Supporting Information

3D hierarchical dual-metal-organic framework heterostructure up-

regulating pre-concentration effect for ultrasensitive fluorescence

detection of tetracycline antibiotics

Chunhua Li,a Weixia Yang,a Xiaoshuo Zhang,a Yong Han,a Wenzhi Tang,a Tianli Yue,a,b Zhonghong

Lia,b*

a College of Food Science and Engineering, Northwest A&F University, Yangling, 712100, Shaanxi,

China

b Laboratory of Quality & Safety Risk Assessment for Agro-products（Yangling），Ministry of

Agriculture，Yangling, 712100, Shaanxi, China.

*Corresponding author. Tel: +86 29 8703 8857; E-mail: steveli@nwsuaf.edu.cn; lizhhsteve@163.com.

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2019

1. Synthesis of amino-functionalized Al-MOF

Amino-functionalized Al-MOF was prepared through the typical hydrothermal method. Typically,

aluminum chloride hexahydrate (AlCl3·6H2O, 0.724 g, 3 mmol) and 2-Aminoterephthalic acid (NH2-

BDC, 0.544 g, 3 mmol) were added in 20 mL ultrapure water to prepare the precursor solution.

The obtained homogeneous precursor was then transferred to a Teflon-lined stainless steel

autoclave and was heated to 150°C for 5 h. After cooling to room temperature, the acquired milky

yellowish precipitate was centrifuged and washed with ultrapure water and methanol for three

times, respectively. The collection of precipitate was ultimately dried at 70°C for 24 h in a vacuum

oven.

2. Preparation of real samples

The water samples were filtered and used for the quantitative analysis without further treatment.

Raw milk was purchased from a local pasture. According to the reported method,1 1% (v/v)

trichloroacetic acid and chloroform was first added and mixed under vortex for 5 min to remove

the proteins, lipids, and other organic substances. Second, the samples were sonicated for 20 min

and centrifuged at 12 000 rpm for 10 min, and then the supernatant was filtered through a 0.22

μM membrane to be used directly for FL analysis.

Figure captions

Fig. S1. EDX spectrum and element content of Al-MOF@Mo/Zn-MOF.

Fig. S2. (a) Zeta pertential of PVP. (b) Zeta pertential of amino-functionalized Al-MOF dissolved in

the reaction solution.

Fig. S3. TGA profiles of Al-MOF and Al-MOF@Mo/Zn-MOF (heating rate 10°C min-1).

Fig. S4. N2 sorption isotherms of Al-MOF@Mo/Zn-MOF.

Fig. S5. (a) The XRD patterns of amino-functionalized Al-MOF and simulated NH2-MIL-53(Al). (b)

The XRD patterns of Mo/Zn-MOF and simulated ZIF-L.

Fig. S6. (a) Fluorescence (FL) spectra of NH2-BDC, amino-functionalized Al-MOF, Mo/Zn-MOFF and

Al-MOF@Mo/Zn-MOF under excitation at 330 nm. (b) The optimization of the excitation

wavelength of Al-MOF@Mo/Zn-MOF. FL intensities of Al-MOF@Mo/Zn-MOF at different pH

values(c), temperatures (d), and times (e). (f) FL stability of Al-MOF@Mo/Zn-MOF for 30 days in

room temperature.

Fig. S7. (a) Pseudo-first model and (b) Intra-particle diffusion kinetic model for TCs adsorption on

Al-MOF@Mo/Zn-MOF.

Fig. S8. Fluorescence quenching efficiencies (QE(%)) of TCs detection on Al-MOF@Mo/Zn-MOF at

different concentrations (a), pH (b) and temperatures (c). (d) Fluorescence intensities of Al-

MOF@Mo/Zn-MOF before and after introduction of TCs under consecutive xenon lamp irradiation.

Fig. S9. UV–vis absorption spectra of TCs and fluorescence spectra of Al-MOF@Mo/Zn-MOF.

Fig. S10 The UV–vis spectra (a), (αhv)2 versus photon energy for calculation of bandgap energies

(b), and Cyclic voltammograms of Al-MOF@Mo/Zn-MOF (c).

Fig. S11. High resolution XPS spectra of (a) Al 2p, (b) Zn 2p and (c) Mo 3d of Al-MOF@Mo/Zn-MOF

before and after detection/adsorption of tetracycline.

Fig. S12. Cyclic application of Al-MOF@Mo/Zn-MOF in adsorbing TCs under room temperature.

Table captions

Table S1. Adsorption kinetics parameters of Al-MOF@Mo/Zn-MOF for TCs adsorption.

Table S2. Isotherm parameters of TCs adsorption on Al-MOF@Mo/Zn-MOF.

Table S3. The comparison of TCs adsorption capacities of Al-MOF@Mo/Zn-MOF with the other

reported adsorbents.

Table S4. Comparison of the TCs detection properties of Al-MOF@Mo/Zn-MOF with others

reported in previous literature.

Table S5. The correction factor (CF) of the IFE (Fcorr/Fobsd) at each concentration of TCs.

Table S6. HOMO and LUMO energies calculated for TCs used at B3LYP/6-311++G** level.

Table S7. The hetero-atoms content (atomic %) before and after tetracycline adsorption.

Fig. S1. EDX spectrum and element content of Al-MOF@Mo/Zn-MOF.

Fig. S2. (a) Zeta pertential of PVP. (b) Zeta pertential of amino-functionalized Al-MOF dissolved in

the reaction solution.

Fig. S3. TGA profiles of Al-MOF and Al-MOF@Mo/Zn-MOF (heating rate 10°C min-1).

Fig. S4. N2 sorption isotherms of Al-MOF@Mo/Zn-MOF.

Fig. S5. (a) The XRD patterns of amino-functionalized Al-MOF and simulated NH2-MIL-53(Al). (b)

The XRD patterns of Mo/Zn-MOF and simulated ZIF-L.

Fig. S6. (a) Fluorescence (FL) spectra of NH2-BDC, amino-functionalized Al-MOF, Mo/Zn-MOFF and

Al-MOF@Mo/Zn-MOF under excitation at 330 nm. (b) The optimization of the excitation

wavelength of Al-MOF@Mo/Zn-MOF. FL intensities of Al-MOF@Mo/Zn-MOF at different pH

values(c), temperatures (d), and times (e). (f) FL stability of Al-MOF@Mo/Zn-MOF for 30 days in

room temperature.

Fig. S7. (a) Pseudo-first model and (b) Intra-particle diffusion kinetic model for TCs adsorption on

Al-MOF@Mo/Zn-MOF.

Fig. S8. Fluorescence quenching efficiencies (QE(%)) of TCs detection on Al-MOF@Mo/Zn-MOF at

different concentrations (a), pH (b) and temperatures (c). (d) Fluorescence intensities of Al-

MOF@Mo/Zn-MOF before and after introduction of TCs under consecutive xenon lamp irradiation.

3. Optimization of detection parameters

An important prerequisite for obtaining satisfactory analytical performance of the fabricated Al-

MOF@Mo/Zn-MOF heterostructure is to optimize detection conditions. Therefore, detection

parameters, including the dosage of the nanoprobe, pH, temperature and the incubation time, are

systematically discussed. The effects of the dosage of Al-MOF@Mo/Zn-MOF on the fluorescence

quenching efficiency (QE) are illustrated in Fig. S8a. The QE diminutively increases with

concentration from 1.5 to 2.5 mg/L and then reaches equilibrium, which is ascribed to the saturate

reaction of TCs with the nanoprobe, so the concentration of 2.5 mg/mL is selected for sensing. In

addition, the influence of pH is investigated by adjusting pH from 2.0–10.0 and the results are

presented in Fig. S8b. The quenching efficiencies steeply rise with the pH increase from 2.0 to 5.0

and an unapparent FL changes at the pH of 5.0–8.0, while the FL intensities contrarily decline at

pH 8.0–10.0 with a slight change of QE. Accordingly, the optimum QE at pH 6.0 is employed as the

medium pH for the subsequent assay. In addition, to validating the applicability in a wide range of

temperatures, the influence of incubation temperature (4–75°C) is investigated and the results are

shown in Fig. S8c. The QE of the nanoprobe for DOX, TET and OTC is almost stationary, implying

that incubation temperature has a negligible influence on the determination of TCs (except for

CTC). It is noted that QE of CTC exhibits a significant drop when the temperature exceeds 55°C,

which attributes to the instability of CTC molecular structure at higher temperatures, but

fortunately, it still can be detected at ambient temperature. Therefore, room temperature is

adopted as the reaction temperature for the detection of TCs. From Fig. S8d, the FL intensities

dramatically decrease within 20 s when TCs are inducing to the sensing system and quickly reach

equilibrium at ~480 s for those four TCs. Meanwhile, no obvious fluctuation is observed within a

longer reaction time. Consequently, 8 min is chosen as the optimal incubation time for this sensing

system.

Fig. S9. UV–vis absorption spectra of TCs and fluorescence spectra of Al-MOF@Mo/Zn-MOF.

Fig. S10 The UV–vis spectra (a), (αhv)2 versus photon energy for calculation of bandgap energies

(b), and Cyclic voltammograms of Al-MOF@Mo/Zn-MOF (c).

Fig. S11. High resolution XPS spectra of (a) Al 2p, (b) Zn 2p and (c) Mo 3d of Al-MOF@Mo/Zn-MOF

before and after detection/adsorption of tetracycline.

Fig. S12. Cyclic application of Al-MOF@Mo/Zn-MOF in adsorbing TCs under room temperature.

Table S1. Adsorption kinetics parameters of Al-MOF@Mo/Zn-MOF for TCs adsorption.

pseudo-second-order pseudo-first-orderTCs qe, exp(mg/g) k2 (g/mg min) qe, cal(mg/g) R2 k1 (min-1) qe (mg/g) R2

TET 121.76±0.17 0.0018±0.0001 122.56±0.89 0.9997 0.0988±0.0116 118.49±2.09 0.9242DOX 149.77±0.45 0.0011±0.0002 150.15±2.15 0.9974 0.0811±0.0150 144.51±2.92 0.9929OTC 73.21±1.26 0.0062±0.0007 73.55±0.65 0.9995 0.3013±0.0515 69.91±1.30 0.9967CTC 142.68±0.16 0.0019±0.0001 147.07±1.22 0.9994 0.1997±0.0180 137.95±2.76 0.9964

intra-particle diffusion model

initial phase secondary phaseTCs

kp1 C1 R2 kp2 C2 R2

TET 5.2908±1.0763 73.2937±6.1519 0.8853 0.7908±0.1403 108.8994±2.0383 0.8603

DOX 7.6057±1.3623 78.7618±7.0627 0.9096 1.248±0.0714 125.5323±0.9586 0.9839

OTC 6.5767±0.8374 33.3366±2.9860 0.9529 0.2714±0.0350 68.3071±0.4099 0.922

CTC 15.3256±1.2994 37.7860±3.2237 0.9787 0.7323±0.1855 128.6939±2.9062 0.7447

Table S2. Isotherm parameters of TCs adsorption on Al-MOF@Mo/Zn-MOF.

Langmuir isotherm Freundlich isotherm

TCs T/Kqm (mg g-1) KL (L mg-1) R2

KF (mg g-1) (L

mg-1)1/nn R2

TET 298 1434.16±29.78 0.0279±0.0039 0.9993 152.05±27.46 2.3391±0.1669 0.9987

308 1560.19±38.35 0.0264±0.0058 0.9988 118.58±26.03 2.0062±0.2251 0.9868

318 1629.07±27.48 0.03357±0.0019 0.9980 129.49±15.54 0.9818±0.1100 0.9902

DOX 298 1514.37±54.09 0.0111±0.0010 0.9964 67.26±13.74 1.9140±0.1501 0.9843

308 1571.65±4.08 0.0189±0.0007 0.9999 104.51±0.55 2.0574±0.0065 0.9989

318 1673.02±78.11 0.0253±0.0025 0.9982 217.65±38.09 2.8204±0.3531 0.9893

OTC 298 1260.75±46.62 0.0366±0.0029 0.9955 121.41±18.97 2.1358±0.1923 0.9466

308 1372.23±18.19 0.0489±0.0010 0.9983 190.08±10.40 2.5943±0.1536 0.9437

318 1564.94±19.20 0.0574±0.0009 0.9991 136.21±3.24 2.1945±0.0478 0.9837

CTC 298 1539.71±45.39 0.0506±0.0019 0.9971 91.51±5.02 1.7664±0.0665 0.9631

308 1635.24±13.83 0.0514±0.0013 0.9991 232.42±20.79 2.4879±0.1411 0.9816

318 1782.99±30.74 0.0628±0.0025 0.9981 298.19±41.83 2.5489±0.2931 0.9155

Table S3. The comparison of TCs adsorption capacities of Al-MOF@Mo/Zn-MOF with the other

reported adsorbents.

materialadsorption

capacity (mg/g)

TCs ref

ferric activated SBA 40.80 TET 2Ag-BN 358.00 TET 3

CTS-g-AMPS 806.60 TET 4MWCNT/MIL-53(Fe) 364.37 TET 5

PCN-128Y 423.00 TET 6In2S3@MIL-125(Ti) 119.20 TET 7

g-MoS2 556.00 DOX 8EGA NaCl 31.35 DOX 9

LXR-BT 438.75 DOX 10MOF (MIL-53-Fe) 332.00 DOX 11

Ni-doped MIL-53(Fe) 397.22 DOX 12MWCNT/MIL-53(Fe) 325.59 OTC 5

BN bundles 93.05 OTC 13ZIF-8 312.50 OTC 14

EGA NaCl 2.01 OTC 9EGA NaNO3 7.67 OTC 9CTS-g-AMPS 876.60 CTC 4

MWCNT/MIL-55(Fe) 180.68 CTC 5CMC-Mt 271.74 CTC 15

MWCNT/NH2-MIL-53(Fe) 254.04 CTC 16Al-MOF@Mo/Zn-MOF 1629.07 TET This workAl-MOF@Mo/Zn-MOF 1673.02 DOX This workAl-MOF@Mo/Zn-MOF 1564.94 OTC This work

Al-MOF@Mo/Zn-MOF 1782.99 CTC This work

Table S4. Comparison of the TCs detection properties of Al-MOF@Mo/Zn-MOF with others

reported in previous literature.

methods materialslinear range

(μM)LOD (nM) TCs types Ref

HPLC - -0.95-3.6 ng

L-1 TCs 17

LC-MS/MS - 25-200 µg kg-12.22-3.59

µg kg-1 TCs 18

CE - 25-250 µg L-1 2-9 µg L-1 TCs 19

ELISA -0.01-100 ng

mL-1 0.14 ng g-1 DOX 20

electrochemical

Au/g-C3N4 0.1-20 30 TET 21

electrochemical

Fe2O3-Bi2WO6 0.01-25 300 TET 22

colorimetricHRP-mimicking

DNAzyme1.0 × 10−2-1.0 × 104 ng mL−1

0.081 ng mL-1 TET 23

colorimetric THMS AuNPs 0.3-10 nM 266 pM TET 24fluorescence GUCDs 0.5-25 165 TET 25fluorescence CDs 10.0-400.0 6000 TET 26fluorescence PCN-128Y 0-1 30 TET 6fluorescence AuNCs 0.375-12.5 150 OTC 27

fluorescence In-sbdc 0-300.28-0.30

μMTET CTC

OTC28

fluorescence NH2-MIL-53(Al) 0-73 26.16 TET 1

fluorescence NH2-MIL-53(Al) 0-66.67 40.36 DOX 1

fluorescence NH2-MIL-53(Al) 0-86 62.05 OTC 1

fluorescence Al-MOF@Mo/Zn-MOF 0.001−53.33 0.53 TETThis work

fluorescence Al-MOF@Mo/Zn-MOF 0.001−46.67 0.56 DOXThis work

fluorescence Al-MOF@Mo/Zn-MOF 0.001−53.33 0.58 OTCThis work

fluorescence Al-MOF@Mo/Zn-MOF 0.001−53.33 0.86 CTCThis work

Table S5. The correction factor (CF) of the IFE (Fcorr/Fobsd) at each concentration of TCs.

Tc (μM) Aex Aem CF Fcor Fobsd Fcor,0/Fcor

0 0.003 0.001 0.998 473.426 472.326 1.000 10 0.107 0.001 1.122 389.138 436.506 1.082 20 0.207 0.002 1.256 359.384 451.520 1.046 40 0.439 0.004 1.598 214.343 342.416 1.379 60 0.678 0.016 2.034 150.953 307.061 1.538 80 1.093 0.018 2.828 89.861 254.158 1.858

TET

100 1.389 0.022 3.470 68.818 238.822 1.978 0 0.004 0.001 1.004 462.011 464.008 1.000 10 0.116 0.003 1.144 367.020 419.888 1.105 20 0.232 0.005 1.301 295.040 383.960 1.208 40 0.478 0.003 1.656 175.843 291.161 1.594 60 0.757 0.001 2.112 116.374 245.799 1.888 80 1.149 0.009 2.893 66.192 191.461 2.424

DOX

100 1.286 0.006 3.151 45.938 144.728 3.206 0 0.007 0.001 1.008 455.151 458.697 1.000 10 0.089 0.004 1.112 380.632 423.321 1.084 20 0.191 0.005 1.247 306.893 382.565 1.199 40 0.410 0.012 1.578 205.110 323.639 1.417 60 0.664 0.023 2.037 126.048 256.732 1.787 80 0.961 0.023 2.592 83.126 215.503 2.128

OTC

100 1.204 0.027 3.113 57.059 177.608 2.583 0 0.005 0.001 0.995 437.785 435.612 1.000 10 0.068 0.008 1.095 402.128 440.461 1.089 20 0.146 0.012 1.203 325.000 390.899 1.114 40 0.303 0.038 1.494 245.896 367.353 1.186 60 0.488 0.051 1.835 178.759 328.013 1.328 80 0.682 0.064 2.243 127.828 286.701 1.519

CTC

100 0.891 0.073 2.709 92.670 251.035 1.735

Table S6. HOMO and LUMO energies calculated for TCs used at B3LYP/6-311++G** level.

TCs HUMO (ev) LUMO (ev) Band Gap (ev)TET -6.2 -3.86 2.34DOX -6.21 -3.84 2.37OTC -6.28 -3.96 2.32

CTC -6.56 -4.23 2.33

Table S7. The hetero-atoms content (atomic %) before and after tetracycline adsorption.

atomic % C 1s O 1s N 1s Al 2p Mo 3d Zn 2p

before adsorption 35.10 45.50 0.54 5.97 2.73 10.16

after adsorption 68.29 26.14 1.82 1.25 0.75 1.76

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