View Article Online View Journal
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Lin, P. Chen, Z. Yuan, J. Ma and H. Chang, Chem. Commun., 2015, DOI: 10.1039/C5CC02342D.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/chemcomm
Page 1 of 4
Journal Name
ChemComm
Dynamic Article Links ► View Article Online
DOI: 10.1039/C5CC02342D
Cite this: DOI: 10.1039/c0xx00000x
ARTICLE TYPE
Isomeric Effect of Mercaptobenzoic Acids on the Preparation and Fluorescent Properties of Copper Nanoclusters Yi-Jyun Lin,┴ Po-Cheng Chen,┴ Zhiqin Yuan and Jia-Ying Ma, Huan-Tsung Chang* 5
10
15
20
25
30
35
40
45
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x An one-pot approach has been developed to synthesize copper nanoclusters (Cu NCs) aggregates from copper nitrate and mercaptobenzoic acid (MBA). Cu NCs prepared separately in the three isomers of MBA exhibit different physical and optical properties. Fluorescent metal nanoclusters (NCs) consisting of several to hundreds of atoms have attracted considerable attention in the past decades.1, 2 Water-dispersible and highly fluorescent Au and Ag NCs are commonly prepared in the presence of proteins3 and DNA templates2b, respectively. Use of a large amount of highcost DNA or protein is however disadvantageous. When compared to Au and Ag NCs, copper (Cu) NCs are less popular, mainly because they are weakly fluorescent and less stable due to easy oxidation.4 Bovine serum albumin and trypsin have been used to synthesize Cu NCs.5 Alternatively, DNA has been used to prepare Cu NCs using ascorbic acid as a reducing agent.6 To prevent using a high-cost protein or DNA as a template, small molecules such as glutathione and D-penicillamine (PA) have been used for the preparation of Cu NCs.7 However, the reported Cu NCs (aggregates) usually have weak fluorescence, poor water dispersibility, and/or less stability against salt, limiting their application. In this study, a facile and rapid method was developed for the preparation of Cu NCs using mercaptobenzoic acid (MBA) as a reducing and capping agent. Three isomers of MBA allowed preparation of Cu NCs aggregates with different physical and optical properties. As-prepared fluorescent Cu NCs aggregates show interesting and different pH-dependence optical properties, allowing differentiation of the three isomers of MBA. The waterdispersible and stable Cu NCs prepared in the presence of 2mercaptobenzoic acid (thiosalicylic acid; TA) are highly selective and sensitive for the detection of CN¯. Although TA-Cu NCs aggregates from Cu2+ and TA can be prepared at various temperatures between 25−70 °C, longer reaction time is needed at lower temperature. Reproducibility was poor when conducted at temperature higher than 70 °C, mainly due to the evaporation of THF. In the absence of MBA, DMF, THF or their mixture at 70 °C could not reduce Cu2+ to form Cu NCs aggregates.8 Time-evolution preparation of TA-Cu NCs aggregates at 70 °C was monitored by recording their absorption and fluorescence spectra (Fig. S1), showing decreased absorption background at the wavelength above 320 nm and increased This journal is © The Royal Society of Chemistry [year]
50
55
60
65
70
75
80
85
90
fluorescence intensity at 420 nm upon increasing reaction time up to 15 min. Such a high absorption background is due to the formation of dark-brown turbidity once the TA and Cu solutions were mixed. After they had reacted for 10 min, the solution became more transparent and the absorption background at the wavelength above 500 nm decreased significantly. With respect to batch-to-batch reproducibility, reaction time of 30 min was selected in this study. Fig. 1a displays that TA-Cu NCs aggregates have a visible absorption shoulder at 338 nm, which is assigned to the TA-Cu moieties.9 The absorption peaks over 270−300 nm are assigned for TA. Lack of a surface plasmon resonance absorption peak in the region of 400−700 nm reveals the absence of any large copper nanoparticles in the solutions.7c The TA-Cu NCs aggregates possess an excitation peak centered at 338 nm and an emission peak centered at 420 nm (Fig. 1a), with a quantum yield (Φf) of 13.2% using quinine sulfate as a reference. The HRTEM image displayed in Fig. 1b allows the determination of the average size of as-prepared TA-Cu NCs aggregates to be 3.7 ± 0.5 nm (100 counts). Their sizes are much larger than the reported NCs, mainly due to the formation of Cu NCs aggregates as a result of π-π stacking of surface TA ligands.10 Fig. S2 displays a small shoulder at 932.8 eV, implying the presence of Cu(0)/Cu(I) states.11 No peaks around 940.3 and 942.8 eV revealed the absence of Cu2+. The diffraction peaks reveal (053), (431), (111) and (311) planes in reference to JCPDS card no. 12-0227, 04-0836, 12-0175, respectively, which further supported the formation of the TA-Cu NCs aggregates (Fig. S3). Therefore, TA-Cu NCs aggregates likely possess a Cu0/Cu+-TA core/shell structure. As mentioned that the surface Ag+ ions play an important role to the fluorescence and stability of Ag NCs,12 we suggested that the Cu+-TA shell is important to stabilize asprepared TA-Cu NCs aggregates. The fluorescence intensity of TA-Cu NCs aggregates at 420 nm increased about one fold upon addition of 1 mM NaBH4 (a strong reducing agent), verifying the existence of Cu+ on the surfaces of as-prepared Cu NCs (Fig. S4). To further investigate the formation of TA-Cu NCs aggregates, Job’s method was applied. At a constant total amount (0.1 M) of TA and Cu2+, TA-Cu NCs aggregates prepared at a TA/Cu2+ molar ratio of 7/3 had the highest fluorescence intensity, showing a similar trend for the preparation of thiol-protected gold NCs.2a Because Cu2+ and TA form a complex in a fashion of 1:2,13 excess TA was used in the formation of strongly fluorescent TACu NCs aggregates. The Cu complexes were then reduced by TA at 70 °C to form Cu(0) cores and Cu(I)–thiolate complexes. The [journal], [year], [vol], 00–00 | 1
ChemComm Accepted Manuscript
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
www.rsc.org/xxxxxx
ChemComm
Page 2 of 4 View Article Online
5
10
15
20
25
30
35
40
45
50
Fig. 1 Characterization of TA-Cu NCs aggregates: (a) UV-Vis absorption spectra of TA (gray dotted line) and TA-Cu NCs aggregates (gray solid line), excitation (black dotted line) and emission spectra (black solid line), (b) HRTEM image. Excitation and emission wavelengths were set at 338 and 420 nm, respectively.
Cu(I)–thiolate complexes and TA on the surfaces of Cu(0) cores further interacted through π-π stacking, leading to the formation of Cu NCs aggregates. 3-MBA and 4-MBA that are the isomers of TA (Fig. 2a) were separately used to prepare 3-MBA- and 4-MBA-Cu NCs aggregates under the same condition. The TEM images of 3MBA-Cu NCs aggregates and 4-MBA-Cu NCs aggregates are displayed in Fig. S6. The 3-MBA-Cu NCs assembled to form netlike aggregates, while 4-MBA-Cu NCs assembled to form slatlike aggregates. Similar assembly behavior was reported in PA protected Ag NCs.14 Unlike TA, 3-MBA and 4-MBA formed complexes with Cu2+ mainly through Cu-S bonding. Their complexes were further reduced to form 3-MBA-, and 4-MBACu NCs aggregates at 70 °C, respectively. Fig. 2b displays different colors of TA-, 3-MBA-, and 4-MBA-Cu NCs aggregates. Relative to transparent TA-Cu NCs solution, 3-MBA-Cu and 4MBA-Cu NCs solutions are relatively turbid due to existence of some large particles. Under UV irradiation (Fig. 2c), TA-Cu NCs and 4-MBA-Cu NCs aggregates have intense blue and red colors of fluorescence, respectively, while 3-MBA-Cu NCs aggregates are weakly fluorescent. Similar to TA-Cu NCs aggregates, 3MBA- and 4-MBA-Cu NCs aggregates separately possess an absorption shoulder at around 340 nm (Fig. S5a and S5b). Higher background at wavelengths > 500 nm was observed in 3- or 4MBA-Cu NCs aggregates, mainly due to the formation of large aggregates. The 3-MBA-Cu NCs aggregates have an excitation peak centered at 334 nm and an emission peak centered at 668 nm (Fig. S5c), with Φf of 0.04%. The 4-MBA-Cu NCs aggregates have an excitation peak centered at 324 nm and an emission peak centered at 646 nm (Fig. S5d), with Φf of 0.5%. Various fluorescence colors and intensities of the Cu aggregates allow differentiation of the three isomers of MBA by the naked eye. The FTIR spectra of the three different Cu NC aggregates (Fig. S7) all do not display an SH stretching peak at 2520 cm-1, confirming the formation of Cu-S bonds.13, 15 On the other hand, a significant downshift of the carbonyl stretching peak (around 1640 cm-1) was only observed in the TA-Cu NCs aggregates, revealing the coordination of Cu with carboxylate. A broad band at 3000-3500 cm-1 was only observed in the TA-Cu NCs aggregates. Water molecule signal was not found either in 3MBA-Cu NCs or 4-MBA-Cu NCs, mainly because intermolecular hydrogen bonds were formed between carboxylate groups of the 3-MBA or 4-MBA on their surfaces.16 Due to the formation of stable intramolecular coordinates of Cu with the carboxylate and thiolate of TA, TA-Cu NCs aggregates relative to 3-MBA- and 4-MBA-Cu NCs aggregates have more compacted structures. 2 | Journal Name, [year], [vol], 00–00
55
60
65
70
75
80
85
90
95
100
105
Fig. 2 Structures (a) of TA, 3-MBA, and 4-MBA used for the preparation of Cu NCs aggregates and photographs of TA-Cu NCs (left), 3-MBA-Cu NCs (middle), and 4-MBA-Cu NCs (right) aggregates under irradiation with (b) room and (c) UV light. The fluorescence of 3-MBA-Cu NCs aggregates was found in the precipitate, not in the solution.
The turbid solutions of 3- and 4-MBA Cu NCs aggregates both became transparent at pH values greater than 9.0. Upon increasing the pH value from pH 3.0 to pH 7.0, the fluorescence intensity of 4-MBA Cu NCs aggregates decreased (ca. 61%, Fig. 3a). Similarly, the fluorescence of 3-MBA-Cu NCs aggregates decreased upon increasing pH value; about a 96% decrease was observed when the pH value was changed from 3.0 to 7.0. By contrast, the fluorescence intensity of TA-Cu NCs aggregates increased upon increasing pH value from 3.0 to 11.0 as shown in Fig. 3b. The increased fluorescence intensity of TA-Cu NCs is due to the formation of more stable TA-Cu NCs aggregates, mainly because of higher negative charges on their surfaces.17 Fig. 3c reveals that the assembly of the 4-MBA Cu NCs aggregates is important in determining their fluorescence intensity. On the other hand, the fluorescence images (Fig. 3d) obtained at pH 3.0 and 7.0 display no obvious assembly of the TA-Cu NCs aggregates. The average size and surface charges of TA-/3MBA/4-MBA-Cu NCs aggregates at pH 3.0 and 7.0 were determined by DLS and zeta potential analyses (Table S1), respectively. Such significant changes of 4-MBA-Cu NCs aggregates in their size (4100 ± 87 µm at pH 3.0 and 833 ± 83 µm at pH 7.0, respectively) and fluorescence induced by varying pH values reveal that aggregation-induced emission (AIE) plays a vital role in determining the pH-dependent fluorescence behavior of 4-MBA-Cu NCs aggregates.18 Repulsion among the carboxylate groups of 4-MBA in the 4-MBA-Cu NCs aggregates increased upon increasing pH values, leading to disassembly of 4MBA-Cu NCs aggregates. Such a pH increment induced aggregate dissolution was also found in PA stabilized Cu NCs and Au/Cu NCs.7d, 18b Because 3-MBA-Cu NCs aggregates tend to form precipitates and their fluorescence intensity was so weak, it was fail to obtain their pH-dependence fluorescence images. The pH-dependence fluorescence of TA-Cu NCs aggregates is reversible (less than 4.0% change) over a pH change cycle (3.0−7.0−3.0), while it is almost reversible (80% retained) for 4MBA-Cu NCs aggregates. The fluorescence decays of TA- and 4-MBA-Cu NCs aggregates, and TA-Cu complexes (formed without being heated at 70 °C) were further investigated to show the differences among their fluorescence. The TA-Cu NCs have two lifetimes of 8.0 ns (78.2%) and 1.0 ns (21.8%), which are comparable to reported polymer or thiolate stabilized metal NCs.1, 19 Based on the fact of an average fluorescence decay of 6.4 ns, the fluorescence of TACu NCs aggregates mainly originates from the Cu core.19b Relative to TA-Cu complexes, TA-Cu NCs aggregates have higher fluorescence intensity (about 20-fold) and a shorter This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
DOI: 10.1039/C5CC02342D
Page 3 of 4
ChemComm View Article Online
45
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
50
55
5
Fig. 3 Fluorescence (a, b) intensities and (c, d) images of 4-MBA-Cu NCs and TA-Cu NCs aggregates. Emission wavelengths were set at 646 nm for 4-MBA-Cu NCs aggregates (a and c) and at 420 nm for TA-Cu NCs aggregates (b and d). Excitation wavelengths were set at 324 and 338 nm for 4-MBA-Cu NCs and TA-Cu NCs aggregates, respectively. A Hg lamp with UV excitation filter was used to obtain the fluorescence images.
60
65
10
15
20
25
30
35
40
average fluorescence life time (6.4 vs. 7.8 ns), but a similar Stokes shift (82 vs. 80 nm). On the other hand, the 4-MBA-Cu NCs aggregates have two lifetimes of 0.5 ns (5.2%) and 121.1 ns (94.8%). The long fluorescence lifetime and large Stokes shift indicate the fluorescence of the 4-MBA-Cu NCs aggregates from interband and/or intraband electronic transition through the ligand to metal charge (LMCT) mechanism.19b, 19c In addition, AIE effect is also an important factor for longer fluorescence lifetimes and a large Stokes shift of 4-MBA-Cu NCs aggregates.18a, 19c The optical properties of TA-, 3-MBA, and 4MBA-Cu NCs aggregates are different, mainly due to their different morphologies and compositions. The carboxylate group of TA interacted with Cu NCs to form TA-Cu NCs aggregates, while the carboxylate groups of 3-/4-MBA on the surfaces of 3-/4MBA Cu NCs aggregates formed intermolecular hydrogen bonds. As a result, the size of TA-Cu NCs aggregates was smaller and their structure was more compact when compared to that of the 3MBA/4-MBA Cu NCs aggregates. Thus the TA-Cu NCs aggregates have a blue emission and a short average lifetime (6.4 ns). On the other hand, the intermolecular hydrogen bonding of 3/4-MBA Cu NCs aggregates results in pH-dependence assembly behavior. The difference (668 vs. 646 nm) between their maximum emission wavelengths is attributed to different degrees of hydrogen bonding of carboxylate groups. It is known that the formation of stronger hydrogen bonds leads to a short distance between metal atoms and a red shift in the fluorescence of Cu NCs.14 The size of 3-MBA-Cu NCs aggregates at pH 3.0 is smaller (960 ± 52 nm) than that of 4-MBA-Cu NCs aggregates (4100 ± 87 nm), supporting a compressed structure of 3-MBA-Cu NCs aggregates. Similar isomeric effects were also found in the preparation of TA-, 3-MBA, and 4-MBA Au or Ag NCs aggregates (Fig. S8). The fluorescence intensities of TA-Au and Ag NCs aggregates are however much weaker when compared to that of Cu NCs aggregates. A broad band in the m/z range 2000-14000 Da is apparent in the MS spectrum of TA-Cu NCs aggregates (Fig. S9a), which revealed the existence of several different sized TA-Cu NCs. This journal is © The Royal Society of Chemistry [year]
70
75
80
85
90
95
100
Such large sizes of Cu NCs were identified, mainly because of their compact structures.20 A band in the m/z range of 200020000 Da is also apparent for TA-Cu complexes (Fig. S9b), which is broader than that found in TA-Cu NCs aggregates, suggesting that TA-Cu NCs aggregates were formed through the size/structure focusing process of TA-Cu complexes.20 The band was not found in TA (Fig. S9c). No signal was acquired from 3and 4-MBA-Cu NCs aggregates (data not shown), mainly due to their loose structures. In addition, TA-Cu NCs aggregates revealed their size becomes larger (m/z from 4000 to 18000) after they reacted with 10 mM NaBH4 (Fig. S9d). Their MS signal intensity is significantly smaller (5 fold), mainly due to poor ionization efficiency of the larger TA-Cu NCs aggregates. The TGA traces of TA-Cu NCs, 3-MBA-Cu NCs and 4-MBACu NCs aggregates under nitrogen atmosphere exhibit different features (Fig. S10). For TA-Cu NCs aggregates, three steps of decomposition were observed in the heating process over a temperature range from 40 to 700 °C. On the other hand, only two steps of decomposition were observed in either 3- or 4-MBACu NCs aggregates. The first drop at 100 ºC due to the loss of H2O found in TA-Cu NCs aggregates is significantly higher (16.7%) than the other two aggregates (5.1% and 11.7%), confirming existence of more water molecules on the surface of TA-Cu NCs aggregates (Fig. S7). The drop at 230 ºC was only observed in TA-Cu NCs aggregates, mainly due to the loss of free TA on their surfaces. Our reasoning was supported with a twosteps decomposition of TA-Cu complexes (Fig. S10a). Around at 320 ºC, there is another loss observed in each of the three Cu NCs, which is due to the loss of capping ligands anchoring on the Cu NC surfaces. Cyanide (CN¯) is an extremely toxic lethal poison.21 Fig. S11a shows an optimal pH value (8.0) for CN¯ detection. At pH values < 8.0, HCN (pKa 9.3) is the major species that interacts weakly with Cu NCs aggregates. At pH values higher than 8.0, the Cu NCs become more stable, CN¯ accesses to the surface of Cu NCs aggregates more difficulty, and interference from OH¯ is serious.22 Fig. S11b reveals slight changes in the PL of TA-Cu NCs aggregates in the presence of NaCl up to 500 mM. Fig. 4a shows the fluorescence of TA-Cu NCs aggregates decreased upon increasing the concentration of CN¯. The insets show two linear response regions over the concentrations of 0.01 to 1 µM (R2 = 0.99) and 1 to 60 µM (R2 = 0.99), with a limit of detection at a signal-to-noise ratio 3 of 5 nM, which is 540 times lower than the maximum contaminant level (2.7 µM) in drinking water permitted by World Health Organization (WHO). Relative to Au NCs and Au nanoparticles based sensing systems,22, 23 the response of the present sensing system is much faster, mainly because it takes longer time to etch larger particles.22, 24 The Stern-Volmer fluorescence quenching constants were calculated from the two plots to be 3.4 × 106 and 2.3 × 105 M-1, respectively. At a high concentration of CN¯ (> 1 µM), it reacted with the Cu NCs aggregates to form Cu(CN)43¯, with a formation constant of 2 × 1030.25 As a result, dissociation of TA-Cu NCs aggregates occurred, with an evidence of a color change from brown to colorless (Fig. S12). At a low concentration of CN¯ (< 1 µM), fluorescence quenching is likely due to the formation of complexes of Cu2+ with TA and CN¯ on the surface of the aggregates. The selectivity (Fig. S13) of the TA-Cu NCs Journal Name, [year], [vol], 00–00 | 3
ChemComm Accepted Manuscript
DOI: 10.1039/C5CC02342D
ChemComm
Page 4 of 4 View Article Online
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
5
10
aggregates towards CN¯ was tested over 19 common anions. Only S2¯ as CN¯ caused significant quenching, mainly due to the formation of insoluble CuS (Ksp 8 × 10-37). Such excellent selectivity over the other anions is due to the specificity of the copper-cyanide chemistry. To minimize the interference from S2¯, Zn2+ (20 µM) was added into the solution as a masking agent (Fig. 4b). Practicality of this sensing system was validated by the analysis of CN¯ in a represented spiked pond water sample (Fig. S14), with a good linear correlation (R2 = 0.99) between the intensity ratio (IF0/IF) at 420 nm and the spiked CN¯ over the concentration range from 0.01 to 1 µM.
50
55
60
65
15
Fig. 4 Detection of CN¯ in standard solutions without (a) and with (b) containing interfering species using TA-Cu NCs aggregates (0.05X). Insets to (a): plots of fluorescence intensity ratio (IF/IF0) vs. CN¯ concentration over the ranges of 0−1.0 µM (top) and 1.0−60.0 µM (bottom). PB solutions (10 mM, pH 8.0) were used to prepare the standard solutions. (b) PB solutions
Conclusions 20
25
30
We demonstrated isomeric effects of MBA on the synthesis and fluorescence of Cu NCs. TA-Cu NCs aggregates have the strongest fluorescence, while 4-MBA-Cu NCs aggregates possess an interesting AIE effect. TA-Cu NCs and 4-MBA-Cu NCs aggregates exhibit different pH-dependent fluorescence properties upon increasing pH values. Practicality of the fluorescent TA-Cu NCs aggregates was validated for sensitive and selective detection of CN¯. This study was supported by the Ministry of Science and Technology of Taiwan (Contract number: NSC101-2113-M-002002-MY3 and 103-2811-M-002-169).
70
75
80
85
Notes and references ┴
35
These authors contributed equally to this work. Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan. E-mail: [email protected]; Fax: +886-2-3366-1171; Tel: +886-2-3366-1171 † Electronic Supplementary Information (ESI) available: Experimental section and Fig. S1–S14. See DOI: 10.1039/c000000x/
90
95 40
45
1. J. Zheng, P. R. Nicovich and R. M. Dickson, Annu. Rev. Phys. Chem., 2007, 58, 409-431. 2. (a)Z. Luo, K. Zheng and J. Xie, Chem. Commun., 2014, 50, 51435155; (b)Z. Yuan, Y.-C. Chen, H.-W. Li and H.-T. Chang, Chem. Commun., 2014, 50, 9800-9815; (c)Y.-C. Shiang, C.-C. Huang, W.-Y. Chen, P.-C. Chen and H.-T. Chang, J. Mater. Chem., 2012, 22, 1297212982; (d)J. Liu, TrAC, Trends Anal. Chem., 2014, 58, 99-111. 3. N. Goswami, K. Zheng and J. Xie, Nanoscale, 2014, 6, 13328-13347. 4. (a)R. Ghosh, A. K. Sahoo, S. S. Ghosh, A. Paul and A. Chattopadhyay, ACS Appl. Mater. Interfaces, 2014, 6, 3822-3828; (b)N. Vilar-Vidal, M.
4 | Journal Name, [year], [vol], 00–00
100
C. Blanco, M. A. López-Quintela, J. Rivas and C. Serra, J. Phys. Chem. C, 2010, 114, 15924-15930. 5. (a)N. Goswami, A. Giri, M. S. Bootharaju, P. L. Xavier, T. Pradeep and S. K. Pal, Anal. Chem., 2011, 83, 9676-9680; (b)C. Wang, C. Wang, L. Xu, H. Cheng, Q. Lin and C. Zhang, Nanoscale, 2014, 6, 1775-1781. 6. (a)Z. Qing, X. He, D. He, K. Wang, F. Xu, T. Qing and X. Yang, Angew. Chem., Int. Ed., 2013, 52, 9719-9722; (b)J. Chen, J. Liu, Z. Fang and L. Zeng, Chem. Commun., 2012, 48, 1057-1059; (c)Z. Zhou, Y. Du and S. Dong, Anal. Chem., 2011, 83, 5122-5127. 7. (a)W. Wei, Y. Lu, W. Chen and S. Chen, J. Am. Chem. Soc., 2011, 133, 2060-2063; (b)J.-Y. Ma, P.-C. Chen and H.-T. Chang, Nanotechnology, 2014, 25, 195502; (c)X. Jia, J. Li and E. Wang, Small, 2013, 9, 3873-3879; (d)X. Jia, X. Yang, J. Li, D. Li and E. Wang, Chem. Commun., 2014, 50, 237-239. 8. (a)I. Chakraborty, T. Udayabhaskararao and T. Pradeep, Chem. Commun., 2012, 48, 6788-6790; (b)Y. Negishi and T. Tsukuda, J. Am. Chem. Soc., 2003, 125, 4046-4047; (c)X. Yang, M. Shi, R. Zhou, X. Chen and H. Chen, Nanoscale, 2011, 3, 2596-2601. 9. M. S. Abu-Bakr, Monatsh. Chem., 1997, 128, 563-570. 10. C. Ma, Q. Zhang, R. Zhang and D. Wang, Chem. -Eur. J., 2006, 12, 420-428. 11. N. Pauly, S. Tougaard and F. Yubero, Surf. Sci., 2014, 620, 17-22. 12. X. Yuan, T. J. Yeow, Q. Zhang, J. Y. Lee and J. Xie, Nanoscale, 2012, 4, 1968-1971. 13. K. Idriss, M. Saleh, H. Sedaira, M. M. Seleim and E. Hashem, Monatsh Chem, 1991, 122, 507-520. 14. X. Jia, J. Li and E. Wang, Chem. Commun., 2014, 50, 9565-9568. 15. Y. Tan, Y. Wang, L. Jiang and D. Zhu, J. Colloid Interface Sci., 2002, 249, 336-345. 16. K. V. Vivekananda, S. Dey, A. Wadawale, N. Bhuvanesh and V. K. Jain, Eur. J. Inorg. Chem., 2014, 2014, 2153-2161. 17. Z. Wu and R. Jin, Nano Lett., 2010, 10, 2568-2573. 18. (a)Z. Luo, X. Yuan, Y. Yu, Q. Zhang, D. T. Leong, J. Y. Lee and J. Xie, J. Am. Chem. Soc., 2012, 134, 16662-16670; (b)P.-C. Chen, J.-Y. Ma, L.-Y. Chen, G.-L. Lin, C.-C. Shih, T.-Y. Lin and H.-T. Chang, Nanoscale, 2014, 6, 3503-3507. 19. (a)Z. Yuan, N. Cai, Y. Du, Y. He and E. S. Yeung, Anal. Chem., 2013, 86, 419-426; (b)X. Le Guevel, B. Hotzer, G. Jung, K. Hollemeyer, V. Trouillet and M. Schneider, J. Phys. Chem. C, 2011, 115, 1095510963; (c)J. Zheng, C. Zhou, M. Yu and J. Liu, Nanoscale, 2012, 4, 40734083. 20. X. Yuan, M. I. Setyawati, A. S. Tan, C. N. Ong, D. T. Leong and J. Xie, NPG Asia Materials, 2013, 5, e39. 21. P. Jensen, M. T. Wilson, R. Aasa and B. G. Malmström, Biochem. J., 1984, 224, 829-837. 22. Y. Liu, K. Ai, X. Cheng, L. Huo and L. Lu, Adv. Funct. Mater., 2010, 20, 951-956. 23. (a)Y. Du, Z. Yuan, D. Xu, N. Cai, Y. He and E. S. Yeung, J. Chin. Chem. Soc. , 2013, 60, 1347-1352; (b)L. Shang, L. Jin and S. Dong, Chem. Commun., 2009, 3077-3079. 24. C.-Y. Liu and W.-L. Tseng, Chem. Commun., 2011, 47, 2550-2552. 25. R. M. Izatt, H. D. Johnston, G. D. Watt and J. J. Christensen, Inorg. Chem., 1967, 6, 132-135.
105
This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
DOI: 10.1039/C5CC02342D
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Lin, P. Chen, Z. Yuan, J. Ma and H. Chang, Chem. Commun., 2015, DOI: 10.1039/C5CC02342D.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/chemcomm
Page 1 of 4
Journal Name
ChemComm
Dynamic Article Links ► View Article Online
DOI: 10.1039/C5CC02342D
Cite this: DOI: 10.1039/c0xx00000x
ARTICLE TYPE
Isomeric Effect of Mercaptobenzoic Acids on the Preparation and Fluorescent Properties of Copper Nanoclusters Yi-Jyun Lin,┴ Po-Cheng Chen,┴ Zhiqin Yuan and Jia-Ying Ma, Huan-Tsung Chang* 5
10
15
20
25
30
35
40
45
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x An one-pot approach has been developed to synthesize copper nanoclusters (Cu NCs) aggregates from copper nitrate and mercaptobenzoic acid (MBA). Cu NCs prepared separately in the three isomers of MBA exhibit different physical and optical properties. Fluorescent metal nanoclusters (NCs) consisting of several to hundreds of atoms have attracted considerable attention in the past decades.1, 2 Water-dispersible and highly fluorescent Au and Ag NCs are commonly prepared in the presence of proteins3 and DNA templates2b, respectively. Use of a large amount of highcost DNA or protein is however disadvantageous. When compared to Au and Ag NCs, copper (Cu) NCs are less popular, mainly because they are weakly fluorescent and less stable due to easy oxidation.4 Bovine serum albumin and trypsin have been used to synthesize Cu NCs.5 Alternatively, DNA has been used to prepare Cu NCs using ascorbic acid as a reducing agent.6 To prevent using a high-cost protein or DNA as a template, small molecules such as glutathione and D-penicillamine (PA) have been used for the preparation of Cu NCs.7 However, the reported Cu NCs (aggregates) usually have weak fluorescence, poor water dispersibility, and/or less stability against salt, limiting their application. In this study, a facile and rapid method was developed for the preparation of Cu NCs using mercaptobenzoic acid (MBA) as a reducing and capping agent. Three isomers of MBA allowed preparation of Cu NCs aggregates with different physical and optical properties. As-prepared fluorescent Cu NCs aggregates show interesting and different pH-dependence optical properties, allowing differentiation of the three isomers of MBA. The waterdispersible and stable Cu NCs prepared in the presence of 2mercaptobenzoic acid (thiosalicylic acid; TA) are highly selective and sensitive for the detection of CN¯. Although TA-Cu NCs aggregates from Cu2+ and TA can be prepared at various temperatures between 25−70 °C, longer reaction time is needed at lower temperature. Reproducibility was poor when conducted at temperature higher than 70 °C, mainly due to the evaporation of THF. In the absence of MBA, DMF, THF or their mixture at 70 °C could not reduce Cu2+ to form Cu NCs aggregates.8 Time-evolution preparation of TA-Cu NCs aggregates at 70 °C was monitored by recording their absorption and fluorescence spectra (Fig. S1), showing decreased absorption background at the wavelength above 320 nm and increased This journal is © The Royal Society of Chemistry [year]
50
55
60
65
70
75
80
85
90
fluorescence intensity at 420 nm upon increasing reaction time up to 15 min. Such a high absorption background is due to the formation of dark-brown turbidity once the TA and Cu solutions were mixed. After they had reacted for 10 min, the solution became more transparent and the absorption background at the wavelength above 500 nm decreased significantly. With respect to batch-to-batch reproducibility, reaction time of 30 min was selected in this study. Fig. 1a displays that TA-Cu NCs aggregates have a visible absorption shoulder at 338 nm, which is assigned to the TA-Cu moieties.9 The absorption peaks over 270−300 nm are assigned for TA. Lack of a surface plasmon resonance absorption peak in the region of 400−700 nm reveals the absence of any large copper nanoparticles in the solutions.7c The TA-Cu NCs aggregates possess an excitation peak centered at 338 nm and an emission peak centered at 420 nm (Fig. 1a), with a quantum yield (Φf) of 13.2% using quinine sulfate as a reference. The HRTEM image displayed in Fig. 1b allows the determination of the average size of as-prepared TA-Cu NCs aggregates to be 3.7 ± 0.5 nm (100 counts). Their sizes are much larger than the reported NCs, mainly due to the formation of Cu NCs aggregates as a result of π-π stacking of surface TA ligands.10 Fig. S2 displays a small shoulder at 932.8 eV, implying the presence of Cu(0)/Cu(I) states.11 No peaks around 940.3 and 942.8 eV revealed the absence of Cu2+. The diffraction peaks reveal (053), (431), (111) and (311) planes in reference to JCPDS card no. 12-0227, 04-0836, 12-0175, respectively, which further supported the formation of the TA-Cu NCs aggregates (Fig. S3). Therefore, TA-Cu NCs aggregates likely possess a Cu0/Cu+-TA core/shell structure. As mentioned that the surface Ag+ ions play an important role to the fluorescence and stability of Ag NCs,12 we suggested that the Cu+-TA shell is important to stabilize asprepared TA-Cu NCs aggregates. The fluorescence intensity of TA-Cu NCs aggregates at 420 nm increased about one fold upon addition of 1 mM NaBH4 (a strong reducing agent), verifying the existence of Cu+ on the surfaces of as-prepared Cu NCs (Fig. S4). To further investigate the formation of TA-Cu NCs aggregates, Job’s method was applied. At a constant total amount (0.1 M) of TA and Cu2+, TA-Cu NCs aggregates prepared at a TA/Cu2+ molar ratio of 7/3 had the highest fluorescence intensity, showing a similar trend for the preparation of thiol-protected gold NCs.2a Because Cu2+ and TA form a complex in a fashion of 1:2,13 excess TA was used in the formation of strongly fluorescent TACu NCs aggregates. The Cu complexes were then reduced by TA at 70 °C to form Cu(0) cores and Cu(I)–thiolate complexes. The [journal], [year], [vol], 00–00 | 1
ChemComm Accepted Manuscript
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
www.rsc.org/xxxxxx
ChemComm
Page 2 of 4 View Article Online
5
10
15
20
25
30
35
40
45
50
Fig. 1 Characterization of TA-Cu NCs aggregates: (a) UV-Vis absorption spectra of TA (gray dotted line) and TA-Cu NCs aggregates (gray solid line), excitation (black dotted line) and emission spectra (black solid line), (b) HRTEM image. Excitation and emission wavelengths were set at 338 and 420 nm, respectively.
Cu(I)–thiolate complexes and TA on the surfaces of Cu(0) cores further interacted through π-π stacking, leading to the formation of Cu NCs aggregates. 3-MBA and 4-MBA that are the isomers of TA (Fig. 2a) were separately used to prepare 3-MBA- and 4-MBA-Cu NCs aggregates under the same condition. The TEM images of 3MBA-Cu NCs aggregates and 4-MBA-Cu NCs aggregates are displayed in Fig. S6. The 3-MBA-Cu NCs assembled to form netlike aggregates, while 4-MBA-Cu NCs assembled to form slatlike aggregates. Similar assembly behavior was reported in PA protected Ag NCs.14 Unlike TA, 3-MBA and 4-MBA formed complexes with Cu2+ mainly through Cu-S bonding. Their complexes were further reduced to form 3-MBA-, and 4-MBACu NCs aggregates at 70 °C, respectively. Fig. 2b displays different colors of TA-, 3-MBA-, and 4-MBA-Cu NCs aggregates. Relative to transparent TA-Cu NCs solution, 3-MBA-Cu and 4MBA-Cu NCs solutions are relatively turbid due to existence of some large particles. Under UV irradiation (Fig. 2c), TA-Cu NCs and 4-MBA-Cu NCs aggregates have intense blue and red colors of fluorescence, respectively, while 3-MBA-Cu NCs aggregates are weakly fluorescent. Similar to TA-Cu NCs aggregates, 3MBA- and 4-MBA-Cu NCs aggregates separately possess an absorption shoulder at around 340 nm (Fig. S5a and S5b). Higher background at wavelengths > 500 nm was observed in 3- or 4MBA-Cu NCs aggregates, mainly due to the formation of large aggregates. The 3-MBA-Cu NCs aggregates have an excitation peak centered at 334 nm and an emission peak centered at 668 nm (Fig. S5c), with Φf of 0.04%. The 4-MBA-Cu NCs aggregates have an excitation peak centered at 324 nm and an emission peak centered at 646 nm (Fig. S5d), with Φf of 0.5%. Various fluorescence colors and intensities of the Cu aggregates allow differentiation of the three isomers of MBA by the naked eye. The FTIR spectra of the three different Cu NC aggregates (Fig. S7) all do not display an SH stretching peak at 2520 cm-1, confirming the formation of Cu-S bonds.13, 15 On the other hand, a significant downshift of the carbonyl stretching peak (around 1640 cm-1) was only observed in the TA-Cu NCs aggregates, revealing the coordination of Cu with carboxylate. A broad band at 3000-3500 cm-1 was only observed in the TA-Cu NCs aggregates. Water molecule signal was not found either in 3MBA-Cu NCs or 4-MBA-Cu NCs, mainly because intermolecular hydrogen bonds were formed between carboxylate groups of the 3-MBA or 4-MBA on their surfaces.16 Due to the formation of stable intramolecular coordinates of Cu with the carboxylate and thiolate of TA, TA-Cu NCs aggregates relative to 3-MBA- and 4-MBA-Cu NCs aggregates have more compacted structures. 2 | Journal Name, [year], [vol], 00–00
55
60
65
70
75
80
85
90
95
100
105
Fig. 2 Structures (a) of TA, 3-MBA, and 4-MBA used for the preparation of Cu NCs aggregates and photographs of TA-Cu NCs (left), 3-MBA-Cu NCs (middle), and 4-MBA-Cu NCs (right) aggregates under irradiation with (b) room and (c) UV light. The fluorescence of 3-MBA-Cu NCs aggregates was found in the precipitate, not in the solution.
The turbid solutions of 3- and 4-MBA Cu NCs aggregates both became transparent at pH values greater than 9.0. Upon increasing the pH value from pH 3.0 to pH 7.0, the fluorescence intensity of 4-MBA Cu NCs aggregates decreased (ca. 61%, Fig. 3a). Similarly, the fluorescence of 3-MBA-Cu NCs aggregates decreased upon increasing pH value; about a 96% decrease was observed when the pH value was changed from 3.0 to 7.0. By contrast, the fluorescence intensity of TA-Cu NCs aggregates increased upon increasing pH value from 3.0 to 11.0 as shown in Fig. 3b. The increased fluorescence intensity of TA-Cu NCs is due to the formation of more stable TA-Cu NCs aggregates, mainly because of higher negative charges on their surfaces.17 Fig. 3c reveals that the assembly of the 4-MBA Cu NCs aggregates is important in determining their fluorescence intensity. On the other hand, the fluorescence images (Fig. 3d) obtained at pH 3.0 and 7.0 display no obvious assembly of the TA-Cu NCs aggregates. The average size and surface charges of TA-/3MBA/4-MBA-Cu NCs aggregates at pH 3.0 and 7.0 were determined by DLS and zeta potential analyses (Table S1), respectively. Such significant changes of 4-MBA-Cu NCs aggregates in their size (4100 ± 87 µm at pH 3.0 and 833 ± 83 µm at pH 7.0, respectively) and fluorescence induced by varying pH values reveal that aggregation-induced emission (AIE) plays a vital role in determining the pH-dependent fluorescence behavior of 4-MBA-Cu NCs aggregates.18 Repulsion among the carboxylate groups of 4-MBA in the 4-MBA-Cu NCs aggregates increased upon increasing pH values, leading to disassembly of 4MBA-Cu NCs aggregates. Such a pH increment induced aggregate dissolution was also found in PA stabilized Cu NCs and Au/Cu NCs.7d, 18b Because 3-MBA-Cu NCs aggregates tend to form precipitates and their fluorescence intensity was so weak, it was fail to obtain their pH-dependence fluorescence images. The pH-dependence fluorescence of TA-Cu NCs aggregates is reversible (less than 4.0% change) over a pH change cycle (3.0−7.0−3.0), while it is almost reversible (80% retained) for 4MBA-Cu NCs aggregates. The fluorescence decays of TA- and 4-MBA-Cu NCs aggregates, and TA-Cu complexes (formed without being heated at 70 °C) were further investigated to show the differences among their fluorescence. The TA-Cu NCs have two lifetimes of 8.0 ns (78.2%) and 1.0 ns (21.8%), which are comparable to reported polymer or thiolate stabilized metal NCs.1, 19 Based on the fact of an average fluorescence decay of 6.4 ns, the fluorescence of TACu NCs aggregates mainly originates from the Cu core.19b Relative to TA-Cu complexes, TA-Cu NCs aggregates have higher fluorescence intensity (about 20-fold) and a shorter This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
DOI: 10.1039/C5CC02342D
Page 3 of 4
ChemComm View Article Online
45
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
50
55
5
Fig. 3 Fluorescence (a, b) intensities and (c, d) images of 4-MBA-Cu NCs and TA-Cu NCs aggregates. Emission wavelengths were set at 646 nm for 4-MBA-Cu NCs aggregates (a and c) and at 420 nm for TA-Cu NCs aggregates (b and d). Excitation wavelengths were set at 324 and 338 nm for 4-MBA-Cu NCs and TA-Cu NCs aggregates, respectively. A Hg lamp with UV excitation filter was used to obtain the fluorescence images.
60
65
10
15
20
25
30
35
40
average fluorescence life time (6.4 vs. 7.8 ns), but a similar Stokes shift (82 vs. 80 nm). On the other hand, the 4-MBA-Cu NCs aggregates have two lifetimes of 0.5 ns (5.2%) and 121.1 ns (94.8%). The long fluorescence lifetime and large Stokes shift indicate the fluorescence of the 4-MBA-Cu NCs aggregates from interband and/or intraband electronic transition through the ligand to metal charge (LMCT) mechanism.19b, 19c In addition, AIE effect is also an important factor for longer fluorescence lifetimes and a large Stokes shift of 4-MBA-Cu NCs aggregates.18a, 19c The optical properties of TA-, 3-MBA, and 4MBA-Cu NCs aggregates are different, mainly due to their different morphologies and compositions. The carboxylate group of TA interacted with Cu NCs to form TA-Cu NCs aggregates, while the carboxylate groups of 3-/4-MBA on the surfaces of 3-/4MBA Cu NCs aggregates formed intermolecular hydrogen bonds. As a result, the size of TA-Cu NCs aggregates was smaller and their structure was more compact when compared to that of the 3MBA/4-MBA Cu NCs aggregates. Thus the TA-Cu NCs aggregates have a blue emission and a short average lifetime (6.4 ns). On the other hand, the intermolecular hydrogen bonding of 3/4-MBA Cu NCs aggregates results in pH-dependence assembly behavior. The difference (668 vs. 646 nm) between their maximum emission wavelengths is attributed to different degrees of hydrogen bonding of carboxylate groups. It is known that the formation of stronger hydrogen bonds leads to a short distance between metal atoms and a red shift in the fluorescence of Cu NCs.14 The size of 3-MBA-Cu NCs aggregates at pH 3.0 is smaller (960 ± 52 nm) than that of 4-MBA-Cu NCs aggregates (4100 ± 87 nm), supporting a compressed structure of 3-MBA-Cu NCs aggregates. Similar isomeric effects were also found in the preparation of TA-, 3-MBA, and 4-MBA Au or Ag NCs aggregates (Fig. S8). The fluorescence intensities of TA-Au and Ag NCs aggregates are however much weaker when compared to that of Cu NCs aggregates. A broad band in the m/z range 2000-14000 Da is apparent in the MS spectrum of TA-Cu NCs aggregates (Fig. S9a), which revealed the existence of several different sized TA-Cu NCs. This journal is © The Royal Society of Chemistry [year]
70
75
80
85
90
95
100
Such large sizes of Cu NCs were identified, mainly because of their compact structures.20 A band in the m/z range of 200020000 Da is also apparent for TA-Cu complexes (Fig. S9b), which is broader than that found in TA-Cu NCs aggregates, suggesting that TA-Cu NCs aggregates were formed through the size/structure focusing process of TA-Cu complexes.20 The band was not found in TA (Fig. S9c). No signal was acquired from 3and 4-MBA-Cu NCs aggregates (data not shown), mainly due to their loose structures. In addition, TA-Cu NCs aggregates revealed their size becomes larger (m/z from 4000 to 18000) after they reacted with 10 mM NaBH4 (Fig. S9d). Their MS signal intensity is significantly smaller (5 fold), mainly due to poor ionization efficiency of the larger TA-Cu NCs aggregates. The TGA traces of TA-Cu NCs, 3-MBA-Cu NCs and 4-MBACu NCs aggregates under nitrogen atmosphere exhibit different features (Fig. S10). For TA-Cu NCs aggregates, three steps of decomposition were observed in the heating process over a temperature range from 40 to 700 °C. On the other hand, only two steps of decomposition were observed in either 3- or 4-MBACu NCs aggregates. The first drop at 100 ºC due to the loss of H2O found in TA-Cu NCs aggregates is significantly higher (16.7%) than the other two aggregates (5.1% and 11.7%), confirming existence of more water molecules on the surface of TA-Cu NCs aggregates (Fig. S7). The drop at 230 ºC was only observed in TA-Cu NCs aggregates, mainly due to the loss of free TA on their surfaces. Our reasoning was supported with a twosteps decomposition of TA-Cu complexes (Fig. S10a). Around at 320 ºC, there is another loss observed in each of the three Cu NCs, which is due to the loss of capping ligands anchoring on the Cu NC surfaces. Cyanide (CN¯) is an extremely toxic lethal poison.21 Fig. S11a shows an optimal pH value (8.0) for CN¯ detection. At pH values < 8.0, HCN (pKa 9.3) is the major species that interacts weakly with Cu NCs aggregates. At pH values higher than 8.0, the Cu NCs become more stable, CN¯ accesses to the surface of Cu NCs aggregates more difficulty, and interference from OH¯ is serious.22 Fig. S11b reveals slight changes in the PL of TA-Cu NCs aggregates in the presence of NaCl up to 500 mM. Fig. 4a shows the fluorescence of TA-Cu NCs aggregates decreased upon increasing the concentration of CN¯. The insets show two linear response regions over the concentrations of 0.01 to 1 µM (R2 = 0.99) and 1 to 60 µM (R2 = 0.99), with a limit of detection at a signal-to-noise ratio 3 of 5 nM, which is 540 times lower than the maximum contaminant level (2.7 µM) in drinking water permitted by World Health Organization (WHO). Relative to Au NCs and Au nanoparticles based sensing systems,22, 23 the response of the present sensing system is much faster, mainly because it takes longer time to etch larger particles.22, 24 The Stern-Volmer fluorescence quenching constants were calculated from the two plots to be 3.4 × 106 and 2.3 × 105 M-1, respectively. At a high concentration of CN¯ (> 1 µM), it reacted with the Cu NCs aggregates to form Cu(CN)43¯, with a formation constant of 2 × 1030.25 As a result, dissociation of TA-Cu NCs aggregates occurred, with an evidence of a color change from brown to colorless (Fig. S12). At a low concentration of CN¯ (< 1 µM), fluorescence quenching is likely due to the formation of complexes of Cu2+ with TA and CN¯ on the surface of the aggregates. The selectivity (Fig. S13) of the TA-Cu NCs Journal Name, [year], [vol], 00–00 | 3
ChemComm Accepted Manuscript
DOI: 10.1039/C5CC02342D
ChemComm
Page 4 of 4 View Article Online
Published on 19 June 2015. Downloaded by University of California - Santa Barbara on 24/06/2015 03:49:21.
5
10
aggregates towards CN¯ was tested over 19 common anions. Only S2¯ as CN¯ caused significant quenching, mainly due to the formation of insoluble CuS (Ksp 8 × 10-37). Such excellent selectivity over the other anions is due to the specificity of the copper-cyanide chemistry. To minimize the interference from S2¯, Zn2+ (20 µM) was added into the solution as a masking agent (Fig. 4b). Practicality of this sensing system was validated by the analysis of CN¯ in a represented spiked pond water sample (Fig. S14), with a good linear correlation (R2 = 0.99) between the intensity ratio (IF0/IF) at 420 nm and the spiked CN¯ over the concentration range from 0.01 to 1 µM.
50
55
60
65
15
Fig. 4 Detection of CN¯ in standard solutions without (a) and with (b) containing interfering species using TA-Cu NCs aggregates (0.05X). Insets to (a): plots of fluorescence intensity ratio (IF/IF0) vs. CN¯ concentration over the ranges of 0−1.0 µM (top) and 1.0−60.0 µM (bottom). PB solutions (10 mM, pH 8.0) were used to prepare the standard solutions. (b) PB solutions
Conclusions 20
25
30
We demonstrated isomeric effects of MBA on the synthesis and fluorescence of Cu NCs. TA-Cu NCs aggregates have the strongest fluorescence, while 4-MBA-Cu NCs aggregates possess an interesting AIE effect. TA-Cu NCs and 4-MBA-Cu NCs aggregates exhibit different pH-dependent fluorescence properties upon increasing pH values. Practicality of the fluorescent TA-Cu NCs aggregates was validated for sensitive and selective detection of CN¯. This study was supported by the Ministry of Science and Technology of Taiwan (Contract number: NSC101-2113-M-002002-MY3 and 103-2811-M-002-169).
70
75
80
85
Notes and references ┴
35
These authors contributed equally to this work. Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan. E-mail: [email protected]; Fax: +886-2-3366-1171; Tel: +886-2-3366-1171 † Electronic Supplementary Information (ESI) available: Experimental section and Fig. S1–S14. See DOI: 10.1039/c000000x/
90
95 40
45
1. J. Zheng, P. R. Nicovich and R. M. Dickson, Annu. Rev. Phys. Chem., 2007, 58, 409-431. 2. (a)Z. Luo, K. Zheng and J. Xie, Chem. Commun., 2014, 50, 51435155; (b)Z. Yuan, Y.-C. Chen, H.-W. Li and H.-T. Chang, Chem. Commun., 2014, 50, 9800-9815; (c)Y.-C. Shiang, C.-C. Huang, W.-Y. Chen, P.-C. Chen and H.-T. Chang, J. Mater. Chem., 2012, 22, 1297212982; (d)J. Liu, TrAC, Trends Anal. Chem., 2014, 58, 99-111. 3. N. Goswami, K. Zheng and J. Xie, Nanoscale, 2014, 6, 13328-13347. 4. (a)R. Ghosh, A. K. Sahoo, S. S. Ghosh, A. Paul and A. Chattopadhyay, ACS Appl. Mater. Interfaces, 2014, 6, 3822-3828; (b)N. Vilar-Vidal, M.
4 | Journal Name, [year], [vol], 00–00
100
C. Blanco, M. A. López-Quintela, J. Rivas and C. Serra, J. Phys. Chem. C, 2010, 114, 15924-15930. 5. (a)N. Goswami, A. Giri, M. S. Bootharaju, P. L. Xavier, T. Pradeep and S. K. Pal, Anal. Chem., 2011, 83, 9676-9680; (b)C. Wang, C. Wang, L. Xu, H. Cheng, Q. Lin and C. Zhang, Nanoscale, 2014, 6, 1775-1781. 6. (a)Z. Qing, X. He, D. He, K. Wang, F. Xu, T. Qing and X. Yang, Angew. Chem., Int. Ed., 2013, 52, 9719-9722; (b)J. Chen, J. Liu, Z. Fang and L. Zeng, Chem. Commun., 2012, 48, 1057-1059; (c)Z. Zhou, Y. Du and S. Dong, Anal. Chem., 2011, 83, 5122-5127. 7. (a)W. Wei, Y. Lu, W. Chen and S. Chen, J. Am. Chem. Soc., 2011, 133, 2060-2063; (b)J.-Y. Ma, P.-C. Chen and H.-T. Chang, Nanotechnology, 2014, 25, 195502; (c)X. Jia, J. Li and E. Wang, Small, 2013, 9, 3873-3879; (d)X. Jia, X. Yang, J. Li, D. Li and E. Wang, Chem. Commun., 2014, 50, 237-239. 8. (a)I. Chakraborty, T. Udayabhaskararao and T. Pradeep, Chem. Commun., 2012, 48, 6788-6790; (b)Y. Negishi and T. Tsukuda, J. Am. Chem. Soc., 2003, 125, 4046-4047; (c)X. Yang, M. Shi, R. Zhou, X. Chen and H. Chen, Nanoscale, 2011, 3, 2596-2601. 9. M. S. Abu-Bakr, Monatsh. Chem., 1997, 128, 563-570. 10. C. Ma, Q. Zhang, R. Zhang and D. Wang, Chem. -Eur. J., 2006, 12, 420-428. 11. N. Pauly, S. Tougaard and F. Yubero, Surf. Sci., 2014, 620, 17-22. 12. X. Yuan, T. J. Yeow, Q. Zhang, J. Y. Lee and J. Xie, Nanoscale, 2012, 4, 1968-1971. 13. K. Idriss, M. Saleh, H. Sedaira, M. M. Seleim and E. Hashem, Monatsh Chem, 1991, 122, 507-520. 14. X. Jia, J. Li and E. Wang, Chem. Commun., 2014, 50, 9565-9568. 15. Y. Tan, Y. Wang, L. Jiang and D. Zhu, J. Colloid Interface Sci., 2002, 249, 336-345. 16. K. V. Vivekananda, S. Dey, A. Wadawale, N. Bhuvanesh and V. K. Jain, Eur. J. Inorg. Chem., 2014, 2014, 2153-2161. 17. Z. Wu and R. Jin, Nano Lett., 2010, 10, 2568-2573. 18. (a)Z. Luo, X. Yuan, Y. Yu, Q. Zhang, D. T. Leong, J. Y. Lee and J. Xie, J. Am. Chem. Soc., 2012, 134, 16662-16670; (b)P.-C. Chen, J.-Y. Ma, L.-Y. Chen, G.-L. Lin, C.-C. Shih, T.-Y. Lin and H.-T. Chang, Nanoscale, 2014, 6, 3503-3507. 19. (a)Z. Yuan, N. Cai, Y. Du, Y. He and E. S. Yeung, Anal. Chem., 2013, 86, 419-426; (b)X. Le Guevel, B. Hotzer, G. Jung, K. Hollemeyer, V. Trouillet and M. Schneider, J. Phys. Chem. C, 2011, 115, 1095510963; (c)J. Zheng, C. Zhou, M. Yu and J. Liu, Nanoscale, 2012, 4, 40734083. 20. X. Yuan, M. I. Setyawati, A. S. Tan, C. N. Ong, D. T. Leong and J. Xie, NPG Asia Materials, 2013, 5, e39. 21. P. Jensen, M. T. Wilson, R. Aasa and B. G. Malmström, Biochem. J., 1984, 224, 829-837. 22. Y. Liu, K. Ai, X. Cheng, L. Huo and L. Lu, Adv. Funct. Mater., 2010, 20, 951-956. 23. (a)Y. Du, Z. Yuan, D. Xu, N. Cai, Y. He and E. S. Yeung, J. Chin. Chem. Soc. , 2013, 60, 1347-1352; (b)L. Shang, L. Jin and S. Dong, Chem. Commun., 2009, 3077-3079. 24. C.-Y. Liu and W.-L. Tseng, Chem. Commun., 2011, 47, 2550-2552. 25. R. M. Izatt, H. D. Johnston, G. D. Watt and J. J. Christensen, Inorg. Chem., 1967, 6, 132-135.
105
This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
DOI: 10.1039/C5CC02342D
