens, L.A.; Lafayette, R.A.; Perrone, R.D.; Levey, A.S. “Laboratory evaluation

of kidney function,” in Diseases of the Kidney and Urinary Tract, R. W. Schrier, Ed., pp. 299–336, Lippincott Williams & Wilkins, Philadelphia, Pa, USA, 8th ed.; 2007. Geigy Scientific Tables, 8th Rev. Ed.; Basle, Switzerland: Ciba-Geigy, 1981–1992. (32) Walker, H.K.; Hall, W.D.; Hurst, J.W. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed.; Boston: Butterworths; 1990, (chapter.193 BUN and creatinine, Adrian O Hosten). (33) Beckman. Beckman Synchron LX Systems Chemistry Information Manual. Beckman Coulter, Inc., Brea, California. 2001. 14 ACS Paragon Plus Environment

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(34) Tanigawa, T. et al. Simple and rapid quantitative assay of

13

C-labelled urea in human

serum using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. J. Chromatogr. B: Biomed. Appl. 1996, 683, 135–142. (35) Kessler, A.; Siekmann, L. Measurement of urea in human serum by isotope dilution mass spectrometry: a reference procedure. Clin. Chem. 1999, 45, 1523–1529.

List of figures and table caption

Figure 1. Characterisation of sensing film (a) Digital photograph and (b) SEM image of the film. (c) The schematic of the testing chamber. (d) I-V characteristic of a sensor made of the GG/Au nanocomposite film with different concentrations of ammonia vapors.

Figure 2 Ammonia sensing of GG/Au nanocomposite film. (a) Schematic of the configuration used for ammonia sensing. (b) Temporal response curve of our GG/Au sensor in 0.1 ppq to 100 ppm range. Temporal response at higher ppm concentrations (10000, 20000, 30000, 50000, 100000 ppm) is shown in the inset marked as 1 to 5, respectively. The response to different concentrations is studied differently though the film is the same and presented together with the baseline adjusted for simplicity. (c) Log-log plot of current versus different ammonia concentration. Dashed line is its linear fit. (d) Semi-log plot of response and recovery time of different ammonia concentration. The solid line is guide to eye. (e) Log-log plot of sensor response with different ammonia concentration. The solid line is the linear fit. Error bars obscured by data points.

Figure 3. Effect of different parameters on sensing performance (a) Current and (b) sensor response with double loading of Au nanocrystals; (c) Stability plot of the sensor for a period of 6 months.(d) sensor response ∆G/Go of ammonia under different natural humidity (%RH). Vertical error bars represent the standard deviation from the mean. Figure 4 Ammonia sensing at different environment. (a) The temporal ammonia response of 1 ppm in different environments (ambient, nitrogen and oxygen). (b) oxygen adsorption occurs on sensor surface and (c) introduction of ammonia removes adsorbed oxygen.


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Figure 5 Characterization of sensor- before and after ammonia exposure (a) FTIR spectra of sensing film (a1) before and (a2) after ammonia sensing experiment; (b) TEM image of sensing film; (c) Image of optical profilometer of the sensor film taken before and ; (d) after ammonia sensing experiment.

Figure 6 Selectivity of sensing film. (a) selectivity response of the sensor towards different analytes in their pure form; (b)The sensor towards different sulphide analytes at 50 ppm. Figure 7 Measurement of BUN and urea in blood serum. (a) Urea and (b) BUN obtained from the serum samples of 6-72 years old patients by using our sensor. A* represents for a diabetic patient with renal disorder and B* represents for another diabetic patient with renal disorder and peptic ulcer. Comparison of the measured value of (c) urea and (d) BUN concentrations with the clinical tested values. Error bars obscured by data points.

Table 1: Summarize results of chemiresistive ammonia sensors.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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a

c

b

d

15 Current (µA)

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10

1 ppq 1 ppt 1ppb 1ppm

5 0 0

10 Voltage (V)

20

Figure.1


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a

Ag

Sensor film Glass

Current (µA)

40 30 20 10

120

c

5

4

3

100

2 80

1

60 40 20 0 0

900

1800

2700

3600

Time (s)

0 0

400

800

1200

100

Current (µA)

baseline 0.1 ppq 1 ppq 100 ppq 1 ppt 100 ppt 1 ppb 100 ppb 1 ppm 100 ppm

Current (µA)

50

b

1600

10

1

0.1 1E-12

d

300

e

250 200

100

1E-4

1

10000

10000

∆G/Go

Response Recovery

150

1E-8

Ammonia concentration (ppm)

Time (s)

Time (s)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1000

100

50 0 1E-12

1E-8

1E-4

1

10000


10 1E-12

1E-8

1E-4

1

10000

Ammonia concentration (ppm) Figure.2


Page 19 of 26

b

200

9600

180

8400

∆G/Go

Current(µA)

a

160

140

120

7200

6000 20000

40000

60000

80000

100000

20000


40000

60000

80000

100000


d

103

4300

101

4200 99

∆G/Go

c % Relative ∆G/Go

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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97 95

4100 4000

93

3900 91 0

50

100

150

200

time (days)

20

30

40

50

60

70

%RH

Figure.3


80

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a

90

2

2

1 2

Current (µA)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

flow on flow off ammonia nitrogen oxygen 2

30

1

1

1

2 1

1

0 0

400

800

time (s)

1200

1600

b

-

O2 - O2 O - O2 - O2 2

-

NH3+O2

c

NH3

Figure.4


Page 21 of 26

a

100

b

a1 a2

95 90

-1

2916 cm

-1

1638 cm

%T

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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-1

3330 cm

85 -1

80

1009 cm

75 70 -1

868 cm

65 800

1600

2400

3200

4000

Wavenumber (cm-1)

c

d

10 µm

10 µm

Figure 5.


-2

in a o

Mercaptoacetic acid

Ammonia

Hydrogen sulfide

∆G/Go

o-xylene

Tetrahydrofuran

Methanol N-butyl acetate

Ethanol

Diethylether

Cyclohexane

Acetonitrile

Acetone

Page 22 of 26

2 l3yte s

3000

4

0

lie fd

G ∆ /o

11000 10500 10000 9500 9000

2

1 A n a

b 4000

Ammonia

Iso propyl alcohol

a 11500

A m

1 0 2 3

0

∆G/Go

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

tcd ie a o rp su n g M H y

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2000 1000 0

Analytes

1

2

3

Analytes

Figure 6.


Page 23 of 26

a

80

A*

60

BUN (mg/dL)

Urea (mg/dL)

b

B*

70

50 40 30 20

40

B* A*

30

20

10

10 0

0

0

10

20

30

40

50

60

70

0

60

d

Urea (mg/dL) 50

Measured value (mg/dL)

c

y = 0.821x + 0.0264 R² = 0.90

40 30 20 10 0 0

10

20

30

40

10

20

30

40

50

60

70

Age (years)

Age (years)

Measured value (mg/dL)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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50

60

Clinical tested value (mg/dl)

70

30

BUN (mg/dL) y = 0.821x + 0.0123 R² = 0.90

20

10

0 0

10

20

30

Clinical tested value (mg/dl)

Figure.7


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Table 1 Active materials

Carbon nanotubes[2] DTBDT-C6 microstripe[7] In2O3 nanotubes[8] MoS2 thin film[9] WO3 thin film[10]

Pt/AlGaN/GaN Schottky-type sensor[11] Acrylic acid doped polyaniline [12] Reduce graphene oxide[13] Ag nanowires based nanojuction[14] Graphene[15]

Pentacene based OTFT[16] Carbon nanotube network[17] VNJ-P3HT diode [18] PTE Si nanowires (porous top

Sensitivity (%)

tres (s)

~100 at 1% NH3 98.6 at 50 ppm 3500 at 25 ppm 0.06 at 20 ppm 5 at 1000 ppm

60120 5-45

4-35

20

20

~10 at 10 ppm ~2.8

trec (s)

T (°C)

Selectivity

Lowest detection limit

Highest detection limit (ppm)

Good

N/A

10

N/A

~5 ppm

N/A

RT

RT

300 ppb 15

60

300

Good

N/A

Poor

10 ppb

N/A

15

60

300

Good

35 ppm

1000

60s

360s

RT

N/A

1 ppm

600

5.5 at 200 ppm

-

-

RT

Poor

200 ppm

2800

138 7% NH3

-

-

RT

N/A

0.7%

7%

~100 at 1000 ppm

3600

3600

N/A

0.5 ppm

N/A

23 at 3 ppm

500

100200

N/A

3

0.5

RT

N/A

~1 ppt*

500

RT

Good

5 ppb

3

40

N/A

500 ppb

10

(100 ) 0.98 at 600 ppm

N/A UV (0.0000278) irradia tion (0.02) ~100 Flushing air 0.35 at ~480 Flushing 1 ppm air


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electrode silicon NW)[19] TiO2 fiber coated PANI[20] PANI/PE-coGMA nanofibrous composite[21] Polyaniline films doped with Ni[22] Polypyrrole[23] GG/Ag nanocomposite[2

0.004 at 50 ppq ~2500% (25)

1585 at 10000 ppm ~2 at 8000 ppm ~18 at 25 ppm

~60

Flushing air

~75

RT

N/A

50 ppq

2x10-4

RT

N/A

0.1

25

Au Nanocomposite Based Chemiresistive Ammonia Sensor for Health

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