Supporting Information

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1 Supporting Information R6G/8-AQ co-functionalized Fe 3 O 2 nanoparticles for fluorescence detection of trace Hg 2+ and Zn 2+ in aqueous solution Yao Gu 1,2, Guowen Meng 1,3*, Meiling Wang 1, Qing Huang 4, Chuhong Zhu 1 and Zhulin Huang 1 1 Key Laboratory of Materials Physics, and Anhui Key Laboratory of Nanomaterials and Nanostructures, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, , China. 2 Guangxi Zhuang Autonomous Region Forestry Research Institute, Nanning, , China. 3 University of Science and Technology of China, Hefei, , China. 4 Institute of Technical Biology and Agriculture Engineering, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, , China. * Corresponding author ( gwmeng@issp.ac.cn) The Supporting Information includes: Part S1 Characterization of R6GOEt- and QIOEt-modified Fe 3 O 2 NPs Part S2 Confirmation of FRET on the surface of R6G/8-AQ co-functionalized Fe 3 O 2 NPs Part S3 Calculation of the average coverage of QIOEt molecules on the sensor Part S4 Research on the reusability of the sensor Fig. S1 to S14

2 Part S1 Characterization of R6GOEt- and QIOEt-modified Fe 3 O 2 NPs FTIR spectra were recorded on a Perkin-Elmer Fourier transform infrared spectrometer as KBr pellets. As shown in Fig. S8A and S8B. The broad band centered at cm 1 represents OH stretching on the surface of modified Fe 3 O 2 NPs and the band at cm 1 represents the bending mode of O H vibrations. It is clear that not all the silanol on core/shell NPs has been covalently modified. Compared with unmodified Fe 3 O 2 NPs, QIOEt-modified or R6GOEt-modified Fe 3 O 2 NPs had additional peaks at 2921 cm 1 and 2948 cm 1 that respectively correspond to the CH vibration of QIOEt and R6GOEt. Part S2 Confirmation of FRET on the surface of R6G/8-AQ co-functionalized Fe 3 O 2 NPs R6G/8-AQ co-functionalized Fe 3 O 2 NPs and R6GOEt-modified Fe 3 O 2 NPs was added to in water solution of 0.05 M HEPES buffer (ph = 7.0) and Hg 2+ ( M). The absorption and fluorescence intensity were recorded respectively (Fig. S11). According to the ratio of the absorption and fluorescence A intensity (A/I F ) in the Fig. S10 and I A FA A I 6 B , it is concluded that there is FRET FB AA AB between QIOEt and R6GOEt definitely ( if there were no FRET contributes to I FB ). I I FA FB Part S3 Calculation of the average coverage of QIOEt molecules on the sensor Assuming that Zn 2+ complexes with QIOEt and the sensor have equal quantum efficiency, the following formulas (1) and (2) reported by Mu [1] can be used to estimate the average coverage of QIOEt on the R6G/8-AQ co-functionalized Fe 3 O 2 NPs: A I R S η S = ηr A S I R A=εbc ----(1) ----(2) Here, η is quantum efficiency, S, R represent the fluorophores fixed on the Fe 3 O 2 and the free fluorophore molecules in the solution, respectively, I is integral intensity of fluorescence, and A is absorbance at excited wavelength. The equation is valid when only single type of fluorophore molecules are modified on the Fe 3 O 2. For the R6G/8-AQ co-functionalized Fe 3 O 2 NPs, according to the data from Fig.

3 S12, we can just roughly estimate the average coverage of QIOEt molecules on the R6G/8-AQ co-functionalized Fe 3 O 2 NPs. Therefore, the 0.4 μg ml 1 R6G/8-AQ co-functionalized Fe 3 O 2 NPs used in our experiments correspond to M QIOEt. Part S4 Research on the reusability of the sensor Reusability of the sensors is interesting in developing recyclable optical sensors for industrial applications. In this procedure, EDTA is an effective striping agent for the removal of Zn 2+ from the complex between Zn 2+ and receptor QIOEt. After EDTA was added to the Zn 2+ complexes of the sensor, the fluorescence intensity decreased extremely (Fig. S13). Thus, the R6G/8-AQ co-functionalized Fe 3 O 2 NPs can be reused after simple treatment with EDTA and recycling by magnet (Fig. S14). Notes and references [1]. L. Mu, W. Shi, J. C. Chang, S. T. Lee, Nano. lett., 8 (2008)

4 Fig. S1 Powder X-ray diffraction spectra of the magnetic nanospheres. Fig. S2 SEM images of the Fe 3 O 4 NPs fabricated with different amount of anhydrous CH 3 COONa: (A) 2.0 g, (B) 1.5 g, and (C) 1.0 g. Fig. S3 SEM images of the Fe 3 O 4 NPs fabricated with different amount of FeCl 3 6H 2 O: (A) 1.0 g, (B) 1.5 g, and (C) 2.0 g.

5 Fig S4 TEM images of the Fe 3 O 4 NPs fabricated with different amount of ethylenediamine: (A) 7.0 ml, (B) 6.0 ml, (C) 5.0 ml, and (D) 4.0 ml. Fig. S5 1 HNMR (CDCl 3, 400 MHz) spectrum of QIOEt. 1 HNMR (400 MHz, CDCl 3 ): δ(ppm) (t, J=8.44 Hz, 2H, Si-CH 2 * CH 2 CH 2 N), (t, J=7.00 Hz, 9H, Si(OCH 2 CH * 3) 3 ), (tt, J=8.40, 6.70 Hz, 2H, SiCH 2 CH 2 * CH 2 N), (q, J=7.00 Hz, 6H, Si(OCH 2 * CH 3 ) 3 )), 6.995(CDCl 3 ), H-Quinoline: (m, 3H), (dd, 1H), (dd, 1H), (dd, 1H), (S, 1H, (CO)CH 2 CNH * ).

6 Fig. S6 13 CNMR (CDCl 3, 400 MHz) spectrum of compound QIOEt. 13 CNMR (400 MHz, CDCl 3 ): δ (ppm) , , , 43.38, 31.90, , 22.67, Fig. S7 Fluorescence emission intensity of the R6G/8-AQ co-functionalized Fe 3 O 2 NPs in presence of twelve different metal ions (Ag +, Mg 2+, Co 2+, Cu 2+, K +, Ce 3+, Cr 3+, Cd 2+, Ba 2+, Zn 2+, Fe 3+ and Ni 2+ : M): λ ex =324 nm. All datas were recorded in the water solution of 0.05 M HEPES buffer (ph = 7.0).

7 Fig. S8 FTIR spectra of (A) unmodified NPs, R6G-functionalized NPs and (B) 8-aminoquinoline functionlized NPs. Fig. S9 Fluorescence emission spectra and titration curves of QIOEt upon addition of increasing amount ( to M) of Zn 2+. All datas were recorded in the water solution of 0.05 M HEPES buffer (ph = 7.0).

8 Fig. S10 The UV-vis absorption spectra of the R6GOEt-Hg 2+ and the fluorescence emission spectrum of QIOEt (λ ex =324 nm). Fig. S11 The UV-vis absorption spectra and the fluorescence emission spectrum of (A) the R6GOEt-modified Fe 3 O 2 NPs and (B) the R6G/8-AQ co-functionalized Fe 3 O 2 NPs towards Hg 2+ ( M) in water solution of 0.05 M HEPES buffer (ph = 7.0). Fig. S12 The fluorescent intensity of M QIOEt-Zn 2+ and 0.4 μg ml 1 Zn 2+ -sensor in the water solution of 0.05 M HEPES buffer (ph=7.0): λ ex =324 nm.

9 Fig. S13 Reusability of the R6G/8-AQ co-functionalized Fe 3 O 2 NPs after treated with EDTA. The marked arabic numbers of 1, 2 and 3 referred to the treatment status of the as-prepared, the Zn 2+ -contaminated, the renewed R6G/8-AQ co-functionalized Fe 3 O 2 NPs, respectively. Fig. S14 Removal of the core@shell NPs from the liquid phase using NdFeB magnet.