Fluorescent nanofibrous membrane (FNFM) for the detection of mercuric ion (II) with high sensitivity and selectivity

Sensors and Actuators B 238 (2017) 120–127

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Fluorescent nanofibrous membrane (FNFM) for the detection of mercuric ion (II) with high sensitivity and selectivity Lijing Ma, Kelan Liu, Meizhen Yin ∗ , Jiao Chang, Yuting Geng, Kai Pan ∗ State Key Laboratory of Chemical Resource Engineering, Key laboratory of carbon fiber and functional polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing, 100029, China

a r t i c l e

i n f o

Article history: Received 25 February 2016 Received in revised form 12 July 2016 Accepted 12 July 2016 Available online 14 July 2016 Keywords: Electrospinning Nanofibrous membrane Mercuric ion detection Sensor

a b s t r a c t A highly sensitive and selective fluorescent nanofibrous membrane (FNFM) for the detection of mercuric ions (II) was prepared via electrospinning and subsequent immobilization. In this process, fluorescent chemosensor dithioacetal-modified perylenediimide (DTPDI) was introduced on the surface of polyacrylonitrile (PAN) nanofibers with high stability under mechanical force by electrostatic interaction. Because DTPDI can be detached from PAN nanofibers due to the hydrolysis of dithioacetals in the presence of Hg2+ and form an oil-soluble fluorescence dye AL. According to the linear correlation between AL and Hg2+ , the obtained FNFM could be employed for the detection of Hg2+ . Results reveal that the FNFM exhibits high sensitivity for the detection of Hg2+ and no interference from other metal ions. The limit of detection for Hg2+ can reach as low as 1 ppb. In addition, the strong fluorescence of FNFM still can be observed even after the repeated use for 7 times. Therefore, FNFM can be developed as a rapid, portable and stable sensor for the detection of Hg2+ . Moreover, FNFM can execute other functions by changing the probe immobilized on the surface of nanofiber. © 2016 Elsevier B.V. All rights reserved.

1. Introduction In recent years, heavy metal pollution has become more and more serious especially in developing countries [1,2]. These heavy metals produced from various industrial sources result in serious hazards to human health even at a low concentration because they are not biodegradable and tend to accumulate in living organisms [3–5]. Mercury, one of the most toxic heavy metal elements, can induce the aberration in microtubules, ion channels, and mitochondria in human body [6]. Moreover, mercuric ion can be converted into methyl mercury by aquatic microorganisms, which is extremely toxic and can damage central nervous system [7–9]. The Environmental Protection Agency (EPA) in United States recommends 2 ppb as the maximum allowable limit for the discharge of Hg2+ into drinking water [10]. Due to its high toxicity and wide application in industry, the development of rapid, highly sensitive and economic detection methods for mercury has been a major concern in analytical chemistry [11]. Several technologies such as inductively coupled plasma mass spectrometry (ICP-MS), electrochemical method [12], gas chro-

∗ Corresponding authors. E-mail addresses: [email protected] (M. Yin), [email protected] (K. Pan). http://dx.doi.org/10.1016/j.snb.2016.07.049 0925-4005/© 2016 Elsevier B.V. All rights reserved.

matography (GC), and atomic absorption/emission spectrometry (AAS/AES) have been developed for the detection of Hg2+ [13–15]. However, these detection methods still have many limitations including the requirements of complex instrumentation and tedious sample preparation. Compared to other methods, sensors are more simple and effective [16–24]. Up to now, many efforts have been made to fabricate chemical sensors based on the strong thiophilic affinity of Hg2+ [25–30]. But the molecules immobilized onto a solid substrate for the detection of mercury are relatively rare [31–34]. Most of chemical sensors should be dissolved in a solution for application, which hinders their practical applications. Therefore, many studies are focused on the preparation of solid-state sensor materials because of the preferred advantages such as operational simplicity, portability, and reusability [35–37]. More recently, the uniform and continuous three-dimensional (3D) nanofiber obtained by electrospinning method as a very versatile and scalable technique has been widely used as solid substrate for its large specific surface area and convenient preparation [38–41]. The relatively large amount of available surface area and high porosity of electrospun nanofibrous membrane has attracted tremendous attentions because these properties can meet the desired requirements for ultrasensitive sensors [42–44]. Inspired by above works, we presented a facile and attractive method to prepare FNFM for the effective detection of Hg2+ in water. In our previous studies, we have reported a chemical fluores-

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

121

Scheme 1. Schematic illustration for the fabrication of FNFM.

cent mercury sensor, a water-soluble dithioacetal-functionalized perylenediimide (DTPDI) with high fluorescence quantum yield [45]. In the present study, DTPDI was introduced on the surface of electrospun PAN nanofibrous membrane to prepare FNFM. Because of the large specific surface area, Hg2+ could attach FNFM effectively and react with DTPDI quickly which relating to high sensitivity for the detection. Remarkably, this procedure promoted the coalescence of fluorescence sensor on the surface of nanofiber to yield a nanostructure fluorescent membrane that can be used as a reliable and stable analytical material for the detection of Hg2+ at the low concentration of 1 ppb in water. 2. Experimental 2.1. Materials Polyacrylonitrile (PAN) (Mw = 150,000 g/mol) was purchased from Sigma-Aldrich Co., Ltd. (Shanghai China). Dimethylformamide (DMF), dichloromethane, sodium hydroxide (NaOH), hydrochloric acid (HCl), ethanol, mercury nitrate (Hg(NO3 )2 ) and chlorate salts of metal ion (K+ , Na+ , Mg2+ , Ca2+ , Cu2+ , Zn2+ , Fe2+ , Fe3+ , Pb2+ , Cr3+ ) were supplied by Beijing Chemical Co., Ltd. (Beijing, China). All reagents were of analytical grade and directly used as received without further purification. Deionized water (distilled) was purified through a Pgeneral pure water system in our laboratory. 2.2. Fabrication of PAN nanofibrous membranes The PAN nanofibrous membranes were prepared by electrospinning method. The detailed process can be found in our previous research [46,47]. Typically, the procedure for electrospinning of PAN nanofibers was as following: The precursor PAN solution used for electrospinning was prepared by dissolving PAN in DMF at 60 ◦ C by gentle magnetic stirring for 12 h. The spinning solution was loaded into syringe with a settled vertically spinneret (D = 0.7 mm). The PAN nanofibers were collected on the aluminium foil at a high voltage ranging from 13 to 16 kV at ambient temperature of 22–25 ◦ C and relative air humidity of 30–35%. The solution feed

rate was 1.0 mL/h, and the distance between the collector and the spinneret was 10 cm. After electrospinning 4 h, the resulting PAN nanofibrous membranes were dried in vacuum oven at 60 ◦ C till constant weight. 2.3. Preparation of FNFM The resulting PAN nanofibrous membranes were firstly hydrolyzed in 10% sodium hydroxide aqueous solution at 60 ◦ C for 2 h. The hydrolyzed PAN nanofibrous membranes, which was negatively charged, was thoroughly washed and rinsed with deionized water before using as the support for immobilization of DTPDI. Then the hydrolyzed PAN nanofibrous membranes (40 mg) were immersed in 50 mL DTPDI aqueous solution (9.1 wt%). The mixture was shaken (100 rpm) in a thermostatic shaker bath at 25 ◦ C for 2 h. Finally, the PAN nanofibrous membranes were taken out, and washed with deionized water for several times to remove the residual DTPDI. The resulting FNFM was dried in vacuum oven at 60 ◦ C till constant weight and then kept in a dry closed box before using. 2.4. Preparation of analyte solutions A stock solution of Hg2+ (1 ppm) was prepared by dissolving an appropriate amount of Hg(NO3 )2 in water and adjusting the volume to 100 mL in a volumetric flask. This was further diluted from 1 ppm to 1 ppb stepwise. The highest concentration was independently confirmed by inductively coupled plasma-optical emission spectrometer. The other metal ions including K+ , Na+ , Mg2+ , Ca2+ , Cu2+ , Zn2+ , Fe2+ , Fe3+ , Pb2+ and Cr3+ were diluted appropriately with water to prepare the analyte solutions (10 ppm). 2.5. Sensing experiments All experiments were carried out at the ambient temperature of 25 ◦ C. For Hg2+ sensing measurement, the FNFM (1.5 mg) was immersed into mentioned Hg2+ solution for 2 h, after thoroughly washed with deionized water, the nanofibrous membranes were dried in vacuum oven. And then, the FNFM was washed with 2 mL

122

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

Fig. 1. SEM image of PAN nanofibers (a), nanofiber diameter distribution (b), and pore diameter distribution (c).

instrument equipped using Al K␣ X-ray source at 0.5 eV. The porosity and pore size distributions of PAN nanofibrous membrane were studied by mercury intrusion porosimetry. The pore size distributions were calculated from the mercury intrusion date by applying the Washburn equation. A contact angle of 140◦ was used for the calculation as well as a surface tension of 480 ergs. The surface morphology of nanofibers was examined by scanning electron microscopy (SEM, Hitachi S-4700, Japan). Hg2+ and other ions concentration were measured with an inductively coupled plasma mass spectrometry (ICP, 7700 series, Agilent technologies). CLSM micrographs were obtained with a Fluo View 500confocal laser scanning microscope (Olympus, Japan). The UV–vis spectra were obtained using TU-1810 UV–vis spectrometer (UV; Pgeneral TU-1810 spectrometer, China). 3. Results and discussion 3.1. Preparation and characterization of FNFM Fig. 2. ATR-FTIR spectra of PAN nanofibrous membrane (a), hydrolyzed PAN nanofibrous membrane (b), and FNFM (c). The enlargement of FNFM is shown in the inset.

dichloromethane, afterwards the UV–vis spectrometer was used to confirm the detection limit of Hg2+ by measuring the absorption spectra of dichloromethane washing solution. To study the selectivity of FNFM for Hg2+ , a similar procedure was carried out for different metal ions in water (K+ , Na+ , Mg2+ , Ca2+ , Cu2+ , Zn2+ , Fe2+ , Fe3+ , Pb2+ and Cr3+ ). 2.6. Investigation of durability For the investigation of durability of the nanofibrous membranes, the FNFM was immersed into mentioned Hg2+ solution for 2 h, and then thoroughly washed with dichloromethane. Next, the FNFM was reused several times, and the corresponding UV–vis absorption spectra were measured. For confocal laser scanning microscopy (CLSM), the nanofibers were coated on separate glass slides and dipped in Hg2+ solution for 2 h. After being washed with dichloromethane, images were taken at a magnification of 100 multiple. 2.7. Characterization The chemical structure of PAN nanofibrous membranes and FNFM were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR, Perkin-Elmer, USA). X-ray photoelectron spectroscopy (XPS; Thermo Electron Corporation ESCALAB 250, USA) and energy dispersive X-ray spectrometer (EDS, GENESIE 2000) was used to confirm the elemental composition on the sample surface, XPS data was recorded on a Kratos Axis Ultra DLD

A schematic illustration of fabrication process for FNFM is demonstrated in Scheme 1. The process was composed of three steps. First, PAN nanofibers were obtained via electrospinning method. Second, the prepared PAN nanofibers were treated with sodium hydroxide solution to introduce carboxyl groups on their surface. Finally, the hydrolyzed PAN nanofibers were immersed in DTPDI solution. Then, FNFM was successfully obtained via electrostatic interaction between negatively charged nanofibers and positively charged DTPDI. In the present study, nanofibers were fabricated via electrospinning from DMF solution containing 8% PAN. By controlling the electrospinning parameters such as voltage and speed, PAN nanofibers with smooth surface, small diameters and narrow diameter distribution were obtained, as shown in Fig. 1. The prepared PAN nanofibers exhibited an average diameter of 250 ± 70 nm and uniform morphology without the formation of beads. Because of the disordered arrangement of nanofibers, porous structure was formed in PAN nanofibrous membrane with the feature of large specific surface area. The high surface area-to-volume ratio and unique porous structure will be beneficial for sensing application. Furthermore, the porosity of PAN nanofibrous membrane can reach up to 80% (measured by mercury intrusion porosimetry), which will be another advantage for sensing application due to lower water-transferring resistance. As shown in Fig. 1c, the pore size distribution of PAN nanofibrous membrane was broad and in the range of 1–5 ␮m. These features of electrospun nanofibrous membrane provide their potential applications in ultrasensitive sensors. In order to confirm the preparation of FNFM, ATR-FTIR spectra of PAN nanofibrous membrane, hydrolyzed PAN nanofibrous membrane, and FNFM were recorded (Fig. 2). Compared with PAN nanofibrous membrane, the ATR-FTIR spectra of FNFM showed the characteristic peak of PAN, such as the peak at 2242 cm−1 due to the

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

123

Fig. 3. SEM images of PAN nanofibrous membrane (a), FNFM (b), and CLSM image of FNFM (␭ex = 552 nm) (c).

Fig. 4. SEM images of FNFM (a), EDS surface analysis of FNFM (b), XPS measurement of FNFM (c), and S 2p core-level spectrum of FNFM (d).

stretching of C N groups, the peaks at 2938 cm−1 (CH stretching) and 1454 cm−1 (CH bending) with high intensity corresponding to the vibration of CH and CH2 groups, respectively [48]. However, for FNFM, two new absorption peaks around 1500 cm−1 and 1590 cm−1 were observed, which are attributed to the symmetrical deformation vibration and asymmetrical deformation vibration of N H in −NH3 + [49]. These results indicate that DTPDI is immobilized on the surface of PAN nanofibers successfully. The SEM images of PAN nanofibrous membrane and FNFM are shown in Fig. 3a and b, respectively. The smooth PAN nanofiber surface and the narrow diameter distribution were observed, which was consistent with the result in Fig. 1b. After the immobilization of DTPDI, only coarse surface of nanofibers without other change were observed (Fig. 3b). In addition, the immobilization of DTPDI on the surface of PAN nanofibers was confirmed through confocal laser scanning microscopy (CLSM). As shown in Fig. 3c, a strong red fluorescence emission of the nanofibers could be observed even by naked eyes, which only comes from DTPDI. The CLSM result is another evidence to prove the immobilization of DTPDI on the surface of PAN nanofibers.

Furthermore, the compositions of FNFM were analyzed by EDS. As shown in Fig. 4b. FNFM was composed of C, N, O and S elements. But pure PAN did not reveal the presence of S. Therefore, S elements should be come from DTPDI, and the Au peak in the spectrum should be come from gold conductive film plated on the surface of the sample through SEM observation. Similarly, XPS measurements were also used to confirm the surface chemical compositions of PAN nanofibrous membrane and FNFM (Fig. 4c). Compared with pure PAN, XPS spectra of FNFM showed 2p spectrum of S and a peak at 172.05 eV. All these results confirm that FNFM has been successfully fabricated. 3.2. Sensing mechanism of FNFM to Hg2+ The sensing mechanism of FNFM to Hg2+ was proposed (Fig. 5). Because of the special sulfur-mercury affinity, DTPDI can rapidly react with Hg2+ and result in the formation of its hydrolysate, AL. When FNFM was immersed in Hg2+ aqueous solution, the C-S-C bonds of DTPDI immobilized on the surface of PAN nanofibers were broken to produce AL, and then the oil-soluble AL was adsorbed on DTPDI through ␲-␲ stacking. Non-polar solvent, such as

124

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

Fig. 5. Schematic illustration for the sensing of FNFM to Hg2+ .

dichloromethane, could dissolve AL without interrupting the interaction between DTPDI and PAN nanofibers. So dichloromethane was used to wash FNFM after immersion in Hg2+ aqueous solution in this process. AL was dissolved in dichloromethane and detached from FNFM while DTPDI was kept on the surface of PAN nanofibers. By measuring the absorption intensity at 561 nm from AL, we can directly determine the detection limit for Hg2+ . 3.3. The sensitivity of FNFM to Hg2+ In order to evaluate the sensing capacity of FNFM to Hg2+ , FNFM was immersed in Hg2+ aqueous solution with various concentrations in the range of 1 ppm to 1 ppb. Then, FNFM was washed with dichloromethane. The washing solution with dichloromethane turned red slowly, which could be easily observed by naked eyes. The UV–vis absorption spectra of dichloromethane solution were measured at room temperature. As shown in Fig. 6, the absorption at 561 nm corresponding to the absorption of AL confirmed that Hg2+ could react with DTPDI to produce AL. The absorption intensity at 561 nm with the monotonic increase as the increase of Hg2+ concentration from 1 ppb to 1 ppm was also observed. In addition, the significant absorption at 561 nm for 1 ppb Hg2+ aqueous solution indicates that FNFM still has better detection capability, and the limit of detection for Hg2+ can reach as low as 1 ppb. The detection limit is better than or at least comparable to previous reports [46,47], which meets the requirement for the detection limit of Hg2+ in drinking water defined by World Health Organization (6 ppb) and

U.S. Environmental Protection Agency (2 ppb). These results show that FNFM has excellent sensitivity for the detection of Hg2+ . 3.4. The selectivity of FNFM In most cases, water can be contaminated with many kinds of heavy metal ions. Here, the selectivity of FNFM was explored by testing the response to common environmentally relevant ions, including K+ , Na+ , Mg2+ , Ca2+ , Cu2+ , Zn2+ , Fe2+ , Fe3+ and Cr3+ ions at the concentrations of 10 ppm (Fig. 7a). FNFM was immersed into each solution for 2 h, and the UV–vis absorption spectra were measured after thoroughly washed with dichloromethane. To our delighted surprise, although the concentration of other metal ions revealed the increase by 10 times compared with Hg2+ , no change in absorbance was observed, except for the slight effect from Pb2+ . These observations clearly confirm that FNFM has excellent selectivity for Hg2+ . In addition, the sensing of FNFM to Hg2+ in the presence of other metal ions was also evaluated. As shown in Fig. 7b, it is clear that the coexistence of most selected metal ions does not interfere with the reaction between Hg2+ and DTPDI, indicating that these co-existent ions have negligible impact on Hg2+ sensing of FNFM. 3.5. The durability of FNFM The durability of the sensor contributes to economic and environmental benefits. In order to examine the durability of FNFM

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

125

Fig. 6. UV–vis absorption spectra in the presence of Hg2+ aqueous solution with various concentrations (a), plot of maximum absorbance versus amount of Hg2+ (b).

Fig. 7. (a) Absorbance of FNFM after immersed into the aqueous solution of metal ions (1 ppm for Hg2+ , and 10 ppm for other mental ions). (b) Absorbance of FNFM after immersed into the aqueous solution of Hg2+ (1 ppm) only, and the aqueous solution containing both Hg2+ (1 ppm) and miscellaneous ions (1 ppm), respectively.

Fig. 8. The durability of FNFM (20 ppb for Hg2+ ) (a), and CLSM image of FNFM with repeated use for 7 times (␭ex = 552 nm) (b).

for the detection of Hg2+ , the nanofibrous membrane was reused for several times. In this procedure, the concentration of Hg2+ was 20 ppb. After one cycle use, FNFM was washed with enough

dichloromethane to ensure no surplus AL on FNFM, and the corresponding UV–vis absorption spectra were measured. It is found that the absorption intensity of dichloromethane solution does not

126

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

reveal an obvious decrease even after repeated use for 7 times (Fig. 8a). The image on the top is their corresponding electronic pictures of dichloromethane solution. Almost no color change is observed in different bottles. The CLSM results of FNFM with repeated use for 7 times exhibited a strong red fluorescence (Fig. 7b), indicating that DTPDI immobilized on the surface of PAN nanofiber is enough for further application. Therefore, FNFM can be used as an economic analytical test for Hg2+ . 4. Conclusions A simple and economic process to fabricate FNFM for the detection of mercury ions has been developed. FNFM reveals excellent sensitivity and selectivity for Hg2+ . The detection limit of FNFM can reach as low as 1 ppb. In addition, the sensing of FNFM to Hg2+ is reversible and FNFM displays high durability for the detection of Hg2+ . Compared to small molecule chemosensors, FNFM has multiple advantages such as simple operation, portability and durability. Moreover, non-covalent bond combination between fluorescent probe and PAN nanofibrous membrane provides the convertibility of FNFM, and this fluorescent probe can be replaced by other kinds of sensors, which makes this approach as a widely applicable strategy. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51521062 and 21574009), the Beijing Natural Science Foundation (2142026), and Beijing Collaborative Innovative Research Center for Cardiovascular Diseases. References [1] D.L. Sparks, Toxic metals in the environment: the role of surfaces, Elements 1 (2005) 193–197. [2] M.A. Tofighy, T. Mohammadi, Adsorption of divalent heavy metal ions from water using carbon nanotube sheets, J. Hazard. Mater. 185 (2011) 140–147. [3] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Fluorescent and colorimetric sensors for detection of lead cadmium, and mercury ions, Chem. Soc. Rev. 41 (2012) 3210–3244. [4] F. Fu, Q. Wang, Removal of heavy metal ions from wastewaters: a review, J. Environ. Manage. 92 (2011) 407–418. [5] Y. Jiang, H. Pang, B. Liao, Removal of copper (II) ions from aqueous solution by modified bagasse, J. Hazard. Mater. 164 (2009) 1–9. [6] D.M. Nguyen, A. Frazer, L. Rodriguez, K.D. Belfield, Fluorescence sensing of zinc and mercury ions with hydrophilic 1,2,3-triazolyl fluorene probes, Chem. Mater. 22 (2010) 3472–3481. [7] E.M. Nolan, S.J. Lippard, Tools and tactics for the optical detection of mercuric ion, Chem. Rev. 108 (2008) 3443–3480. [8] P.B. Tchounwou, W.K. Ayensu, N. Ninashvili, D. Sutton, Environmental exposure to mercury and its toxicopathologic implications for public health, Environ. Toxicol. 18 (2003) 149–175. [9] H.H. Harris, I.J. Pickering, G.N. George, The chemical form of mercury in fish, Science 301 (2003), 1203–1203. [10] R.P. Mason, W.F. Fitzgerald, F.M. Morel, The biogeochemical cycling of elemental mercury: anthropogenic influences, Geochim. Cosmochim. Acta 58 (1994) 3191–3198 (United States Environmental Protection Agency Roadma for Mercury, 2006, EPA-HQ-OPPT-2005-0013). [11] F. Deiss, S. Laurent, E. Descamps, T. Livache, N. Sojic, Opto-electrochemical nanosensor array for remote DNA detection, Analyst 136 (2011) 327–331. [12] C. Chen, J. Zhang, Y. Du, X. Yang, E. Wang, Microfabricated on-chip integrated Au-Ag-Au three-electrode system for in situ mercury ion determination, Analyst 135 (2010) 1010–1014. [13] Y. Zhao, J. Zheng, L. Fang, Q. Lin, Y. Wu, Z. Xue, F. Fu, Speciation analysis of mercury in natural water and fish samples by using capillary electrophoresis-inductively coupled plasma mass spectrometry, Talanta 89 (2012) 280–285. [14] K. Leopold, M. Foulkes, P.J. Worsfold, Gold-coated silica as a preconcentration phase for the determination of total dissolved mercury in natural waters using atomic fluorescence spectrometry, Anal. Chem. 81 (2009) 3421–3428. [15] Y. Li, C. Chen, B. Li, J. Sun, J. Wang, Y. Gao, Y. Zhao, Z. Chai, Elimination efficiency of different reagents for the memory effect of mercury using ICP-MS, J. Anal. At. Spectrom. 21 (2006) 94–96. [16] S.V. Wegner, A. Okesli, P. Chen, C. He, Design of an emission ratiometric biosensor from MerR family proteins: a sensitive and selective sensor for Hg2+ , J. Am. Chem. Soc. 129 (2007) 3474–3475.

[17] P. Chen, C. He, A general strategy to convert the MerR family proteins into highly sensitive and selective fluorescent biosensors for metal ions, J. Am. Chem. Soc. 126 (2004) 728–729. [18] M. Sun, K. Müllen, M. Yin, Water-soluble perylenediimides: design concept and biological applications, Chem. Soc. Rev. (2016), http://dx.doi.org/10.1039/ c5cs00754b. [19] B. Xu, Y. Zhang, W. Liu, Hydrogen-bonding toughened hydrogels and emerging CO2 -responsive shape memory effect, Macromol. Rapid Commun. 36 (2015) 1585–1591. [20] K. Liu, Z. Xu, M. Yin, Perylenediimide-cored dendrimers and their bioimaging and gene delivery applications, Prog. Polym. Sci. 46 (2015) 25–54. [21] G. Wei, F. Xu, Z. Li, D.K. Jandt, Protein-promoted synthesis of Pt nanoparticles on carbon nanotubes for electrocatalytic nanohybrids with enhanced glucose sensing, J. Phys. Chem. C 115 (2011) 11453–11460. [22] M. Chen, M. Yin, Design and development of fluorescent nanostructures for bioimaging, Prog. Polym. Sci. 39 (2014) 365–395. [23] Z. Gao, Z. Lin, X. Chen, Z. Lai, Z. Huang, Carbon dots-based fluorescent probe for trace Hg2+ detection in water sample, Sens. Actuators B Chem. 222 (2016) 965–971. [24] M.L. Satnamia, S.K. Vaishanava, R. Nagwanshi, K.K. Ghosh, Spectrofluorometric determination of mercury and lead by colloidal CdS nanomaterial, J. Disper. Sci. Technol. 37 (2016) 196–204. [25] G. Chen, Z. Guo, G. Zeng, L. Tang, Fluorescent and colorimetric sensors for environmental mercury detection, Analyst 140 (2015) 5400–5443. [26] C. Yuan, K. Zhang, Z. Zhang, S. Wang, Highly selective and sensitive detection of mercuric ion based on a visual fluorescence method, Anal. Chem. 84 (2012) 9792–9801. [27] W. Lin, X. Cao, Y. Ding, L. Yuan, Q. Yu, A reversible fluorescent Hg2+ chemosensor based on a receptor composed of a thiol atom and an alkene moiety for living cell fluorescence imaging, Org. Biomol. Chem. 8 (2010) 3618–3620. [28] D. Zhang, M. Wang, C. Wang, M. Li, Y. Ye, Y. Zhao, Two highly sensitive and selective colorimetric off-on rhodamine-based fluorescent chemosensor for Hg (II) in aqueous media, J. Fluoresc. 23 (2013) 1045–1052. [29] J. Li, Y. Wu, F. Song, G. Wei, Y. Cheng, C. Zhu, A highly selective and sensitive polymer-based off-on fluorescent sensor for Hg2+ detection incorporating salen and perylenyl moieties, J. Mater. Chem. 22 (2012) 478–482. [30] C. Díez-Gil, A. Caballero, I. Ratera, A. Tárraga, P. Molina, J. Veciana, Naked-eye and selective detection of mercury (II) ions in mixed aqueous media using a cellulose-based support, Sensors 7 (2007) 3481–3488. [31] I. Chakraborty, T. Udayabhaskararao, T. Pradeep, Luminescent sub-nanometer clusters for metal ion sensing: a new direction in nanosensors, J. Hazard. Mater. 211-212 (2012) 396–403. [32] Y. Bhattacharjee, A. Chakraborty, Label-free cysteamine-capped silver nanoparticle-based colorimetric assay for Hg(II) detection in water with subnanomolar exactitude, ACS Sustainable Chem. Eng. 2 (2014) 2149–2154. [33] Y. Tian, W. Shi, J. Luo, F. Ma, H. Mi, Y. Lei, Carbazole-based conjugated polymer covalently coated Fe3 O4 nanoparticle as efficient and reversible Hg2+ optical probe, J. Polym. Sci. Part A: Polym. Chem. 51 (2013) 3636–3645. [34] G. Ramesh, T. Radhakrishnan, A universal sensor for mercury (Hg, HgI: HgII) based on silver nanoparticle-embedded polymer thin film, ACS Appl. Mater. Interfaces 3 (2011) 988–994. [35] Y.-R. Kim, H.J. Kim, J.S. Kim, H. Kim, Rhodamine-based turn-on fluorescent chemodosimeter for Cu(II) on ultrathin platinum films as molecular switches, Adv. Mater. 20 (2008) 4428–4432. [36] R. Nishiyabu, S. Ushikubo, Y. Kamiya, Y. Kubo, A boronate hydrogel film containing organized two-component dyes as a multicolor fluorescent sensor for heavy metal ions in water, J. Mater. Chem. A 2 (2014) 15846–15852. [37] Z.Q. Tou, T.W. Koh, C.C. Chan, Poly(vinyl alcohol) hydrogel based fiber interferometer sensor for heavy metal cations, Sens. Actuators B 202 (2014) 185–193. [38] D. Aussawasathien, S. Sahasithiwat, L. Menbangpung, C. Teerawattananon, Poly(o-anisidine)-polystyrene composite fibers via electrospinning process: surface morphology and chemical vapor sensing, Sens. Actuators B 151 (2011) 341–350. [39] X. He, L. Tan, X. Wu, C. Yan, D. Chen, X. Meng, F. Tang, Electrospun quantum dots/polymer composite porous fibers for turn-on fluorescent detection of lactate dehydrogenase, J. Mater. Chem. 22 (2012) 18471–18478. [40] D. Chen, Y.-E. Miao, T. Liu, Electrically conductive polyaniline/polyimide nanofiber membranes prepared via a combination of electrospinning and subsequent in situ polymerization growth, ACS Appl. Mater. Interfaces 5 (2013) 1206–1212. [41] W. Liu, J. Wei, Y. Chen, P. Huo, Y. Wei, Electrospinning of poly(L-lactide) nanofibers encapsulated with water-soluble fullerenes for bioimaging application, ACS Appl. Mater. Interfaces 5 (2013) 680–685. [42] M. Sun, B. Ding, J. Yu, Y.-L. Hsieh, G. Sun, Self-assembled monolayer of 3-mercaptopropionic acid on electrospun polystyrene membranes for Cu2+ detection, Sens. Actuators B 161 (2012) 322–328. [43] M. Min, X. Wang, Y. Chen, L. Wang, H. Huang, J. Shi, Highly sensitive and selective Cu2+ sensor based on electrospun rhodamine dye doped poly(ether sulfones) nanofibers, Sens. Actuators B 188 (2013) 360–366. [44] B. Ding, M. Wang, X. Wang, J. Yu, G. Sun, Electrospun nanomaterials for ultrasensitive sensors, Mater. Today 13 (2010) 16–27. [45] K. Liu, Z. Xu, M. Yin, W. Yang, B. He, W. Wei, J. Shen, A multifunctional perylenediimide derivative (DTPDI) can be used as a recyclable specific Hg2+

L. Ma et al. / Sensors and Actuators B 238 (2017) 120–127

[46]

[47]

[48]

[49]

ion sensor and an efficient DNA delivery carrier, J. Mater. Chem. B: Chem. 2 (2014) 2093–2096. J. Wang, K. Pan, Q. He, B. Cao, Polyacrylonitrile/polypyrrole core/shell nanofiber mat for the removal of hexavalent chromium from aqueous solution, J. Hazard. Mater. 244 (2013) 121–129. J. Wang, C. Luo, G. Qi, K. Pan, B. Cao, Mechanism study of selective heavy metal ion removal with polypyrrole-functionalized polyacrylonitrile nanofiber mats, Appl. Surf. Sci. 316 (2014) 245–250. C. Zhang, Q. Yang, N. Zhan, L. Sun, H. Wang, Y. Song, Y. Li, Silver nanoparticles grown on the surface of PAN nanofiber: preparation, characterization and catalytic performance, Colloids Surf. A 362 (2010) 58–64. S.Y. Venyaminov, N. Kalnin, Quantitative IR spectrophotometry of peptide compounds in water (H2 O) solutions: i. Spectral parameters of amino acid residue absorption bands, Biopolymers 30 (1990) 1243–1257.

Biographies Lijing Ma obtained her B.E degree in Polymer Science and Engineering from Hebei University of Science & Technology in 2013. Then she began her graduate studies under the supervision of Associate Professor Kai Pan in Beijing University of Chemical Technology and obtained her M.E. degree in 2016. Her thesis focuses on design and synthesis of nanofibers for fluorescent sensors and detection. Kelan Liu obtained her B.E degree in Biological functional materials from Beijing University of Chemical Technology in 2012. Then she begins her graduate studies under the supervision of Professor Meizhen Yin in Beijing University of Chemical Technology. Her current Ph.D thesis focuses on design and synthesis of fluorescent sensors.

127

Meizhen Yin got her Ph.D in Organic Chemistry under the supervision of Prof. Brigitte Voit and Prof. Wolf Habicher from Dresden University of Technology (TUD), Germany in 2004. Afterwards, she worked as a postdoctor in Prof. Klaus Muellen group in Max Planck Institute for Polymer Research, Mainz, Germany. Since 2009, she has been as a full professor in Beijing University of Chemical Technology (BUCT), China. She awarded Ministry of Education “New Century Excellent Talents” in 2010. She has rich experience on organic synthesis and invented many specific bioprobe and biosensor. Her research interests focus on the design and synthesis of functional fluorescent macromolecules, multifunctional organic/inorganic nanoparticles and their biological applications. Jiao Chang received his B.E degree from North China University of Science and Technology in 2013. Then she begins her graduate studies under the supervision of Associate Professor Kai Pan in Beijing University of Chemical Technology and obtained her M.E degree in 2016. Her thesis focuses on detection of heavy metal using nanofibers. Yuting Geng received his B.E degree (2014) in polymer science from Yantai University in 2014. Then she begins her graduate studies under the supervision of Associate Professor Kai Pan in Beijing University of Chemical Technology. Her current thesis focuses on design and synthesis of nanofibers with heterostructure. Kai Pan received his Ph.D in Polymer Science and Engineering, Sichuan University (China) under the supervision of Prof. Yi Dan in 2007 and B. Eng. in Polymer Materials Science, Sichuan University (China) in 2000. From 2007 to 2011, he has been Lectuer in Beijing University of Chemical Technology, 2012 he has been an Associate Professor in Beijing University of Chemical Technology. From 2012 to 2013 he was a Visiting scholar in Cornell University (America), in Giannelis group, He focus on and has rich experience on functional polymer nanofiber preparation and application, using electrospinning method to fabricate nanofibers for separation, detection, and purification etc.