Dalton Transactions View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
PAPER
Cite this: Dalton Trans., 2014, 43, 4762
View Journal | View Issue
A novel functionalized silver nanoparticles solid chemosensor for detection of Hg(II) in aqueous media ZhuHong Cheng, Gang Li,* Na Zhang and Hai-ou Liu We report a simple strategy for the fabrication of a highly selective and sensitive Hg(II) chemosensor based on HMS-Ag composite functionalized rhodamine derivative (R). The prepared chemosensor HMS-Ag-R was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis spectrum and Fourier transform infrared spectroscopy (FT-IR). HMS-Ag-R has both fluorescence and colorimetry performance, and it can realize onsite and real-time detection of Hg(II) with a high sensitivity (0.7 ppb) in aqueous solution. In high concentration of mercury ions, the fluorescence intensity of HMS-Ag-R against Hg(II) sufficiently showed a typical sigmoidal shape. Moreover, HMS-Ag-R presents excellent anti-disturbance ability when exposed to a series of competitive cations such as Ag(I), K(I), Li(I),
Received 15th September 2013, Accepted 3rd December 2013
Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II). It can be applied to the determination of Hg(II) in aqueous media. The interaction between HMS-Ag-R and Hg(II) could occur in a short
DOI: 10.1039/c3dt52540f
time (90 s). Importantly, HMS-Ag-R could be regenerated with tetrapropyl ammonium hydroxide (TPAOH)
www.rsc.org/dalton
solution.
1 Introduction Hg(II) is considered to be one of the most toxic and highly dangerous metal ions, because both elemental and ionic mercury can be converted into methyl mercury by bacteria in the environment, and the mercury subsequently bioaccumulates through the food chain.1–3 However, current main approaches for monitoring Hg(II) in waste water are costly, time-consuming methods like atomic absorption/emission spectroscopy or inductively coupled plasma mass spectrometry.4–6 These methods are not very convenient for onsite and real-time detection. Fortunately, the use of chemosensors is a good choice for the detection of Hg(II). In order to expand the application of chemosensors, the most efficient method is to improve their hydrophilicity and recycling performance. Recently, the use of organic–inorganic hybrid materials has attracted considerable interest.7–23 The receptor-immobilized inorganic materials such as SiO2, MCM-41, SBA-15 and HMS have some important advantages24–30 as a solid chemosensor. However, most of these chemosensors were synthesized by introducing silane agents as connectors, which could easily destroy the pore structure of the inorganic materials. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024, P. R. China. E-mail: [email protected]; Fax: +86-411-8498-6113; Tel: +86-411-8498-6113
4762 | Dalton Trans., 2014, 43, 4762–4769
During the past few decades, noble metal nanoparticles (Au NPs or Ag NPs) have received great attention for colorimetric sensing31–33 owing to their efficient integration of the unique optical properties, the well-defined nanostructure and the excellent surface/interface recognition ability.34–37 It has been proven that the fluorescence can be enhanced several fold by a metal nanoparticle.38–42 Such a fluorescence enhancement phenomenon is well-known as the metal-enhanced fluorescence (MEF) effect. In our previous work, we used gold nanoparticles instead of silane agents as connectors to prepare an Au-HMS-probe chemosensor, and excellent hydrophilicity and selectivity for Hg(II) in aqueous media could be achieved.43 However, this chemosensor exhibited a higher detection limit. To the best of our knowledge, there is not yet a report about the metal-surface fluorescence enhancement effect for this kind of chemosensor. Here, as shown in Scheme 1, we report a new highly selective and sensitive fluorescence platform for onsite and real-time monitoring Hg(II), and the metalenhanced fluorescence effect for this chemosensor was studied. Firstly, the nanocomposite HMS-Ag was prepared by adding Ag NPs in the synthesis process of mesoporous material HMS. Then, the templating agent dodecylamine was removed by extraction. Last, this new chemosensor was established by tethering the rhodamine derivative (R) on the Ag NPs based on HMS through Ag–N bonds. This chemosensor HMS-Ag-R exhibited excellent performance for detection of Hg(II) due to the following advantages: the selectivity for Hg(II)
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
Scheme 1
Schematic illustration of the preparation of chemosensor HMS-Ag-R and plausible binding mechanism of HMS-Ag-R with Hg(II).
offered by R, the metal-surface fluorescence enhancement effect in virtue of Ag NPs and the channels for complexation of R with Hg(II) enabled by mesoporous material HMS.
2
Experimental
2.1
Reagents
Rhodamine B, tris(2-aminoethyl)amine were purchased from J&K. Anhydrous sodium sulphate (Na2SO4), dichloromethane, ethanol, methanol and toluene were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Tetraethylorthosilicate (TEOS), dodecylamine (DDA) and H2O2 (30 wt%) were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. AgNO3 was purchased from Shanghai Chemical Reagent Co., Ltd. All chemicals were used as received from the suppliers without further purification. 2.2
Paper
Characterization
Transmission electron microscopy (TEM) images were taken on a FEI Company Tecnai G2 20 Stwin instrument with an acceleration voltage of 300 kV. Scanning electron microscopy (SEM) images were obtained on an HITACHI FE-SEM S-4800 scanning electron microscope. The specimen was prepared by first dispersing the chemosensor material in ethanol through supersonic, then placing the drop onto a carbon-coated copper
This journal is © The Royal Society of Chemistry 2014
grid. X-Ray diffraction (XRD) patterns were obtained at room temperature on a Rigaku D/MAX-2400 X-ray powder diffraction (Japan) using Cu Kα radiation, operating at 40 kV and 100 mA. N2 physical adsorption–desorption isotherms were measured at 77 K using a Quantachrome AUTOSORB-1 physical adsorption apparatus. The samples were outgassed in vacuum at 573 K before measurement. The specific surface area and poresize distribution were calculated by the Brunauer–Emmett– Teller (BET) method based on the adsorption data and Barrett–Joyner–Halenda (BJH) adsorption model. FT-IR spectra were recorded on a Bruker EQUINOX 55 spectrometer, using the KBr pellet technique. UV-vis spectra were measured on a Jasco UV-550 spectrophotometer. Fluorescence spectra measurements were performed on a Hitachi F-7000 fluorescence spectrophotometer at room temperature. Spectra were recorded with excitation and emission slit widths of 5 nm, 600 V of voltage and excitation at 520 nm. The absorption spectra were acquired on a PE Lambda 750 s spectrometer. 1 H NMR spectra were measured on a Varian INOVA 400 MHz spectrometer (in CDCl3, TMS as internal standard). Mass spectra were carried out on a TSQ Quantum Ultra spectrometer using methanol–water (1 : 1) as mobile phase. 2.3
Preparation of HMS-Ag
HMS-Ag metal-nanocomposite was synthesized following the reported method with proper modifications.43 The
Dalton Trans., 2014, 43, 4762–4769 | 4763
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Paper
Dalton Transactions
nanocomposite HMS-Ag was prepared by a one step synthesis process. Phase A: 5 mL solution of Ag(NH3)2+ (0.024 M) was mixed with 10 mL of ice-cold hydrogen peroxide solution (0.3 wt%) under vigorous stirring for 30 min. Phase B: 1.25 g DDA was dissolved in 9.6 mL ethanol. Then Phase A was added slowly to Phase B under vigorous stirring. After that, 2.9 mL diluent HCl solution (0.48 M) was added. 30 minutes later, 5.6 mL TEOS was dropwise added into the mixed system, and then aged for 18 h. DDA was extracted by ethanol at ambient temperature. After washing with deionized water and drying at 353 K for 6 h, HMS-Ag composite was obtained finally. 2.4
Synthesis of rhodamine derivative
According to the literature.11 To a 100 mL flask, under nitrogen, 1 g rhodamine B and 5 mL tris(2-aminoethyl)amine dissolved in methanol (60 mL) was kept at 353 K for several hours until the solution color turned to yellow from pink. After cooling to room temperature, the solvent was evaporated in vacuo. CH2Cl2 (100 mL) and deionized water (200 mL) were added into the residue after evaporation and the organic layer was separated. The CH2Cl2 layer was washed several times with deionized water followed by drying with anhydrous Na2SO4 overnight. After filtration of sodium sulphate, a yellow oil denoted as R was obtained after evaporating the solvent in vacuo. 1H NMR (400 MHz, CDCl3): δ = 7.90–7.88 (m, 1H), 7.45–7.43 (m, 2H), 7.1–7.08 (m, 1H), 6.42–6.39 (m, 4H), 6.29–6.26 (m, 2H), 5.30 (s, 4H), 3.37–3.32 (m, 8H), 3.18–3.14 (m, 2H), 2.55–2.50 (m, 6H), 2.34 (t, J = 8.0 Hz, 4H), 1.17 (t, J = 8.0 Hz, 12H). MS (TSQ Quantum Ultra) calcd for [C34H46N6O2]+ m/z = 570.37, found m/z = 571.39 [M + H]+; calcd for [C34H46N6O2]2+ m/z = 285.19, found m/z = 286.24 [M + 2H]2+. 2.5
Synthesis of HMS-Ag-R chemosensor
Under nitrogen atmosphere, HMS-Ag (1 g) and R (0.57 g) were dissolved in anhydrous toluene (50 mL) and stirred for 48 h at ambient temperature. The collected powder was washed several times with toluene to remove excess R. After washing and drying HMS-Ag-R chemosensor was obtained. The detailed synthetic route of HMS-Ag-R was illustrated in Scheme 1. 2.6
Fluorescent detection of metal ions
Concentration of stock solutions of the aqueous nitric acid salts (Ag(I), K(I), Li(I), Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II), Zn(II) and Hg(II)) was 1.25 × 10−4 M. The suspension solutions of HMS-Ag-R (0.1 g L−1) were prepared in aqueous solution. Each time, a 2 mL suspension solution of HMS-Ag-R was added to a quartz cuvette of 1 cm optical path length, and different stock solutions were gradually added into the quartz cuvette by micro-syringe.
3. Results and discussion 3.1
Characteristics of HMS-Ag-R chemosensor
The SEM and TEM images of HMS-Ag and HMS-Ag-R were shown in Fig. 1. SEM image of HMS-Ag exhibited irregular
4764 | Dalton Trans., 2014, 43, 4762–4769
Fig. 1 SEM image of HMS-Ag (a) and HMS-Ag-R (b), TEM images of HMS-Ag (c, d).
spherical particles with diameters of ∼300 nm (Fig. 1a). The surface of the particles became a little rough after immobilizing the rhodamine derivative (R) on the Ag NPs (Fig. 1b). The TEM study was carried out in order to detect the porous structure of HMS-Ag, as well as the size distribution of the Ag nanoparticles. HMS-Ag sample presented typical wormhole-like mesopores. The silver nanoparticles size distributed within the scope of 5–15 nm (Fig. 1c). Ag nanoparticles located in both the channel wall (Fig. 1d) and the outer surface of the nanocomposite (Fig. 1d inset). These silver nanoparticles provide active sites for immobilizing rhodamine derivatives (R) which could go through the mesoporous channels. The small angle and wide angle powder X-ray diffraction patterns of HMS-Ag nanocomposite and HMS-Ag-R chemosensor are given in Fig. 2. HMS-Ag nanocomposite presented a strong reflection peak at 2.3°, which is a characteristic peak of the wormhole mesoporous structure.44 For HMS-Ag-R, the peak became weaker and wider, which meant the order of the mesoporous structure decreased. The possible reason is the introduction of R. In the wide angle XRD patterns, both samples presented intense X-ray reflections at 2θ = 38.1°, 44.3°, 64.4° and 77.4°, which correspond to the (111), (220), (200) and (311) planes of the Ag NPs. Fig. 3 showed the nitrogen adsorption–desorption isotherm and the BJH pore size distribution (Fig. 3 inset) of HMS-Ag nanocomposite. We could observe that HMS-Ag exhibited type IV isotherm with a H1-type hysteresis loop and a sharp step at a relative pressure of 0.4. According to the IUPAC classification,45 this type of hysteresis loop indicated the presence of textural mesoporous cylindrical pores, which clearly indicated that HMS-Ag exhibited uniform textural porosity (Fig. 3). This result was consistent with the small angle XRD result (Fig. 2a). The texture parameters of the nanocomposite HMS-Ag are shown in Table 1, the specific surface area of the HMS-Ag was 540.6 m2 g−1 and the cumulative pore volume was 0.44 cm3 g−1. The FT-IR spectra of HMS-Ag and HMS-Ag-R are shown in Fig. 4. Compared with the FT-IR spectrum of HMS-Ag, new
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Paper Table 1
Structural properties of HMS-Ag
d100 a (nm)
a0 b (nm)
Pore diameterc (nm)
Wall thicknessd (nm)
BET surface area (m2 g−1)
Pore volumee (cm3 g−1)
3.9
4.5
2.7
1.8
540.6
0.44
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
a
b
1/2
c
Calculated from XRD analysis. a0 = 2d100/3 . Calculated from adsorption branch of nitrogen isotherm using BJH model. d Wall thickness = a0 − pore diameter. e Calculated from the volume adsorbed of P/P0 at 0.99.
Fig. 4
Fig. 2 The Small angle (a) and wide angle (b) X-ray diffraction patterns of HMS-Ag and HMS-Ag-R.
FT-IR spectra of HMS-Ag and HMS-Ag-R.
The diffuse reflectance UV-vis spectra were used to confirm the existence of Ag nanoparticles and R. The spectrum of HMS-Ag-R exhibited a significant peak at a wavelength ∼400 nm (Fig. 5 inset), which did not exist in the spectrum of HMS and could be attributed to the Plasmon resonance absorbance of the Ag nanoparticles. This was another valid evidence that the Ag nanoparticles existed in the composite. Fig. 5 further showed that R anchored on the surface of Ag nanoparticles. A series of characteristic bands at 240, 280 and 320 nm emerged in the spectra of both R and HMS-Ag-R, which implied the successful incorporation of R onto the surface of Ag nanoparticles. These bands could be attributed to the typical electronic transition of the aromatic ring.11,14 In the spectrum of HMS-Ag-R, a slight blue shift for the intense
Fig. 3 N2 adsorption–desorption isotherm of HMS-Ag. Inset: the BJH pore size distribution of HMS-Ag.
transmission bands 2973 and 2924 cm−1 were observed in the spectrum of HMS-Ag-R, which were assigned to the asymmetric and symmetric stretching vibrations of the methylene group (CH2) in the alkyl chain. New bands centered at around 1200–1700 cm−1 were attributed to the C–H stretching and the aromatic stretching vibrations of the rhodamine group. These features also appeared in the FT-IR spectrum of R, suggesting successful grafting of R onto the HMS-Ag composite.
This journal is © The Royal Society of Chemistry 2014
Fig. 5
UV-vis spectra of HMS, HMS-Ag, HMS-Ag-R and R.
Dalton Trans., 2014, 43, 4762–4769 | 4765
View Article Online
Paper
Dalton Transactions
absorption band at 320 nm could also be seen. These observations indicated that the organic group was covalently grafted onto the composite HMS-Ag. Moreover, the weak peak centered at ∼550 nm in Fig. 5 was due to the existence of a little fraction of the rhodamine group in an opening-Spirolactam form, which gave a slightly pink color.
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
3.2
HMS-Ag-R responses to Hg(II)
Metal-enhanced fluorescence spectra are shown in Fig. 6. Compared with HMS + R which was a mixture of HMS and R, a fluorescence intensity enhancement was observed in the fluorescence spectrum of HMS-Ag-R (at 584 nm) without Hg(II). Moreover, in the presence of Hg(II), the fluorescence intensity of HMS-Ag-R was also significantly enhanced compared to HMS + R (at 584 nm), which was induced by the metalenhanced fluorescence (MEF) effect of Ag nanoparticles. Taking the fluorescence quantum yield of rhodamine B (Φf = 0.31) in water as a reference, HMS-Ag-R showed a higher fluorescence quantum yield of 0.25 in water compared with that of the mixture of HMS + R (Φ = 0.11). Fig. 7 showed the fluorescence changes of HMS-Ag-R with Hg(II) in 2 mM aqueous HEPES buffer medium. Free HMS-Ag-
Fig. 6
Metal-enhanced fluorescence spectra of HMS + R and HMS-Ag-R.
Fig. 7 Fluorescence spectra of HMS-Ag-R (0.1 g L−1 pH = 7.0) with different concentrations of Hg(II) (0–5 ppm) in 2 mM aqueous HEPES buffer medium. Inset: the fluorescence change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
4766 | Dalton Trans., 2014, 43, 4762–4769
Fig. 8 UV-vis absorption spectra of HMS-Ag-R with different concentrations of Hg(II) (0–5 ppm) in 2 mM aqueous HEPES buffer medium. Inset: the color change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
R solution showed very weak fluorescence intensity at about 584 nm (excited at 520 nm). Upon addition of Hg(II), a significant enhancement of fluorescence intensity at 584 nm was observed. Meanwhile, the solution showed an orange fluorescence change (Fig. 7 inset). Such changes of fluorescence were reasonably attributed to the spirolactam (nonfluorescent) to ring opened amide (fluorescent) equilibrium, which was induced by the complexation of Hg(II).46,47 The absorption spectra of HMS-Ag-R with varying Hg(II) concentrations in 2 mM aqueous HEPES buffered medium are shown in Fig. 8. Free HMS-Ag-R was colorless and exhibited almost no absorption peak in the visible wavelength range (>450 nm) due to the closed spirolactam ring. In the presence of Hg(II), the absorbance was enhanced obviously and a new peak at 562 nm was observed. Meanwhile, the color of HMS-Ag-R changed from colorless to pink (Fig. 8 inset). This result demonstrated that HMS-Ag-R could serve as a “nakedeye” chemosensor for Hg(II). The limit of detection (LOD) was calculated by the equation LOD = 3S0/k, where 3 was the factor at the 99% confidence level, S0 was the standard deviation of the blank measurements (n = 10), and k was the slope of the calibration curve. The detection limit of HMS-Ag-R for Hg(II) was determined to be as low as 0.7 ppb (Fig. 9). This result demonstrated that determination of trace amounts of Hg(II) at the parts per billion level was feasible with HMS-Ag-R chemosensor. HMS-Ag-R had a much lower detection limit than the solid chemosensor reported in our previous work.43 Furthermore, the curve of the fluorescence intensity of HMS-Ag-R against high Hg(II) concentration in the aqueous media sufficiently showed a typical sigmoidal shape (Fig. 10). This means that a mercury ion concentration can be obtained based on the fluorescence intensity from this sigmoidal curve. At the same time, with the increase of mercury ions, the color of the HMS-Ag-R suspension gradually deepened (Fig. 10 inset). Response time is an important analytical feature for the chemosensor. Fig. 11 showed the fluorescence intensity (584 nm) of HMS-Ag-R at different time intervals after adding
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
Fig. 9 Linear calibration plot for Hg(II) in low concentration. The fluorescence intensity was measured at an excitation wavelength of 520 nm, and monitored at a wavelength of 584 nm.
Fig. 10 Plot of the fluorescence intensity (584 nm) of HMS-Ag-R suspension (0.1 g L−1 pH = 7.0) with Hg(II) in high concentration. Inset: the color change of HMS-Ag-R with different concentrations of Hg(II).
Fig. 11
Response time of HMS-Ag-R with Hg(II).
3 ppm Hg(II). The fluorescence intensity increased quickly within 90 s and then remained constant with time, which showed that the Hg(II) complexation process has completed. So HMS-Ag-R could provide fast detection of Hg(II) within 90 s. We also investigated the competition-based fluorescence emission changes of HMS-Ag-R, upon addition of various
This journal is © The Royal Society of Chemistry 2014
Paper
Fig. 12 Fluorescence of HMS-Ag-R to other metal ions (30 ppm, the black bar) and to Hg(II) or the mixture of other metal ions with Hg(II) (3 ppm, the red bar).
biologically and environmentally relevant metal ions such as Ag(I), K(I), Li(I), Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions (Fig. 12). Typically, 30 ppm of competing metal ions were added into the HMS-Ag-R suspension (0.1 g L−1, pH = 7.0). After 2 min incubation, the fluorescence intensities of the resulting solutions were measured. Then, 3 ppm of Hg(II) was added to the former solution for another measurement. The fluorescence intensities of HMS-Ag-R showed no significant changes in the presence of competitive metal ions. After adding Hg(II) an obvious fluorescence response was induced, indicating the chemosensor had a high selectivity for Hg(II). The special selectivity was probably due to the following factors: the suitable coordination geometry conformation of the receptor, the larger radius of the Hg(II), the nitrogen-affinity of Hg(II) and the amide deprotonation ability of the Hg(II).48 Furthermore, the reusability and reproducibility of an excellent chemosensor are of particular interest in developing recyclable hybrid optical sensors, which could highlight their important characteristic features and desirability for industrial applications. The repeated detection/regeneration cycles were extensively studied. In these procedures, the use of specific concentrations of TPAOH made the removal of Hg(II) (decomplexation) possible. The regeneration ability of HMS-Ag-R was shown in Fig. 13. It was found that free HMS-Ag-R in 2 mM aqueous HEPES buffer medium without Hg(II) displayed a very weak fluorescence, while a significant increase of fluorescence was observed with the addition of Hg(II). However, the addition of TPAOH to the HMS-Ag-R-Hg solution caused an immediate fluorescence decrease. Subsequently, addition of Hg(II) into the suspension of HMS-Ag-R gave increased fluorescence again, and the analytical process was entirely visualized by the naked eye (Fig. 13 inset). HMS-Ag-R could reversibly bind with Hg(II) and could be used repeatedly at least for four cycles with a slight decrease in sensitivity. Finally, this chemosensor was applied to the determination of Hg(II) in tap water. Because there was no Hg(II) contained in the tap water as determined by inductively coupled plasma mass spectrometry (ICP-MS), Hg(II) was deliberately added to
Dalton Trans., 2014, 43, 4762–4769 | 4767
View Article Online
Paper
Dalton Transactions
for many practical applications in chemical, environmental and biological systems.
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Acknowledgements The authors acknowledge the financial support from the Program for New Century Excellent Talents in University (NCET-04-0270) and Central University basic research fund (DUT10LK11).
Fig. 13 Reversibility of HMS-Ag-R with the addition of Hg(II) (3 ppm) and TPAOH. Inset: the color change of HMS-Ag-R in the regeneration process.
Fig. 14 Fluorescence spectra of HMS-Ag-R (0.1 g L−1) with different concentrations of Hg(II) (0–5 ppm) in tap water. Inset: the fluorescence (top) and color (bottom) change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
simulate contaminated water. As shown in Fig. 14, the fluorescence intensity of HMS-Ag-R in tap water showed a remarkable enhancement with addition of Hg(II) (0–5 ppm) and the fluorescent color changed to bright yellow finally (Fig. 14 inset (top)). More importantly, the color of the sample also visibly changed from colorless to red (Fig. 14 inset (bottom)). The result indicated the suitability of HMS-Ag-R for the determination of Hg(II) in a natural water sample.
4.
Conclusion
In conclusion, a novel metal-enhanced fluorescence chemosensor HMS-Ag-R for Hg(II) has been prepared via a simple and effective method. The output signals include color and fluorescence, which were reversibly transduced through simply opening the spirolactam ring upon Hg(II) complexation. In the presence of competitive metal ions, HMS-Ag-R exhibited high selectivity for Hg(II) sensing in aqueous media. We believe that this metal-enhanced fluorescence platform could be explored
4768 | Dalton Trans., 2014, 43, 4762–4769
Notes and references 1 A. Renzoni, F. Zino and E. Franchi, Environ. Res., 1998, 77, 68–72. 2 G. Cabana and J. B. Rasmussen, Nature, 1994, 372, 255– 257. 3 C. J. Watras, R. C. Back, S. Halvorsen, R. J. M. Hudson, K. A. Morrison and S. P. Wente, Sci. Total Environ., 1998, 219, 183–208. 4 D. Beauchemin, Anal. Chem., 2010, 82, 4786–4810. 5 L. Ebdon, M. S. Cresser and C. W. McLeod, J. Anal. At. Spectrom., 1987, 2, 1R–28R. 6 R. Ma, C. W. McLeod, K. Tomlinson and R. K. Poole, Electrophoresis, 2004, 25, 2469–2477. 7 W. Huang, X. Zhu, D. Wua, C. He, X. Hu and C. Duan, Dalton Trans., 2009, 10457–10465. 8 L. Gao, Y. Wang, J. Wang, L. Huang, L. Shi, X. Fan, Z. Zou, T. Yu, M. Zhu and Z. Li, Inorg. Chem., 2006, 45, 6844–6850. 9 P. Mahato, S. Saha, E. Suresh, R. Di Liddo, P. P. Parnigotto, M. T. Conconi, M. K. Kesharwani, B. Ganguly and A. Das, Inorg. Chem., 2012, 51, 1769–1777. 10 J. Hatai, S. Pal, G. P. Jose and S. Bandyopadhyay, Inorg. Chem., 2012, 51, 10129–10135. 11 M. H. Lee, S. J. Lee, J. H. Jung, H. Lim and J. S. Kim, Tetrahedron, 2007, 63, 12087–12092. 12 D. T. Quang and J. S. Kim, Chem. Rev., 2010, 110, 6280– 6301. 13 C. Wang, S. Tao, W. Wei, C. Meng, F. Liu and M. Han, J. Mater. Chem., 2010, 20, 4635–4641. 14 P. Zhou, Q. Meng, G. He, H. Wu, C. Duan and X. Quan, J. Environ. Monit., 2009, 11, 648–653. 15 H. Lu, S. Qi, J. Mack, Z. Li, J. Lei, N. Kobayashi and Z. Shen, J. Mater. Chem., 2011, 21, 10878–10882. 16 J. Liu, C. Li and F. Li, J. Mater. Chem., 2011, 21, 7175–7181. 17 C. Song, X. Zhang, C. Jia, P. Zhou, X. Quan and C. Duan, Talanta, 2010, 81, 643–649. 18 N. Zhang, G. Li, J. Zhao and T. Liu, New J. Chem., 2013, 37, 458–463. 19 S. Saha, M. U. Chhatbar, P. Mahato, L. Praveen, A. K. Siddhanta and A. Das, Chem. Commun., 2012, 48, 1659–1661. 20 T. Liu, G. Li, N. Zhang and Y. Chen, J. Hazard. Mater., 2012, 201–202, 155–161.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
21 M. Yin, Z. Li, Z. Liu, X. Yang and J. Ren, ACS Appl. Mater. Interfaces, 2012, 4, 431–437. 22 W. Huang, C. Song, C. He, G. Lv, X. Hu, X. Zhu and C. Duan, Inorg. Chem., 2009, 48, 5061–5072. 23 C. Kaewtong, B. Wanno, Y. Uppa, N. Morakot, B. Pulpoka and T. Tuntulani, Dalton Trans., 2011, 40, 12578–12583. 24 L. Mercier and T. J. Pinnavaia, Adv. Mater., 1997, 9, 500–503. 25 U. Bach, D. Lupo, P. Comte, J. E. Moser, F. Weissörtel, J. Salbeck, H. Spreitzer and M. Grätzel, Nature, 1998, 395, 583–585. 26 M. Vallet-Regí, J. C. Doadrio, A. L. Doadrio, I. IzquierdoBarba and J. Pérez-Pariente, Solid State Ionics, 2004, 172, 435–439. 27 I. I. Slowing, J. L. Vivero-Escoto, C.-W. Wu and V. S. Y. Lin, Adv. Drug Delivery Rev., 2008, 60, 1278–1288. 28 I. I. Slowing, B. G. Trewyn, S. Giri and V. S. Y. Lin, Adv. Funct. Mater., 2007, 17, 1225–1236. 29 H. H. P. Yiu and P. A. Wright, J. Mater. Chem., 2005, 15, 3690–3700. 30 W. Huang, D. Wu, G. Wu and Z. Wang, Dalton Trans., 2012, 41, 2620–2625. 31 Y. Tao, Y. Lin, Z. Huang, J. Ren and X. Qu, Talanta, 2012, 88, 290–294. 32 V. Tharmaraj and K. Pitchumani, Nanoscale, 2011, 3, 1166– 1170. 33 Z. Huang, F. Pu, Y. Lin, J. Ren and X. Qu, Chem. Commun., 2011, 47, 3487–3489. 34 J. B. Jackson and N. J. Halas, J. Phys. Chem. B, 2001, 105, 2743–2746.
This journal is © The Royal Society of Chemistry 2014
Paper
35 M. Hu, J. Chen, Z.-Y. Li, L. Au, G. V. Hartland, X. Li, M. Marquez and Y. Xia, Chem. Soc. Rev., 2006, 35, 1084– 1094. 36 Y. Sun, B. Mayers and Y. Xia, Adv. Mater., 2003, 15, 641– 646. 37 A. Verma and V. M. Rotello, Chem. Commun., 2005, 303– 312. 38 K. Aslan, M. Wu, J. R. Lakowicz and C. D. Geddes, J. Am. Chem. Soc., 2007, 129, 1524–1525. 39 K. Aslan, Z. Leonenko, J. R. Lakowicz and C. D. Geddes, J. Fluoresc., 2005, 15, 643–654. 40 J. Yang, F. Zhang, Y. Chen, S. Qian, P. Hu, W. Li, Y. Deng, Y. Fang, L. Han, M. Luqman and D. Zhao, Chem. Commun., 2011, 47, 11618–11620. 41 C. D. Geddes and J. R. Lakowicz, J. Fluoresc., 2002, 12, 121– 129. 42 J. A. Dieringer, K. L. Wustholz, D. J. Masiello, J. P. Camden, S. L. Kleinman, G. C. Schatz and R. P. Van Duyne, J. Am. Chem. Soc., 2009, 131, 849–854. 43 N. Zhang, G. Li, Z. Cheng and X. Zuo, J. Hazard. Mater., 2012, 229–230, 404–410. 44 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 865–867. 45 A. Y. Khodakov, A. Griboval-Constant, R. Bechara and F. Villain, J. Phys. Chem. B, 2001, 105, 9805–9811. 46 Y. K. Yang, K. J. Yook and J. Tae, J. Am. Chem. Soc., 2005, 127, 16760–16761. 47 V. Dujols, F. Ford and A. W. Czarnik, J. Am. Chem. Soc., 1997, 119, 7386–7387. 48 D. Wu, W. Huang, C. Duan, Z. Lin and Q. Meng, Inorg. Chem., 2007, 46, 1538–1540.
Dalton Trans., 2014, 43, 4762–4769 | 4769
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
PAPER
Cite this: Dalton Trans., 2014, 43, 4762
View Journal | View Issue
A novel functionalized silver nanoparticles solid chemosensor for detection of Hg(II) in aqueous media ZhuHong Cheng, Gang Li,* Na Zhang and Hai-ou Liu We report a simple strategy for the fabrication of a highly selective and sensitive Hg(II) chemosensor based on HMS-Ag composite functionalized rhodamine derivative (R). The prepared chemosensor HMS-Ag-R was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis spectrum and Fourier transform infrared spectroscopy (FT-IR). HMS-Ag-R has both fluorescence and colorimetry performance, and it can realize onsite and real-time detection of Hg(II) with a high sensitivity (0.7 ppb) in aqueous solution. In high concentration of mercury ions, the fluorescence intensity of HMS-Ag-R against Hg(II) sufficiently showed a typical sigmoidal shape. Moreover, HMS-Ag-R presents excellent anti-disturbance ability when exposed to a series of competitive cations such as Ag(I), K(I), Li(I),
Received 15th September 2013, Accepted 3rd December 2013
Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II). It can be applied to the determination of Hg(II) in aqueous media. The interaction between HMS-Ag-R and Hg(II) could occur in a short
DOI: 10.1039/c3dt52540f
time (90 s). Importantly, HMS-Ag-R could be regenerated with tetrapropyl ammonium hydroxide (TPAOH)
www.rsc.org/dalton
solution.
1 Introduction Hg(II) is considered to be one of the most toxic and highly dangerous metal ions, because both elemental and ionic mercury can be converted into methyl mercury by bacteria in the environment, and the mercury subsequently bioaccumulates through the food chain.1–3 However, current main approaches for monitoring Hg(II) in waste water are costly, time-consuming methods like atomic absorption/emission spectroscopy or inductively coupled plasma mass spectrometry.4–6 These methods are not very convenient for onsite and real-time detection. Fortunately, the use of chemosensors is a good choice for the detection of Hg(II). In order to expand the application of chemosensors, the most efficient method is to improve their hydrophilicity and recycling performance. Recently, the use of organic–inorganic hybrid materials has attracted considerable interest.7–23 The receptor-immobilized inorganic materials such as SiO2, MCM-41, SBA-15 and HMS have some important advantages24–30 as a solid chemosensor. However, most of these chemosensors were synthesized by introducing silane agents as connectors, which could easily destroy the pore structure of the inorganic materials. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024, P. R. China. E-mail: [email protected]; Fax: +86-411-8498-6113; Tel: +86-411-8498-6113
4762 | Dalton Trans., 2014, 43, 4762–4769
During the past few decades, noble metal nanoparticles (Au NPs or Ag NPs) have received great attention for colorimetric sensing31–33 owing to their efficient integration of the unique optical properties, the well-defined nanostructure and the excellent surface/interface recognition ability.34–37 It has been proven that the fluorescence can be enhanced several fold by a metal nanoparticle.38–42 Such a fluorescence enhancement phenomenon is well-known as the metal-enhanced fluorescence (MEF) effect. In our previous work, we used gold nanoparticles instead of silane agents as connectors to prepare an Au-HMS-probe chemosensor, and excellent hydrophilicity and selectivity for Hg(II) in aqueous media could be achieved.43 However, this chemosensor exhibited a higher detection limit. To the best of our knowledge, there is not yet a report about the metal-surface fluorescence enhancement effect for this kind of chemosensor. Here, as shown in Scheme 1, we report a new highly selective and sensitive fluorescence platform for onsite and real-time monitoring Hg(II), and the metalenhanced fluorescence effect for this chemosensor was studied. Firstly, the nanocomposite HMS-Ag was prepared by adding Ag NPs in the synthesis process of mesoporous material HMS. Then, the templating agent dodecylamine was removed by extraction. Last, this new chemosensor was established by tethering the rhodamine derivative (R) on the Ag NPs based on HMS through Ag–N bonds. This chemosensor HMS-Ag-R exhibited excellent performance for detection of Hg(II) due to the following advantages: the selectivity for Hg(II)
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
Scheme 1
Schematic illustration of the preparation of chemosensor HMS-Ag-R and plausible binding mechanism of HMS-Ag-R with Hg(II).
offered by R, the metal-surface fluorescence enhancement effect in virtue of Ag NPs and the channels for complexation of R with Hg(II) enabled by mesoporous material HMS.
2
Experimental
2.1
Reagents
Rhodamine B, tris(2-aminoethyl)amine were purchased from J&K. Anhydrous sodium sulphate (Na2SO4), dichloromethane, ethanol, methanol and toluene were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Tetraethylorthosilicate (TEOS), dodecylamine (DDA) and H2O2 (30 wt%) were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. AgNO3 was purchased from Shanghai Chemical Reagent Co., Ltd. All chemicals were used as received from the suppliers without further purification. 2.2
Paper
Characterization
Transmission electron microscopy (TEM) images were taken on a FEI Company Tecnai G2 20 Stwin instrument with an acceleration voltage of 300 kV. Scanning electron microscopy (SEM) images were obtained on an HITACHI FE-SEM S-4800 scanning electron microscope. The specimen was prepared by first dispersing the chemosensor material in ethanol through supersonic, then placing the drop onto a carbon-coated copper
This journal is © The Royal Society of Chemistry 2014
grid. X-Ray diffraction (XRD) patterns were obtained at room temperature on a Rigaku D/MAX-2400 X-ray powder diffraction (Japan) using Cu Kα radiation, operating at 40 kV and 100 mA. N2 physical adsorption–desorption isotherms were measured at 77 K using a Quantachrome AUTOSORB-1 physical adsorption apparatus. The samples were outgassed in vacuum at 573 K before measurement. The specific surface area and poresize distribution were calculated by the Brunauer–Emmett– Teller (BET) method based on the adsorption data and Barrett–Joyner–Halenda (BJH) adsorption model. FT-IR spectra were recorded on a Bruker EQUINOX 55 spectrometer, using the KBr pellet technique. UV-vis spectra were measured on a Jasco UV-550 spectrophotometer. Fluorescence spectra measurements were performed on a Hitachi F-7000 fluorescence spectrophotometer at room temperature. Spectra were recorded with excitation and emission slit widths of 5 nm, 600 V of voltage and excitation at 520 nm. The absorption spectra were acquired on a PE Lambda 750 s spectrometer. 1 H NMR spectra were measured on a Varian INOVA 400 MHz spectrometer (in CDCl3, TMS as internal standard). Mass spectra were carried out on a TSQ Quantum Ultra spectrometer using methanol–water (1 : 1) as mobile phase. 2.3
Preparation of HMS-Ag
HMS-Ag metal-nanocomposite was synthesized following the reported method with proper modifications.43 The
Dalton Trans., 2014, 43, 4762–4769 | 4763
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Paper
Dalton Transactions
nanocomposite HMS-Ag was prepared by a one step synthesis process. Phase A: 5 mL solution of Ag(NH3)2+ (0.024 M) was mixed with 10 mL of ice-cold hydrogen peroxide solution (0.3 wt%) under vigorous stirring for 30 min. Phase B: 1.25 g DDA was dissolved in 9.6 mL ethanol. Then Phase A was added slowly to Phase B under vigorous stirring. After that, 2.9 mL diluent HCl solution (0.48 M) was added. 30 minutes later, 5.6 mL TEOS was dropwise added into the mixed system, and then aged for 18 h. DDA was extracted by ethanol at ambient temperature. After washing with deionized water and drying at 353 K for 6 h, HMS-Ag composite was obtained finally. 2.4
Synthesis of rhodamine derivative
According to the literature.11 To a 100 mL flask, under nitrogen, 1 g rhodamine B and 5 mL tris(2-aminoethyl)amine dissolved in methanol (60 mL) was kept at 353 K for several hours until the solution color turned to yellow from pink. After cooling to room temperature, the solvent was evaporated in vacuo. CH2Cl2 (100 mL) and deionized water (200 mL) were added into the residue after evaporation and the organic layer was separated. The CH2Cl2 layer was washed several times with deionized water followed by drying with anhydrous Na2SO4 overnight. After filtration of sodium sulphate, a yellow oil denoted as R was obtained after evaporating the solvent in vacuo. 1H NMR (400 MHz, CDCl3): δ = 7.90–7.88 (m, 1H), 7.45–7.43 (m, 2H), 7.1–7.08 (m, 1H), 6.42–6.39 (m, 4H), 6.29–6.26 (m, 2H), 5.30 (s, 4H), 3.37–3.32 (m, 8H), 3.18–3.14 (m, 2H), 2.55–2.50 (m, 6H), 2.34 (t, J = 8.0 Hz, 4H), 1.17 (t, J = 8.0 Hz, 12H). MS (TSQ Quantum Ultra) calcd for [C34H46N6O2]+ m/z = 570.37, found m/z = 571.39 [M + H]+; calcd for [C34H46N6O2]2+ m/z = 285.19, found m/z = 286.24 [M + 2H]2+. 2.5
Synthesis of HMS-Ag-R chemosensor
Under nitrogen atmosphere, HMS-Ag (1 g) and R (0.57 g) were dissolved in anhydrous toluene (50 mL) and stirred for 48 h at ambient temperature. The collected powder was washed several times with toluene to remove excess R. After washing and drying HMS-Ag-R chemosensor was obtained. The detailed synthetic route of HMS-Ag-R was illustrated in Scheme 1. 2.6
Fluorescent detection of metal ions
Concentration of stock solutions of the aqueous nitric acid salts (Ag(I), K(I), Li(I), Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II), Zn(II) and Hg(II)) was 1.25 × 10−4 M. The suspension solutions of HMS-Ag-R (0.1 g L−1) were prepared in aqueous solution. Each time, a 2 mL suspension solution of HMS-Ag-R was added to a quartz cuvette of 1 cm optical path length, and different stock solutions were gradually added into the quartz cuvette by micro-syringe.
3. Results and discussion 3.1
Characteristics of HMS-Ag-R chemosensor
The SEM and TEM images of HMS-Ag and HMS-Ag-R were shown in Fig. 1. SEM image of HMS-Ag exhibited irregular
4764 | Dalton Trans., 2014, 43, 4762–4769
Fig. 1 SEM image of HMS-Ag (a) and HMS-Ag-R (b), TEM images of HMS-Ag (c, d).
spherical particles with diameters of ∼300 nm (Fig. 1a). The surface of the particles became a little rough after immobilizing the rhodamine derivative (R) on the Ag NPs (Fig. 1b). The TEM study was carried out in order to detect the porous structure of HMS-Ag, as well as the size distribution of the Ag nanoparticles. HMS-Ag sample presented typical wormhole-like mesopores. The silver nanoparticles size distributed within the scope of 5–15 nm (Fig. 1c). Ag nanoparticles located in both the channel wall (Fig. 1d) and the outer surface of the nanocomposite (Fig. 1d inset). These silver nanoparticles provide active sites for immobilizing rhodamine derivatives (R) which could go through the mesoporous channels. The small angle and wide angle powder X-ray diffraction patterns of HMS-Ag nanocomposite and HMS-Ag-R chemosensor are given in Fig. 2. HMS-Ag nanocomposite presented a strong reflection peak at 2.3°, which is a characteristic peak of the wormhole mesoporous structure.44 For HMS-Ag-R, the peak became weaker and wider, which meant the order of the mesoporous structure decreased. The possible reason is the introduction of R. In the wide angle XRD patterns, both samples presented intense X-ray reflections at 2θ = 38.1°, 44.3°, 64.4° and 77.4°, which correspond to the (111), (220), (200) and (311) planes of the Ag NPs. Fig. 3 showed the nitrogen adsorption–desorption isotherm and the BJH pore size distribution (Fig. 3 inset) of HMS-Ag nanocomposite. We could observe that HMS-Ag exhibited type IV isotherm with a H1-type hysteresis loop and a sharp step at a relative pressure of 0.4. According to the IUPAC classification,45 this type of hysteresis loop indicated the presence of textural mesoporous cylindrical pores, which clearly indicated that HMS-Ag exhibited uniform textural porosity (Fig. 3). This result was consistent with the small angle XRD result (Fig. 2a). The texture parameters of the nanocomposite HMS-Ag are shown in Table 1, the specific surface area of the HMS-Ag was 540.6 m2 g−1 and the cumulative pore volume was 0.44 cm3 g−1. The FT-IR spectra of HMS-Ag and HMS-Ag-R are shown in Fig. 4. Compared with the FT-IR spectrum of HMS-Ag, new
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Paper Table 1
Structural properties of HMS-Ag
d100 a (nm)
a0 b (nm)
Pore diameterc (nm)
Wall thicknessd (nm)
BET surface area (m2 g−1)
Pore volumee (cm3 g−1)
3.9
4.5
2.7
1.8
540.6
0.44
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
a
b
1/2
c
Calculated from XRD analysis. a0 = 2d100/3 . Calculated from adsorption branch of nitrogen isotherm using BJH model. d Wall thickness = a0 − pore diameter. e Calculated from the volume adsorbed of P/P0 at 0.99.
Fig. 4
Fig. 2 The Small angle (a) and wide angle (b) X-ray diffraction patterns of HMS-Ag and HMS-Ag-R.
FT-IR spectra of HMS-Ag and HMS-Ag-R.
The diffuse reflectance UV-vis spectra were used to confirm the existence of Ag nanoparticles and R. The spectrum of HMS-Ag-R exhibited a significant peak at a wavelength ∼400 nm (Fig. 5 inset), which did not exist in the spectrum of HMS and could be attributed to the Plasmon resonance absorbance of the Ag nanoparticles. This was another valid evidence that the Ag nanoparticles existed in the composite. Fig. 5 further showed that R anchored on the surface of Ag nanoparticles. A series of characteristic bands at 240, 280 and 320 nm emerged in the spectra of both R and HMS-Ag-R, which implied the successful incorporation of R onto the surface of Ag nanoparticles. These bands could be attributed to the typical electronic transition of the aromatic ring.11,14 In the spectrum of HMS-Ag-R, a slight blue shift for the intense
Fig. 3 N2 adsorption–desorption isotherm of HMS-Ag. Inset: the BJH pore size distribution of HMS-Ag.
transmission bands 2973 and 2924 cm−1 were observed in the spectrum of HMS-Ag-R, which were assigned to the asymmetric and symmetric stretching vibrations of the methylene group (CH2) in the alkyl chain. New bands centered at around 1200–1700 cm−1 were attributed to the C–H stretching and the aromatic stretching vibrations of the rhodamine group. These features also appeared in the FT-IR spectrum of R, suggesting successful grafting of R onto the HMS-Ag composite.
This journal is © The Royal Society of Chemistry 2014
Fig. 5
UV-vis spectra of HMS, HMS-Ag, HMS-Ag-R and R.
Dalton Trans., 2014, 43, 4762–4769 | 4765
View Article Online
Paper
Dalton Transactions
absorption band at 320 nm could also be seen. These observations indicated that the organic group was covalently grafted onto the composite HMS-Ag. Moreover, the weak peak centered at ∼550 nm in Fig. 5 was due to the existence of a little fraction of the rhodamine group in an opening-Spirolactam form, which gave a slightly pink color.
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
3.2
HMS-Ag-R responses to Hg(II)
Metal-enhanced fluorescence spectra are shown in Fig. 6. Compared with HMS + R which was a mixture of HMS and R, a fluorescence intensity enhancement was observed in the fluorescence spectrum of HMS-Ag-R (at 584 nm) without Hg(II). Moreover, in the presence of Hg(II), the fluorescence intensity of HMS-Ag-R was also significantly enhanced compared to HMS + R (at 584 nm), which was induced by the metalenhanced fluorescence (MEF) effect of Ag nanoparticles. Taking the fluorescence quantum yield of rhodamine B (Φf = 0.31) in water as a reference, HMS-Ag-R showed a higher fluorescence quantum yield of 0.25 in water compared with that of the mixture of HMS + R (Φ = 0.11). Fig. 7 showed the fluorescence changes of HMS-Ag-R with Hg(II) in 2 mM aqueous HEPES buffer medium. Free HMS-Ag-
Fig. 6
Metal-enhanced fluorescence spectra of HMS + R and HMS-Ag-R.
Fig. 7 Fluorescence spectra of HMS-Ag-R (0.1 g L−1 pH = 7.0) with different concentrations of Hg(II) (0–5 ppm) in 2 mM aqueous HEPES buffer medium. Inset: the fluorescence change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
4766 | Dalton Trans., 2014, 43, 4762–4769
Fig. 8 UV-vis absorption spectra of HMS-Ag-R with different concentrations of Hg(II) (0–5 ppm) in 2 mM aqueous HEPES buffer medium. Inset: the color change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
R solution showed very weak fluorescence intensity at about 584 nm (excited at 520 nm). Upon addition of Hg(II), a significant enhancement of fluorescence intensity at 584 nm was observed. Meanwhile, the solution showed an orange fluorescence change (Fig. 7 inset). Such changes of fluorescence were reasonably attributed to the spirolactam (nonfluorescent) to ring opened amide (fluorescent) equilibrium, which was induced by the complexation of Hg(II).46,47 The absorption spectra of HMS-Ag-R with varying Hg(II) concentrations in 2 mM aqueous HEPES buffered medium are shown in Fig. 8. Free HMS-Ag-R was colorless and exhibited almost no absorption peak in the visible wavelength range (>450 nm) due to the closed spirolactam ring. In the presence of Hg(II), the absorbance was enhanced obviously and a new peak at 562 nm was observed. Meanwhile, the color of HMS-Ag-R changed from colorless to pink (Fig. 8 inset). This result demonstrated that HMS-Ag-R could serve as a “nakedeye” chemosensor for Hg(II). The limit of detection (LOD) was calculated by the equation LOD = 3S0/k, where 3 was the factor at the 99% confidence level, S0 was the standard deviation of the blank measurements (n = 10), and k was the slope of the calibration curve. The detection limit of HMS-Ag-R for Hg(II) was determined to be as low as 0.7 ppb (Fig. 9). This result demonstrated that determination of trace amounts of Hg(II) at the parts per billion level was feasible with HMS-Ag-R chemosensor. HMS-Ag-R had a much lower detection limit than the solid chemosensor reported in our previous work.43 Furthermore, the curve of the fluorescence intensity of HMS-Ag-R against high Hg(II) concentration in the aqueous media sufficiently showed a typical sigmoidal shape (Fig. 10). This means that a mercury ion concentration can be obtained based on the fluorescence intensity from this sigmoidal curve. At the same time, with the increase of mercury ions, the color of the HMS-Ag-R suspension gradually deepened (Fig. 10 inset). Response time is an important analytical feature for the chemosensor. Fig. 11 showed the fluorescence intensity (584 nm) of HMS-Ag-R at different time intervals after adding
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
Fig. 9 Linear calibration plot for Hg(II) in low concentration. The fluorescence intensity was measured at an excitation wavelength of 520 nm, and monitored at a wavelength of 584 nm.
Fig. 10 Plot of the fluorescence intensity (584 nm) of HMS-Ag-R suspension (0.1 g L−1 pH = 7.0) with Hg(II) in high concentration. Inset: the color change of HMS-Ag-R with different concentrations of Hg(II).
Fig. 11
Response time of HMS-Ag-R with Hg(II).
3 ppm Hg(II). The fluorescence intensity increased quickly within 90 s and then remained constant with time, which showed that the Hg(II) complexation process has completed. So HMS-Ag-R could provide fast detection of Hg(II) within 90 s. We also investigated the competition-based fluorescence emission changes of HMS-Ag-R, upon addition of various
This journal is © The Royal Society of Chemistry 2014
Paper
Fig. 12 Fluorescence of HMS-Ag-R to other metal ions (30 ppm, the black bar) and to Hg(II) or the mixture of other metal ions with Hg(II) (3 ppm, the red bar).
biologically and environmentally relevant metal ions such as Ag(I), K(I), Li(I), Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions (Fig. 12). Typically, 30 ppm of competing metal ions were added into the HMS-Ag-R suspension (0.1 g L−1, pH = 7.0). After 2 min incubation, the fluorescence intensities of the resulting solutions were measured. Then, 3 ppm of Hg(II) was added to the former solution for another measurement. The fluorescence intensities of HMS-Ag-R showed no significant changes in the presence of competitive metal ions. After adding Hg(II) an obvious fluorescence response was induced, indicating the chemosensor had a high selectivity for Hg(II). The special selectivity was probably due to the following factors: the suitable coordination geometry conformation of the receptor, the larger radius of the Hg(II), the nitrogen-affinity of Hg(II) and the amide deprotonation ability of the Hg(II).48 Furthermore, the reusability and reproducibility of an excellent chemosensor are of particular interest in developing recyclable hybrid optical sensors, which could highlight their important characteristic features and desirability for industrial applications. The repeated detection/regeneration cycles were extensively studied. In these procedures, the use of specific concentrations of TPAOH made the removal of Hg(II) (decomplexation) possible. The regeneration ability of HMS-Ag-R was shown in Fig. 13. It was found that free HMS-Ag-R in 2 mM aqueous HEPES buffer medium without Hg(II) displayed a very weak fluorescence, while a significant increase of fluorescence was observed with the addition of Hg(II). However, the addition of TPAOH to the HMS-Ag-R-Hg solution caused an immediate fluorescence decrease. Subsequently, addition of Hg(II) into the suspension of HMS-Ag-R gave increased fluorescence again, and the analytical process was entirely visualized by the naked eye (Fig. 13 inset). HMS-Ag-R could reversibly bind with Hg(II) and could be used repeatedly at least for four cycles with a slight decrease in sensitivity. Finally, this chemosensor was applied to the determination of Hg(II) in tap water. Because there was no Hg(II) contained in the tap water as determined by inductively coupled plasma mass spectrometry (ICP-MS), Hg(II) was deliberately added to
Dalton Trans., 2014, 43, 4762–4769 | 4767
View Article Online
Paper
Dalton Transactions
for many practical applications in chemical, environmental and biological systems.
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Acknowledgements The authors acknowledge the financial support from the Program for New Century Excellent Talents in University (NCET-04-0270) and Central University basic research fund (DUT10LK11).
Fig. 13 Reversibility of HMS-Ag-R with the addition of Hg(II) (3 ppm) and TPAOH. Inset: the color change of HMS-Ag-R in the regeneration process.
Fig. 14 Fluorescence spectra of HMS-Ag-R (0.1 g L−1) with different concentrations of Hg(II) (0–5 ppm) in tap water. Inset: the fluorescence (top) and color (bottom) change (a) HMS-Ag-R (b) HMS-Ag-R + 5 ppm Hg(II).
simulate contaminated water. As shown in Fig. 14, the fluorescence intensity of HMS-Ag-R in tap water showed a remarkable enhancement with addition of Hg(II) (0–5 ppm) and the fluorescent color changed to bright yellow finally (Fig. 14 inset (top)). More importantly, the color of the sample also visibly changed from colorless to red (Fig. 14 inset (bottom)). The result indicated the suitability of HMS-Ag-R for the determination of Hg(II) in a natural water sample.
4.
Conclusion
In conclusion, a novel metal-enhanced fluorescence chemosensor HMS-Ag-R for Hg(II) has been prepared via a simple and effective method. The output signals include color and fluorescence, which were reversibly transduced through simply opening the spirolactam ring upon Hg(II) complexation. In the presence of competitive metal ions, HMS-Ag-R exhibited high selectivity for Hg(II) sensing in aqueous media. We believe that this metal-enhanced fluorescence platform could be explored
4768 | Dalton Trans., 2014, 43, 4762–4769
Notes and references 1 A. Renzoni, F. Zino and E. Franchi, Environ. Res., 1998, 77, 68–72. 2 G. Cabana and J. B. Rasmussen, Nature, 1994, 372, 255– 257. 3 C. J. Watras, R. C. Back, S. Halvorsen, R. J. M. Hudson, K. A. Morrison and S. P. Wente, Sci. Total Environ., 1998, 219, 183–208. 4 D. Beauchemin, Anal. Chem., 2010, 82, 4786–4810. 5 L. Ebdon, M. S. Cresser and C. W. McLeod, J. Anal. At. Spectrom., 1987, 2, 1R–28R. 6 R. Ma, C. W. McLeod, K. Tomlinson and R. K. Poole, Electrophoresis, 2004, 25, 2469–2477. 7 W. Huang, X. Zhu, D. Wua, C. He, X. Hu and C. Duan, Dalton Trans., 2009, 10457–10465. 8 L. Gao, Y. Wang, J. Wang, L. Huang, L. Shi, X. Fan, Z. Zou, T. Yu, M. Zhu and Z. Li, Inorg. Chem., 2006, 45, 6844–6850. 9 P. Mahato, S. Saha, E. Suresh, R. Di Liddo, P. P. Parnigotto, M. T. Conconi, M. K. Kesharwani, B. Ganguly and A. Das, Inorg. Chem., 2012, 51, 1769–1777. 10 J. Hatai, S. Pal, G. P. Jose and S. Bandyopadhyay, Inorg. Chem., 2012, 51, 10129–10135. 11 M. H. Lee, S. J. Lee, J. H. Jung, H. Lim and J. S. Kim, Tetrahedron, 2007, 63, 12087–12092. 12 D. T. Quang and J. S. Kim, Chem. Rev., 2010, 110, 6280– 6301. 13 C. Wang, S. Tao, W. Wei, C. Meng, F. Liu and M. Han, J. Mater. Chem., 2010, 20, 4635–4641. 14 P. Zhou, Q. Meng, G. He, H. Wu, C. Duan and X. Quan, J. Environ. Monit., 2009, 11, 648–653. 15 H. Lu, S. Qi, J. Mack, Z. Li, J. Lei, N. Kobayashi and Z. Shen, J. Mater. Chem., 2011, 21, 10878–10882. 16 J. Liu, C. Li and F. Li, J. Mater. Chem., 2011, 21, 7175–7181. 17 C. Song, X. Zhang, C. Jia, P. Zhou, X. Quan and C. Duan, Talanta, 2010, 81, 643–649. 18 N. Zhang, G. Li, J. Zhao and T. Liu, New J. Chem., 2013, 37, 458–463. 19 S. Saha, M. U. Chhatbar, P. Mahato, L. Praveen, A. K. Siddhanta and A. Das, Chem. Commun., 2012, 48, 1659–1661. 20 T. Liu, G. Li, N. Zhang and Y. Chen, J. Hazard. Mater., 2012, 201–202, 155–161.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 December 2013. Downloaded by Northeastern University on 28/10/2014 00:38:16.
Dalton Transactions
21 M. Yin, Z. Li, Z. Liu, X. Yang and J. Ren, ACS Appl. Mater. Interfaces, 2012, 4, 431–437. 22 W. Huang, C. Song, C. He, G. Lv, X. Hu, X. Zhu and C. Duan, Inorg. Chem., 2009, 48, 5061–5072. 23 C. Kaewtong, B. Wanno, Y. Uppa, N. Morakot, B. Pulpoka and T. Tuntulani, Dalton Trans., 2011, 40, 12578–12583. 24 L. Mercier and T. J. Pinnavaia, Adv. Mater., 1997, 9, 500–503. 25 U. Bach, D. Lupo, P. Comte, J. E. Moser, F. Weissörtel, J. Salbeck, H. Spreitzer and M. Grätzel, Nature, 1998, 395, 583–585. 26 M. Vallet-Regí, J. C. Doadrio, A. L. Doadrio, I. IzquierdoBarba and J. Pérez-Pariente, Solid State Ionics, 2004, 172, 435–439. 27 I. I. Slowing, J. L. Vivero-Escoto, C.-W. Wu and V. S. Y. Lin, Adv. Drug Delivery Rev., 2008, 60, 1278–1288. 28 I. I. Slowing, B. G. Trewyn, S. Giri and V. S. Y. Lin, Adv. Funct. Mater., 2007, 17, 1225–1236. 29 H. H. P. Yiu and P. A. Wright, J. Mater. Chem., 2005, 15, 3690–3700. 30 W. Huang, D. Wu, G. Wu and Z. Wang, Dalton Trans., 2012, 41, 2620–2625. 31 Y. Tao, Y. Lin, Z. Huang, J. Ren and X. Qu, Talanta, 2012, 88, 290–294. 32 V. Tharmaraj and K. Pitchumani, Nanoscale, 2011, 3, 1166– 1170. 33 Z. Huang, F. Pu, Y. Lin, J. Ren and X. Qu, Chem. Commun., 2011, 47, 3487–3489. 34 J. B. Jackson and N. J. Halas, J. Phys. Chem. B, 2001, 105, 2743–2746.
This journal is © The Royal Society of Chemistry 2014
Paper
35 M. Hu, J. Chen, Z.-Y. Li, L. Au, G. V. Hartland, X. Li, M. Marquez and Y. Xia, Chem. Soc. Rev., 2006, 35, 1084– 1094. 36 Y. Sun, B. Mayers and Y. Xia, Adv. Mater., 2003, 15, 641– 646. 37 A. Verma and V. M. Rotello, Chem. Commun., 2005, 303– 312. 38 K. Aslan, M. Wu, J. R. Lakowicz and C. D. Geddes, J. Am. Chem. Soc., 2007, 129, 1524–1525. 39 K. Aslan, Z. Leonenko, J. R. Lakowicz and C. D. Geddes, J. Fluoresc., 2005, 15, 643–654. 40 J. Yang, F. Zhang, Y. Chen, S. Qian, P. Hu, W. Li, Y. Deng, Y. Fang, L. Han, M. Luqman and D. Zhao, Chem. Commun., 2011, 47, 11618–11620. 41 C. D. Geddes and J. R. Lakowicz, J. Fluoresc., 2002, 12, 121– 129. 42 J. A. Dieringer, K. L. Wustholz, D. J. Masiello, J. P. Camden, S. L. Kleinman, G. C. Schatz and R. P. Van Duyne, J. Am. Chem. Soc., 2009, 131, 849–854. 43 N. Zhang, G. Li, Z. Cheng and X. Zuo, J. Hazard. Mater., 2012, 229–230, 404–410. 44 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 865–867. 45 A. Y. Khodakov, A. Griboval-Constant, R. Bechara and F. Villain, J. Phys. Chem. B, 2001, 105, 9805–9811. 46 Y. K. Yang, K. J. Yook and J. Tae, J. Am. Chem. Soc., 2005, 127, 16760–16761. 47 V. Dujols, F. Ford and A. W. Czarnik, J. Am. Chem. Soc., 1997, 119, 7386–7387. 48 D. Wu, W. Huang, C. Duan, Z. Lin and Q. Meng, Inorg. Chem., 2007, 46, 1538–1540.
Dalton Trans., 2014, 43, 4762–4769 | 4769
