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Selective detection of picric acid using functionalized reduced graphene oxide sensor device
Sensors and Actuators B 196 (2014) 567–573
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Selective detection of picric acid using functionalized reduced graphene oxide sensor device Jiarui Huang a,∗ , Liyou Wang a , Chengcheng Shi a , Yijuan Dai a , Cuiping Gu a,∗ , Jinhuai Liu b a
College of Chemistry and Materials Science, Center for Nano Science and Technology, Anhui Normal University, Wuhu 241000, PR China Research Center for Biomimetic Functional Materials and Sensing Devices, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031, PR China b
a r t i c l e
i n f o
Article history: Received 19 June 2013 Received in revised form 2 February 2014 Accepted 13 February 2014 Available online 22 February 2014 Keywords: Graphene Reduced graphene oxide Picric acid -Cyclodextrin Sensor
a b s t r a c t A reduced graphene oxide sensor device was fabricated through self-assembling graphene oxide onto an interdigitated gold microelectrode followed by electrochemically reducing. After modification with 1pyrenebutyl-amino--cyclodextrin, the sensor exhibits high sensitivity and selectivity to picric acid. The sensor response (I) increases linearly with concentration in the range of 5 M to 215 M. The sensitivity and detection limit of this method were estimated to be 0.00613 A M−1 and 0.54 M, respectively. The improved performance can be attributed to the unique structure of -cyclodextrin (hydrophobic internal cavity and hydrophilic external surface), which endows its great tendency to integrate with hydrophobic –NO2 groups of picric acid. Picric acid extracted from real water by ether can be determined effectively with this method, which demonstrates that the present method is sensitive and suitable for the determination of picric acid in drinking water sources. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Phenol is one of the most common organic water pollutants, because it is toxic even at low concentrations for human and animals [1–3]. Picric acid, one of the various phenols, will do massive damages to human eyes, skin and respiratory systems [4]. The detection of picric acid is of great importance because a large amount of industries such as organic synthesis and drugs analysis all inevitably involve picric acid [5], which imposes severe risks on human health and the environment. As a consequence, many efforts have been devoted to the development of efficient technologies for the determination of picric acid in the environment. In the past decades, various approaches have been explored to quantify the picric acid effluents, such as fluorimetry chemical technologies [6], chemical methods [7], capillary electrophoresis [8] and spectrophotometry [9]. For example, Venkatramaiah et al., have successfully developed a fluorescent chemosensor based on fluoranthene for the detection of picric acid, in which static fluorescence quenching is the dominant process by intercalative
∗ Corresponding author. Tel.: +86 553 3869 303/+86 138 553 93091; fax: +86 553 3869 303. E-mail addresses: [email protected] (J. Huang), [email protected] (C. Gu). http://dx.doi.org/10.1016/j.snb.2014.02.050 0925-4005/© 2014 Elsevier B.V. All rights reserved.
– interactions between fluoranthene and nitroaromatics [6]. Junqueira et al., have reported an electrochemical method for quantitative analysis of picric acid explosive based on its electrochemical reduction at copper surfaces [7]. Parham et al., have reported a spectrophotometric method for removal, preconcentration and determination of trace amounts of picric acid in water samples [9]. However, most of these methods require a complicated sample pretreatment process, long analysis time, expensive instruments and some of them may also bring secondary pollutants, which limited their applications in the determination of picric acid in real samples. Hence, it is still essential to further explore a new analytical technique with simple operation. It is widely recognized that graphene, a two dimensional monolayer sheet of sp2 hybridized carbon [10], is a novel and highly promising carbon material due to its unique nanostructure and extraordinary properties [11–13], such as good mechanical flexibility [14], large surface area [15] and excellent electrical conductivity [16], etc. People have investigated these properties [17] and fabricated various microelectrical devices, such as field-effect transistors [18–21], ultrasensitive sensors [22–26], and electromechanical resonators [27]. In addition, cyclodextrins (CDs) are famous for forming an inclusion complex with multiple guest molecules due to their special molecular structure-hydrophobic internal cavity and hydrophilic external surface [28,29]. The novel structure endows them with great tendency to combine with
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hydrophobic groups -NO2 of picric acid. Therefore, a graphene sensor modified with -cyclodextrin could be an effective method for detection of picric acid. In this paper, we report a novel method for the determination of picric acid using a reduced graphene oxide (rGO) sensor modified with 1-pyrenebutyl-amino--cyclodextrin (PyCD). The PyCD-rGO sensor can be fabricated through four steps involving the synthesis of graphene oxide (GO), the self-assembly of GO, the electrochemical reduction of graphene oxide (rGO) and modification with PyCD. Both the rGO sensor and PyCD-rGO sensor exhibit good sensitivity and recovery to picric acid. As expected, the PyCD-rGO sensor exhibits higher response and wider linear range to picric acid than rGO sensor.
kept at room temperature for one day. The precipitate which formed was collected by filtration and washed with acetone and deionized water to give a pale yellow solid (0.17 g, 68%). 1 H NMR (300 MHz, DMSO-d6 ) ␦: 1.07–3.0 (m, 4H, NCH2 CH2 N), 3.30–3.64 (m, CD-H2-6), 4.50 (s, 2H, CH2 CO), 4.51–4.70 (m, 6H, CD-OH6), 4.84–4.90 (m, 7H, CD-H1), 5.71–5.77 (m, 14H, CD-OH2), 7.74–8.41 (m, 9H, pyrene-H) ppm; IR (KBr) : 3391.60, 2929.85, 1651.38, 1545.34, 1420.25, 154.27, 1139.20, 950.47, 852.71, 763.79, 710.57, 577.46 cm−1 ; UV–vis max : 267, 325 nm (pyrene-); HRMS (EI) Calcd. for C62 H86 O35 N2 : 1418.5088, found 1419.9923 [M + H]+ , 1442.4538 [M + Na]+ .
2. Experimental details
The interdigitated gold microelectrode (gold 20 nm, titanium 10 nm) with 20-m gaps was fabricated using electron beam lithography on a Si wafer with a 1-m coating of SiO2 . The electrode was sonicated for 0.5 h and then rinsed thoroughly with deionized water several times. In a typical procedure, 0.2 L of GO dispersion was pipetted onto the surface of the interdigitated electrode. After about 5 h, the homogeneous dispersion would diffuse to form a GO film which connected the channel of the electrode, followed by drying in air for 4 h. After that two gold wires were welded on the soldered dots by silver paste and dried at 120 ◦ C for 6 h. Ultimately, the GO sensor with two gold wires as a working electrode was immersed into 20 mM KH2 PO4 solution and a cathodic potential of −0.7 V was applied to the GO sensor by using potentiostat for about 10 min [32]. In this way, the rGO sensor was successfully prepared after the GO film was reduced to rGO film. PyCD decoration of rGO sensor: Before assembling PyCD molecules on the rGO surface, the device was washed with DMF twice. Then 0.1 g of PyCD was dissolved in 5 mL DMF. Subsequently, the device was dipped into PyCD solution for 12 h and then washed with deionized water several times. Fig. 1 illustrates the fabrication process of rGO sensor. The reduction of GO and all electrical measurements were performed on an electrochemical workstation (BAS Epsilon).
2.1. Synthesis and characterization of graphene oxide All the chemicals are of analytical grade and used as received without further purification. The graphene oxide was synthesized from graphite flakes using a modified Hummers method involving the steps of graphite oxidation, exfoliation [30]. Typically, 180 mL of concentrated H2 SO4 and 20 mL of concentrated H3 PO4 were slowly added to a mixture of 1.0 g of graphite and 6.0 g of KMnO4 with continuous stirring and cooling. Then the mixture was heated to 50 ◦ C and stirred for 12 h. The reaction was cooled to room temperature and poured onto 400 mL ice with 3 mL 30% H2 O2 . The obtained product was collected by centrifugation, washed repeatedly with deionized water, 30% HCl and ethanol and vacuum-dried overnight at room temperature. Finally, 5 mg of as-synthesized GO nanosheets were dispersed in deionized water (20 mL) by ultrasonic treatment for 12 h to form a homogeneous dispersion. The sensor devices were characterized by scanning electron microscopy (SEM, Hitachi S-4800, operated at 5.0 kV) and atomic force microscopy (AFM, SPA-300HV &SPI3800N, Seiko). The Raman spectra of GO and rGO were obtained at room temperature with an Olympus BX41 Micro-Raman spectrometer in back-scattering geometry with the laser excitation of 532 nm at a power level of 1.7 mW.
2.3. Fabrication of rGO sensor
3. Results and discussion 3.1. Structure and morphology of the sensor
2.2. Synthesis of PyCD Mono-6-deoxy-6-amino--cyclodextrin (-CD-NH2 , 98.5%) was purchased from Shandong Binzhou Zhiyuan Bio-Technology Co., Ltd. 1 H NMR (300 MHz, D2 O) ␦: 2.75-2.95 (t, 2H, NH2 ), 3.00–3.15 (m, 28H, H4, H5, H6), 3.40–3.70 (m, 13H, OH-6, H3), 3.70–4.00 (d, 7H, H2), 5.03 (m, 21H, OH-2,3, H1) ppm. IR (KBr) : 3414.16, 2934.35, 1642.35, 1411.47, 1152.77, 1133.19, 949.72, 700.79, 582.22 cm−1 ; HRMS (EI) Calcd. For C42 H71 O34 N: 1133.3934, found 1134.4175 [M + H]+ . Preparation of 1-pyrenebutyl-amino--cyclodextrin [31]: acid (0.06 g, 0.2 mmol), N-(3-dimethyl1-pyrenebutylic aminopropyl)-N -ethylcarbodiimide hydrochloride (EDC·HCl, 0.0383 g, 0.2 mmol), 4-methylmorpholine N-oxide (NMM, 0.0404 g, 0.4 mmol) and 6-chloro-1-hydroxibenzotriazol (CHBT, 0.0339 g, 0.2 mmol) were dissolved in N,N-dimethylformamide (DMF, 10 mL) in the presence of a small amount of molecular sieves under an atmosphere of N2 . A DMF solution (5 mL) of -CD-NH2 (0.2 g, 0.18 mmol) was then added dropwise. The mixture was stirred for one day in an ice bath and then for another day at room temperature, before being left to stand for 5 h until no more precipitate deposited. The precipitate was removed by filtration, and the filtrate was poured into acetone (50 mL). The precipitate formed in acetone was collected by filtration. The crude product was dissolved in deionized water (10 mL) and
Structure of the sensor device and morphology of the GO film were characterized by SEM. Fig. 2a and b show the SEM images of the sensor device. It clearly shows that the uniformly formed interdigitated electrodes were separated by a 20 m gap. GO film deposited on the interdigitated electrodes was verified by SEM, as shown in Fig. 2c and d. Compared with Fig. 2a and c demonstrates that continuous and uniform GO film is deposited on the gap between the interdigitated electrodes. The GO film deposited on sensor device displays the characteristic wrinkle morphology, as observed in the SEM image (Fig. 2d), which further verifies the high dispersibility of the GO. Furthermore, it should be noted here that the polar surface functional groups made GO highly dispersible in aqueous medium. Therefore, GO dispersion can form an even and uniform film on the interdigitated electrodes. AFM analysis was employed to characterize the thickness of the GO film deposited on the sensor device. Fig. 3 shows the AFM image and the height profile of GO film. A continuous and uniform GO film was observed. The thickness of the prepared GO film was 1.0–3.6 nm, corresponding to 1–3 layers of GO film. The average thickness of GO sheets was about 1.0 nm, which was in good agreement with previous reports [33]. The surface root-mean-square roughness (Rq ) of the GO film was analyzed. The Rq value of the GO film was 2.75 nm, which were comparable to those of GO films prepared by Wang et al. [34]. Fig. 4 shows the typical Raman spectra of GO and rGO on the sensor
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Fig. 1. Schematic demonstration of the fabrication process of the rGO based sensor. (a) Self-assembly of GO, (b) electrochemical reduction of GO and modification with PyCD, (c) sensing measurement.
substrate. The Raman spectrum of GO, rGO displays a D-band at 1345 cm−1 and a G-band at 1599 cm−1 . The D-to-G band intensity ratio (ID /IG ) of rGO was calculated to be 1.08, which is higher than that of GO (0.902), suggesting the formation of new sp2 clusters upon reduction [35]. 3.2. Electrical property of the sensors The rGO was modified with a cyclodextrin derivative due to its hydrophobic inner cavity and hydrophilic outer surface, which acts as a good receptor for organic molecule in aqueous solution. -cyclodextrin consisting of seven glucopyranose units is an external hydrophilic and internal oil-wet hydrophobic cavity structure molecular. The unique structure endows its great tendency to form inclusion complex with numerous of hydrophobic organic com˚ pounds. Furthermore, the cavity size of -cyclodextrin is 6–6.5 A, which matches well with size of benzene molecule. Therefore, cyclodextrin is chosen for recognizing picric acid. As we known, pyrene can stack on the surface of rGO by – interactions. So PyCD was synthesized and modified onto the surface of rGO for detecting picric acid. Before fabricating rGO sensor, the device was sonicated for half an hour to remove the stain covered on the device. The
stain may connect the interdigitated electrodes and influence the electrical conductivity of the sensor device. To identify the electrical properties of the GO sensor, rGO sensor and PyCD-rGO sensor, current versus voltage (I–V) analyses were carried out. Linear I–V plots of rGO sensor and PyCD-rGO sensor (Fig. 5) in voltage range from −1.0 V to +1.0 V had linear ohmic behavior. In comparison with rGO sensor, the GO sensor output very weak current signal upon varying the applied voltage (Fig. 5), which indicates that GO is typically insulating. Because the sp2 bonded graphitic structure is destroyed by the electronegative oxygen atoms in oxygen functional groups [36]. Compared with the GO counterpart, the electrical conductivity of the rGO is dramatically improved and also higher than chemically reduced graphene oxide [37]. After modified with PyCD, the sensor exhibits stable I–V curve and outstanding electrical conductivity as shown in Fig. 5. Because rGO is a p-type semiconductor (hole-transporting) [38,39] and –OH is an electron-withdrawing group, the modification of rGO with –OH groups (-cyclodextrin) leads rGO to be further hole-doped [37]. Hence, the conductance of the PyCD-rGO sensor increased significantly. These results demonstrate that PyCD has been assembled onto rGO surface. As a result, recognition of the phenols can be monitored by observing the conductance of the PyCD-rGO sensor.
Fig. 2. SEM images of the pristine device (a and b) and GO film on the Au electrodes (c and d).
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Fig. 5. Current versus voltage (I–V) curves of GO sensor, rGO sensor and PyCD-rGO sensor. (Vds scan rate = 10 mV s−1 ).
Fig. 3. AFM image of GO film as deposited on the sensor.
3.3. Phenols-sensing properties of the sensors Fig. 6a shows the PyCD-rGO sensor responses for various concentrations of picric acid. It can be seen that the response current increases dramatically with the increase of the concentration of picric acid. Fig. 6b shows the average change in current (I) with concentration of picric acid (The response data for picric acid
Fig. 4. Raman spectrum of the GO and rGO films as deposited on the sensor showing the D band at 1345 cm−1 , the G band at 1599 cm−1 .
was measured for 3 times). At a low concentration of picric acid (5 M), the sensor response (I) is approximately 0.0095 A, and the response time was 5 s. The sensor response increases linearly with concentration in the range of 5 M to 215 M. The straight line obeys the equation (I = −0.0192 + 0.00613(Cpicric acid /(M)) (R = 0.9976). The sensitivity determined using the slope of the calibration plot between 5 M and 215 M was found to be, on an average, 0.00613 A M−1 . According to the IUPAC rules, the limit of detection is derived from the smallest measure that can be detected with reasonable certainty for a given analytical procedure. The limit of detection can be determined as 3Sb /m in according to IUPAC, where Sb is the standard deviation of three measures of blank and m is the sensitivity. The detection limit of this method was estimated to be 0.54 M, which is much below the permissible concentration (2.2 M) in drinking water source set by the China (GB 3838-2002) [40]. The detection limit of the proposed method is also higher than that of electrochemical method (6.0 M) [7]. However, the detection limit of the proposed method is lower than those of spectrophotometric method (0.031 M) [9] and fluorescent oligofluoranthene chemosensor (6.0 pM) [41]. For comparison, the sensing property of rGO sensor was also investigated. Fig. 6c shows the responses of rGO sensor upon exposure to picric acid with different concentrations. It can be seen that the sensor response increases slowly with the increase of the concentration of picric acid. From Fig. 6d, it can be clearly seen that the sensor response increases linearly with concentration in the range of 5 M to 65 M. After that the sensor response increases slowly with the increase of the concentration of picric acid. The sensitivity determined using the slope of the calibration plot between 5 M and 65 M (R = 0.99945) was found to be, on an average, 0.00728 A M−1 . The slight increase in sensor conductance is attributed to the electron-withdrawing –NO2 groups of picric acid, which has the equivalent effect of the hole carrier injection into the p-type rGO sensor. The schematic view of sensor structure and its interaction with picric acid are offered, as presented in Fig. 7. As we expected, the PyCD-rGO sensor exhibits wider linear range to picric acid than rGO sensor. The superior performance of the PyCD-rGO sensor is ascribed to the special recognition of PyCD for picric acid. For one reason, the –NO2 groups of picric acid are electron-withdrawing groups, tending to adsorb on electron-rich sites such as the lone-pair electrons of O atoms in –OH groups of -cyclodextrin and increase the doping level of the rGO film. For another reason, the –NO2 groups are hydrophobic groups. When encountering -cyclodextrin, the –NO2 groups can be bitten by the hydrophobic cavity and form an inclusion complex. Therefore, the
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Fig. 6. Real time response curve and average sensor response of the PyCD-rGO sensor upon exposure to different concentrations of picric acid (a and b); Real time response curve and average sensor response of the rGO sensor upon exposure to different concentrations of picric acid (c and d). The response data for each concentration was measured for 3 times.
conductance of the PyCD-rGO sensor increases dramatically when it is exposure to picric acid. Compared with rGO sensor, PyCD-rGO sensor exhibits wider linear range to picric acid because it can integrate with more picric acid molecule. Furthermore, the PyCD-rGO sensor exhibits good reversibility when it is washed with deionized water. Hence, PyCD-rGO sensor can be used to detect specific phenol with high selectivity and affinity. To further investigate the sensing property of the as-prepared sensor, another three kinds of phenols (p-cresol, 2,4-xylenol, 2nitrophenol) have been tested. Fig. 8a displays the response curves
Fig. 7. Schematic view of sensor structure and its interaction with picric acid molecule.
of the sensor to p-cresol, 2,4-xylenol and 2-nitrophenol with concentrations in the range of 25 M to 525 M, 12.5 M to 562 M, and 12.5 M to 450 M, respectively. The sensitivities of the sensor to p-cresol, 2,4-xylenol and 2-nitrophenol determined using the slope of the calibration plot were found to be 0.00046 A M−1 , 0.00026 A M−1 and 0.00071 A M−1 , respectively. In according to IUPAC, the detection limit of sensor to p-cresol, 2,4-xylenol and 2-nitrophenol were estimated to be 7.2 M, 12.7 M and 4.6 M, respectively. It can been seen that PyCD-rGO sensor also exhibits sensor response to p-cresol, 2,4-xylenol and 2-nitrophenol with low sensitivities. Fig. 8b displays sensor responses of the PyCD-rGO sensor for 500 M picric acid, p-cresol, 2,4-xylenol and 2-nitrophenol, respectively. Obviously, the PyCD-rGO sensor exhibits excellent selectivity for picric acid. p-cresol, 2,4-xylenol and 2-nitrophenol only slightly increased the conductance of the PyCD-rGO sensor. Similar to picric acid, p-cresol, 2,4-xylenol and 2nitrophenol also have hydrophobic groups and can form inclusion complexes with -cyclodextrin, which can increase the conductance of the PyCD-rGO sensor. Different from the –NO2 , –CH3 is an electron-donating group and it can weaken the withdrawing ability of the groups on -cyclodextrin. As a result, the hole carrier density of rGO film is partly decreased and the conductance of the PyCD-rGO sensing film increases slightly when it is exposure to p-cresol and 2,4-xylenol. Compared with p-cresol comprising one –CH3 group, 2,4-xylenol comprising two –CH3 groups can further weaken the withdrawing ability of the groups on -cyclodextrin and exhibits lower response. On the contrary, the –NO2 group of 2nitrophenol makes it exhibit higher response than those of p-cresol and 2,4-xyleno. This matches well with our experimental results. Furthermore, additional five PyCD-rGO sensors were fabricated
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standard deviation of the responses is 0.48% (n = 10). This result demonstrates that the PyCD-rGO sensor has a well stability. 4. Conclusions In summary, we have developed a simple way to fabricate rGO sensor by self-assembling GO on the interdigitated gold microelectrode followed by electrochemically reducing. The rGO sensor was modified with 1-pyrenebutyl-amino--cyclodextrin through – interactions. The PyCD-rGO sensor exhibits good sensitivity and selectivity to picric acid. Compared with rGO sensor, PyCD-rGO sensor exhibits wider linear range to picric acid. The improved performance is attributed to the unique structure of -cyclodextrin (hydrophobic internal cavity and hydrophilic external surface), which endows its great tendency to integrate with hydrophobic –NO2 groups of picric acid. The fact that the picric acid in real water is extracted by ether and determined effectively with this method has been reconfirmed. Therefore, the present method is sensitive and suitable for the determination of picric acid in drinking water sources. Acknowledgments This work was supported by the National Nature Science Foundation of China (Project nos. 21105001, 61203212), Anhui Provincial Natural Science (Project no. 10040606Q34), and ¨ “973State Key Project of Fundamental Research for Nanoscience and Nanotechnology (2011CB933700). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2014.02.050. Fig. 8. (a) Real time response curves and sensor responses (insert) of PyCD-rGO sensor to different concentrations of p-cresol, 2,4-xylenol and 2-nitrophenol; (b) average responses of PyCD-rGO sensor to 500 M picric acid, p-cresol, 2,4-xylenol and 2-nitrophenol. The response data for each target was measured for 3 times.
under the same process. Four of them exhibited similar sensing property, which suggests the good repeatability of the PyCD-rGO sensors. To assay real water samples, picric acid in real water (obtained from Changjiang River) was extracted by ether, and then determined using the PyCD-rGO sensor. For example, 50.0 mL picric acid water sample was extracted for 6 min by 2.0 mL ether. The responses of PyCD-rGO sensor to different concentrations of picric acid in Changjiang River water were shown in Fig. S4. The sensor response increases linearly with concentration in the range of 2 M to 20 M. The straight line obeys the equation (I = 0.2111 + 0.01328(Cpicric acid /(M)) (R = 0.9986). The sensitivity determined using the slope of the calibration plot between 2 M and 20 M was found to be 0.01328 A M−1 . The detection limit of this method was estimated to be 0.28 M in according to IUPAC, which is also below the permissible concentration (2.2 M) in drinking water source set by the China (GB 3838-2002). The fact that the picric acid in real water can be extracted and determined effectively with this method has thus been reconfirmed. Therefore, the present method is precise, sensitive and suitable for the determination of picric acid in drinking water sources. The sensing stability of the PyCD-rGO sensor is very important for its further application. So we monitored the responses of PyCD-rGO sensor upon exposure to 20 M picric acid for ten times in ten days, as shown in Fig. S5. It can be seen that the sensor responses have not shown obvious decrease and the relative
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Biographies Jiarui Huang was born in Shouxian Anhui Province. He received the B.S. degree in chemistry from Anhui Normal University, College of Chemistry and Materials Science, in 2000 and the M.S. degree in synthetic organic chemistry from Nanjing University of Technology, Chemistry Department, in 2003 and the Ph.D. degree in inorganic chemistry from University of Science and Technology of China, Department of Chemistry, in 2006. He is an associate professor of Inorganic Chemistry at Anhui Normal University. Now his work mainly focuses on the sensing materials, gas sensor and biochemistry sensors. Liyou Wang was born in Anqing Anhui Province. She received the B.S. degree in chemistry from Anqing Teachers College, Chemistry Department in 2012. She is currently working toward the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Chengcheng Shi was born in Fuyang Anhui Province. She received the B.S. degree in chemistry from Anqing Teachers College, Chemistry Department in 2011. She is currently working toward the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Yijuan Dai was born in Shouxian Anhui Province. She received the B.S. degree in Chemistry from Anqing Teachers College, Department of Chemical and Chemical Engineering, in 2010. She is currently working towards the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Cuiping Gu was born in Xuancheng Anhui Province. She received the B.S. degree in chemistry from Anhui Normal University, College of Chemistry and Materials Science, in 2000 and the M.S. degree in polymer chemistry from Anhui University, School of Chemistry and Chemical Engineering, in 2005 and the Ph.D. degree in inorganic chemistry from Anhui University, School of Chemistry and Chemical Engineering, in 2008. She is a lecturer of inorganic chemistry at Anhui Normal University. Now her work mainly focuses on the sensing materials and biochemistry sensors. Jinhuai Liu was born in Bengbu Anhui Province. He received the B.S. in inorganic chemistry from Yunnan University, in 1982 and the Ph.D. degree in inorganic chemistry from Institute of Plasma Physics, Chinese Academy of Science, in 2003. He is a Professor & Vice Director of Hefei Institute of Intelligent Machines, CAS, a Editor ¨ a group leader of nanomaof “International Journal of Information Acquisitionand terials and nanosensors. Prof. Liu has focused his research primarily on sensitive material, bionic material, nanomaterial and nanodevice, and sensitive technology.
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Selective detection of picric acid using functionalized reduced graphene oxide sensor device Jiarui Huang a,∗ , Liyou Wang a , Chengcheng Shi a , Yijuan Dai a , Cuiping Gu a,∗ , Jinhuai Liu b a
College of Chemistry and Materials Science, Center for Nano Science and Technology, Anhui Normal University, Wuhu 241000, PR China Research Center for Biomimetic Functional Materials and Sensing Devices, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031, PR China b
a r t i c l e
i n f o
Article history: Received 19 June 2013 Received in revised form 2 February 2014 Accepted 13 February 2014 Available online 22 February 2014 Keywords: Graphene Reduced graphene oxide Picric acid -Cyclodextrin Sensor
a b s t r a c t A reduced graphene oxide sensor device was fabricated through self-assembling graphene oxide onto an interdigitated gold microelectrode followed by electrochemically reducing. After modification with 1pyrenebutyl-amino--cyclodextrin, the sensor exhibits high sensitivity and selectivity to picric acid. The sensor response (I) increases linearly with concentration in the range of 5 M to 215 M. The sensitivity and detection limit of this method were estimated to be 0.00613 A M−1 and 0.54 M, respectively. The improved performance can be attributed to the unique structure of -cyclodextrin (hydrophobic internal cavity and hydrophilic external surface), which endows its great tendency to integrate with hydrophobic –NO2 groups of picric acid. Picric acid extracted from real water by ether can be determined effectively with this method, which demonstrates that the present method is sensitive and suitable for the determination of picric acid in drinking water sources. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Phenol is one of the most common organic water pollutants, because it is toxic even at low concentrations for human and animals [1–3]. Picric acid, one of the various phenols, will do massive damages to human eyes, skin and respiratory systems [4]. The detection of picric acid is of great importance because a large amount of industries such as organic synthesis and drugs analysis all inevitably involve picric acid [5], which imposes severe risks on human health and the environment. As a consequence, many efforts have been devoted to the development of efficient technologies for the determination of picric acid in the environment. In the past decades, various approaches have been explored to quantify the picric acid effluents, such as fluorimetry chemical technologies [6], chemical methods [7], capillary electrophoresis [8] and spectrophotometry [9]. For example, Venkatramaiah et al., have successfully developed a fluorescent chemosensor based on fluoranthene for the detection of picric acid, in which static fluorescence quenching is the dominant process by intercalative
∗ Corresponding author. Tel.: +86 553 3869 303/+86 138 553 93091; fax: +86 553 3869 303. E-mail addresses: [email protected] (J. Huang), [email protected] (C. Gu). http://dx.doi.org/10.1016/j.snb.2014.02.050 0925-4005/© 2014 Elsevier B.V. All rights reserved.
– interactions between fluoranthene and nitroaromatics [6]. Junqueira et al., have reported an electrochemical method for quantitative analysis of picric acid explosive based on its electrochemical reduction at copper surfaces [7]. Parham et al., have reported a spectrophotometric method for removal, preconcentration and determination of trace amounts of picric acid in water samples [9]. However, most of these methods require a complicated sample pretreatment process, long analysis time, expensive instruments and some of them may also bring secondary pollutants, which limited their applications in the determination of picric acid in real samples. Hence, it is still essential to further explore a new analytical technique with simple operation. It is widely recognized that graphene, a two dimensional monolayer sheet of sp2 hybridized carbon [10], is a novel and highly promising carbon material due to its unique nanostructure and extraordinary properties [11–13], such as good mechanical flexibility [14], large surface area [15] and excellent electrical conductivity [16], etc. People have investigated these properties [17] and fabricated various microelectrical devices, such as field-effect transistors [18–21], ultrasensitive sensors [22–26], and electromechanical resonators [27]. In addition, cyclodextrins (CDs) are famous for forming an inclusion complex with multiple guest molecules due to their special molecular structure-hydrophobic internal cavity and hydrophilic external surface [28,29]. The novel structure endows them with great tendency to combine with
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hydrophobic groups -NO2 of picric acid. Therefore, a graphene sensor modified with -cyclodextrin could be an effective method for detection of picric acid. In this paper, we report a novel method for the determination of picric acid using a reduced graphene oxide (rGO) sensor modified with 1-pyrenebutyl-amino--cyclodextrin (PyCD). The PyCD-rGO sensor can be fabricated through four steps involving the synthesis of graphene oxide (GO), the self-assembly of GO, the electrochemical reduction of graphene oxide (rGO) and modification with PyCD. Both the rGO sensor and PyCD-rGO sensor exhibit good sensitivity and recovery to picric acid. As expected, the PyCD-rGO sensor exhibits higher response and wider linear range to picric acid than rGO sensor.
kept at room temperature for one day. The precipitate which formed was collected by filtration and washed with acetone and deionized water to give a pale yellow solid (0.17 g, 68%). 1 H NMR (300 MHz, DMSO-d6 ) ␦: 1.07–3.0 (m, 4H, NCH2 CH2 N), 3.30–3.64 (m, CD-H2-6), 4.50 (s, 2H, CH2 CO), 4.51–4.70 (m, 6H, CD-OH6), 4.84–4.90 (m, 7H, CD-H1), 5.71–5.77 (m, 14H, CD-OH2), 7.74–8.41 (m, 9H, pyrene-H) ppm; IR (KBr) : 3391.60, 2929.85, 1651.38, 1545.34, 1420.25, 154.27, 1139.20, 950.47, 852.71, 763.79, 710.57, 577.46 cm−1 ; UV–vis max : 267, 325 nm (pyrene-); HRMS (EI) Calcd. for C62 H86 O35 N2 : 1418.5088, found 1419.9923 [M + H]+ , 1442.4538 [M + Na]+ .
2. Experimental details
The interdigitated gold microelectrode (gold 20 nm, titanium 10 nm) with 20-m gaps was fabricated using electron beam lithography on a Si wafer with a 1-m coating of SiO2 . The electrode was sonicated for 0.5 h and then rinsed thoroughly with deionized water several times. In a typical procedure, 0.2 L of GO dispersion was pipetted onto the surface of the interdigitated electrode. After about 5 h, the homogeneous dispersion would diffuse to form a GO film which connected the channel of the electrode, followed by drying in air for 4 h. After that two gold wires were welded on the soldered dots by silver paste and dried at 120 ◦ C for 6 h. Ultimately, the GO sensor with two gold wires as a working electrode was immersed into 20 mM KH2 PO4 solution and a cathodic potential of −0.7 V was applied to the GO sensor by using potentiostat for about 10 min [32]. In this way, the rGO sensor was successfully prepared after the GO film was reduced to rGO film. PyCD decoration of rGO sensor: Before assembling PyCD molecules on the rGO surface, the device was washed with DMF twice. Then 0.1 g of PyCD was dissolved in 5 mL DMF. Subsequently, the device was dipped into PyCD solution for 12 h and then washed with deionized water several times. Fig. 1 illustrates the fabrication process of rGO sensor. The reduction of GO and all electrical measurements were performed on an electrochemical workstation (BAS Epsilon).
2.1. Synthesis and characterization of graphene oxide All the chemicals are of analytical grade and used as received without further purification. The graphene oxide was synthesized from graphite flakes using a modified Hummers method involving the steps of graphite oxidation, exfoliation [30]. Typically, 180 mL of concentrated H2 SO4 and 20 mL of concentrated H3 PO4 were slowly added to a mixture of 1.0 g of graphite and 6.0 g of KMnO4 with continuous stirring and cooling. Then the mixture was heated to 50 ◦ C and stirred for 12 h. The reaction was cooled to room temperature and poured onto 400 mL ice with 3 mL 30% H2 O2 . The obtained product was collected by centrifugation, washed repeatedly with deionized water, 30% HCl and ethanol and vacuum-dried overnight at room temperature. Finally, 5 mg of as-synthesized GO nanosheets were dispersed in deionized water (20 mL) by ultrasonic treatment for 12 h to form a homogeneous dispersion. The sensor devices were characterized by scanning electron microscopy (SEM, Hitachi S-4800, operated at 5.0 kV) and atomic force microscopy (AFM, SPA-300HV &SPI3800N, Seiko). The Raman spectra of GO and rGO were obtained at room temperature with an Olympus BX41 Micro-Raman spectrometer in back-scattering geometry with the laser excitation of 532 nm at a power level of 1.7 mW.
2.3. Fabrication of rGO sensor
3. Results and discussion 3.1. Structure and morphology of the sensor
2.2. Synthesis of PyCD Mono-6-deoxy-6-amino--cyclodextrin (-CD-NH2 , 98.5%) was purchased from Shandong Binzhou Zhiyuan Bio-Technology Co., Ltd. 1 H NMR (300 MHz, D2 O) ␦: 2.75-2.95 (t, 2H, NH2 ), 3.00–3.15 (m, 28H, H4, H5, H6), 3.40–3.70 (m, 13H, OH-6, H3), 3.70–4.00 (d, 7H, H2), 5.03 (m, 21H, OH-2,3, H1) ppm. IR (KBr) : 3414.16, 2934.35, 1642.35, 1411.47, 1152.77, 1133.19, 949.72, 700.79, 582.22 cm−1 ; HRMS (EI) Calcd. For C42 H71 O34 N: 1133.3934, found 1134.4175 [M + H]+ . Preparation of 1-pyrenebutyl-amino--cyclodextrin [31]: acid (0.06 g, 0.2 mmol), N-(3-dimethyl1-pyrenebutylic aminopropyl)-N -ethylcarbodiimide hydrochloride (EDC·HCl, 0.0383 g, 0.2 mmol), 4-methylmorpholine N-oxide (NMM, 0.0404 g, 0.4 mmol) and 6-chloro-1-hydroxibenzotriazol (CHBT, 0.0339 g, 0.2 mmol) were dissolved in N,N-dimethylformamide (DMF, 10 mL) in the presence of a small amount of molecular sieves under an atmosphere of N2 . A DMF solution (5 mL) of -CD-NH2 (0.2 g, 0.18 mmol) was then added dropwise. The mixture was stirred for one day in an ice bath and then for another day at room temperature, before being left to stand for 5 h until no more precipitate deposited. The precipitate was removed by filtration, and the filtrate was poured into acetone (50 mL). The precipitate formed in acetone was collected by filtration. The crude product was dissolved in deionized water (10 mL) and
Structure of the sensor device and morphology of the GO film were characterized by SEM. Fig. 2a and b show the SEM images of the sensor device. It clearly shows that the uniformly formed interdigitated electrodes were separated by a 20 m gap. GO film deposited on the interdigitated electrodes was verified by SEM, as shown in Fig. 2c and d. Compared with Fig. 2a and c demonstrates that continuous and uniform GO film is deposited on the gap between the interdigitated electrodes. The GO film deposited on sensor device displays the characteristic wrinkle morphology, as observed in the SEM image (Fig. 2d), which further verifies the high dispersibility of the GO. Furthermore, it should be noted here that the polar surface functional groups made GO highly dispersible in aqueous medium. Therefore, GO dispersion can form an even and uniform film on the interdigitated electrodes. AFM analysis was employed to characterize the thickness of the GO film deposited on the sensor device. Fig. 3 shows the AFM image and the height profile of GO film. A continuous and uniform GO film was observed. The thickness of the prepared GO film was 1.0–3.6 nm, corresponding to 1–3 layers of GO film. The average thickness of GO sheets was about 1.0 nm, which was in good agreement with previous reports [33]. The surface root-mean-square roughness (Rq ) of the GO film was analyzed. The Rq value of the GO film was 2.75 nm, which were comparable to those of GO films prepared by Wang et al. [34]. Fig. 4 shows the typical Raman spectra of GO and rGO on the sensor
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Fig. 1. Schematic demonstration of the fabrication process of the rGO based sensor. (a) Self-assembly of GO, (b) electrochemical reduction of GO and modification with PyCD, (c) sensing measurement.
substrate. The Raman spectrum of GO, rGO displays a D-band at 1345 cm−1 and a G-band at 1599 cm−1 . The D-to-G band intensity ratio (ID /IG ) of rGO was calculated to be 1.08, which is higher than that of GO (0.902), suggesting the formation of new sp2 clusters upon reduction [35]. 3.2. Electrical property of the sensors The rGO was modified with a cyclodextrin derivative due to its hydrophobic inner cavity and hydrophilic outer surface, which acts as a good receptor for organic molecule in aqueous solution. -cyclodextrin consisting of seven glucopyranose units is an external hydrophilic and internal oil-wet hydrophobic cavity structure molecular. The unique structure endows its great tendency to form inclusion complex with numerous of hydrophobic organic com˚ pounds. Furthermore, the cavity size of -cyclodextrin is 6–6.5 A, which matches well with size of benzene molecule. Therefore, cyclodextrin is chosen for recognizing picric acid. As we known, pyrene can stack on the surface of rGO by – interactions. So PyCD was synthesized and modified onto the surface of rGO for detecting picric acid. Before fabricating rGO sensor, the device was sonicated for half an hour to remove the stain covered on the device. The
stain may connect the interdigitated electrodes and influence the electrical conductivity of the sensor device. To identify the electrical properties of the GO sensor, rGO sensor and PyCD-rGO sensor, current versus voltage (I–V) analyses were carried out. Linear I–V plots of rGO sensor and PyCD-rGO sensor (Fig. 5) in voltage range from −1.0 V to +1.0 V had linear ohmic behavior. In comparison with rGO sensor, the GO sensor output very weak current signal upon varying the applied voltage (Fig. 5), which indicates that GO is typically insulating. Because the sp2 bonded graphitic structure is destroyed by the electronegative oxygen atoms in oxygen functional groups [36]. Compared with the GO counterpart, the electrical conductivity of the rGO is dramatically improved and also higher than chemically reduced graphene oxide [37]. After modified with PyCD, the sensor exhibits stable I–V curve and outstanding electrical conductivity as shown in Fig. 5. Because rGO is a p-type semiconductor (hole-transporting) [38,39] and –OH is an electron-withdrawing group, the modification of rGO with –OH groups (-cyclodextrin) leads rGO to be further hole-doped [37]. Hence, the conductance of the PyCD-rGO sensor increased significantly. These results demonstrate that PyCD has been assembled onto rGO surface. As a result, recognition of the phenols can be monitored by observing the conductance of the PyCD-rGO sensor.
Fig. 2. SEM images of the pristine device (a and b) and GO film on the Au electrodes (c and d).
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Fig. 5. Current versus voltage (I–V) curves of GO sensor, rGO sensor and PyCD-rGO sensor. (Vds scan rate = 10 mV s−1 ).
Fig. 3. AFM image of GO film as deposited on the sensor.
3.3. Phenols-sensing properties of the sensors Fig. 6a shows the PyCD-rGO sensor responses for various concentrations of picric acid. It can be seen that the response current increases dramatically with the increase of the concentration of picric acid. Fig. 6b shows the average change in current (I) with concentration of picric acid (The response data for picric acid
Fig. 4. Raman spectrum of the GO and rGO films as deposited on the sensor showing the D band at 1345 cm−1 , the G band at 1599 cm−1 .
was measured for 3 times). At a low concentration of picric acid (5 M), the sensor response (I) is approximately 0.0095 A, and the response time was 5 s. The sensor response increases linearly with concentration in the range of 5 M to 215 M. The straight line obeys the equation (I = −0.0192 + 0.00613(Cpicric acid /(M)) (R = 0.9976). The sensitivity determined using the slope of the calibration plot between 5 M and 215 M was found to be, on an average, 0.00613 A M−1 . According to the IUPAC rules, the limit of detection is derived from the smallest measure that can be detected with reasonable certainty for a given analytical procedure. The limit of detection can be determined as 3Sb /m in according to IUPAC, where Sb is the standard deviation of three measures of blank and m is the sensitivity. The detection limit of this method was estimated to be 0.54 M, which is much below the permissible concentration (2.2 M) in drinking water source set by the China (GB 3838-2002) [40]. The detection limit of the proposed method is also higher than that of electrochemical method (6.0 M) [7]. However, the detection limit of the proposed method is lower than those of spectrophotometric method (0.031 M) [9] and fluorescent oligofluoranthene chemosensor (6.0 pM) [41]. For comparison, the sensing property of rGO sensor was also investigated. Fig. 6c shows the responses of rGO sensor upon exposure to picric acid with different concentrations. It can be seen that the sensor response increases slowly with the increase of the concentration of picric acid. From Fig. 6d, it can be clearly seen that the sensor response increases linearly with concentration in the range of 5 M to 65 M. After that the sensor response increases slowly with the increase of the concentration of picric acid. The sensitivity determined using the slope of the calibration plot between 5 M and 65 M (R = 0.99945) was found to be, on an average, 0.00728 A M−1 . The slight increase in sensor conductance is attributed to the electron-withdrawing –NO2 groups of picric acid, which has the equivalent effect of the hole carrier injection into the p-type rGO sensor. The schematic view of sensor structure and its interaction with picric acid are offered, as presented in Fig. 7. As we expected, the PyCD-rGO sensor exhibits wider linear range to picric acid than rGO sensor. The superior performance of the PyCD-rGO sensor is ascribed to the special recognition of PyCD for picric acid. For one reason, the –NO2 groups of picric acid are electron-withdrawing groups, tending to adsorb on electron-rich sites such as the lone-pair electrons of O atoms in –OH groups of -cyclodextrin and increase the doping level of the rGO film. For another reason, the –NO2 groups are hydrophobic groups. When encountering -cyclodextrin, the –NO2 groups can be bitten by the hydrophobic cavity and form an inclusion complex. Therefore, the
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Fig. 6. Real time response curve and average sensor response of the PyCD-rGO sensor upon exposure to different concentrations of picric acid (a and b); Real time response curve and average sensor response of the rGO sensor upon exposure to different concentrations of picric acid (c and d). The response data for each concentration was measured for 3 times.
conductance of the PyCD-rGO sensor increases dramatically when it is exposure to picric acid. Compared with rGO sensor, PyCD-rGO sensor exhibits wider linear range to picric acid because it can integrate with more picric acid molecule. Furthermore, the PyCD-rGO sensor exhibits good reversibility when it is washed with deionized water. Hence, PyCD-rGO sensor can be used to detect specific phenol with high selectivity and affinity. To further investigate the sensing property of the as-prepared sensor, another three kinds of phenols (p-cresol, 2,4-xylenol, 2nitrophenol) have been tested. Fig. 8a displays the response curves
Fig. 7. Schematic view of sensor structure and its interaction with picric acid molecule.
of the sensor to p-cresol, 2,4-xylenol and 2-nitrophenol with concentrations in the range of 25 M to 525 M, 12.5 M to 562 M, and 12.5 M to 450 M, respectively. The sensitivities of the sensor to p-cresol, 2,4-xylenol and 2-nitrophenol determined using the slope of the calibration plot were found to be 0.00046 A M−1 , 0.00026 A M−1 and 0.00071 A M−1 , respectively. In according to IUPAC, the detection limit of sensor to p-cresol, 2,4-xylenol and 2-nitrophenol were estimated to be 7.2 M, 12.7 M and 4.6 M, respectively. It can been seen that PyCD-rGO sensor also exhibits sensor response to p-cresol, 2,4-xylenol and 2-nitrophenol with low sensitivities. Fig. 8b displays sensor responses of the PyCD-rGO sensor for 500 M picric acid, p-cresol, 2,4-xylenol and 2-nitrophenol, respectively. Obviously, the PyCD-rGO sensor exhibits excellent selectivity for picric acid. p-cresol, 2,4-xylenol and 2-nitrophenol only slightly increased the conductance of the PyCD-rGO sensor. Similar to picric acid, p-cresol, 2,4-xylenol and 2nitrophenol also have hydrophobic groups and can form inclusion complexes with -cyclodextrin, which can increase the conductance of the PyCD-rGO sensor. Different from the –NO2 , –CH3 is an electron-donating group and it can weaken the withdrawing ability of the groups on -cyclodextrin. As a result, the hole carrier density of rGO film is partly decreased and the conductance of the PyCD-rGO sensing film increases slightly when it is exposure to p-cresol and 2,4-xylenol. Compared with p-cresol comprising one –CH3 group, 2,4-xylenol comprising two –CH3 groups can further weaken the withdrawing ability of the groups on -cyclodextrin and exhibits lower response. On the contrary, the –NO2 group of 2nitrophenol makes it exhibit higher response than those of p-cresol and 2,4-xyleno. This matches well with our experimental results. Furthermore, additional five PyCD-rGO sensors were fabricated
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standard deviation of the responses is 0.48% (n = 10). This result demonstrates that the PyCD-rGO sensor has a well stability. 4. Conclusions In summary, we have developed a simple way to fabricate rGO sensor by self-assembling GO on the interdigitated gold microelectrode followed by electrochemically reducing. The rGO sensor was modified with 1-pyrenebutyl-amino--cyclodextrin through – interactions. The PyCD-rGO sensor exhibits good sensitivity and selectivity to picric acid. Compared with rGO sensor, PyCD-rGO sensor exhibits wider linear range to picric acid. The improved performance is attributed to the unique structure of -cyclodextrin (hydrophobic internal cavity and hydrophilic external surface), which endows its great tendency to integrate with hydrophobic –NO2 groups of picric acid. The fact that the picric acid in real water is extracted by ether and determined effectively with this method has been reconfirmed. Therefore, the present method is sensitive and suitable for the determination of picric acid in drinking water sources. Acknowledgments This work was supported by the National Nature Science Foundation of China (Project nos. 21105001, 61203212), Anhui Provincial Natural Science (Project no. 10040606Q34), and ¨ “973State Key Project of Fundamental Research for Nanoscience and Nanotechnology (2011CB933700). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2014.02.050. Fig. 8. (a) Real time response curves and sensor responses (insert) of PyCD-rGO sensor to different concentrations of p-cresol, 2,4-xylenol and 2-nitrophenol; (b) average responses of PyCD-rGO sensor to 500 M picric acid, p-cresol, 2,4-xylenol and 2-nitrophenol. The response data for each target was measured for 3 times.
under the same process. Four of them exhibited similar sensing property, which suggests the good repeatability of the PyCD-rGO sensors. To assay real water samples, picric acid in real water (obtained from Changjiang River) was extracted by ether, and then determined using the PyCD-rGO sensor. For example, 50.0 mL picric acid water sample was extracted for 6 min by 2.0 mL ether. The responses of PyCD-rGO sensor to different concentrations of picric acid in Changjiang River water were shown in Fig. S4. The sensor response increases linearly with concentration in the range of 2 M to 20 M. The straight line obeys the equation (I = 0.2111 + 0.01328(Cpicric acid /(M)) (R = 0.9986). The sensitivity determined using the slope of the calibration plot between 2 M and 20 M was found to be 0.01328 A M−1 . The detection limit of this method was estimated to be 0.28 M in according to IUPAC, which is also below the permissible concentration (2.2 M) in drinking water source set by the China (GB 3838-2002). The fact that the picric acid in real water can be extracted and determined effectively with this method has thus been reconfirmed. Therefore, the present method is precise, sensitive and suitable for the determination of picric acid in drinking water sources. The sensing stability of the PyCD-rGO sensor is very important for its further application. So we monitored the responses of PyCD-rGO sensor upon exposure to 20 M picric acid for ten times in ten days, as shown in Fig. S5. It can be seen that the sensor responses have not shown obvious decrease and the relative
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Biographies Jiarui Huang was born in Shouxian Anhui Province. He received the B.S. degree in chemistry from Anhui Normal University, College of Chemistry and Materials Science, in 2000 and the M.S. degree in synthetic organic chemistry from Nanjing University of Technology, Chemistry Department, in 2003 and the Ph.D. degree in inorganic chemistry from University of Science and Technology of China, Department of Chemistry, in 2006. He is an associate professor of Inorganic Chemistry at Anhui Normal University. Now his work mainly focuses on the sensing materials, gas sensor and biochemistry sensors. Liyou Wang was born in Anqing Anhui Province. She received the B.S. degree in chemistry from Anqing Teachers College, Chemistry Department in 2012. She is currently working toward the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Chengcheng Shi was born in Fuyang Anhui Province. She received the B.S. degree in chemistry from Anqing Teachers College, Chemistry Department in 2011. She is currently working toward the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Yijuan Dai was born in Shouxian Anhui Province. She received the B.S. degree in Chemistry from Anqing Teachers College, Department of Chemical and Chemical Engineering, in 2010. She is currently working towards the M.S. degree at Anhui Normal University. Now her work mainly focuses on the sensing materials and chemical sensors. Cuiping Gu was born in Xuancheng Anhui Province. She received the B.S. degree in chemistry from Anhui Normal University, College of Chemistry and Materials Science, in 2000 and the M.S. degree in polymer chemistry from Anhui University, School of Chemistry and Chemical Engineering, in 2005 and the Ph.D. degree in inorganic chemistry from Anhui University, School of Chemistry and Chemical Engineering, in 2008. She is a lecturer of inorganic chemistry at Anhui Normal University. Now her work mainly focuses on the sensing materials and biochemistry sensors. Jinhuai Liu was born in Bengbu Anhui Province. He received the B.S. in inorganic chemistry from Yunnan University, in 1982 and the Ph.D. degree in inorganic chemistry from Institute of Plasma Physics, Chinese Academy of Science, in 2003. He is a Professor & Vice Director of Hefei Institute of Intelligent Machines, CAS, a Editor ¨ a group leader of nanomaof “International Journal of Information Acquisitionand terials and nanosensors. Prof. Liu has focused his research primarily on sensitive material, bionic material, nanomaterial and nanodevice, and sensitive technology.