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A New Fluorescence Probe Based on Hybrid Mesoporous Silica/ Quantum Dot/Molecularly Imprinted Polymer for Detection of Tetracycline Liang Zhang, and Ligang Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b04381 • Publication Date (Web): 09 Jun 2016 Downloaded from http://pubs.acs.org on June 11, 2016

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ACS Applied Materials & Interfaces

A New Fluorescence Probe Based on Hybrid Mesoporous Silica/Quantum Dot/Molecularly Imprinted Polymer for Detection of Tetracycline Liang Zhang, Ligang Chen* Department of Chemistry, College of Science, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China ABSTRACT: A newly designed fluorescence probe made from a hybrid quantum dot/mesoporous silica/molecularly imprinted polymer (QD/MS/MIP) was successfully created, and the probe was used for the detection of tetracycline (TC) in serum sample. QD/MS/MIP was characterized by transmission electron microscope, Fourier transform infrared spectroscopy, UV spectroscopy, X-ray powder diffraction, nitrogen adsorption–desorption experiment and fluorescence spectroscopy. Tetracycline, which is a type of broad-spectrum antibiotic, was selected as the template. The monomer and the template were combined by covalent bonds. After the template was removed to form a binding site, a hydrogen bonding interaction formed between the hole and the target molecule. Moreover, when rebinding TC, a new complex was produced between the amino group of QD/MS/MIP and the hydroxyl group of TC. After that, the energy of the QDs could transfer to the complex, which explains the fluorescence quenching phenomenon. The fluorescent intensity of QD/MS/MIP decreased in 10 min, and an excellent linearity from 50 to 1000 ng mL-1 was correspondingly obtained. This composite material has a high selectivity with an imprinting factor of 6.71. In addition, the confirmed probe strategy was successfully applied to serum sample analyses, and the recoveries were 90.2%-97.2% with relative standard deviations of 2.2%-5.7%. This current work offers a novel and suitable method to synthesize QD/MS/MIP with a highly selective recognition ability. This composite material will be valuable for use in fluorescence probe applications. KEYWORDS: fluorescence probe, quantum dot, mesoporous silica, molecularly imprinted polymer, tetracycline

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1. INTRODUCTION The substance produced by a microbe that can not only kill bacteria but also has good inhibition and sterilization effects towards other pathogenic microorganisms is called antibiotic. Generally speaking, antibiotic is used to treat a variety of non-viral infections. Tetracycline (TC) is a type of broad-spectrum antibiotic that has various applications.1-3 Apart from the treatment of human disease, TC is widely used in animal breeding as a drug additive for the prevention of intestinal infection, growth-promotion, etc. because of its high practicability and low price. In addition, it has a wide range of applications in aquaculture. However, the abuse of TC may greatly harm people’s health. The abuse of TC can generate the drug resistance of bacteria. Furthermore, the excessive use of TC in animals may cause drug residuals. The residual TC could be transmitted to humans through the food chain and would be harmful to human health. At present, there are many methods established by scientists all over the world to determine the content of TC.4,5 The most common approach is high-performance liquid chromatography (HPLC). Though the HPLC method has high selectivity and good separation, the results show poor reproducibility, the cost of the analysis is high, and the analysis is lengthy when used for the detection of low concentration samples. Therefore, finding an efficient, fast and low-cost method to detect TC residue is important to human health and ecological civilization. Molecular imprinting technology is known as an excellent method for synthesizing functional receptors with predetermined binding sites.6-8 Organic polymers are usually used as the matrix material of the molecularly imprinted polymer (MIP). However, the organic polymers are so easy-swelling that they can change the morphology, possibly losing the size, shape and relative position of their molecular recognition site.9,10 The preparation and application of silica-based MIPs are beneficial to overcoming this shortcoming. However, the traditional silica-based imprinted material has a certain internal extension resistance, which can create an issue when combining with the recognition site, and the decrease of the binding rate leads to a low adsorption capacity and slow recognition dynamics.11,12 2


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Mesoporous silica materials have received great attention in the field of nanotechnology for their large surface area, ordered structure and uniform tunable pore size.13-15 As the carrier of molecular imprinting sites, mesoporous silica can accelerate the speed of adsorption and separation and force the imprinted molecules to combine with the mesoporous material pore wall for rapid point position recognition. In recent years, MIPs have been combined with a variety of different energy conversion devices to create light, electricity, quality and other sensors.16-18 Fluorescent materials have become a very important to sensors because of their high sensitivity and good stability.19-23 As new fluorescent materials, quantum dots (QDs) have greatly drawn the attention of researchers because of their advantages such as narrow and symmetric emission spectrum, large Stokes shift, low background noise, etc.24-26 Some researchers have reported the application of MIPs in fluorescence sensors.27-29 For fluorescence detection systems, the introduction of QDs capped by MIPs can clearly improve the selectivity and sensitivity. Our group has performed several studies regarding the preparation of QD-MIPs composite materials, which have been used for the detection of chlorpyrifos30, cyphenothrin31 and nicosulfuron.32 However, traditional imprinting strategies, whether pre-assembly (covalent interactions) or self-assembly (non-covalent interactions), have their own advantages and shortcomings.33,34 Covalent bonding to a binding group of a fixed array in space can produce the selective direction and holes of binding groups, but may be too strong and unsuitable for the rapid combination and release of the separation process. Non-covalent interactions belong to the category of supramolecular chemistry and are fast and suitable for the reversible binding of the polymer and the template; however, they exhibit poor direction and lack specificity with ionic bonds and hydrophobic interactions.35-37 It is essential to combine both covalent and non-covalent molecular imprinting methods. In this work, we constructed a fluorescence probe based on a hybrid quantum dot/mesoporous silica/molecularly imprinted polymer (QD/MS/MIP) for detecting TC via the photoinduced electron 3



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transfer (PET) fluorescence quenching mechanism. The monomer and the template molecule (TC) were combined by covalent bonds. Then, a sol-gel reaction occurred between the monomer-template complex, tetraethoxysilane and cetyltrimethylammonium bromide. Because the thermally reversible urethane bond was relatively easy to break under high-temperature conditions, the template was easily extracted, and hydrogen bonding formed between the hole of the material and the target molecule. Moreover, when TC was again bonded to QD/MS/MIP, a new complex was created, which led to the fluorescence quenching of the QDs. Apart from the characterization of the probe, a series of tests were systematically carried out to determine the stability, incubation time, sensitivity, and selectivity of the probe. Finally, the fluorescence probe was successfully used for detecting TC in serum samples, showing its potential value to the selective recognition and the determination of TC in complicated samples.

2. EXPERIMENTAL SECTION 2.1. Materials The TC standard was obtained from Energy Chemical (Shanghai, China). Donor equine serum was purchased from HyClone (HyClone, Logan, UT, USA). Zinc sulfate heptahydrate (ZnSO4·7H2O) was obtained from Shuangchuan (Tianjin, China). Manganese (II) chloride tetrahydrate (MnCl2·4H2O) was obtained from Bodi (Tianjin, China). Sodium sulfide (Na2S·9H2O) was obtained from Kaitong (Tianjin, China). Cetyltrimethylammonium bromide (CTAB), tetraethoxysilane (TEOS), dimethyl sulfoxide (DMSO), ethanol, tetrahydrofuran (THF) and sodium hydroxide were obtained

from

Kermel

(Tianjin,

China).

Ditin

butyl

dilaurate

(DBDU),

(3-mercaptopropyl)trimethoxysilane (KH-590), (3-aminopropyl)triethoxysilane (APTES) and (3-isocyanatopropyl)triethoxysilane (ICPTES) were obtained from Aladdin (Shanghai, China). All of the above reagents were of analytical grade. The water used in this study was high-purity water that was prepared using a Milli-Q water system (Millipore, Billerica, MA, USA). 2.2. Synthesis of mesoporous silica based molecular imprinted polymer (MS/MIP). 4


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First, TC (1.50 g), ICPTES (6 mL), DBDU (1 mL) were added to THF (30 mL), and the mixture was stirred at 373 K in an atmosphere of nitrogen for 24 h. After the reaction, the THF was removed through rotary evaporation. The product (0.10 g) was stirred in a mixture of CTAB (0.45 g), TEOS (2.75 mL), a NaOH solution (2 mol L-1, 0.875 mL), ethanol (37.5 mL) and water (30 mL) at room temperature for 2 h. After that, the solution was placed in a high-temperature reactor and then reacted at 393 K for 48 h. CTAB was removed by reflux condensation with ethanol for 20 h. To remove the template molecule, the product was added to DMSO together with several drops of water and heated at 433 K for 8 h under continuous stirring. The final product was filtered, washed with ethanol and water several times, and then dried in an oven. To ensure the bonding of the non-imprinted polymer (NIP) is consistent with that of the MIP after the removal of the template, APTES was chosen to replace TC and ICPTES without changing the other steps being, thus, yielding MS/NIP. 2.3. Preparation of the Mn-doped ZnS QDs The preparation of the Mn-doped ZnS QDs can be divided into three steps.38 Firstly, MnCl2·4H2O (0.198 g), ZnSO4·7H2O (3.595 g) and water (40 mL) were mixed together by constant stirring for 20 min in a nitrogen atmosphere. Secondly, a Na2S·9H2O solution (10 mL) was dropped into the mixture while stirring for another 30 min. Thirdly, the product was centrifuged and washed with ethanol three times. 2.4. Synthesis of QD/MS/MIP QD/MS/MIP was prepared by adding MS/MIP (0.250 g), the Mn-doped ZnS QDs (0.125 g), ethanol (1.0 mL) and KH-590 (0.4 mL) to water (7 mL) while stirring at room temperature for 24 h, followed by centrifugation and washing with ethanol three times. QD/MS/NIP was prepared using MS/NIP instead of MS/MIP. 2.5. Characterization The morphology of QD/MS/MIP was examined using a transmission electron microscope (TEM) (H7650, Hitachi, Japan). The Fourier transform infrared spectral analysis of QD/MS/MIP was 5



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obtained with a FT-IR360 spectrometer (Nicolet, Madison, WI, USA) using the KBr method. The ultraviolet spectrum analysis of QD/MS/MIP was conducted with a TU-1901 spectrometer (PERSEE, Beijing, China). The X-ray diffraction (XRD) spectrum analysis of QD/MS/MIP was performed using a Shimadzu XRD-600 diffractometer (Kyoto, Japan). The Brunauer-Emmett-Teller (BET) surface area analysis was obtained from nitrogen adsorption/desorption experiments at 77 K using a Quadrasorb SI-MP (Quantachrome, Florida, UK). The fluorescence intensity study was conducted with a F-4600 fluorescence spectrophotometer (Hitachi, Japan). The samples were dispersed using a KQ5200E ultrasonic apparatus (Kunshan Instrument, Kunshan, China). 2.6. Fluorescence Measurement The fluorescence measurements were performed using a fluorescence spectrophotometer with a quartz cell (1 cm path length). The scanning wavelength range was 500-700 nm with an excitation wavelength of 300 nm. Other parameters were set as follows: the slit width was 10 nm; the scan speed was 240 nm min-1; and the excitation voltage was 550 V. In addition, each spectrum was obtained after three parallel scans. A series of different concentrations of TC solutions (pH = 8) were added to 0.1 mg mL-1 QD/MS/MIP solution in a volume ratio of 1:1. The fluorescence analysis was carried out after fully mixing. 2.7. Analysis of serum samples The donor equine serum was frozen (-20 °C) for preservation and was heated to room temperature. Then, 10 mL of serum was diluted five times with water. A series of different concentrations of TC in serum samples ranging from 50 to 1000 ng mL-1 was obtained by adding different amounts of TC to the diluted donor equine serum. The diluted serum spiked with TC was added to the 0.1 mg mL-1 QD/MS/MIP solution in a volume ratio of 1:1. After fully mixing for 10 min and then centrifugation for 10 min, the supernatant was removed, and QD/MS/MIP was re-dispersed into water (pH = 8) for the fluorescent measurement of TC.

3. RESULTS AND DISCUSSION 6


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3.1. Synthesis of QD/MS/MIP The preparation of QD/MS/MIP presented in Figure 1 contains the following three steps: the synthesis of MS/MIP, the formation of the Mn-doped ZnS QDs, and the combination of these two materials to obtain the final product. MS/MIP was prepared by sol−gel process using TC as template, ICPTES as functional monomer, CTAB as structure-directing surfactant, DBDU as catalyst and TEOS as cross-linker. In the complex, TC was attached to the silyl groups of TEOS via thermally reversible urethane bonds. Because of the thermally reversible property of the urethane bond at high temperatures, we could easily extract the template and obtain a hydrogen bonding interaction between the hole and the target molecule. Moreover, the Mn-doped ZnS QDs were obtained. Mn2+ was doped into the ZnS QDs to improve their luminescence property. Finally, KH-590 was used to link MS-MIP and the QDs. 3.2. Characterization of QD/MS/MIP Figure 2a shows the Mn-doped ZnS QDs as nearly spherical particles with dimensions of approximately 5 nm. The readily visible mesoporous structure can be observed in Figure 2b. XRD was used to further study the purity and crystalline structure of the nanoparticles. As we can see from Figure 2c, the synthesized QD/MS/MIP exhibited a face-centered cubic structure with peaks assigned to (111), (220), and (311), which further confirm the successful fabrication of QD/MS/MIP. The results of the infrared spectrum analysis of QD/MS/MIP are shown in Figure 2d. There is a wide and intensive peak at 1108 cm-1 attributed to the asymmetric vibration of the Si–O–Si band. The peaks at 799 cm-1 and 468 cm-1 are assigned to the vibration of the Si–O band. The peaks at 2928 cm-1 (C-H band), 3421 and 1635 cm-1 (N-H band) represent the aminopropyl group. The peak at 2928 cm-1 is the C–H stretching vibration. The nitrogen adsorption and desorption experiment was performed to study the mesoporous silica structure of QD/MS/MIP (Figure 2e and 2f). The BET surface area is 388.89 m2 g-1, and the average pore volume is 0.55 cm3 g-1. The average Barrett–Joyner–Halenda (BJH) pore size obtained by the adsorption isotherm is approximately 4.4 nm. As we can see from the adsorption isotherm, the 7



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obvious IV-type curve exhibits a quick rise from a relative pressure of 0.4 to 0.6, which clearly indicates that there are uniform mesopores in QD/MS/MIP. This structure is beneficial to reduce the mass transfer resistance and enhance the accessibility of the site. In addition, the suitable shape of the material likely improves the moving rate and the binding capacity of the specific recognition of TC. 3.3. Stability of the QD/MS/MIP fluorescence emission measurement The stability of the QD/MS/MIP fluorescence emission was studied by testing its fluorescent intensity every 5 min. As shown in the results in Figure 3a, the emission of QD/MS/MIP is stable and the relative standard deviation (RSD) is 0.3%. 3.4. Effect of pH The acidity and basicity of the solution plays a vital role in the fluorescent properties. A pH range between 4 and 12 was studied to find the most suitable pH condition, and the results are shown in Figure 3b. The fluorescent intensity of the solution is low when the pH is less than 7, which can be explained by the decomposition of the Mn-doped ZnS QDs by forming H2S in the acidic solution.38 As the pH increases from 6 to 8, the fluorescent intensity increases and reaches a maximum value at pH 8. Changes in the fluorescent quenching of QD/MS/MIP in response to TC show a similar trend to the changes in fluorescent intensity in the absence of TC. The imprinted silica layers would be ionized at pH > 8, which decreases the interaction between the imprinting cavities and TC. Moreover, at higher and lower pH, TC may be slightly denatured. Therefore, the detection was carried out at pH 8. 3.5. Influence of incubation time The effect of incubation time on the fluorescent intensity was studied (Figure 3c). The fluorescent intensity decreases rapidly upon adding TC. The reaction between QD/MS/MIP and TC was completed within 10 min. After that, the fluorescent intensity remains stable for at least 1.5 h. 3.6. Possible fluorescence quenching mechanism of QD/MS/MIP with TC The fluorescent intensity of QD/MS/MIP was studied by changing the excitation wavelength between 280-350 nm. The weak blue peak at approximately 449 nm is the defect peak of the ZnS QDs, 8


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and the strong orange peak at approximately 595 nm can be explained by the transition of the Mn2+ ions from 4T1 to 6A1.39 The maximum in emission intensity appears at 595 nm when the excitation wavelength was set as 300 nm. As we can see from Figure S1, the fluorescent intensity of QD/MS/MIP is relatively weak but is dramatically restored after the removal of the template. The position and shape of the two spectrums are the same. The results show that the fluorescent intensity of spectrum b is nearly the same as that of spectrum a (QD/MS/NIP), which proves that the template molecule was completely removed. When the template molecule TC was re-added, QD/MS/MIP could interact with TC, which led to the fluorescence quenching. We suggest that an electron transfer between the QDs and TC is responsible for the fluorescence quenching. Such an electron transfer mechanism has also been reported by Tu et al.40 and Wang et al. 41 As we can see from the absorption spectra of QD/MS/MIP in Figure 4, the ultraviolet absorption band of TC is close to the band gap. There is no spectral overlap between the emission spectrum of QD/MS/MIP and the absorption spectra of TC. Hence, we do not think that the fluorescence quenching is caused by the energy transfer mechanism. The specific recognition and detection processes of TC using our established QD/MS/MIP method are demonstrated in Figure 5. It is not hard to see that the phenomenon of the fluorescence quenching can be explained by the electron-transfer between the hydroxyl group of TC and the amino group of QD/MS/MIP, with a complex forming between QD/MS/MIP and TC. The energy of the QDs would then be transferred to the complex, which leads to its fluorescence quenching. In addition, the fluorescence quenching mechanism can be explained by the molecular orbital theory. As we can see from Figure 5b, the electron of QD is excited from the valence band (ground-state) to the conduction band after accepting the ultraviolet photon. Afterwards, the excited electron goes back to the valence band, and the QD produces the fluorescence signal. In addition, in the presence of the template TC, there is a hydrogen bonding interaction between the amino groups of the QD and TC. The interaction force is so strong that it can result in the transfer of the electron between TC and the QD. The excited electron is able to directly transition into the LUMO of the 9



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complex. The excited electron of the QD would then return to the ground state with no fluorescence signal generation as a result of the energy level of the complex being higher than that of the QD, which explains the phenomenon of fluorescence quenching. Hence, the fluorescence detection of TC is completed in this way. 3.7. QD/MS/MIP with template molecule of different concentrations To prove the specific recognition ability of QD/MS/MIP and QD/MS/NIP, a series of different concentrations of TC in a range of 50–1000 ng mL-1 was added to the 0.1 mg mL-1 QD/MS/MIP solution in a volume ratio of 1:1. The fluorescent intensity of the QD/MS/MIP decreases as the concentration of the TC solution increases. Usually, the decrease in the fluorescent intensity can be attributed to the affinity between TC and QD/MS/MIP. It is not difficult to see that the decline of the fluorescent intensity for QD/MS/MIP is more clear than that for QD/MS/NIP for the same concentration of the TC solution (Figure S2b). The fluorescent probe exhibits an outstanding response to different concentrations of TC solution, which is an extremely useful property and appropriate for prospective applications. The phenomenon of the fluorescence quenching can be interpreted using the Stern–Volmer law, as follows: F0/F = KSV Cq + 1 where F0 is the fluorescence intensity in the absence of TC, F is the fluorescence intensity in the presence of TC, KSV is the Stern–Volmer constant, and Cq is the concentration of TC added. Furthermore, the Stern–Volmer plots of QD/MS/MIP with different concentrations of TC solution added are shown in Figure 6. The inserts in Figure 6a show the fluorescence changes with the absence and the presence of TC in QD/MS/MIP. The quenching material of QD/MS/MIP with TC satisfies the following Stern–Volmer law: F0/F = 0.0015Cq + 0.9811, with a correlation coefficient of 0.9992 in a liner range from 50 to 1000 ng mL-1. The limit of detection (LOD) was obtained as the ratio of 3σ to K, where σ is the standard deviation of blank measurements (n = 11) and K is the slope of the calibration curve. The LOD of this method is 15.0 ng mL-1. 3.8. Selective adsorption on QD/MS/MIP 10


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To check the selectivity of the QD/MS/MIP prepared in this method, some compounds with similar structures including the analogue, chlortetracycline (CTC), and the reference compound, bisphenol A (BPA), were measured. Their chemical structures are shown in Figure S3. The obtained relationships are given in Figure S2. From the results in Figure 6b, the QD/MS/MIP displays the highest specific recognition ability for TC. Therefore, because of the structural difference of TC, BPA and CTC were not able to enter in the specific recognition cavities of QD/MS/MIP. The imprinting factor (IF), as defined by the ratio of KSV, MIP to KSV, NIP, was also calculated, and the results are summarized in Table 1. The result (IF = 6.71) indicates that QD/MS/MIP has the highest affinity for TC. The effects of other interfering ions, including inorganic ions and biomolecules, were also measured (Table 2). The coexisting substances did not influence the detection of TC through the established QD/MS/MIP method. All of the results suggest the specific selective recognition of TC by QD/MS/MIP. 3.9. Application to serum sample analysis To investigate the applicability of the proposed method, the determination of TC in serum samples was explored. A series of TC solutions with different concentrations was obtained by adding different amounts of TC to diluted donor equine serum. After that, the spiked serum samples were analyzed using our method. The relative standard deviations (RSDs) obtained by this QD/MS/MIP method are 2.2%-5.7% with the recoveries ranging from 90.2% to 97.2%. Furthermore, we compared our QD/MS/MIP method with some related methods that have previously been reported for detecting TC (Table 3). The recovery and RSD are comparable with those methods. However, the LOD is higher than some of the methods. As we all know, different approaches have different superiorities and disadvantages dealing with precision, specific recognition and analysis time. When compared with chromatographic analysis, the fluorescence analysis method contains no complex pre-separation procedure and shows a series of attractive properties, such as being simple, quick and reliable. Meanwhile, the selective recognition ability of the fluorescence

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detection can be increased by using QD/MS/MIP. However, we need to make some efforts to improve the sensitivity of the QD/MS/MIP system while retaining the high selectivity. 4. CONCLUSIONS In summary, a newly designed fluorescence probe based on a hybrid quantum dot/mesoporous silica/molecularly imprinted polymer was successfully created, and the probe was used for the detection of tetracycline in serum samples through a photoinduced electron transfer quenching mechanism. The selectivity of this probe was validated via the molecular imprinting technique. At the same time, the fluorescence technique has a good sensitivity, and the mesoporous silica structure reduces the mass transfer resistance and improves the sites’ selectivity. In addition, the suitable shape of the material improves the moving rate and the binding capacity of the specific recognition to tetracycline. This method possesses advantages including a simple preparation process, a favorable selectivity and stability, a reduced cost and a short analysis time and will have a wide range of applications. In the future, we will make further efforts to apply this composite material to the analysis of other sample matrices, such as food samples.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: (1) Fluorescence spectra of QD/MS/NIP and QD/MS/MIP after and before the removal of the template molecule TC (Figure S1); (2) Fluorescence emission spectra of QD/MS/MIP and QD/MS/NIP with addition of the indicated concentrations of TC, CTC and BPA (Figure S2); (3) Chemical structures of TC, CTC and BPA (Figure S3).

AUTHOR INFORMATION Corresponding author * E-mail: [email protected]. Tel.: +86-451-82190679. 12


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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by Fundamental Research Funds for the Central Universities (No.2572014EB06) and National Natural Science Foundation of China (No. 21205010).

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15


Membranes

for


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Figure captions: Figure 1. Schematic illustration for fabricating QD/MS/MIP. Figure 2. (a) Transmission electron microscope images of QDs. Transmission electron microscope images (b), the X-ray diffraction pattern (c), the Fourier transform infrared spectroscopy spectrum (d), N2 sorption isotherms (e) and the pore size distribution (f) of QD/MS/MIP. Figure 3. (a) The stability of the QD/MS/MIP fluorescence emission measurement. (b) The pH influence on the fluorescence intensity of QD/MS/MIP (F0) and on the fluorescence quenching between QD/MS/MIP and TC (F). (c) The study of the influence of incubation time on the fluorescence quenching reaction between QD/MS/MIP and TC. Figure 4. UV spectra of TC (curve 1) and QD/MS/MIP (curve 2). The fluorescence emission spectra of QD/MS/MIP (curve 3). Figure 5. Schematic of the QD fluorescence quenching mechanism on the basis of the electron-transfer-induced energy transfer (a) and molecular orbital theory (b). Figure 6. (a) Comparison of the TC calibration curve for QD/MS/MIP with that for QD/MS/NIP. (b) The Stern–Volmer quenching constants of QD/MS/MIP and QD/MS/MIP for different target molecules.

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1

20


Page 20 of 29

Page 21 of 29

b)

a)

d)

c) 1200

80 70

( 311)

1000

60 800

1635

T (%)

50

600 ( 220)

799 468

2928

40 30

( 311)

400

3431

20 200

350

20

30 40 50 2 θ (degrees)

60

0 4000 3500 3000 2500 2000 1500 1000 σ (cm-1)

70

f)

Desorption Adsorption

dV / dP (cm3 nm -1 g -1)

e)

1108

10

0 10

Adsorption volume (cm3 g-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


300

250

200

150 0.0

0.6 0.5 0.4 0.3 0.2 0.1 0.0

0.2

0.4 0.6 0.8 Relative pressure (P/ P0)

1.0

3

4

Figure 2

21


5

6 7 8 Pore size (nm)

9

10

11

500


a) 5000

b) 5000 Flourescence intensity

3000

2000

1000

4000 3000 2000 1000 0

10

20

30 40 t (min) 5000

50

60

3

4

5

6

c)

4000 Fluorescence intensity

0

F0

F

4000 Fluorescence intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 29

3000

2000

1000

0

0

20

40 60 t (m in)

80

100

Figure 3

22


7

8 9 pH

10

11 12 13

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1

5500 5000 4500 4000 3

3500 3000 2500

1

2000

2

1500 1000 500 200 250 300 350 400 450 500 550 600 650 700 Wavelength (nm)

Figure 4

23


Fluorescence intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Absorbance (a.u.)

Page 23 of 29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

b)

Conduction band LUMO UV LUMO vis Blue light

Orange light Mn2+ HOMO

Valence band

TC species

Figure 5

24


Page 24 of 29

Page 25 of 29

a)

1.5

b)

QD/MS/MIP QD/MS/NIP

15

QD/MS/MIP -1 -1

KSV(10 (ng mL ) )

1.2

0.9

(F0 / F)-1

0.6

QD/MS/NIP

0.3

0.0

10

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0

200

400 600 -1 c ( ng mL )

800

1000

5

0

TC

Figure 6

25


CTC

BPA


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 29

Table 1. Partition Coefficient and Imprinting Factor (IF) for QD/MS/MIP and QD/MS/NIP TC

CTC

BPA

KSV,MIP (*104)

14.82

5.43

2.30

KSV, NIP(*104)

2.21

2.30

2.13

IF

6.71

2.36

1.08

26


Page 27 of 29

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Table 2. Influence of Interfering Substances of QD/MS/MIP Solution System. Interfering materials

Concentration (µ mol L-1)

K Na+

2000 2000

Relative error (％) + 1.05 + 0.95

Ca2+

1000

+ 0.90

2+

1000

+ 1.32

Cl

500

- 2.36

Serine

1000

- 1.87

Proline

1000

- 2.18

Valine

1000

- 3.23

Glutathione

1000

+ 3.02

Fructose

1000

+ 1.32

Sucrose

500

+ 1.75

Glucose

500

- 2.43

Starch

1000

+ 2.37

Sucrose

1000

- 2.97

Lactamine

1000

+ 3.51

Histidine

1000

+ 4.01

Lactose

1000

+ 3.87

Maltose

1000

+ 3.26

Tryptophan

1000

+ 2.71

Glycine

1000

+ 1.79

Urea

1000

+ 2.67

Amylum

500

- 1.98

+

Mg

-1

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 29

Table 3. Comparison of Different Methods for Determination of TC in Different Samples Pretreatment method

Detection method

Samples

LOD (ng mL-1)

Recovery (%)

RSD (%)

Ref.

Solid-phase extraction

LC–MS

Sewage effluent

0.23

75–98

4.3–9.8

42


UHPLC–PAD

Lake water

2

84.7–88.7

1.8–2.5

43


HPLC–UV

Honey

16.1

64.8–78.8

5.4–9.3

44


HPLC–UV

Milk

10.2

98.2–100.1

2.1–3.8

45

Fluorescence probe based QD/MS/MIP

Fluorescence spectrophotometer

Donor equine serum

15

90.2–97.2

2.2–5.7

This study

28


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TOC

29


Quantum

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