In this work, high surface area and porous Pb(Ac)2 anchored nanofibers (NFs) that ... sensitivity, slow response speed, and high limit of detection. ...
May 23, 2018 - Thus far, in order to detect leakage of H2S gas in industrial sectors, Pb(Ac)2 has been used as an indicator in the form of test papers with a ...
With strong acids, lead acetate forms irritating vapors of acetic acid. Reaction with some oxidizing agents, for example chlorates and bromates, can be violent. See Bretherick's Handbook of Reactive Chemical Hazards for details and for other incompat
Received September 24. 1914. The basic acetates of lead owe a considerable importance in applied chemistry to the fact that, for a large class of crude ...
Nov 27, 2012 - A new enzyme-free signal amplification-based assay for microRNA (miRNA) detection is developed by using hybridization chain reaction ...
Nov 27, 2012 - ABSTRACT: A new enzyme-free signal amplification-based assay for. microRNA (miRNA) detection is developed by using hybridization chain.
27 Nov 2012 - A new enzyme-free signal amplification-based assay for microRNA (miRNA) detection ..... An Impedimetric-Fluorescence Double-Checking Biosensor with .... Min-Kyo Seo , Bong Hyun Chung , Yongwon Jung , Bongsoo Kim.
Nov 27, 2012 - ABSTRACT: A new enzyme-free signal amplification-based assay for. microRNA (miRNA) detection is developed by using hybridization chain.
brands of litharge exhibit varying behaviors when ... of a certain made and brand. DUDLEY HAINES .... 147, New York, Longmans, Green &. Co., 1923. (6) Ibjd.
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Article
Sub-ppm H2S Colorimetric Sensor: Lead Acetate Anchored Nanofibers toward Halitosis Diagnosis Jun-Hwe Cha, Dong-Ha Kim, Seon-Jin Choi, Won-Tae Koo, and Il-Doo Kim Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b01273 • Publication Date (Web): 23 May 2018 Downloaded from http://pubs.acs.org on May 23, 2018
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ABSTRACT Lead(II) acetate (Pb(Ac)2) reacts with hydrogen sulfide to form colored brownish precipitates of lead sulfide. Thus far, in order to detect leakage of H2S gas in industrial sectors, Pb(Ac)2 has been used as an indicator in the form of test papers with a detection limit only as low as 5 ppm. Diagnosis of halitosis by exhaled breath needs sensors able to detect down to 1 ppm of H2S gas. In this work, high surface area and porous Pb(Ac)2 anchored nanofibers (NFs) that overcome limitations of conventional Pb(Ac)2 based H2S sensor are successfully achieved. First, lead(II) acetate, which melts at 75 °C, and polyacrylonitrile (PAN) polymer are mixed and stirred in DMF solvent at 85 °C, enabling uniform dispersion of fine liquid droplets in the electrospinning solution. During the subsequent electrospinning, Pb(Ac)2 anchored NFs are obtained, providing an ideal nanostructure with high thermal stability against particle aggregation, numerous reactions sites and enhanced diffusion of H2S into 3D networked NF web. This newly obtained sensing material can detect down to 400 ppb of H2S at a relative humidity of 90%, exhibiting high potential feasibility as a high performance colorimetric sensor platform for diagnosis of halitosis.
colorimetric sensors, lead acetate(II), electrospinning, nanofibers, hydrogen sulfide Exhaled breath contains hundreds of species of volatile organic compounds (VOCs) such as hydrogen sulfide (H2S), nitrogen monoxide (NO), ammonia (NH3), toluene (C6H5CH3), and acetone (CH3COCH3), which are known biomarkers for halitosis,1 asthma,2 kidney failure,3 lung cancer,4 and diabetes,5 respectively. Recently, substantial research has been devoted to realization of disease diagnosis through exhaled breath by means of gas sensors.6-10 In particular, chemiresistive gas sensors based on metal oxides such as SnO2, WO3, and TiO2 have been considered as potential candidates for portable gas sensors for disease diagnosis via exhaled breath due to their remarkable sensitivity and feasible integration in portable devices.11-15 However, to measure and digitize the degree of change in resistance, it is inevitable that power sources are required and precise calibration should be checked before use. As for colorimetric sensors, however, as-prepared sensing materials can immediately be employed in form of test papers without introduction of measurement systems and electric circuit design, since color transition is noticeable with the naked eye.16,17 Nevertheless, disease diagnosis using colorimetric sensors still remains challenging due to relatively poor sensing characteristics, i.e., low sensitivity, slow response speed, and high limit of detection. Lead(II) acetate (Pb(Ac)2) is a well-known dye that reacts with hydrogen sulfide to form dark brown precipitates of lead sulfide (PbS). Although paper-based colorimetric sensors impregnated with Pb(Ac)2 for detection of H2S are already available in the market, they can be narrowly used to detect leakage of H2S in industrial sectors due to low detection limit between 5 and 10 ppm.18 For practical diagnosis of halitosis through exhaled breath, it is inevitable to enhance the detection limit down to 1 ppm of H2S since halitosis patients exhale up to 2 ppm of H2S.19-21 In an effort to improve sensing performance, Ramaier et al. introduced optosensing method for H2S analysis through lead(II) acetate test papers by reflectance measurement through
optical fibers.22 Although the sensor enables detection below 1 ppm of H2S, subsidiary equipment such as optical fibers and reflectance analyzers should be included as part of colorimetric sensors. More recently, Samuel et al. demonstrated bismuth-based colorimetric sensors for detection of H2S with noticeable detection limit of 30 ppb.18 However, the pH of colorimetric sensors should be maintained at 11 for practical detection of H2S gas. This necessitated storage of the sensors under nitrogen at room temperature. For simplicity and ease of use, it is highly desirable to develop considerably sensitive colorimetric gas sensors without the need for additional equipment and controlling of surrounding environment. One dimensional nanofibers show a high degree of porosity and considerable surface-tovolume ratio, providing numerous reaction sites toward target gas molecules.23,24 Considering their striking advantages, nanofibers can be regarded as ideal scaffolds for gas sensors. In addition, nanofibers can be readily mass-produced through electrospinning, which is the most efficient technique for facile synthesis of one-dimensional nanofibers.25 Therefore, it is reasonable to expect that the use of nanofibers as a scaffold to anchor Pb(Ac)2 particles can significantly enhance colorimetric sensing properties toward H2S gas. In this work, high surface area and porous lead(II) acetate anchored nanofibers (hereafter denoted as Pb(Ac)2@NFs) are synthesized for the first time by employing high temperature stirring (HTS) and electrospinning. In addition, we investigated morphology tuning of Pb(Ac)2 particles on surroudning temperature. For synthesis of Pb(Ac)2@NFs, trihydrate lead(II) acetate is employed due to its relatively lower melting temperature (75 ˚C) than that of anhydrous lead(II) acetate (280 ˚C). Therefore, dye particles are readily liquefied into droplets with great dispersion in a viscous polymer during stirring at 85 ˚C, leading to scaling of dye nanoparticles. Afterwards, dispersed Pb(Ac)2 particles in the electrospinning solution are anchored to
polyacrylonitrile nanofibers (PAN NFs) upon electrospinning. Final drying enables this newly obtained sensing material to detect sub ppm concentration of H2S gas even in high relative humidity (~90% RH) with a limit of detection of 400 ppb. For possible application for halitosis diagnosis, our colorimetric sensors were exposed to simulated breath containing traces of H2S and numerous interfering gases, and their performance was evaluated through RGB analysis.
EXPERIMENTAL SECTION Dyes and Materials. Polyacrylonitrile (PAN, Mw = 150,000 g mol-1), trihydrate lead(II) acetate (Pb(C2H3O2)·3H2O, Mw = 379.33 g mol-1), and N, N-dimethylformamide (DMF, 99.8%) were purchased from Sigma-Aldrich (St. Louis, USA). All chemicals were used without further purification. Ball-milled particles were obtained by milling trihydrate lead(II) acetate using a ball milling machine (Pulverisette 6, Fritsch). Two kinds of zirconia balls with radius of 0.5 cm and 1 cm were used as grinders. Prior to ball milling, 10 zirconia balls (radius: 1 cm) and 30 zirconia balls (radius: 0.5 cm) were introduced in a steel container containing 10 g of trihydrate lead(II) acetate, and the mixture was sealed. Trihydrate lead(II) acetate was reduced to nanoscale Pb(Ac)2 particles after ball-milling for 5 h, with intermittent resting time of 20 min after every 1 h of ball milling.
Colorimetric Sensor Preparation. The schematic in Figure 1 presents preparation procedures for Pb(Ac)2@NFs via electrospinning. To prepare colorimetric gas sensors based on Pb(Ac)2@NFs, 0.25 g of PAN and 0.4 g of trihydrate lead(II) acetate (Pb(Ac)2) were dissolved in
3 g of DMF to make an electrospinning solution. The solution was vigorously stirred at 85 °C for 10 h. Note that Pb(Ac)2 particles are nearly insoluble in DMF due to negligible solubility. Upon stirring at a temperature of 85 °C, which is above the melting point of Pb(Ac)2, dye particles in the electrospinning solution can be liquefied into fine droplets with great dispersion in a viscous PAN polymer. Subsequent quenching procedure was performed. During quenching, the vial containing the heated electrospinning solution was kept in a beaker containing water at 25 °C for 1 min to restrain particle growth while cooling. Note that the electrospinning solution hardened when it was quenched below 20 °C due to lowering of PAN solubility. After that, the singlespinneret (23 gauge) electrospinning was carried out at a rate of 2 µL min-1 by applying a voltage of 15 kV between the needle tip and the collecting substrate at a separation distance of 20 cm. Finally, Pb(Ac)2 particles anchored NFs were obtained, followed by drying in an oven at 50 °C for 3 h. For comparison, Pb(Ac)2 particle anchored NFs based on room temperature stirred solution (hereafter, RTS-Pb(Ac)2@NFs) were also synthesized using equal amounts of Pb(Ac)2, DMF, and PAN polymer.
Gas exposure equipment. The gas sensing characteristics were evaluated using a homemade testing equipment. A schematic illustration of gas exposure equipment is depicted in Figure S1. The flow unit of sccm is a flow measurement term indicating cc/min at standard temperature and pressure. Gas flow rate for each line was modulated by mass flow controller (MFC). The external gas source was a cylinder containing 20 ppm of H2S balanced with air. In the case of 1 ppm exposure, humid air and H2S (20 ppm) at 950 sccm and 50 sccm, respectively, were mixed to dilute the concentration of H2S to 1 ppm. Then half of the mixture (i.e. 500 sccm) containing 1 ppm of H2S was flowed onto the colorimetric sensor (Figure S1a). The colorimetric
gas sensors were exposed to H2S at concentrations ranging from 5 ppm to 0.1 ppm (100 ppb) for 1 min. To further investigate the response time, the gas sensors were exposed to 1 ppm of H2S for various exposure times from 60 to 10 sec. The outlet tube for H2S was about 1 cm in radius, and the distance between the outlet and the gas sensors was maintained at about 0.3 cm. As for breath tests, exhaled breath samples captured in tedlar bags were used instead of humid air (Figure S1b). It is noteworthy that gas flow rate of a single outbreathing from adult men (tidal volume: 500 ml/breath, respiratory rate: 12 to 20 breaths/min) ranges from 6000 to 10000 sccm.26-28
Quantitative Evaluation of color change. The image of each sample was taken by a cellphone camera with a Sony IMX260 image sensor at a distance of 15 cm between samples and the camera. The captured images were cropped into 0.5 × 0.5 cm2 areas. For quantitative evaluation of color change using RGB data, the mean RGB values of the cropped images were extracted using ImageJ, which is an image processing program. The ∆R, ∆G, and ∆B values were calculated by determining differences between the RGB values obtained before and after exposure to H2S at various conditions. To examine the reliability of RGB analysis in this shooting condition, various parts of an image taken before exposure to H2S were cropped and designated by notation #1 through #16 (Figure S2a and b). The mean RGB values from each cropped image were extracted and compared with each other (Figure S2c). A slight variation in RGB sums was observed for the samples from #1 to #7 and from #11 to #16 due to differences in contrast. However, when images were cropped horizontally from #7 to #11, the degree of variation in sums became higher than that of the vertical scanning. This was possibly due to variation in thickness of the electrospun fibrous web. In the Commision Internationale
I’Eclairage Lab (CIE L*a*b*) system, the RGB values can be converted into L*, a*, and b* values according to conversion equations.29,30 Then, the color difference (∆E) can be calculated by applying the formula ∆E=[(∆L*)2+ (∆a*)2+ (∆b*)2]1/2.31 Note that in dentistry, color differences of teeth with ∆E values greater than or equal to 3.3 are considered clinically unacceptable since it can be perceived with the naked eye.32,33
RESULTS AND DISCUSSION Temperature dependency of Pb(Ac)2 particle growth. High surface area of Pb(Ac)2 particles is necessary to increase reaction sites for target gas molecules. However, nanoscale Pb(Ac)2 particles easily grow into large particles because they are highly subject to ambient temperature change. Aggregated particles in nanoscale readily bring about particle growth at relatively low temperature. As shown in Figure S3a, commercially available Pb(Ac)2 particles have size distribution of approximately 100 to 200 µm. To verify temperature effect on Pb(Ac)2 particle sizes, ball-milling of Pb(Ac)2 was carried out. It was confirmed in Figure 2a that sizes of ball-milled Pb(Ac)2 particles ranged from hundreds of nanometers to a few micrometers, which were much smaller than that of as-purchased Pb(Ac)2 particles. However, when the ball-milled particles were dried at 50 °C for 12 h, small particles started to agglomerate into a platy structure (Figure 2b). The particle growth can cause a decrease in reaction sites of Pb(Ac)2 particles, leading to inferior sensitivity. In detail, particle growth occurs only when clusters of small Pb(Ac)2 particles are formed before gaining heat energy. Therefore, a scaffold into which Pb(Ac)2 particles can be uniformly scattered is required to suppress unwanted particle growth for improved sensitivity of Pb(Ac)2 particles. In this sense, one-dimensional structures of nanofibers
can be a suitable scaffold for supporting scattered particles. Uniformly scattered Pb(Ac)2 particles on the surface of NFs showed much higher temperature stability compared to agglomerated ones.
High temperature stirring (HTS) of Pb(Ac)2. To achieve homogeneously dispersed fine dye particles, high temperature stirring (HTS) was introduced during preparation of electrospinning solution. Trihydrate lead(II) acetate has low melting temperature (75 ˚C) compared to anhydrous lead(II) acetate (280 ˚C). It is much more reasonable to take advantage of low melting temperature of trihydrate lead(II) acetate for facile scaling of Pb(Ac)2 particles with lower heat energy. During HTS process, dye particles were liquefied and stirred at 85 ˚C with a magnetic bar, enabling uniform dispersion of fine liquid droplets in the electrospinning solution. The stirring temperature of 85 ˚C was selected because it is between melting temperature of trihydrate lead(II) acetate and glass transition temperature (95 ˚C) of matrix polymer (PAN). Note that when the solution was stirred at 85 °C, the transparency increased compared to the room temperature solution (opaque) in Figure S4. As mentioned in the previous section, the solidified Pb(Ac)2 particles are likely to grow larger on cooling. Therefore, to prevent particle growth during cooling, the vial containing as-prepared electrospinning solution was kept in a beaker containing water at 25 ˚C for 1 min, subsequently followed by electrospinning. To confirm Pb(Ac)2 particle size upon HTS, as-purchased Pb(Ac)2 particles were mixed in DMF with and without PAN polymer and stirred with a magnetic bar at 85 ˚C for 5 h. A droplet of each obtained solution was dropped onto a glass substrate and dried at room temperature. After that, each sample was observed by scanning electron microscope (SEM). The results shown in Figure 2c prove that HTS can reduce the size of Pb(Ac)2 particles to a few hundred nanometers,
keeping Pb(Ac)2 particles unaggregated. On the contrary, without the polymer in Figure 2d, Pb(Ac)2 particles agglomerate and grow into microscale platy particles. It should be noted that viscosity of the polymer played an important role for homogeneous dispersion of Pb(Ac)2 particles during HTS, preventing particles aggregation. Particle size distribution of HTS-Pb(Ac)2 with PAN polymer was depicted in histogram (Figure S5) and the average particle size was estimated to be ca. 0.323 µm. Figure 2e shows SEM image of Pb(Ac)2@NFs electrospun from HTS-based solution. Energy-dispersive X-ray analysis in Figure S3b and c reveals that particles anchored to NFs are composed of Pb. Figure 2f and its inset show Pb(Ac)2@NFs and NFs, respectively. Compared to usual NFs that showed a single surface morphology, Pb(Ac)2@NFs featured two different morphologies: PAN polymer area and Pb(Ac)2 particle area.
Effect of drying after sensor preparation. As already discussed, Pb(Ac)2 particles grew into a platy structure when drying was carried out above room temperature. Figure 3a exhibits SEM image of Pb(Ac)2 particles with curvy morphology characterized after ball-milling in DMF. On contrary, Figure 3b shows that Pb(Ac)2 particles grew into a platy structure after the ballmilled particles were dried at 50 ˚C for 30 min. Based on this observation, we rationally assumed that a platy structure can offer higher or faster reactivity toward H2S molecules due to broader edge area. Therefore, as-prepared Pb(Ac)2@NFs were dried at 50 ˚C for 3 h to investigate the influence of particle structures on sensing characteristics. Subsequently, as-prepared Pb(Ac)2@NFs and oven-dried Pb(Ac)2@NFs were exposed to 5 ppm of H2S for 1 min, and the results are shown in Figure 3c and d, respectively. It was found that the color changed area of oven-dried Pb(Ac)2@NFs was larger than that of as-prepared Pb(Ac)2@NFs, indicating that the platy structure of oven-dried Pb(Ac)2@NFs possibly featured more reactive sites. In addition,
comparison of RGB values from the cropped images before and after exposure to H2S confirmed that oven-dried Pb(Ac)2@NFs outperformed as-prepared Pb(Ac)2@NFs as shown in Figure S6.
Color change evaluation on exposure to H2S. The gas sensing performance of Pb(Ac)2@NFs was evaluated upon exposure to various concentrations of H2S in humid condition at room temperature. First, Pb(Ac)2@NFs was exposed to 1-5 ppm of H2S for 1 min. As described in Figure 4a, degree of color change from white to brown lightened with a decrease in H2S concentration. However, it is worth pointing out that the color change of Pb(Ac)2@NFs even at 1 ppm of H2S was still noticeable with the naked eye. To investigate exposure time dependency, exposure time was varied from 50 to 10 s at the fixed H2S concentration of 1 ppm (Figure 4b). As the exposure time approached 10 s, color transition from white to brown toward H2S grew less distinct. These results prove that colorimetric gas sensing performance of Pb(Ac)2@NFs enables identification on presence of sub-ppm H2S during the given exposure time of 1 min. It is, therefore, highly expected that Pb(Ac)2@NFs can be applied not only in industrial sectors for detection of H2S leakage, but also in diagnosis of halitosis by detecting traces of H2S in patients’ breath. To determine the limit of detection, Pb(Ac)2@NFs were exposed to H2S below 1 ppm for 1 min (Figure 4c). Despite exposure to traces of H2S, color change of Pb(Ac)2@NFs was identified with the naked eye until 600 ppb, below which the color change became difficult to recognize based on the cropped images on computer screen. For clarity, modified images were included as insets in each image in Figure 4. Moreover, quantitative evaluation of color difference recognizable with bare eyes was carried out as discussed in the next section. To study the selectivity property of Pb(Ac)2@NFs, the NFs were exposed to acetone, NO2, NH3, CO, CH4, and methyl mercaptan (CH3SH), which is a volatile
sulfuric compound (see insets in Figure 4d). As shown in the figure, no color transition occurred, which means that Pb(Ac)2 shows superior selectivity toward H2S, in agreement with the previous study.16 The striking sensing characteristics can be attributed to high surface area resulting from NFs scaffold with nanoscale diameters and the HTS-Pb(Ac)2 particles. To verify the effect of HTS on particle scaling, RTS-Pb(Ac)2@NFs were employed. For comparison with HTSPb(Ac)2@NFs, the colorimetric sensing characteristic of RTS-Pb(Ac)2@NFs was investigated upon exposure to H2S in humid condition at room temperature (Figure S7). The captured images show that RTS-Pb(Ac)2@NFs were less sensitive than HTS-Pb(Ac)2@NFs due to relatively huge Pb(Ac)2 particles on NFs as verified by SEM observation (Figure S8a and b). This finding reveals that HTS is not only an alternative to a time-consuming and complex method such as ball-milling in realizing Pb(Ac)2 particle scaling but also can enhance colorimetric sensitivity to H2S. To investigate morphology and chemical state changes of Pb(Ac)2@NFs before and after exposure to H2S, we performed scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. As displayed in Figure S9a, a bundle of Pb(Ac)2 nanoplates was well anchored to polymer nanofibers before it was exposed to H2S. Upon exposure to H2S, the bundle of the nanoplates flattened on the surface (Figure S9b). Figure S10 displays XPS spectra of Pb(Ac)2@NFs before and after exposure to H2S. The survey scan of XPS spectra in Figure S10a and b displayed the presence of Pb, S, O, N, and C elements in Pb(Ac)2@NFs before and after exposure. As shown in Figure S10c, the Pb-S bonding peaks for the HTS-Pb(Ac)2@NFs showed negligible content of sulfur element before exposure to H2S. In Figure S10d, however, strong Pb-S bonding peaks at around 137.3 and 142.2 eV were observed upon exposure of the HTS-Pb(Ac)2@NFs to H2S, indicating that PbS particles are well formed on the surface of the nanofibers. In addition, the peak at the binding energy of 160.2 eV for the S 2p XPS spectra,
which is assignable to the Pb-S bond, was enhanced after exposure as displayed in Figure S10e and f.34-36
RGB analysis from the cropped images. The degree of naked-eye detectable color change of HTS-Pb(Ac)2@NFs could differ from one person to the other. For accurate quantitative analysis of color change, samples were evaluated by means of RGB analysis. ∆Sum is a value obtained by summing up all the RGB changes. In other words, higher ∆Sum means that the colorimetric gas sensor is more sensitive to H2S gas. Figure 4d corresponds to ∆Sum data of HTS-Pb(Ac)2@NFs after exposure to 5 ppm of different kinds of gases for 1 min. As discussed in the previous section, HTS-Pb(Ac)2@NFs display noticeable selectivity toward H2S. Negligible change of RGB values obtained from exposure to other gases could result from contrast, not from color transition. Figure 5a presents ∆Sum data of HTS-Pb(Ac)2@NFs and RTS-Pb(Ac)2@NFs samples after exposure to 0.1-5 ppm of H2S for 1 min. HTS-Pb(Ac)2@NFs exhibits enhanced sensing characteristics compared to RTS-Pb(Ac)2@NFs. It is noteworthy that HTS-Pb(Ac)2@NFs were capable of detecting down to 0.4 ppm of H2S while RTSPb(Ac)2@NFs were sensitive to as low as 0.6 ppm. Figure 5b displays ∆R (red), ∆G (green), and ∆B (blue) values determined from difference of RGB values before and after exposure to H2S at each condition. It is worth pointing out that a change in the blue element was the most pronounced, while the red element rarely altered, possibly due to color shift from white to brown. As the exposure time was shortened, slighter variations in all the indicators were observed. In dentistry, color differences of teeth are determined by calculation of ∆E values. Typically, ∆E values greater than or equal to 3.3 are considered visually perceptible.37-39 In this work, ∆E was calculated using the extracted RGB values before and after H2S exposure as shown in Table 1
(for more details see Table S1). It was confirmed that as the exposure time and gas concentration decrease, ∆E decreases and becomes less perceivable. However, all values above 400 ppb were higher than 3.3, meaning that the color differences can be observed with the naked eye. To investigate the potential feasibility of halitosis diagnosis with HTS-Pb(Ac)2@NFs, we performed breath tests with simulated halitosis breath. First, exhaled breath samples were collected in tedlar bags from 10 healthy subjects consisting of 8 males and 2 females nonsmoking individuals. The collected breath samples were mixed with 1 ppm of H2S, and the mixture was passed onto HTSPb(Ac)2@NFs. Figure 5c shows RGB sum values obtained before and after exposure of HTSPb(Ac)2@NFs to 10 simulated halitosis breaths (See images in Figure S11). A decrease in the values after exposure implies that HTS-Pb(Ac)2@NFs are capable of detecting 1 ppm of H2S even in human breath containing thousands of interfering gases with negligible variations. In Figure 5d, 10 dark brown diamonds displayed in the ∆RGB space were located for ∆R, ∆G, and ∆B values from each simulated breath sample. Similarly, black circles were plotted in the space matching with ∆R, ∆G, and ∆B values calculated upon exposure of HTS-Pb(Ac)2@NFs to various concentrations of H2S in humid air. Plotting made it possible to confirm that a cluster of dark brown diamonds was formed between 0.8 and 1 ppm of H2S in humid air. Therefore, we can reasonably expect that the use of RGB to analyze sensing performance of HTSPb(Ac)2@NFs allows for estimates of concentrations of H2S existing in breath, suggesting possible application to colorimetric sensors for diagnosis of halitosis.
In summary, we took advantage of ball-milling, low melting temperature (75 ˚C) of trihydrate lead(II) acetate, and electrospinning to synthesis Pb(Ac)2@NFs for H2S colorimetric sensors. Nanoscale Pb(Ac)2 particles were readily achieved through high temperature stirring (HTS) of the electrospinning solution containing Pb(Ac)2 microparticles followed by quenching of the solution at 25 °C. Subsequent electrospinning of the solution enabled a facile synthesis of HTS-Pb(Ac)2@NFs. Uniform anchoring of Pb(Ac)2 particles on NFs scaffold prevented aggregation, and maintained the particle sizes on nanoscale even above 50 °C despite dependence of dye sizes on temperature. HTS-Pb(Ac)2@NFs sensors exhibited noticeable color change on exposure to H2S of 1 ppm at 90% RH. The excellent sensing property of Pb(Ac)2@NFs based sensors was achieved without introduction of additional equipment and controlling of surrounding environment. Through RGB analysis, it was confirmed that HTSPb(Ac)2@NFs can detect as low as 400 ppb of H2S. Furthermore, high feasibility for application to selective diagnosis of halitosis by selectively detecting H2S in exhaled breath was confirmed through demonstration of breath tests with simulated halitosis breath.
ASSOCIATED CONTENT Supporting Information. “This material is available free of charge via the Internet at http://pubs.acs.org.” AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]
Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Ministry of Science, ICT & Future Planning through Biomedical Treatment Technology Development Project (2015M3A9D7067418). This work was also supported
by
Wearable
Platform
Materials
Technology
Center
(WMC)
(NRF-
2016R1A5A1009926) funded by the NRF of Korea government (Ministry of Science, ICT and Future Planning). This research was also supported by Multi-Ministry Collaborative R&D Program (Development of Techniques for Identification and Analysis of Gas Molecules to Protect Against Toxic Substances) through the National Research Foundation of Korea (NRF) funded by KNPA, MSIT, MOTIE, ME, NFA (2017M3D9A1073501). REFERENCES (1) Khalid, T. Y.; Saad, S.; Greenman, J.; Costello, B. D.; Probert, C. S. J.; Ratcliffe, N. M. J. Breath Res. 2013, 7, 017114. (2) Tseliou, E.; Bessa, V.; Hillas, G.; Delimpoura, V.; Papadaki, G.; Roussos, C.; Papiris, S.; Bakakos, P.; Loukides, S. CHEST 2010, 138, 107-113. (3) Timmer, B.; Olthuis, W.; van den Berg, A. Sens. Actuators, B 2005, 107, 666-677. (4) Peng, G.; Tisch, U.; Adams, O.; Hakim, M.; Shehada, N.; Broza, Y. Y.; Billan, S.; AbdahBortnyak, R.; Kuten, A.; Haick, H. Nat. Nanotech. 2009, 4, 669-673. (5) Dong, L.; Shen, X. Z.; Deng, C. H. Anal. Chim. Acta. 2006, 569, 91-96. (6) Kim, S.-J.; Choi, S.-J.; Jang, J.-S.; Cho, H.-J.; Kim, I.-D. Acc. Chem. Res. 2017, 50, 15871596.. (7) Konvalina, G.; Haick, H. Acc. Chem. Res. 2014, 47, 66-76. (8) Hakim, M.; Broza, Y. Y.; Barash, O.; Peled, N.; Phillips, M.; Amann, A.; Haick, H. Chem. Rev. 2012, 112, 5949-5966. (9) Broza, Y. Y.; Haick, H. Nanomedicine 2013, 8, 785-806. (10) Turner, A. P. F.; Magan, N. Nat. Rev. Microbiol. 2004, 2, 161-166. (11) Jang, J. S.; Yu, S. M.; Choi, S. J.; Kim, S. J.; Koo, W. T.; Kim, I. D. Small 2016, 12, 59895997. (12) Choi, S. J.; Kim, S. J.; Koo, W. T.; Cho, H. J.; Kim, I. D. Chem. Commun. 2015, 51, 26092612. (13) Choi, S. J.; Lee, I.; Jang, B. H.; Youn, D. Y.; Ryu, W. H.; Park, C. O.; Kim, I. D. Anal. Chem. 2013, 85, 1792-1796. (14) Kim, I. D.; Rothschild, A.; Lee, B. H.; Kim, D. Y.; Jo, S. M.; Tuller, H. L. Nano Lett. 2006, 6, 2009-2013. (15) Choi, S. J.; Persano, L.; Camposeo, A.; Jang, J. S.; Koo, W. T.; Kim, S. J.; Cho, H. J.; Kim, I. D.; Pisignano, D. Macromol. Mater. Eng. 2017, 302, 1600569.
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Figure 1. Schematic illustrations of (a) high temperature stirring (HTS), (b) electrospinning for synthesis of Pb(Ac)2@NFs, and (c) color change of Pb(Ac)2@NFs on exposure to H2S gas molecules.
Figure 2. Scanning electron microscopy (SEM) images of (a) ball-milled Pb(Ac)2 particles, (b) ball-milled Pb(Ac)2 particles after oven-drying at 50 ˚C for 12 h, Pb(Ac)2 particles after HTS process (c) with and (d) without PAN polymer, (e) HTS-Pb(Ac)2@NFs, and (f) a strand of HTSPb(Ac)2@NFs (scale bar in the inset corresponds to 500 nm).
Figure 3. Scanning electron microscopy (SEM) images of (a) DMF wet ball-milled Pb(Ac)2 particles, (b) DMF wet ball-milled Pb(Ac)2 particles after oven-drying at 50 ˚C for 30 min. Photography images of color change obtained from HTS-Pb(Ac)2@NFs on exposure to 5 ppm of H2S for 1 min (c) before and (d) after oven-drying.
Figure 4. Photography images of HTS-Pb(Ac)2@NFs after (a) exposure to various concentrations (5 to 1 ppm) of H2S for 1 min, (b) exposure to 1 ppm of H2S for various exposure times (50 to 10 s), and (c) exposure to H2S the concentration range from 800 to 100 ppb for 1 min (The insets indicate images modified to +20 % lightness and -40 % contrast). (d) RGB sum variations of HTS-Pb(Ac)2@NFs on exposure to 5 ppm of various gases (acetone, NO2, NH3, CO, CH4, and methyl mercaptan (CH3SH)) for 1 min (insets display cropped images before and after exposure).
Figure 5. (a) RGB sum variations of HTS-Pb(Ac)2@NFs and RTS-Pb(Ac)2@NFs on exposure to various concentrations of H2S for 1 min, (b) RGB color change profile of HTS-Pb(Ac)2@NFs after exposure to 1 ppm of H2S for 1 ppm for exposure times from 60 to 10 s), (c) RGB sum profile of HTS-Pb(Ac)2@NFs before and after exposure to simulated halitosis breath with 1 ppm of H2S for 1 min and (d) RGB color change coordinates: RGB variations of HTS-Pb(Ac)2@NFs in humid air containing various concentration of H2S (black circles) and in simulated exhaled breath with 1 ppm of H2S (dark brown diamonds) for the exposure time of 1 min.
Table 1. ∆E values obtained from RGB values of HTS-Pb(Ac)2@NFs images before and after exposure to 1 ppm of H2S during various exposure times (50 to 10 s), and exposure to 800 to 100 ppb of H2S for 1 min.
