ZnS quantum dots embedded molecularly imprinted organogel nanofibers

Sensors and Actuators B 234 (2016) 122–129

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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Fabrication of a fluorescent sensor by organogelation: CdSe/ZnS quantum dots embedded molecularly imprinted organogel nanofibers Youngdo Kim, Ji Young Chang ∗ Department of Materials Science and Engineering, College of Engineering, Seoul National University, Seoul 151-744, Republic of Korea

a r t i c l e

i n f o

Article history: Received 25 November 2015 Received in revised form 27 April 2016 Accepted 28 April 2016 Available online 29 April 2016 Keywords: Organogelation Quantum dots Fluorescent sensor Molecularly imprinted polymers Organogel nanofibers Histamine

a b s t r a c t We describe a molecularly imprinted polymer (MIP)-based fluorescent sensor fabricated through an organogelation process. The sensor was comprised of a molecularly imprinted nanofiber as a receptor and a CdSe/ZnS quantum dot (QD) as a signal transducer. The sensor fabrication was carried out in three steps: (1) organogelation of a polymerizable gelator (PG) in the presence of the QD and a template, (2) gel-state polymerization and (3) extraction of the template. We chose histamine as a model template. PG had two different polymerizable groups: an acrylate and a diacetylene. As a functional monomer for complexation with the template, an acrylate having a carboxyl group was used. The QD and template-containing organogel formed in n-decane were polymerized in the presence of a photoinitiator and a cross-linker by UV irradiation to produce highly cross-linked organogel nanofibers. The template molecules were removed by extraction with methanol/acetic acid (9:1 v/v) to give the QD-incorporated, histamine imprinted organogel nanofibers (QD-HIOGNF). QD-HIOGNF showed high molecular recognition properties toward histamine in respects to both sensitivity and selectivity. The fluorescence intensity of QD-HIOGNF was quenched sensitively as the concentration of histamine increased. QD-HIOGNF could be reused for sensing after removing the bound analytes. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The molecular imprinting technique provides a platform for the fabrication of selective synthetic receptors [1]. In the molecular imprinting process, a complex of a functional monomer with a template is polymerized in the presence of a cross-linking agent and the template is subsequently removed to generate a binding cavity in a cross-linked polymer matrix. Molecularly imprinted polymers (MIPs) as synthetic receptors have potential advantages such as high physiochemical stability, simple preparation and broad range of working conditions compared to natural receptors [2–4]. Poor binding site accessibility and low selectivity have been considered as drawbacks when molecularly imprinted polymers are prepared as large particles, but these shortcomings are less severe when using nanosized imprinting matrices such as nanoparticles [5–7] or nanofibers [8–12] where binding sites are formed at the surface or in the proximity of the surface. An organogel is a viscoelastic material consisting of a large amount of solvent molecules and a nanofiber network produced by self-assembly process of low mass gelator molecules [13]. Some

∗ Corresponding author. E-mail address: [email protected] (J.Y. Chang). http://dx.doi.org/10.1016/j.snb.2016.04.161 0925-4005/© 2016 Elsevier B.V. All rights reserved.

organogels showed gel to sol or gel to gel transitions in the presence of chemicals such as anions with accompanying fluorescent emission changes. [14–17]. The efficiency of these sensing systems relies on fast phase transitions through specific interactions of an analyte with a gelator molecule, which is often difficult to achieve. Here we report a novel MIP-based fluorescent sensor fabricated through an organogelation process. The formation of organogel nanofibers is of great interest in the fabrication of MIPs. However, supramolecular nanofiber structures are easily disrupted by thermal and mechanical stimuli. To overcome this disadvantage, we used an organogelator bearing two different polymerizable groups for the preparation of molecularly imprinted nanofibers [10]. In the development of MIP-based sensors, transformation of binding events into measurable signals is a major concern [18–28]. We used a fluorescent CdSe/ZnS quantum dot (QD) as a signal transducer. QDs are finding increasing utility in sensing applications because of their discrete size-dependent optical properties and good photostability [29–35]. The QDs capped with ligands having long alkyl chains were incorporated into organogel nanofibers through the interactions between the ligands and the gelator molecules [36]. We chose histamine as a model template. Histamine is a representative biogenic amine which is formed by decarboxylation of an amino acid. The reliable determination of histamine at low concentrations is of great importance in

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clinical chemistry and food science. Histamine is a neurotransmitter and involved in various physiological functions. It is released during allergic reactions, which causes irritation and inflammation [37,38]. A high level of histamine is also found in spoiled foods. The detection of histamine in conjunction with different analytical approaches such as high performance liquid chromatography, enzyme-linked immunosorbent assay and capillary electrophoresis has been attempted [39–41]. 2. Experimental 2.1. Materials 10,12-Tricosadiynoic acid (96%) was purchased from Alfa Aesar. Divinylbenzene (DVB) and N,N-(dimethylamino)pyridine (DMAP, 99%) were purchased from Aldrich. Histamine (97%) and serotonin hydrochloride (98%) were purchased from Acros Organics. Allopurinol (98%), dopamine hydrochloride (98%), 6-bromo-1-hexanol (95%), 4 -hydroxy-4-biphenyl-carboxylic acid (98%), 2,6-di-tertbutylphenol (98%), N,N-diethylaniline (99%), acryloyl chloride (95%), 4,4 -biphenol (99%) and N,N-dicyclohexylcarbodiimide (DCC, 98%) were purchased from Tokyo Chemical Industry. CdSe/ZnS quantum dot (particle size: ∼3.4 nm, capping agent: trioctylphosphine oxide) was obtained from Nanosquare Inc. 2,2,Dimethoxy-2-phenylacetophenone (DMPA) was obtained from Ciba Specialty. All chemicals and reagents were used as received. Tetrahydrofuran (THF) was dried over sodium metal and distilled. 2.2. Measurements 1 H and 13 C NMR spectra were recorded on a Bruker Avance DPX300 (300 MHz for 1 H NMR) spectrometer and a Bruker Avance 600 (150 MHz for 13 C NMR) spectrometer. Fourier transform infrared (FT-IR) spectra were measured on a Nicolet 6700 FT-IR spectrophotometer (Thermo Scientific, USA) using KBr pellets. Scanning electron microscopy (SEM) images were measured by a Carl Zeiss SUPRA 55VP. High resolution transmission electron microscopy (HRTEM) images were obtained by a FEI Tecnai F20 operating at 200 kV. UV–vis spectrum was obtained by a SCINCO S-3150 instrument. Fluorescence measurements were performed using a Shimadzu RF-5301PC spectrofluorometer.

2.3. Synthesis of 4-[4-(6-acryloyloxyhexyloxy)phenyl]benzoic acid (FM) This compound was prepared as a functional monomer according to our previous report [42]. To a solution of 4[4-(6-hydroxyhexyloxy)phenyl]benzoic acid (2.5 g, 7.95 mmol), N,N-diethylaniline (1.0 g, 8.35 mmol) and a catalytic amount of 2,6-di-tert-butylphenol in 1,4-dioxane (30 mL) was added acryloyl chloride (2.2 g, 23.9 mmol) dropwise. The reaction mixture was stirred at 25 ◦ C for 24 h and then was poured into cold water. The precipitate was isolated by filtration and washed three times with distilled water. The product was purified by recrystallization from ethanol: yield 2.1 g (70%). 2.4. Synthesis of 4-hydroxy-4 -[6-(acryloyl)hexyloxy]biphenyl This compound was synthesized according to our previous report [43]. Potassium carbonate (1.95 g, 14.1 mmol), potassium iodide (catalytic amount) and 6-bromohexyl acrylate (3.0 g, 12.75 mmol) were added to a solution of 4,4 -biphenol (2.55 g, 14.1 mmol) in DMF (20 mL). The reaction mixture was stirred at ◦ 60 C for 20 h and was cooled to room temperature. The resulting solution was poured into distilled water (150 mL). The precipitates were collected by filtration, washed with distilled water and dried

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over MgSO4 . The crude product was recrystallized from ethanol and further purified by column chromatography on silica gel using THF and n-hexane (2:3) as eluents: yield 2.4 g (55%). 2.5. Synthesis of 4 -(6-(acryloyloxy)hexyloxy)biphenyl-4-yl tricosa-10,12-diynoate (PG) DCC (0.76 g, 2.7 mmol) and DMAP (0.080 g, 0.74 mmol) were added to a solution of 4-hydroxy-4 -[6-(acryloyl)hexyoxy]biphenyl (1.04 g, 3.06 mmol) and 10,12-tricosadiynoic acid (0.60 g, 3.06 mmol) in methylene chloride (50 mL), and the mixture was stirred for 12 h at room temperature. Insoluble solids were removed by filtration. After evaporation of the solvent, the crude product was purified by column chromatography on the silica gel using THF and n-hexane (1:5) as eluents to give white solids; yield 1.13 g (68.9%). 1 H NMR (300 MHz, CDCl3 ) ␦H 7.44 (4H, dd, overlap, Ar), 7.12 (2H, d, J = 8.4 Hz, COOAr), 6.94 (2H, d, J = 8.4 Hz, −OAr), 6.43 (1H, d, J = 17.4 Hz, CH), 6.12 (1H, dd, J = 10.5, 10.5 Hz, CH), 5.82 (1H, d, J = 10.2 Hz, CH), 4.18 (2H, t, J = 6.6 Hz, −OCH2 ), 4.00 (2H, t, J = 6.6 Hz, −ArOCH2 −), 2.57 (2H, t, J = 7.2 Hz, −OCOCH2 −), 2.25 (2H, t, J = 5.1 Hz, CCH2 −), 1.85–1.72 (2H, overlap, CCCH2 −, 2H, −ArOCCH2 −, 2H, −COOCCH2 −, 2H, −OCOCCH2 −), 1.54–1.26 (26H, m, −CH2 −), 0.88 (3H, t, J = 6.5 Hz, −CH3 ); 13 C NMR (150 MHz, CDCl3 ) ␦C 169.1, 165.1, 157.8, 151.7, 134.0, 130.4, 128.7, 128.3, 128.0, 127.7, 121.6, 115.0, 75.7, 72.3, 66.7, 62.9, 33.9, 31.9, 29.6, 29.3, 29.1, 28.9, 28.8, 28.2, 27.2, 26.5, 26.3, 25.2, 23.1, 18.2, 15.9 ppm. IR (KBr): max /cm−1 2921, 2852, 2242, 2145, 1745, 1721, 1639, 1607, 1499, 1470, 1410, 1388, 1324, 1290, 1272, 1249, 1216, 1196, 1170, 1153, 1035, 996, 925, 892, 823, 718. Elemental analysis (Found: C, 79.08; H, 9.09; O, 11.72. Calc. for C44 H60 O5 : C, 79.00; H, 9.04; O, 11.96%). 2.6. Preparation of CdSe/ZnS QD-incorporated, histamine imprinted organogel nanofibers (QD-HIOGNF) Histamine (2.0 mg, 0.018 mmol), FM (13 mg, 0.036 mmol) and DMPA (30 mg) were dissolved in n-decane (0.5 mL). To the solution, PG (38 mg) and DVB (3.7 mg) were added and the mixture ◦ was stirred at 65 C until a clear solution was obtained. After the subsequent addition of CdSe/ZnS quantum dots (0.5 mL, 5 mg mL−1 in n-decane), the solution was cooled to room temperature to form a stable organogel. The photopolymerization of the organogel was performed by UV irradiation (a high-pressure mercury arc lamp, 3 mWcm−2 ) for 3 h at room temperature. Histamine was extracted by stirring the reaction mixture in methanol/acetic acid (20 mL, 9:1 v/v) for 24 h and Soxhlet extraction with methanol for 48 h. The resulting histamine imprinted nanofibers were isolated by filtration and dried in vacuo. CdSe/ZnS QD-incorporated, non-imprinted organogel nanofibers (QD-NIOGNF) were prepared using the same procedure as that used for the preparation of QD-HIOGNF, except that no histamine was added. 2.7. Kinetic binding test QD-HIOGNF (3.0 mg) was dispersed in a solution of histamine (500 ng mL−1 ) in methanol (20 mL) and the fluorescence spectrum was measured every 10 min. 2.8. Rebinding test QD-HIOGNF or QD-NIOGNF (3.0 mg) was immersed in different concentrations of histamine solutions (100–700 ng mL−1 ) in methanol (20 mL). After stirring for 10 min, the fluorescence spectrum of each solution was measured.

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Scheme 1. Synthesis of the polymerizable organogelator (PG).

Fig. 1. Schematic route of the preparation of QD-incorporated, histamine imprinted organogel nanofibers (QD-HIOGNF).

2.9. Selectivity test Allopurinol, serotonin and dopamine were used as analogs of histamine. QD-HIOGNF or QD-NIOGNF (3.0 mg) was dispersed in solutions of different concentrations of the analogs (100–700 ng mL−1 ) in methanol (20 mL). After stirring for 10 min, the fluorescence spectrum of each solution was obtained. 2.10. Recyclability test QD-HIOGNF (3.0 mg) was added to a solution of histamine (100 ng mL−1 ) in methanol (20 mL) and the fluorescence spectrum of the mixture was measured after stirring for 30 min. After evaporation of methanol, the solid residue was stirred in methanol/acetic acid (20 mL, 9:1 v/v) for 12 h and Soxhlet-extracted with methanol for 12 h. QD-HIOGNF was isolated by filtration, dried and reused for the binding test. 3. Results and discussion 3.1. Synthesis and preparation of QD-HIOGNF The approach used in this study to fabricate a fluorescent sensor by organogelation is described in Fig. 1. The sensor fabrication was

carried out in three steps: 1) organogelation of a polymerizable gelator (PG) in the presence of the QD and the template, 2) gel-state polymerization and 3) extraction of the template. A heterobifunctional organogelator (PG) bearing two different polymerizable groups was prepared by an esterification reaction of an acrylate having a phenolic group with a diacetylene-containing carboxylic acid (Scheme 1). PG showed an ability to gelate organic solvents such as n-decane, methanol and ethanol. The critical gelation concentration was 1.5 wt% in n-decane. As a functional monomer for complexation with the template, we used an acrylate having a carboxyl group. Histamine (template) is an aminoalkylated imidazole which could form ionic and hydrogen bondings with a carboxyl group. Since both the functional monomer (FM) and the organogelator (PG) had a similar acrylate structure bearing a hexyloxybiphenyl group, they were expected to be co-assembled into nanofibers during organogelation. The template-monomer complex was prepared by dissolving histamine (2.0 mg) and functional monomer FM (13 mg) together with photoinitiator DMPA (30 mg) in n-decane (0.5 mL). After addition of organogelator PG (38 mg) and cross-linker DVB (3.7 mg), the mixture was heated ◦ at 65 C until a clear solution was obtained. After addition of trioctylphosphine oxide capped CdSe/ZnS quantum dots (0.5 mL, 5 mg mL−1 in n-decane), the solution was cooled down to room temperature to form a stable organogel. The organogel of PG alone

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as a signal transducer. The QDs would interact preferentially with the analytes which were bound to the recognition sites in the fiber. As a result, a change in the fluorescence intensity of the QDs would ensue possibly via the charge transfer mechanism [46,47]. 3.3. Rebinding performance and sensitivity of QD-HIOGNF

Fig. 2. Photographs of the organogel of PG alone under day light, the organogel containing QDs under day light and UV light (from left to right).

formed in n-decane was milky white in color (Fig. 2). The QDcontaining organogel appeared yellowish green and emitted a bright green luminescence under UV light irradiation. We expected that CdSe/ZnS quantum dots were incorporated into the organogel nanofibers through interactions between long alkyl chains of the QD capping agent and the organogelator. The QD-containing organogel was UV irradiated for 3 h at room temperature. In this process, acrylate, diacetylene groups and DVB were polymerized to produce highly cross-linked, CdSe/ZnS QD-incorporated, histamine embedded organogel nanofibers (QD-His-OGNF). The template molecules embedded in QD-His-OGNF were removed by washing with methanol/acetic acid (9:1 v/v) and Soxhlet extraction with methanol, resulting in the formation of the QD-incorporated, histamine imprinted organogel nanofibers (QD-HIOGNF). 3.2. Structural and morphological analysis of organogel nanofibers The structures of the organogel, QD-His-OGNF and QD-HIOGNF were characterized by FT-IR spectroscopy (Fig. 3). The two absorptions at 2242 and 2145 cm−1 corresponding to the diacetylene groups were observed in the dried organogel [44], but disappeared after polymerizaion, indicating that the polymerizaion proceeded via 1,4-addition reaction. The peak for the newly formed C C bonds was hardly noticeable, probably due to their symmetric structure. The successful removal of histamine from the nanofiber was confirmed from the FT-IR spectra of QD-His-OGNF and QD-HIOGNF. QD-His-OGNF showed the asymmetric and symmetric stretching vibration bands for ammonium group of histamine at 3165 and 3065 cm−1 , respectively [45]. After the extraction, they disappeared. The morphological features of organogel nanofibers were investigated by SEM and high resolution TEM (HRTEM) measurements. Fig. 4A and B show representative SEM images of the organogel nanofibers obtained by drying the organogel of PG alone formed in n-decane and the QD-incorporated imprinted nanofibers (QDHIOGNF), respectively. The SEM image of the dried organogel exhibited entangled fibers with an average diameter of 50 nm. QD-HIOGNF had more distinct fibrillar structures with the same diameters compared to the dried organogel, implying that the polymerization occurred within the organogel nanofibers. The QDs incorporated in the histamine imprinted organogel nanofibers were clearly observed in the HRTEM analysis (Fig. 4C). They were well dispersed in the fiber, which would be essential for them to act

As shown in Fig. S1, QD-HIOGNF exhibited a strong fluorescence peak at 550 nm in addition to the Rayleigh scattering peaks at 330 and 660 nm when excited at 330 nm. A weak fluorescence around 370–500 nm was ascribed to the emission of a polydiacetylene chain having a short conjugation length. To investigate the kinetic binding profile of QD-HIOGNF for histamine, the QD-HIOGNF (3.0 mg) were dispersed in a solution of histamine (500 ng mL−1 ) in methanol (20 mL) with stirring and the fluorescence intensity was measured at 10 min intervals (Fig. S2). The fluorescence intensity decreased rapidly with time in the first 10 min. The maximum quenching occurred within 30 min, demonstrating that the binding cavities had a high sensitivity toward the template. We also examined the sensitivity of QD-HIOGNF to the concentration of histamine. The fluorescence of QD-HIOGNF was measured in 10 min after mixing QD-HIOGNF with a solution of histamine in methanol. As depicted in Fig. 5A and B, the fluorescence intensity of QD-HIOGNF decreased as the concentration of histamine increased in the range between 100 and 700 ng mL−1 . Below the histamine concentration of 100 ng mL−1 , a fluorescence quenching was hardly observed. On the other hand, QD-incorporated, non-imprinted organogel nanofibers (QDNIOGNF) showed much smaller changes in their fluorescence than QD-HIOGNF with increasing concentration of histamine (Fig. 5F). QD-NIOGNF was prepared using the same procedure as that used for the preparation of QD-HIOGNF, except that no histamine was added. 3.4. Selectivity of QD-HIOGNF The selectivity of QD-HIOGNF was investigated by testing its fluorescence quenching response in the presence of potential structural analogs of histamine, including allopurinol, serotonin and dopamine. Allopurinol (AL) is an isomer of hypoxanthine and can cause injury in intestinal, renal, heart and brain tissue owing to the inhibitory effect of xanthine oxidase [48]. Serotonin (SR) and dopamine (DA) are biogenic amine neurotransmitters in biological systems, playing an important role in the renal, hormonal and emotion functioning [49,50]. The selectivity experiments were conducted in the same manner as mentioned above. A diminutive change in fluorescence intensity of QD-HIOGNF was observed in the case of all analogs (Fig. 5C–E), indicating that these structural analogs had poor binding affinity to the imprinted sites. The behavior of fluorescence quenching can be described by the Stern-Volmer equation (Eq. (1)) [51] F 0 /F = 1 + K SV [C]

(1)

where F0 and F are the fluorescence intensities QD-HIOGNF in the absence and presence of an analyte, respectively. [C] is the concentration of an analyte and KSV is the Stern-Volmer quenching constant. This equation can be utilized to quantify the selectivity toward the sensing molecule. Both QD-HIOGNF and QD-NIOGNF exhibited a linear Stern-Volmer relationship as regards histamine and its structural analogs (Fig. 5G and H). The selectivity of QDHIOGNF was evaluated by the Stern-Volmer quenching constant (KSV ) estimated from the slopes of the Stern-Volmer plots of QDHIOGNF. A quenching constant of QD-HIOGNF for histamine was more than ten times higher than that for histamine analogs (Fig. 6). The imprinting factor calculated from the ratio of the quenching

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Fig. 3. FT-IR spectra of dried organogel, QD-His-OGNF and QD-HIOGNF.

Fig. 4. (A) SEM image of the dried organogel of PG alone. (B) SEM image of QD-HIOGNF. (C) HRTEM image of QD-HIOGNF.

constant of QD-HIOGNF for histamine to that of QD-NIOGNF was 16.8, also showing the high sensitivity of QD-HIOGNF toward histamine. 3.5. Recyclability of QD-HIOGNF The recyclability of QD-HIOGNF was evaluated by successive binding, extraction and rebinding experiments. QD-HIOGNF (3.0 mg) was incubated in a solution of histamine (100 ng mL−1 ) in methanol (20 mL) for 30 min, allowing most binding cavities to be occupied by the template, and the bound template was then

removed following the extraction procedure mentioned above. QDHIOGNF recovered its initial fluorescence intensity after extraction. While repeating the binding-extraction cycles seven times, the fluorescence intensity of QD-HIOGNF decreased only 10% compared to that of as-prepared QD-HIOGNF (Fig. S3). 4. Conclusions We demonstrated a novel approach to fabricate a fluorescent sensor of histamine. A CdSe/ZnS QD and histamine embedded organogel nanofiber was prepared by organogelation. Subsequent

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Fig. 5. (A) Fluorescence emission spectra of QD-HIOGNF (150 ␮g mL−1 ) taken after 10 min stirring with an increase on histamine concentration in methanol. Amount of fluorescence quenching (%) [=(1 − F/F0 )100] of QD-HIOGNF (150 ␮g mL−1 ) obtained after 10 min stirring with an increasing concentration of histamine (B), allopurinol (C), dopamine (D) and serotonin (E) in methanol. (F) Fluorescence quenching (%) of QD-NIOGNF (150 ␮g mL−1 ) measured after 10 min stirring with an increasing concentration of histamine in methanol. (G) Estimated Stern-Volmer plots of QD-HIOGNF. (H) Estimated Stern-Volmer plots of QD-NIOGNF.

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Fig. 6. Stern-Volmer constants (KSV ) of QD-HIOGNF and QD-NIOGNF toward different target analytes.

in-situ polymerization followed by extraction of histamine produced the polymerized nanofiber bearing QDs and binding cavities as a signal transducer and a receptor, respectively. QD-HIOGNF showed high molecular recognition properties toward histamine in terms of both sensitivity and selectivity. Because of the adequate proximity of the recognition sites to the QDs, a notable, concentration-sensitive fluorescence quenching was observed. Acknowledgements This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2010-0017552, 2015R1A2A2A01006585). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2016.04.161. References [1] K. Haupt, K. Mosbach, Molecularly imprinted polymers and their use in biomimetic sensors, Chem. Rev. 100 (2000) 2495–2504. [2] G. Wulff, Enzyme-like catalysis by molecularly imprinted polymers, Chem. Rev. 102 (2002) 1–27. [3] M.J. Whitcombe, E.N. Vulfson, Imprinted polymers, Adv. Mater. 13 (2001) 467–478. [4] L. Ye, K. Mosbach, Molecular imprinting: synthetic materials as substitutes for biological antibodies and receptors, Chem. Mater. 20 (2008) 859–868. [5] S. Ambrosini, S. Beyazit, K. Haupt, B. Tse Sum Bui, Solid-phase synthesis of molecularly imprinted nanoparticles for protein recognition, Chem. Commun. 49 (2013) 6746–6748. [6] W. Wan, Q. Han, X. Zhang, Y. Xie, J. Sun, M. Ding, Selective enrichment of proteins for MALDI-TOF MS analysis based on molecular imprinting, Chem. Commun. 51 (2015) 3541–3544. [7] S. Sykora, A. Cumbo, G. Belliot, P. Pothier, C. Arnal, Y. Dudal, P.F.-X. Corvini, P. Shahgaldian, Virus-like particles as virus substitutes to design artificial virus-recognition nanomaterials, Chem. Commun. 51 (2015) 2256–2258. [8] I.S. Chronakis, B. Milosevic, A. Frenot, L. Ye, Generation of molecular recognition sites in electrospun polymer nanofibers via molecular imprinting, Macromolecules 39 (2006) 357–361. [9] K. Yoshimatsu, L. Ye, P. Stenlund, I.S. Chronakis, A simple method for preparation of molecularly imprinted nanofiber materials with signal transduction ability, Chem. Commun. (2008) 2022–2024. [10] W.J. Kim, B.M. Jung, S.H. Kang, J.Y. Chang, Molecular imprinting into organogel nanofibers, Soft Matter 7 (2011) 4160–4162. [11] W.J. Kim, J.Y. Chang, Molecularly imprinted polyimide nanofibers prepared by electrospinning, Mater. Lett. 65 (2011) 1388–1391. [12] Y. Li, Q. Bin, Z. Lin, Y. Chen, H. Yang, Z. Cai, G. Chen, Synthesis and characterization of vinyl-functionalized magnetic nanofibers for protein imprinting, Chem. Commun. 51 (2015) 202–205. [13] P.D. Wadhavane, R.E. Galian, M.A. Izquierdo, J. Aguilera-Sigalat, F. Galindo, L. Schmidt, M.I. Burguete, J. Pérez-Prieto, S.V. Luis, Photoluminescence enhancement of CdSe quantum dots: a case of organogel-nanoparticle symbiosis, J. Am. Chem. Soc. 134 (2012) 20554–20563.

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Biographies Youngdo Kim graduated from the University of Michigan Ann Arbor and received his Ph.D. degree from the Seoul National University under the supervision of Prof. Ji Young Chang in 2016. His research interests include synthesis, characterization and application of molecularly imprinted nanomaterials. Ji Young Chang received his B.S. degree from the Seoul National University and Ph.D. degree in Chemistry from the University of Michigan Ann Arbor, and was a postdoctoral scientist at the Pennsylvania State University. He is currently a Professor of Materials Science and Engineering, Seoul National University. His research covers organic nanostructured materials, biomimetic and bioanalogous materials, and high-performance polymers.