Chemiluminescent properties of a fluorescent SiC·SiO_x composite

Abstract

Chemiluminescence (CL) happened in chemical reactions, in which electronically excited intermediates or products were obtained and subsequently released energy with emission of light. CL is a useful approach to investigate active radicals involved in one system. In the present work, we first found SiC·SiO_x, a new kind of zero-dimensional silicon-based nanomaterial, owned CL properties in the presence of Ce(IV)–Na₂SO₃. The CL mechanism was further investigated by the CL, ultraviolet-visible light (UV-vis), and electron spin resonance (ESR) spectra. Mechanistic investigation indicated SiC·SiO_x increased the generation of singlet oxygen in the Ce(IV)–Na₂SO₃ system and excited SiC·SiO_x could be produced from the combination of hole and electron injected SiC·SiO_x. This opens up an avenue for investigating the CL properties of SiC·SiO_x and promotes their application in various fields.

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Introduction

Silicon carbide (SiC) with one-dimensional nanostructures occurs as nanowires,¹ nanoparticles,² nanoflakes,³ nanobelts, nanowhiskers, nanoneedles, nanorods, and nanoflowers, which have drawn extensive attention, due to their wide band-gap, thermal stability, chemical stability and biocompatibility. Silicon carbide has been widely used in high power devices, nanomedicines,⁴ and biosensors.⁴ However, little research reports their new chemiluminescent characteristics. Chemiluminescence (CL) happens in chemical reactions in which electronically excited intermediates or products are obtained and subsequently release energy with emission of light. CL is a new useful phenomenon for radical investigations⁵ and widely applied in analytical chemistry for its high sensitivity, wide linear range, simple instrumentation and low background.

Traditional molecular and nanomaterials enhanced CL systems have attracted lots of attentions to extend the applications of traditional CL system.^6–8 Nanomaterials, such as noble metal nanoparticles^9,10 or nanoclusters, colloidal semiconductor nanocrystals,^11,12 carbon based nanomaterials^13,14 and layer double hydroxides¹⁵ have CL enhancing property. They act as catalysts, reactants, luminophores or energy acceptors in CL systems.¹⁶ Nanomaterials based CL systems own more advantages in contrast to traditional molecular based systems due to their excellent and distinctive optical and electronic properties, which results in improved sensitivity and stability. Nevertheless, some nanomaterials with CL enhancing property are expensive or contain heavy-metal, which are not convenient for their widely applications. The exploration of new kind of nanomaterials with excellent CL property and facile preparation method has been the new focus of CL investigation.

The reaction of sulphite (SO₃²⁻) with Ce(IV) is a famous CL system but with a low quantum efficiency and exhibited low CL emission, which has been reported extensively.^17,18 The reactions between Ce(IV)–Na₂SO₃ system and some organic compounds have gained many attentions.^19,20

Herein, we developed a simple one-pot hydrothermal method for the synthesis of highly fluorescent SiC in amorphous SiO_x composite. Furthermore, new CL property of SiC·SiO_x in the presence of Ce(IV)–Na₂SO₃ was firstly discovered. The CL mechanism was further investigated by the CL, ultraviolet-visible light (UV-vis), and electron spin resonance (ESR) spectra. This may intrigue an avenue for investigating the CL property of SiC·SiO_x and promote their applications in the new optical fields. Furthermore, the finding will extend the range of nanomaterials that can be utilized in CL systems.

Experimental

Materials and reagents

NaOH, HCl, NaCl, H₂SO₄, Na₂SO₃, KBr, 1,4-diazabicyclo[2.2.2]octane (DABCO), quinine sulphate and thiourea were purchased from Sinopharm Chemical Reagent Co., Ltd (China), (3-aminopropyl) triethoxysilane (APTES), L-histidine and tetraammonium cerium(IV) sulfate dihydrate were purchased from Aladdin® Chemical Reagent Co., Ltd (China). Sodium azide (NaN₃) was bought from Xiya reagent Co., Ltd (Sichuan, China). Dialysis bag (MWCO 500–1000 Da) was purchased from Spectrum Laboratories (Rancho Dominguez, CA). Other chemicals were all analytical grade and used as received. Deionized water used throughout all experiments was purified through a Millipore system (Merck Millipore, Billerica, MA, USA).

Apparatus and characterization

The batch experiment was performed with a Centro LB 960 Microplate Luminometer from Berthold Technologies (Germany). A MPI-B flow injection analysis system (Xi'an Ruimai Electronic Equipments Company, China) was used in the flow injection experiment. Transmission electron microscopy image was recorded by a JEM 2010 electron microscope (JEOL, Japan). The X-ray photoelectron spectrum (XPS) was measured by a Thermo ESCALAB 250Xi using Al-Kα as the exciting source (1486.6 eV) and binding energy calibration was based on C 1s at 284.8 eV. The UV absorption spectra were collected by a UV-2450 spectrophotometer (Shimadzu, Japan). The fluorescent spectra were performed using a FL-4600 spectrofluorometer (Hitachi, Japan). Electron spin resonance (ESR) spectra were measured on a JEOL spectrometer (JES-FA200, Japan).

Synthesis of SiC·SiO_x

APTES with different volume (125, 250, 500, 1000, 2000 μL) was dispersed with deionized water to 11 mL and transferred to autoclave. Nitrogen was bubbled into the solution to displace oxygen and the solution was heated at 180 °C for 16 h. The transparent solution turned to be brown-yellow and filtered through 0.2 μm membrane. The solution was then dialyzed against pure water through a dialysis membrane (the cut-off of the dialysis membrane equivalent to MW 500–1000 Da) for 24 h and stored at 4 °C before using. The solution exhibited strong fluorescence under UV irradiation.

CL from SiC·SiO_x–Ce(IV)–Na₂SO₃ CL system

CL kinetic curves were obtained by batch experiments, which were carried out in microplate. 50 μL SiC·SiO_x and 50 μL Ce(IV) were premixed, and then 50 μL Na₂SO₃ was injected by an auto-microliter syringe from the upper injection port. The addition orders of the reagent were changed to investigate the interaction of the reagent and design the CL flow injection analysis system.

The flow injection CL system consisted of four flow lines. SiC·SiO_x carried by H₂O were firstly mixed with Ce(IV), and then reacted with Na₂SO₃ in the flow cell installed in front of the PMT (see Fig. S1†). The CL signal was collected by the MPI-B flow injection analysis system. The peak height of the signal recorded was measured as CL intensity.

Results and discussion

Synthesis and characterization

When APTES was heated at 180 °C for 16 h in the sealed autoclave, APTES was first hydrolyzed to produce (3-aminopropyl)trihydroxylsilane and C₂H₅OH, and (3-aminopropyl)trihydroxylsilane was used as silicon source,²¹ C₂H₅OH as carbon source,²² and alkylamine on the (3-aminopropyl)trihydroxylsilane acted as the reductant. During the formation of SiC, the alkaline condition provided by amino group on (3-aminopropyl)trihydroxylsilane is suitable for the formation of polymeric silica (SiO_x).^23,24 The effects of synthesized temperature, heating time and the amount of APTES on the fluorescence intensity of SiC·SiO_x have been investigated (ESI (Fig. S2†)). SiC·SiO_x with high fluorescent intensity and well water solubility could be obtained by heating of APTES at 180 °C for 16 h, and the optimized amount of APTES was 1 mL.

TEM showed that SiC·SiO_x was sphere shape with a diameter of 8–10 nm. The inter-planar spacing perpendicular to SiC is about 0.25 nm, which is consistent with the (111) planes pace of 3C–SiC, suggesting that the growth direction of SiC along [111]^3,25 (Fig. 1). There existed some amorphous SiO_x particles, which have the similar sized with 3C–SiC and could not be separated. Hence, we used SiC·SiO_x to define the prepared material. The SiC·SiO_x solution exhibited strong fluorescence under UV irradiation. The maximum fluorescence emission located at 440 nm with an excitation wavelength of 360 nm (Fig. 2). The quantum yield (λ_ex = 360 nm) for the SiC·SiO_x was 7.14%, which was obtained by using quinine sulfate (in 0.1 mol L⁻¹ H₂SO₄) as the reference (Fig. S3†).

Fig. 1 Transmission electron microscopy (TEM) image of SiC·SiO_x.

Fig. 2 Fluorescence spectra and visible-ultraviolet absorbance for SiC·SiO_x (A) and fluorescence spectra of SiC·SiO_x with different concentrations (B). The inset in panel (A) is the photograph of the SiC·SiO_x under visible light (left) and under 365 nm UV light (right).

Fourier transform infrared spectroscopy (FT-IR) (Fig. S4†) showed bending vibrations of N–H (1580 cm⁻¹), stretch vibration absorption of N–H (3340 cm⁻¹)²⁶ and Si–O bond (1150 cm⁻¹),²⁷ which revealed the potential existence of these groups on SiC·SiO_x. The Si–C peak at 805 cm⁻¹ indicated the formation of SiC.²⁸ From the elemental analysis, the weight ratio of Si, C, O and N elements in the SiC·SiO_x is 13.14 : 51.06 : 23.86 : 11.94. The N was the residue from reaction of APTES. The emergence of the peak centered at 102.06 eV in the Si 2p spectrum is consistence with the formation of Si–C bond, whereas the peak around 102.75 eV is attributed to Si–O/Si–O–Si bond.^29,30 C 1s core-level spectra confirm the formation of C–Si, C–C/C=C, C–N, C–O bond. The N 1s core-level spectra with binding energy of 398.91 eV and 400.28 eV are attributable to C–N/NH₂ and O=C–NH, respectively (Fig. 3).

Fig. 3 X-ray photoelectron spectrum of SiC·SiO_x and Si, C, N, O elements.

CL from SiC·SiO_x–Ce(IV)–Na₂SO₃ CL system

Fig. 4 showed the CL reaction between Ce(IV) and Na₂SO₃ happened quickly with light emission of 2000 counts. With the introducing of Na₂SO₃ to the mixed solution of Ce(IV) and SiC·SiO_x, CL intensity increased to 14 840 counts within 0.25 s. The mixing time of Ce(IV) and SiC·SiO_x had slight effect on the CL intensity (Fig. S5A†). There was no CL emission observed with the mixing of Na₂SO₃ and SiC·SiO_x. The CL intensity increased with the concentration of SiC·SiO_x. The linear equation of y = 817 + 41.3x with correlation coefficient of 0.9946 (Fig. S6†), which indicated the CL phenomena could be developed for the determination of SiC·SiO_x or SiC·SiO_x-labeled subjects (Fig. 4B).

Fig. 4 CL reaction kinetics of Ce(IV)–Na₂SO₃–SiC·SiO_x system. Experimental conditions: 5.0 × 10⁻⁴ mol L⁻¹ Ce(IV) (in 0.05 mol L⁻¹ H₂SO₄), 5.0 × 10⁻³ mol L⁻¹ Na₂SO₃, 28.7 μg mL⁻¹ SiC·SiO_x, sample volume was 50 μL.

The highest CL intensity was obtained by using Na₂SO₃, Ce(IV) and H₂SO₄ with a concentration of 5.0 × 10⁻³ mol L⁻¹, 5.0 × 10⁻⁴ mol L⁻¹ and 5.0 × 10⁻² mol L⁻¹, respectively (Fig. S5).

CL mechanism of the SiC·SiO_x–Ce(IV)–Na₂SO₃ CL system

The visible-ultraviolet absorption spectra showed the absorption band around 320 nm (ref. 31) ascribing to Ce(IV) decreased after its reaction with Na₂SO₃, and disappeared after its reaction with Na₂SO₃ and SiC·SiO_x (Fig. S7†). The phenomena indicated the adequate reaction among Ce(IV), Na₂SO₃ and SiC·SiO_x. The fluorescence of SiC·SiO_x disappeared after its reaction with Ce(IV) and Na₂SO₃, which revealed that SiC·SiO_x participated in the CL reaction and had structural change after the reaction (Fig. S7†).

ESR was used to confirm the emitting species and intermediates that were generated in the CL system. We explored 5,5-dimethyl-1-pyrroline N-oxide (DMPO), a target molecule of ˙OH and ˙SO₃⁻,^32–34 to investigate the role of SiC·SiO_x involved in the CL reaction. Fig. 5A showed ˙SO₃⁻ radicals were generated in Ce(IV)–Na₂SO₃ CL system. SiC·SiO_x decreased the production of ˙SO₃⁻ greatly in Ce(IV)–Na₂SO₃ CL system (Fig. 5B), which indicated the reaction between SiC·SiO_x and ˙SO₃⁻.

Fig. 5 ESR spectra of radicals captured by DMPO in Na₂SO₃–Ce(IV) (A) and SiC·SiO_x–Na₂SO₃–Ce(IV) (B) systems, ESR spectra of radicals captured by TEMP in Na₂SO₃–Ce(IV) (C) and SiC·SiO_x–Na₂SO₃–Ce(IV) (D) systems. Experimental conditions: 0.05 mol L⁻¹ DMPO and TEMP (in 0.05 mol L⁻¹ deoxidized phosphate buffer, pH 7.4), 5.0 × 10⁻³ mol L⁻¹ Na₂SO₃, 8.6 mg mL⁻¹ SiC·SiO_x, 5.0 × 10⁻³ mol L⁻¹ Ce(IV) (in 0.1 mol L⁻¹ H₂SO₄).

2,2,6,6-Tetramethyl-4-piperidine (TEMP), as a specific target molecule of ¹O₂, reacted with ¹O₂ to form the adduct 2,2,6,6-tetramethyl-4-piperidine-N-oxide (TEMPO).³² TEMPO is a stable nitroxide radical with ESR spectrum. Fig. 5C and D confirmed the increased production of ¹O₂ in SiC·SiO_x–Ce(IV)–Na₂SO₃ system compared with that generated in Ce(IV)–Na₂SO₃ system, when TEMP was utilized as the trapping reagent.

Furthermore, the ground-state properties of luminescent species in the SiC·SiO_x were investigated by ESR and showed a singly occupied orbital in ground-state SiC·SiO_x³⁵ (Fig. S8†). The ESR signal of SiC·SiO_x changed after its CL reaction with Ce(IV)–Na₂SO₃, which indicated that SiC·SiO_x could serve as the electron donor or acceptor in the CL reaction. ˙SO₃⁻ generated from the reaction of Ce(IV)–Na₂SO₃ donated its electron to SiC·SiO_x (reaction (1) and (2)).¹⁶ Oxygen in the solution injected hole into SiC·SiO_x to produce O₂˙⁻ (reaction (3)).³⁶ Both the reactions decreased the amount of ˙SO₃⁻ and increased the generation of O₂˙⁻, which resulted in the increased production of oxygen in excited state (reaction (6)–(10)). The electrons–hole annihilation in SiC·SiO_x also contributed to the enhanced-CL intensity in SiC·SiO_x–Ce(IV)–Na₂SO₃ system (reaction (4) and (5)).^37,38

Ce(IV) + SO₃²⁻ → ˙SO₃⁻ + Ce(III) (ref. 39) (1)

˙SO₃⁻ + SiC·SiO_x → SiC·SiO_x˙⁻ + SO₃ (ref. 16) (2)

O₂ + SiC·SiO_x → SiC·SiO_x˙⁺ + O₂˙⁻ (ref. 36) (3)

SiC·SiO_x˙⁺ + SiC·SiO_x˙⁻ → 2SiC·SiO_x* (ref. 37 and 40) (4)

SiC·SiO_x* → SiC·SiO_x + hv (5)

˙O₂⁻ + H⁺ → HO₂˙ (6)

HO₂˙ + HO₂˙ → ¹O₂ + H₂O₂ (7)

¹O₂ → ³O₂ + hv (8)

¹O₂ + ¹O₂ → (O₂)₂* (ref. 41) (9)

(O₂)₂* → 2O₂ + hv (10)

In order to further verify the interesting SiC·SiO_x enhanced-CL phenomena, CL spectra of the system were collected. The CL wavelengths at 460 nm, 560 nm and 620 nm may be assigned to the transition from (O₂)₂*^42–44 (Fig. S9†), which was produced from the chain reactions 6–10. Sodium azide (NaN₃)⁴⁵ and DABCO⁴⁶ were reported quenchers for singlet oxygen (¹O₂) through a physical process. NaN₃ with a concentration as low as 1.0 × 10⁻⁴ M still show inhibition effect on the CL intensity. DABCO with a concentration ranging from 1.0 × 10⁻⁴ M to 0.1 M quenched the CL emission. Both results strongly revealed that ¹O₂ was generated in the SiC·SiO_x–Ce(IV)–Na₂SO₃ system (Table 1).

Table 1 Effects of radical scavengers on chemiluminescence of Ce(IV)–Na₂SO₃–SiC·SiO_x

Concentration (mol L^−1)	Relative CL intensity (%)
	NaN3	DABCO
1 × 10^−6	99.33	95.74
1 × 10^−5	97.07	94.88
1 × 10^−4	88.62	82.46
1 × 10^−3	0.88	44.10
1 × 10^−2	0.40	6.26
1 × 10^−1	0.08	0.07

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The CL emission around 510 nm is ascribed to the radiative recombination of oxidant-injected holes and electrons in SiC·SiO_x.³⁷ The CL spectra exhibited a little red-shift compared with the maximum FL due to the smaller energy separations of the SiC·SiO_x surface states.³⁷

Based on the above study, the CL mechanism for the SiC·SiO_x–Ce(IV)–Na₂SO₃ system could be illustrated as shown in Fig. 6. The ˙SO₃⁻ generated from the reaction from Ce(IV)–Na₂SO₃ donated its electron to SiC·SiO_x. Oxygen in the solution injected hole into SiC·SiO_x to produce O₂˙⁻.³⁶ Both the reactions decreased the amount of ˙SO₃⁻ and increased the generation of O₂˙⁻, which resulted in the increased production of oxygen in excited state (CL route 2). The electrons–hole annihilation of SiC·SiO_x to produce SiC·SiO_x in excited states also contributed to the enhanced-CL intensity in SiC·SiO_x–Ce(IV)–Na₂SO₃ system (CL route 1).

Fig. 6 Schematic illustration of CL mechanism of SiC·SiO_x–Ce(IV)–Na₂SO₃ system.

Application of SiC·SiO_x in reducing substances sensing

Some reducing substances, such as dopamine, ascorbic acid, glutathione, cysteine and uric acid have an inhibitory effect on the CL emission from SiC·SiO_x–Ce(IV)–Na₂SO₃ system. The inhibition is due to their competitive reaction with Ce(IV) and thus reduces the CL reaction of SiC·SiO_x–Ce(IV)–Na₂SO₃ system. The CL phenomena could be developed as a universal detection method for these compounds. Under the optimized determination conditions of these compounds, the linear equations for dopamine, ascorbic acid, glutathione, cysteine and uric acid are y = 0.5475x + 4.5690, y = 0.2946x + 8.3343, y = 0.4622x + 8.3165, y = 0.7269x + 5.7649, y = 0.0724x + 6.3591, with the limit of detection (S/N = 3) of 1.0 × 10⁻⁸, 5.0 × 10⁻⁸, 1.0 × 10⁻⁸, 1.0 × 10⁻⁸ and 5.0 × 10⁻⁸ mol L⁻¹, respectively (Fig. S10†).

Conclusions

In summary, the present study reports the CL properties of SiC·SiO_x and the fundamental luminescence mechanism investigation indicated SiC·SiO_x increased the generation of singlet oxygen in Ce(IV)–Na₂SO₃ system and excited SiC·SiO_x could be produced from the combination of hole and electron injected SiC·SiO_x. These findings may encourage more efforts to use SiC·SiO_x to design optical sensor and expand their applications in bioscience and energy technology. The inhibition of reducing substances on the CL from SiC·SiO_x–Ce(IV)–Na₂SO₃ could be developed as a universal detection method for these compounds.

Acknowledgements

The authors gratefully acknowledge the financial support of National Natural Science Foundation of China (No. 21305015), National High Technology and Development of China (No. 2012AA022604), National Natural Science Foundation of China (No. 21275028), National Science Foundation for Distinguished Young Scholars of Fujian Province (No. 2016J06019), Natural Science Foundation of Fujian Province of China (No. 2014J05014), Program for Fujian University Outstanding Youth Scientific Research (No. 2015b026), and Program for Fujian Top-notch Innovative Personnel.

Notes and references

1. Z. Pan, H. L. Lai, F. C. K. Au, X. Duan, W. Zhou, W. Shi, N. Wang, C. S. Lee, N. B. Wong and S. T. Lee, Adv. Mater., 2000, 12, 1186–1190.
2. R. Rajarao, R. Ferreira, S. H. F. Sadi, R. Khanna and V. Sahajwalla, Mater. Lett., 2014, 120, 65–68.
3. M. Dragomir, M. Valant, M. Fanetti and Y. Mozharivskyj, RSC Adv., 2016, 6, 21795–21801.
4. J. S. Ponraj, S. C. Dhanabalan, G. Attolini and G. Salviati, Crit. Rev. Solid State Mater. Sci., 2016, 1–17.
5. X. Dou, Z. Lin, H. Chen, Y. Zheng, C. Lu and J. M. Lin, Chem. Commun., 2013, 49, 5871–5873.
6. Z. Yan, Z. Zhang, Y. Yan, L. Zhen and J. Chen, Food Chem., 2016, 190, 20–24.
7. X. You, Y. Li, B. Li and J. Ma, Talanta, 2016, 147, 63–68.
8. D. L. Giokas, A. G. Vlessidis, G. Z. Tsogas and N. P. Evmiridis, TrAC, Trends Anal. Chem., 2010, 29, 1113–1126.
9. H. Cui, J. Z. Guo, N. Li and L. J. Liu, J. Phys. Chem. C, 2008, 112, 11319–11323.
10. Z. F. Zhang, H. Cui, C. Lai and L. J. Liu, Anal. Chem., 2005, 77, 3324–3329.
11. L. Zhang, C. Xu and B. Li, Microchem. J., 2010, 95, 186–191.
12. S. K. Poznyak, D. V. Talapin, E. V. Shevchenko and H. Weller, Nano Lett., 2004, 4, 693–698.
13. L. Zhao, F. Di, D. Wang, L. H. Guo, Y. Yang, B. Wan and H. Zhang, Nanoscale, 2013, 5, 2655–2658.
14. Z. Yan, G. Sun, H. Yang, J. Yu, Y. Mei and X. Song, Biosens. Bioelectron., 2016, 79, 55–62.
15. Z. Wang, F. Liu and C. Lu, Biosens. Bioelectron., 2012, 38, 284–288.
16. W. Xue, Z. Lin, H. Chen, C. Lu and J.-M. Lin, J. Phys. Chem. C, 2011, 115, 21707–21714.
17. M. Yamada, T. Nakada and S. Suzuki, Anal. Chim. Acta, 1983, 147, 401–404.
18. H. Han and Y. Zeng, Anal. Lett., 2004, 37, 143–155.
19. J. Zhang, J. Li and Y. Tu, Luminescence, 2010, 25, 317–321.
20. C. Ruiz-Capillas and F. Jiménez-Colmenero, Food Chem., 2009, 112, 487–493.
21. J. Prakash, R. Venugopalan, B. M. Tripathi, S. K. Ghosh, J. K. Chakravartty and A. K. Tyagi, Prog. Solid State Chem., 2015, 43, 98–122.
22. T. Li, L. Xu, L. Wang, L. Yang and Y. Qian, J. Alloys Compd., 2009, 484, 341–346.
23. J. Kákoš, M. Mikula and L. Harmatha, Microelectron. J., 2008, 39, 1626–1628.
24. M. E. Coltrin, P. Ho, H. K. Moffat and R. J. Buss, Thin Solid Films, 2000, 365, 251–263.
25. S. Dong, M. Li, P. Hu, Y. Cheng and B. Sun, J. Cryst. Growth, 2016, 453, 7–12.
26. Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S. T. Lee and Y. He, J. Am. Chem. Soc., 2013, 135, 8350–8356.
27. R. Lockwood, S. Mcfarlane, J. R. R. Núñez, X. Y. Wang, J. G. C. Veinot and A. Meldrum, J. Lumin., 2011, 131, 1530–1535.
28. A. Jannat, W. Lee, M. S. Akhtar, Z. Y. Li and O. B. Yang, Appl. Surf. Sci., 2016, 369, 545–551.
29. X. Liu, H. Cheng, T. Zhao and C. Zhang, J. Colloid Interface Sci., 2014, 426, 117–123.
30. R. P. Chaukulkar, K. D. Peuter, P. Stradins, S. Pylypenko, J. P. Bell, Y. Yang and S. Agarwal, ACS Appl. Mater. Interfaces, 2014, 6, 185–188.
31. Z. Lin, W. Xue, H. Chen and J. M. Lin, Chem. Commun., 2012, 48, 1051–1053.
32. H. R. Li, L. Z. Wu and C. H. Tung, J. Am. Chem. Soc., 2000, 122, 2446–2451.
33. R. Li, T. Kameda, A. Toriba, K. Hayakawa and J. M. Lin, Anal. Chem., 2012, 84, 3215–3221.
34. F. A. Villamena, E. J. Locigno, R. Antal, C. M. Hadad and J. L. Zweier, J. Phys. Chem. A, 2006, 110, 13253–13258.
35. Y. Tang, Y. Su, N. Yang, L. Zhang and Y. Lv, Anal. Chem., 2014, 86, 4528–4535.
36. D. Kovalev and M. Fujii, Adv. Mater., 2006, 17, 2531–2544.
37. Z. Ding, B. M. Quinn, S. K. Haram, L. E. Pell, B. A. Korgel and A. J. Bard, Science, 2002, 296, 1293–1297.
38. Z. Lin, W. Xue, H. Chen and J. M. Lin, Anal. Chem., 2011, 83, 8245–8251.
39. N. Lian, H. Zhao and C. Sun, Chem. J. Chin. Univ., 2002, 23, 564–566.
40. Y. Dong, N. Zhou, X. Lin, J. Lin, Y. Chi and G. Chen, Chem. Mater., 2010, 22, 5895–5899.
41. J. Stauff, H. Schmidkunz and G. Hartmann, Nature, 1963, 198, 281–282.
42. J. M. Lin and Y. Masaaki, Anal. Chem., 2000, 72, 1148–1155.
43. A. U. Khan and M. Kasha, J. Am. Chem. Soc., 1970, 92, 3293–3300.
44. A. Waldemar, D. V. Kazakov and V. P. Kazakov, Chem. Rev., 2005, 105, 3371–3387.
45. J. M. Lin and M. Yamada, Anal. Chem., 2000, 72, 1148–1155.
46. S. Elena, E. O. Danilov, K. Solen, I. E. Pomestchenko, A. D. Tregubov, C. Frank, R. Pascal, Z. Raymond and F. N. Castellano, Inorg. Chem., 2007, 46, 3038–3048.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra14477b

‡ The first two authors (Z. Lin and N. M. Wu) contribute equally to the present manuscript.

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