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organic hybrid nanoparticles
Journal of Industrial and Engineering Chemistry 44 (2016) 82–89
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Selective fluorescence sensing of 3,5-dinitrosalicylic acid based on pyrenesulfonamide-functionalized inorganic/organic hybrid nanoparticles Ashwani Kumar, Ju-Young Lee, Hong-Seok Kim * Department of Applied Chemistry, School of Applied Chemical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea
A R T I C L E I N F O
Article history: Received 8 April 2016 Received in revised form 8 August 2016 Accepted 16 August 2016 Available online 24 August 2016 Keywords: Fe3O4@SiO2 nanoparticle Monomer emission 3,5-DNSA HEPES–acetonitrile
A B S T R A C T
Pyrenesulfonamide-functionalized inorganic/organic hybrid Fe3O4@SiO2 nanoparticles were prepared for the selective and sensitive detection of 3,5-dinitrosalicylic acid (3,5-DNSA) among a series of aromatic carboxylic acids. The monomer fluorescence emission intensity of pyrene at 380 nm was switched off on interaction with 3,5-DNSA. The minimum detection limit for 3,5-DNSA was 10 nM in 4(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)–CH3CN (8:2; pH 7.4). The inorganic/organic hybrid Fe3O4@SiO2 nanoparticles were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. ß 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Carboxylic acids play crucial roles in biological and metabolic processes [1,2]. A number of these acids, e.g., citric, malic, lactic, tartaric, and gluconic acids, are used as additives in the food industry [3–5]. Aromatic carboxylic acids (ACAs) are used in wood preservatives and paints. Perfluorocarboxylic acids are used in the production of fluoroelastomers and as components of fireretardant foams. Carboxylic acids also have widespread applications in medical diagnosis [6,7] and process control [8]. The medicinal properties, particularly fever reduction, of salicylic acid (SA), have been known since ancient times. SA also has analgesic and anti-inflammatory properties. In modern medicine, SA and its derivatives are used as constituents of some drugs and skin-care products, e.g., methyl salicylate, which is used as a liniment to reduce joint and muscle pain, and choline salicylate, which is used topically to relieve the pain of mouth ulcers, and in the treatment of seborrheic dermatitis, acne, psoriasis, calluses, corns, acanthosis nigricans, ichthyosis, and warts [9]. SA has been used in shampoos to treat dandruff [10]. SA derivatives are also widely used in cosmetics, medical diagnosis, pharmaceuticals, food technology, and environmental monitoring [11–14]; for example, in plants, SA is involved in the regulation of defenses against pathogens and
* Corresponding author. Fax: +82 53 9506594. E-mail address: [email protected] (H.-S. Kim).
insects and affects a number of physiological processes such as fruit yield, seed germination, protein synthesis, and nutrient uptake [15–18]. SA can cause allergic contact dermatitis, one of the most prevalent forms of immunotoxicity found in humans [19,20]. Consequently, monitoring and quantitative determination of SA in aqueous solutions is important [21]. Selective recognition of SA derivatives is necessary for detailed studies of their physiological properties, and effects and functions. 3,5-Dinitrosalicylic acid (3,5-DNSA) is used in a colorimetric biomedical assay for the detection of reducing sugars [22–24]. Many research groups have focused their attention on carboxylic acid detection and sensing because of their widespread use in various fields [25–28]. In analytical detection, methods based on fluorescence intensity changes have many advantages over other techniques. This method is significantly more sensitive than other methods and enables in situ monitoring of analyte concentrations in real time and space. Ureas, amides, a-aminopyridines/a-amidopyridines, and quaternary ammonium/imidazolium salts containing appropriate fluorescent units have been used in the development of carboxylic acid sensors [29–32]. Carboxylic acid sensing in aqueous media is rare, because most organic sensors function in polar or non-polar solvents. Recently, we reported recognition between SA derivatives and pyrene-1sulfonamide imidazolium salt derivatives based on fluorescence measurements. As the solvent changes from polar or non-polar to mixed aqueous solutions, the binding behavior of SA derivatives
http://dx.doi.org/10.1016/j.jiec.2016.08.010 1226-086X/ß 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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changes from multi-hydrogen bonding to intermolecular p–p interactions [33–35], with little increased selectivity. The association constant for binding is affected by the substituents on both the pyrene and SA moieties; fluorescence titration and density functional theory methods show that the binding strengths of SA derivatives decrease in the following order: 3,5-DNSA > 5nitirosalicylic acid (5-NSA) > 5-iodosalicylic acid (5-ISA). These differences depend on the electron-withdrawing nature of the aromatic substituents on SA. The aim of this study, which is a continuation of our previous studies of optical/voltammetric molecular probes, was to increase the selectivity and reusability of pyrene-1-sulfonamide imidazolium salts and to widen their use [36–38]. Many organic-inorganic hybrid nanoparticles have been successfully synthesized and used for sensing purposes [39–43]. Recently Fe3O4-nano particles were prepared and utilized for detection of many analytes [44–48]. In this paper, we reported the synthesis and application of pyrene-1-sulfonamide imidazoliumfunctionalized iron oxide nanoparticles (3; Fe@SiO-IMS NPs) for selective and sensitive detection of 3,5-DNSA in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)–CH3CN (8:2, pH = 7.4) solution. Probe 3 was found to be novel in terms of selectivity and sensitivity toward 3,5-DNSA among a range of different of aromatic carboxylic acids (ACAs) in an aqueous solution with a limit of detection (LOD) of 10 nM. To the best of our knowledge, this is the first report of pyrene-1-sulfonamide imidazolium-functionalized iron oxide NPs for 3,5-DNSA detection in aqueous media. The iron in 3 played a more significant role in monitoring the selectivity and sensitivity compared to the free organic molecular probe 4 that showed sensitivity toward 5-ISA[3_TD$IF], [8_TD$IF]5NSA[3_TD$IF], and [9_TD$IF]3,5-DNSA[3_TD$IF] [33]. Experimental
Fig. 1. HRTEM image of 3 NPs.
with an Al Ka X-ray source at 15KV and 25 W. The emission angle of the photoelectrons, u, was kept constant at 458. Analytical-grade CH3CN was purchased from Merck. All other materials for the syntheses were purchased from the Aldrich Chemical Co. and used as received. Pyrene-1-sulfonamide propylimidazole (4) was prepared according to the literature procedure [33]. Synthesis of pyrenesulfonamide-functionalized inorganic/organic hybrid magnetic network
General Ultraviolet–visible absorption spectra were recorded using a Shimadzu UV-1650PC spectrophotometer. Fluorescence spectra were obtained using a Shimadzu RF-5301 fluorescence spectrometer equipped with a xenon discharge lamp, with 1 cm quartz cells and a 3 nm slit width. HEPES was used to maintain the pH of a water–CH3CN (8:2) solution at 7.4. All measurements were made at 298 K. The morphology and size of the Fe3O4@SiO2 NPs were investigated using transmission electron microscopy (TEM; Titan G2 Chemi STEM Cs Probe, FEI Co.). The structural properties of the Fe3O4@SiO2 NPs were studied using X-ray diffraction (XRD; RIGAKU D/MAX-2500). Changes in the functional groups on the Fe3O4@SiO2 NPs were identified using Fourier-transform infrared (FT-IR) spectroscopy (Frontier, PerkinElmer). Thermogravimetric analysis (TGA) of the NPs was performed using a Mettler TA Q600 analyzer. X-ray photoelectron spectroscopy (XPS) analysis of the NPs was conducted with a PHI Quantera SXM (ULVAC-PHI. Inc.)
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Synthesis of core-shell Fe3O4@SiO2 NPs Fe3O4@SiO2 NPs were prepared using a previously reported procedure [49,50]. Modification of Fe3O4@SiO2 NPs The surfaces of Fe3O4@SiO2 NPs (Fe@SiO, 1) were silanized using (3-chloropropyl)triethoxysilane (ClPTES). The Fe@SiO NPs (1, 500 mg) in toluene (50 mL) in a 250 mL round-bottomed flask were vigorously stirred under argon using a mechanical stirrer; the mixture was heated to 110 8C for 0.5 h. ClPTES solution (25.0 mmol, 6 mL) was then added using a syringe. The reaction mixture was kept at 110 8C for 48 h and then cooled to room temperature. The chloro-modified Fe@SiO NPs (Fe@SiO-ClPT, 2) were collected by magnetic separation, washed sequentially with toluene, dichloromethane, and ethanol, and suspended in CH3CN.
Scheme 1. Synthesis of Fe3O4@SiO2-IMS (3).
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Fig. 2. (a) HAADF-TEM image of 3 NPs; (b) HAADF-TEM image of 3 with Fe inside NPs shown in blue; (c) HAADF-TEM image of 3 with oxygen of silica-covered iron oxide NPs shown in red; (d) HAADF-TEM image of 3 with silicon of silica-covered iron oxide NPs shown in green. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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The 2 NPs were reacted with pyrene-1-sulfonamide propylimidazole [33] as follows: 2 (400 mg) and pyrene-1-sulfonamide propylimidazole (1.56 g, 4.0 mmol) were mixed in toluene (50 mL) under argon for 30 min. The mixture was refluxed for 48 h. After the reaction, the resultant Fe@SiO-IMS NPs (3) were collected by magnetic separation, washed sequentially with toluene, ethanol, and CH3CN, and suspended in CH3CN. Results and discussion Characterization of 1–3 NPs The TEM image of the magnetic probe 3 NPs (Fig. 1) shows that they were of different sizes and varied in shapes from spherical to elliptical; their average diameter was 20 3.0 nm. The highresolution TEM (HRTEM) image of the 3 NPs in the inset to Fig. 1 clearly shows the core–shell structure of magnetic silica NPs, with the SiO2 shell structure marked with cyan line bars and the Fe3O4 core indicated with the arrow. Dark colored 3 NPs in Fig. 1 shows the aggregation/accumulation of many nanoparticles at the same place (Scheme 1). High-angle annular dark-field (HAADF)-TEM images of the probe 3 NPs are shown in Fig. 2. Fig. 2b shows the Fe core (Fe3O4) inside the NPs in blue, Fig. 2c shows the oxygen of the silica coated on the Fe3O4 NPs in red, and Fig. 2d shows the silicon of the silica layer as green shells with small black cores of Fe3O4. Fig. 2 therefore clearly shows the formation of 3 NPs. The XRD pattern of 1 shows reflections corresponding to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3), indicating Fe3O4 with a crystalline cubic spinel structure. The broad peak
Fig. 3. XRD patterns of 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 4. FT-IR spectra of 1 (blue), 2 (red), and 3 (black) NPs (inset shows the FT-IR of 1– 3 NPs from 3100–2800 cm 1). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
at 2u = 15–308 comes from amorphous silica and confirms that a silica layer was successfully coated on the surfaces of the Fe3O4 NPs (Fig. 3). In the XRD pattern of the 2 NPs, the intensity of the broad peak at 2u = 15–308 from amorphous silica peak shifts to a slightly higher value, showing that ClPTES bonded with silica, but the other peaks were unchanged; in case of 3 NPs, the intensity of the broad peak at 2u = 15–308 from amorphous part decreased. The decreased intensity of the broad reflection peak at 2u = 15– 308 from amorphous silica in the case of the 3 NPs and the small
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Fig. 5. TGA curves for 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
changes in the peak intensities for (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3) show that pyrene-1-sulfonamide propylimidazole-coated Fe3O4@SiO2 NPs were obtained, with the crystalline structure of the Fe3O4 NPs intact (Fig. 3). The slight changes in the peak intensities from 1 to 3 [10_TD$IF]shows that the NP structures remained intact. The FT-IR spectra of Fe@SiO (1), Fe@SiO-ClPT (2), and Fe@SiOIMS NPs (3) are shown in Fig. 4. FT-IR bands for O–H, Si–O–Si, and
Fig. 6. Partial XPS curves (from 0–600 eV) for 1 (blue), 2 (red), and 3 (black) NPs (for complete spectra, see ESI-Figs. S1–S4). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 7. XPS curves for peaks O1s and C1s of 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fe–O stretching were observed at 3424, 1093, and 582 cm 1[7_TD$IF], respectively. The band at 3020–3000 cm 1 is ascribed to C–H stretching in 2. The C–H stretching band at 3020–3000 cm 1 in the 3 NP spectrums was broader, because of the presence of an aromatic structure; this clearly indicates the presence of pyrene-1sulfonamide propylimidazole (Fig. 4). The TGA curves for the functionalized 1, 2, and 3 NPs are shown in Fig. 5. The weight loss is attributed to the evaporation of physically and chemically adsorbed water. The weight percentage of adsorbed water for 1 is 6.7%. The amount of ClPTES on the 2 NP surfaces is about 1.5%. In the case of 3, there are two weight losses, a loss of 2.2% due to the decomposition of pyrene-1-sulfonamide, and another loss of 4.2% due to the imidazolium and two propyl chains connected to it on the surface (Fig. 5). XPS was further used to characterize the surface composition of the three kinds of NPs: Fe@SiO (1), Fe@SiO-ClPT (2), and Fe@SiOIMS NPs (3) (Figs. S1–S4 and Fig. 6). A moderate concentration of carbon (20.9% atom) is found on the surface of 1 in Fig. S1, owing to the binding energy for C1s (285.0 eV) as the internal reference. In addition, the XPS spectrum of 1 also shows an O1s peak at 534.0 eV, O2s peak at 28.0 eV, and Fe signals at about 56.0 eV for Fe3p and 712.0 and 724.0 eV for Fe2p, while Si signals are observed at about 155.0 eV for Si1s and at 104.0 eV for Si2p (Fig. S1 and Fig. 6). In the XPS spectrum of 2, the percentage of carbon (C1s) increased to 44.3% from 20.9% in 1, because of the successful binding of ClPTES
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on silica surface. Also, for 2,, the peak intensities for C1s Si1s, and Si2p increased in comparison to the signals for Fe, with the development of new signals for Cl at 271.0 eV for Cl1s and at 200.0 eV for Cl2p (Fig. S2 and Fig. 6). In the case of 3, the XPS spectrum shows the presence of signals observed for 2; in addition, new signals are observed: one for N1s at 401.0 eV, and other signals for S, with one peak at 233.0 eV for S1s and another at about 169.0 eV for S2p, that clearly showed the successful immobilization of pyrene-1-sulfonamide imidazolium unit on the surface of 3 NPs (Fig. S3 and Fig. 6). In Fig. 7, the comparison of the XPS spectrum peaks for O1s and C1s of 1, 2, and 3 NPs clearly showed the variation in maxima, and intensity changes with surface immobilization of 1 NPs with organic molecules clearly supported the synthesis of 3 NPs. UV–vis and fluorescence analyses The UV–vis spectra of the probe 3 NPs (0.1 g/L, HEPES-CH3CN[12_TD$IF] (8:2) pH 7.4) showed absorption maxima at lmax = 336, 350, and 355 nm (Fig. S5); this shows the presence of pyrene-1-sulfonamide propylimidazole units coated on the 2 NPs, i.e., confirms the formation of 3. On excitation at 336 nm, the 3 NPs [0.1 g/L, HEPES– CH3CN (8:2), pH 7.4] showed a highly intense fluorescence emission maximum at 382 nm (monomer) (Fig. S6). We tested probe 3 as a carboxylic acid sensor. Various ACAs, i.e., benzoic acid
Fig. 8. Fluorescence relative intensity bar diagram for 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] on addition of various ACAs (1.0 10 4 M) at lex = 336 nm; inset shows blue fluorescence was switched off with 3,5-DNSA under 365 nm irradiation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 9. (a) Fluorescence titration of 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] with 3,5-DNSA (1.0 10 DNSA]; and points show experimental values and lines show curve fits.
(BA), 3-iodobenzoic acid (3-IBA), 3-nitrobenzoic acid (3-NBA), 4aminobenzoic acid (4-ABA), 3-chlorobenzoic acid (3-ClBA), 3,5dinitrobenzoic acid (3,5-DNBA), picolinic acid (PCA), indole-2carboxylic acid (IND-2-A), nicotinic acid (NA), phthalic acid (PA), isophthalic acid (IPA), terephthalic acid (TPA), uric acid (UA), SA, 3methylsalicylic acid (3-MSA), 5-methylsalicylic acid (5-MSA), [7_TD$IF]5ISA[3_TD$IF], [8_TD$IF]5-NSA[3_TD$IF], and [9_TD$IF]3,5-DNSA[3_TD$IF] were added to a solution of 3 NPs [0.1 g/ L, HEPES–CH3CN (8:2), pH 7.4]. Quenching of the emission intensity was observed selectively for 3,5-DNSA (>95%), whereas the other ACAs did not show any significant changes in their fluorescence intensities (Fig. 8 and Fig. S6).
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5
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M) at lex = 336 nm. (b) Linear relationship between I382 nm and [3,5-
On gradual addition of aliquots of 3,5-DNSA to the probe 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4], the emission intensity at 380 nm decreased sharply and was completely quenched with 1 mM of 3,5-DNSA (Fig. 9 and Fig. S7). The linear relationship between the fluorescence emission intensity at lmax = 382 nm, i.e., I382 vs [3,5-DNSA], R2[1_TD$IF] = 0.9911, on titration of 3 with 3,5-DNSA shows that the minimum limit of detection (LOD) was 10 nM (inset in Fig. 9). For the 3 NPs, polymeric interactions with 3,5-DNSA are not possible, because the presence of 3,5-DNSA leads to the formation of p–p interactions between the benzene rings of the pryrene-1-sulfonamide propylimidazole units bonded with the
Fig. 10. Fluorescence relative intensity bar diagram for probe 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] in presence of 3,5-DNSA (10 mM) with various ACAs (100 mM) at lex = 336 nm (Io = intensity of 3, I = intensity of [3 + 3,5-DNSA + ACA] at 382 nm).
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Scheme 2. Plausible mechanism for detection of 3,5-DNSA with 3 NPs.
silica-coated Fe3O4 NPs. If we assume 1:1 interactions between one silica-bonded pyrenesulfonamide unit and one 3,5-DNSA, the association constant, Ka = 2.66 106 M 1, is good enough for the 3,5-DNSA, LOD to be 10 nM. Interference with 3,5-DNSA detection by other ACAs was checked by adding 100 mM ACAs to a solution of a complex of 3 + 3,5-DNSA (10 mM); probe 3 detected 3,5-DNSA[6_TD$IF] even in the presence of other ACAs (Fig. 10). We compared the results using 3 NPs with those using 2 NPs (with no fluorescent pyrene) by studying the fluorescence of 2 with ACAs. We found that none of the ACAs caused any changes in the fluorescence emission intensity of 2 (Fig. S8). A significant difference between the fluorescence properties of 3 and the organic molecular probe 4 [33] (synthesized by the procedure reported in literature) is that the 3 NPs showed higher selectivity toward 3,5-DNSA than other ACAs, but in the case of probe 4, the fluorescence was quenched with salicylic acid derivatives in the following order: 3,5-DNSA 5-NSA > and 5-ISA. So probe 3 was found to be novel in terms of selectivity and sensitivity toward 3,5DNSA in aqueous solutions with an LOD of 10 nM. Thus the combination of the pyrene-1-sulfonamide imidazolium salt and iron oxide NPs in 3 provides a clue regarding the crucial role played by iron in iron oxide 3 NPs in controlling the selectivity and increase in sensitivity, as compared to free organic molecular probe 4 that exhibited sensitivity toward 5-ISA, 5-NSA, and 3,5DNSA. The 3 NPs had a very high fluorescence intensity because of the presence of free pyrene units in solution. 3,5-DNSA binds with the pyrene-1-sulfonamide unit through p–p interactions, leading to energy transfer from the electron-rich pyrene unit to the electrondeficient benzene ring of 3,5-DNSA, resulting in quenching of the fluorescence emission. This quenching as a result of energy transfer was further supported by the overlap of the UV-vis spectrum of 3,5-DNSA and the fluorescence of 3 NPs (Fig. S9). Based on these results, we propose a plausible scheme for sensing of 3,5-DNSA using 3 NPs (Scheme 2). Conclusions A novel organic-inorganic hybrid probe 3 made of Fe@SiO-IMS NPs was synthesized and characterized well using HR-TEM, FTIR, TGA, XRD, and XPS for the selective sensing of 3,5-DNSA in aqueous media. Pyrenesulfonamide-functionalized inorganic/organic hybrid
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Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Selective fluorescence sensing of 3,5-dinitrosalicylic acid based on pyrenesulfonamide-functionalized inorganic/organic hybrid nanoparticles Ashwani Kumar, Ju-Young Lee, Hong-Seok Kim * Department of Applied Chemistry, School of Applied Chemical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea
A R T I C L E I N F O
Article history: Received 8 April 2016 Received in revised form 8 August 2016 Accepted 16 August 2016 Available online 24 August 2016 Keywords: Fe3O4@SiO2 nanoparticle Monomer emission 3,5-DNSA HEPES–acetonitrile
A B S T R A C T
Pyrenesulfonamide-functionalized inorganic/organic hybrid Fe3O4@SiO2 nanoparticles were prepared for the selective and sensitive detection of 3,5-dinitrosalicylic acid (3,5-DNSA) among a series of aromatic carboxylic acids. The monomer fluorescence emission intensity of pyrene at 380 nm was switched off on interaction with 3,5-DNSA. The minimum detection limit for 3,5-DNSA was 10 nM in 4(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)–CH3CN (8:2; pH 7.4). The inorganic/organic hybrid Fe3O4@SiO2 nanoparticles were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. ß 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Introduction Carboxylic acids play crucial roles in biological and metabolic processes [1,2]. A number of these acids, e.g., citric, malic, lactic, tartaric, and gluconic acids, are used as additives in the food industry [3–5]. Aromatic carboxylic acids (ACAs) are used in wood preservatives and paints. Perfluorocarboxylic acids are used in the production of fluoroelastomers and as components of fireretardant foams. Carboxylic acids also have widespread applications in medical diagnosis [6,7] and process control [8]. The medicinal properties, particularly fever reduction, of salicylic acid (SA), have been known since ancient times. SA also has analgesic and anti-inflammatory properties. In modern medicine, SA and its derivatives are used as constituents of some drugs and skin-care products, e.g., methyl salicylate, which is used as a liniment to reduce joint and muscle pain, and choline salicylate, which is used topically to relieve the pain of mouth ulcers, and in the treatment of seborrheic dermatitis, acne, psoriasis, calluses, corns, acanthosis nigricans, ichthyosis, and warts [9]. SA has been used in shampoos to treat dandruff [10]. SA derivatives are also widely used in cosmetics, medical diagnosis, pharmaceuticals, food technology, and environmental monitoring [11–14]; for example, in plants, SA is involved in the regulation of defenses against pathogens and
* Corresponding author. Fax: +82 53 9506594. E-mail address: [email protected] (H.-S. Kim).
insects and affects a number of physiological processes such as fruit yield, seed germination, protein synthesis, and nutrient uptake [15–18]. SA can cause allergic contact dermatitis, one of the most prevalent forms of immunotoxicity found in humans [19,20]. Consequently, monitoring and quantitative determination of SA in aqueous solutions is important [21]. Selective recognition of SA derivatives is necessary for detailed studies of their physiological properties, and effects and functions. 3,5-Dinitrosalicylic acid (3,5-DNSA) is used in a colorimetric biomedical assay for the detection of reducing sugars [22–24]. Many research groups have focused their attention on carboxylic acid detection and sensing because of their widespread use in various fields [25–28]. In analytical detection, methods based on fluorescence intensity changes have many advantages over other techniques. This method is significantly more sensitive than other methods and enables in situ monitoring of analyte concentrations in real time and space. Ureas, amides, a-aminopyridines/a-amidopyridines, and quaternary ammonium/imidazolium salts containing appropriate fluorescent units have been used in the development of carboxylic acid sensors [29–32]. Carboxylic acid sensing in aqueous media is rare, because most organic sensors function in polar or non-polar solvents. Recently, we reported recognition between SA derivatives and pyrene-1sulfonamide imidazolium salt derivatives based on fluorescence measurements. As the solvent changes from polar or non-polar to mixed aqueous solutions, the binding behavior of SA derivatives
http://dx.doi.org/10.1016/j.jiec.2016.08.010 1226-086X/ß 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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changes from multi-hydrogen bonding to intermolecular p–p interactions [33–35], with little increased selectivity. The association constant for binding is affected by the substituents on both the pyrene and SA moieties; fluorescence titration and density functional theory methods show that the binding strengths of SA derivatives decrease in the following order: 3,5-DNSA > 5nitirosalicylic acid (5-NSA) > 5-iodosalicylic acid (5-ISA). These differences depend on the electron-withdrawing nature of the aromatic substituents on SA. The aim of this study, which is a continuation of our previous studies of optical/voltammetric molecular probes, was to increase the selectivity and reusability of pyrene-1-sulfonamide imidazolium salts and to widen their use [36–38]. Many organic-inorganic hybrid nanoparticles have been successfully synthesized and used for sensing purposes [39–43]. Recently Fe3O4-nano particles were prepared and utilized for detection of many analytes [44–48]. In this paper, we reported the synthesis and application of pyrene-1-sulfonamide imidazoliumfunctionalized iron oxide nanoparticles (3; Fe@SiO-IMS NPs) for selective and sensitive detection of 3,5-DNSA in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)–CH3CN (8:2, pH = 7.4) solution. Probe 3 was found to be novel in terms of selectivity and sensitivity toward 3,5-DNSA among a range of different of aromatic carboxylic acids (ACAs) in an aqueous solution with a limit of detection (LOD) of 10 nM. To the best of our knowledge, this is the first report of pyrene-1-sulfonamide imidazolium-functionalized iron oxide NPs for 3,5-DNSA detection in aqueous media. The iron in 3 played a more significant role in monitoring the selectivity and sensitivity compared to the free organic molecular probe 4 that showed sensitivity toward 5-ISA[3_TD$IF], [8_TD$IF]5NSA[3_TD$IF], and [9_TD$IF]3,5-DNSA[3_TD$IF] [33]. Experimental
Fig. 1. HRTEM image of 3 NPs.
with an Al Ka X-ray source at 15KV and 25 W. The emission angle of the photoelectrons, u, was kept constant at 458. Analytical-grade CH3CN was purchased from Merck. All other materials for the syntheses were purchased from the Aldrich Chemical Co. and used as received. Pyrene-1-sulfonamide propylimidazole (4) was prepared according to the literature procedure [33]. Synthesis of pyrenesulfonamide-functionalized inorganic/organic hybrid magnetic network
General Ultraviolet–visible absorption spectra were recorded using a Shimadzu UV-1650PC spectrophotometer. Fluorescence spectra were obtained using a Shimadzu RF-5301 fluorescence spectrometer equipped with a xenon discharge lamp, with 1 cm quartz cells and a 3 nm slit width. HEPES was used to maintain the pH of a water–CH3CN (8:2) solution at 7.4. All measurements were made at 298 K. The morphology and size of the Fe3O4@SiO2 NPs were investigated using transmission electron microscopy (TEM; Titan G2 Chemi STEM Cs Probe, FEI Co.). The structural properties of the Fe3O4@SiO2 NPs were studied using X-ray diffraction (XRD; RIGAKU D/MAX-2500). Changes in the functional groups on the Fe3O4@SiO2 NPs were identified using Fourier-transform infrared (FT-IR) spectroscopy (Frontier, PerkinElmer). Thermogravimetric analysis (TGA) of the NPs was performed using a Mettler TA Q600 analyzer. X-ray photoelectron spectroscopy (XPS) analysis of the NPs was conducted with a PHI Quantera SXM (ULVAC-PHI. Inc.)
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83
Synthesis of core-shell Fe3O4@SiO2 NPs Fe3O4@SiO2 NPs were prepared using a previously reported procedure [49,50]. Modification of Fe3O4@SiO2 NPs The surfaces of Fe3O4@SiO2 NPs (Fe@SiO, 1) were silanized using (3-chloropropyl)triethoxysilane (ClPTES). The Fe@SiO NPs (1, 500 mg) in toluene (50 mL) in a 250 mL round-bottomed flask were vigorously stirred under argon using a mechanical stirrer; the mixture was heated to 110 8C for 0.5 h. ClPTES solution (25.0 mmol, 6 mL) was then added using a syringe. The reaction mixture was kept at 110 8C for 48 h and then cooled to room temperature. The chloro-modified Fe@SiO NPs (Fe@SiO-ClPT, 2) were collected by magnetic separation, washed sequentially with toluene, dichloromethane, and ethanol, and suspended in CH3CN.
Scheme 1. Synthesis of Fe3O4@SiO2-IMS (3).
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Fig. 2. (a) HAADF-TEM image of 3 NPs; (b) HAADF-TEM image of 3 with Fe inside NPs shown in blue; (c) HAADF-TEM image of 3 with oxygen of silica-covered iron oxide NPs shown in red; (d) HAADF-TEM image of 3 with silicon of silica-covered iron oxide NPs shown in green. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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The 2 NPs were reacted with pyrene-1-sulfonamide propylimidazole [33] as follows: 2 (400 mg) and pyrene-1-sulfonamide propylimidazole (1.56 g, 4.0 mmol) were mixed in toluene (50 mL) under argon for 30 min. The mixture was refluxed for 48 h. After the reaction, the resultant Fe@SiO-IMS NPs (3) were collected by magnetic separation, washed sequentially with toluene, ethanol, and CH3CN, and suspended in CH3CN. Results and discussion Characterization of 1–3 NPs The TEM image of the magnetic probe 3 NPs (Fig. 1) shows that they were of different sizes and varied in shapes from spherical to elliptical; their average diameter was 20 3.0 nm. The highresolution TEM (HRTEM) image of the 3 NPs in the inset to Fig. 1 clearly shows the core–shell structure of magnetic silica NPs, with the SiO2 shell structure marked with cyan line bars and the Fe3O4 core indicated with the arrow. Dark colored 3 NPs in Fig. 1 shows the aggregation/accumulation of many nanoparticles at the same place (Scheme 1). High-angle annular dark-field (HAADF)-TEM images of the probe 3 NPs are shown in Fig. 2. Fig. 2b shows the Fe core (Fe3O4) inside the NPs in blue, Fig. 2c shows the oxygen of the silica coated on the Fe3O4 NPs in red, and Fig. 2d shows the silicon of the silica layer as green shells with small black cores of Fe3O4. Fig. 2 therefore clearly shows the formation of 3 NPs. The XRD pattern of 1 shows reflections corresponding to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3), indicating Fe3O4 with a crystalline cubic spinel structure. The broad peak
Fig. 3. XRD patterns of 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 4. FT-IR spectra of 1 (blue), 2 (red), and 3 (black) NPs (inset shows the FT-IR of 1– 3 NPs from 3100–2800 cm 1). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
at 2u = 15–308 comes from amorphous silica and confirms that a silica layer was successfully coated on the surfaces of the Fe3O4 NPs (Fig. 3). In the XRD pattern of the 2 NPs, the intensity of the broad peak at 2u = 15–308 from amorphous silica peak shifts to a slightly higher value, showing that ClPTES bonded with silica, but the other peaks were unchanged; in case of 3 NPs, the intensity of the broad peak at 2u = 15–308 from amorphous part decreased. The decreased intensity of the broad reflection peak at 2u = 15– 308 from amorphous silica in the case of the 3 NPs and the small
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Fig. 5. TGA curves for 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
changes in the peak intensities for (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0), and (5 3 3) show that pyrene-1-sulfonamide propylimidazole-coated Fe3O4@SiO2 NPs were obtained, with the crystalline structure of the Fe3O4 NPs intact (Fig. 3). The slight changes in the peak intensities from 1 to 3 [10_TD$IF]shows that the NP structures remained intact. The FT-IR spectra of Fe@SiO (1), Fe@SiO-ClPT (2), and Fe@SiOIMS NPs (3) are shown in Fig. 4. FT-IR bands for O–H, Si–O–Si, and
Fig. 6. Partial XPS curves (from 0–600 eV) for 1 (blue), 2 (red), and 3 (black) NPs (for complete spectra, see ESI-Figs. S1–S4). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 7. XPS curves for peaks O1s and C1s of 1 (blue), 2 (red), and 3 (black) NPs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fe–O stretching were observed at 3424, 1093, and 582 cm 1[7_TD$IF], respectively. The band at 3020–3000 cm 1 is ascribed to C–H stretching in 2. The C–H stretching band at 3020–3000 cm 1 in the 3 NP spectrums was broader, because of the presence of an aromatic structure; this clearly indicates the presence of pyrene-1sulfonamide propylimidazole (Fig. 4). The TGA curves for the functionalized 1, 2, and 3 NPs are shown in Fig. 5. The weight loss is attributed to the evaporation of physically and chemically adsorbed water. The weight percentage of adsorbed water for 1 is 6.7%. The amount of ClPTES on the 2 NP surfaces is about 1.5%. In the case of 3, there are two weight losses, a loss of 2.2% due to the decomposition of pyrene-1-sulfonamide, and another loss of 4.2% due to the imidazolium and two propyl chains connected to it on the surface (Fig. 5). XPS was further used to characterize the surface composition of the three kinds of NPs: Fe@SiO (1), Fe@SiO-ClPT (2), and Fe@SiOIMS NPs (3) (Figs. S1–S4 and Fig. 6). A moderate concentration of carbon (20.9% atom) is found on the surface of 1 in Fig. S1, owing to the binding energy for C1s (285.0 eV) as the internal reference. In addition, the XPS spectrum of 1 also shows an O1s peak at 534.0 eV, O2s peak at 28.0 eV, and Fe signals at about 56.0 eV for Fe3p and 712.0 and 724.0 eV for Fe2p, while Si signals are observed at about 155.0 eV for Si1s and at 104.0 eV for Si2p (Fig. S1 and Fig. 6). In the XPS spectrum of 2, the percentage of carbon (C1s) increased to 44.3% from 20.9% in 1, because of the successful binding of ClPTES
[(Fig._8)TD$IG]
on silica surface. Also, for 2,, the peak intensities for C1s Si1s, and Si2p increased in comparison to the signals for Fe, with the development of new signals for Cl at 271.0 eV for Cl1s and at 200.0 eV for Cl2p (Fig. S2 and Fig. 6). In the case of 3, the XPS spectrum shows the presence of signals observed for 2; in addition, new signals are observed: one for N1s at 401.0 eV, and other signals for S, with one peak at 233.0 eV for S1s and another at about 169.0 eV for S2p, that clearly showed the successful immobilization of pyrene-1-sulfonamide imidazolium unit on the surface of 3 NPs (Fig. S3 and Fig. 6). In Fig. 7, the comparison of the XPS spectrum peaks for O1s and C1s of 1, 2, and 3 NPs clearly showed the variation in maxima, and intensity changes with surface immobilization of 1 NPs with organic molecules clearly supported the synthesis of 3 NPs. UV–vis and fluorescence analyses The UV–vis spectra of the probe 3 NPs (0.1 g/L, HEPES-CH3CN[12_TD$IF] (8:2) pH 7.4) showed absorption maxima at lmax = 336, 350, and 355 nm (Fig. S5); this shows the presence of pyrene-1-sulfonamide propylimidazole units coated on the 2 NPs, i.e., confirms the formation of 3. On excitation at 336 nm, the 3 NPs [0.1 g/L, HEPES– CH3CN (8:2), pH 7.4] showed a highly intense fluorescence emission maximum at 382 nm (monomer) (Fig. S6). We tested probe 3 as a carboxylic acid sensor. Various ACAs, i.e., benzoic acid
Fig. 8. Fluorescence relative intensity bar diagram for 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] on addition of various ACAs (1.0 10 4 M) at lex = 336 nm; inset shows blue fluorescence was switched off with 3,5-DNSA under 365 nm irradiation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 9. (a) Fluorescence titration of 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] with 3,5-DNSA (1.0 10 DNSA]; and points show experimental values and lines show curve fits.
(BA), 3-iodobenzoic acid (3-IBA), 3-nitrobenzoic acid (3-NBA), 4aminobenzoic acid (4-ABA), 3-chlorobenzoic acid (3-ClBA), 3,5dinitrobenzoic acid (3,5-DNBA), picolinic acid (PCA), indole-2carboxylic acid (IND-2-A), nicotinic acid (NA), phthalic acid (PA), isophthalic acid (IPA), terephthalic acid (TPA), uric acid (UA), SA, 3methylsalicylic acid (3-MSA), 5-methylsalicylic acid (5-MSA), [7_TD$IF]5ISA[3_TD$IF], [8_TD$IF]5-NSA[3_TD$IF], and [9_TD$IF]3,5-DNSA[3_TD$IF] were added to a solution of 3 NPs [0.1 g/ L, HEPES–CH3CN (8:2), pH 7.4]. Quenching of the emission intensity was observed selectively for 3,5-DNSA (>95%), whereas the other ACAs did not show any significant changes in their fluorescence intensities (Fig. 8 and Fig. S6).
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5
87
M) at lex = 336 nm. (b) Linear relationship between I382 nm and [3,5-
On gradual addition of aliquots of 3,5-DNSA to the probe 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4], the emission intensity at 380 nm decreased sharply and was completely quenched with 1 mM of 3,5-DNSA (Fig. 9 and Fig. S7). The linear relationship between the fluorescence emission intensity at lmax = 382 nm, i.e., I382 vs [3,5-DNSA], R2[1_TD$IF] = 0.9911, on titration of 3 with 3,5-DNSA shows that the minimum limit of detection (LOD) was 10 nM (inset in Fig. 9). For the 3 NPs, polymeric interactions with 3,5-DNSA are not possible, because the presence of 3,5-DNSA leads to the formation of p–p interactions between the benzene rings of the pryrene-1-sulfonamide propylimidazole units bonded with the
Fig. 10. Fluorescence relative intensity bar diagram for probe 3 NPs [0.1 g/L HEPES–CH3CN (8:2), pH 7.4] in presence of 3,5-DNSA (10 mM) with various ACAs (100 mM) at lex = 336 nm (Io = intensity of 3, I = intensity of [3 + 3,5-DNSA + ACA] at 382 nm).
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Scheme 2. Plausible mechanism for detection of 3,5-DNSA with 3 NPs.
silica-coated Fe3O4 NPs. If we assume 1:1 interactions between one silica-bonded pyrenesulfonamide unit and one 3,5-DNSA, the association constant, Ka = 2.66 106 M 1, is good enough for the 3,5-DNSA, LOD to be 10 nM. Interference with 3,5-DNSA detection by other ACAs was checked by adding 100 mM ACAs to a solution of a complex of 3 + 3,5-DNSA (10 mM); probe 3 detected 3,5-DNSA[6_TD$IF] even in the presence of other ACAs (Fig. 10). We compared the results using 3 NPs with those using 2 NPs (with no fluorescent pyrene) by studying the fluorescence of 2 with ACAs. We found that none of the ACAs caused any changes in the fluorescence emission intensity of 2 (Fig. S8). A significant difference between the fluorescence properties of 3 and the organic molecular probe 4 [33] (synthesized by the procedure reported in literature) is that the 3 NPs showed higher selectivity toward 3,5-DNSA than other ACAs, but in the case of probe 4, the fluorescence was quenched with salicylic acid derivatives in the following order: 3,5-DNSA 5-NSA > and 5-ISA. So probe 3 was found to be novel in terms of selectivity and sensitivity toward 3,5DNSA in aqueous solutions with an LOD of 10 nM. Thus the combination of the pyrene-1-sulfonamide imidazolium salt and iron oxide NPs in 3 provides a clue regarding the crucial role played by iron in iron oxide 3 NPs in controlling the selectivity and increase in sensitivity, as compared to free organic molecular probe 4 that exhibited sensitivity toward 5-ISA, 5-NSA, and 3,5DNSA. The 3 NPs had a very high fluorescence intensity because of the presence of free pyrene units in solution. 3,5-DNSA binds with the pyrene-1-sulfonamide unit through p–p interactions, leading to energy transfer from the electron-rich pyrene unit to the electrondeficient benzene ring of 3,5-DNSA, resulting in quenching of the fluorescence emission. This quenching as a result of energy transfer was further supported by the overlap of the UV-vis spectrum of 3,5-DNSA and the fluorescence of 3 NPs (Fig. S9). Based on these results, we propose a plausible scheme for sensing of 3,5-DNSA using 3 NPs (Scheme 2). Conclusions A novel organic-inorganic hybrid probe 3 made of Fe@SiO-IMS NPs was synthesized and characterized well using HR-TEM, FTIR, TGA, XRD, and XPS for the selective sensing of 3,5-DNSA in aqueous media. Pyrenesulfonamide-functionalized inorganic/organic hybrid
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