Letter Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
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Fine Tuning of Polymer-Coated Gold Nanohybrids: Sensor for the Selective Detection of Quinalphos and Device Fabrication for Water Purification Richa Rani,† Mayank,† Pandiyan Thangarasu,‡ and Narinder Singh*,† †
Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India Faculted de Química, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Coyoacán 04510, México D. F., México
‡
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S Supporting Information *
ABSTRACT: Noble polymer P1 was synthesized and utilized to produce organic nanoparticles (ONPs). The ONPs were used to formulate Au@ONP nanohybrids. The Au@ONP was subsequently fine-tuned for the selective detection of quinalphos via decorating Cu2+ on its surface. The selective detection of quinalphos in an aqueous medium was achieved, and a detection limit of 2.4 nM was obtained. To validate triple-layered Cu(II)-Au@ONP for quinalphos sensing, simulated real sample analysis was done. Finally silica coating of Cu(II)-Au@ONP was utilized for solid-state quinalphos sensing and removal from contaminated water samples using its cartridgebased assembly.
KEYWORDS: polymer, organic nanoparticles, reprecipitation, quinalphos, water, device, sensor
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the quick detection of quinalphos under aqueous conditions.9 Furthermore, despite the availability of multiple forms of chromatography, gravimetric, and photophysical techniques, we have here anticipated the incorporation of fluorescence spectroscopy for sensor development. In the present work, we have synthesized the thiourea-linked polymer (Scheme 1) as a starting entity to develop a sensor for quinalphos detection. Using organic nanoparticles (ONPs) of P1, Au@ONPs were produced and characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. The reason for the selection of such a type of specific system was explained in section S1 in the Supporting Information. Further Cu2+ was decorated on the surface of Au@ONPs, and the proper formation of Cu(II)-Au@ ONPs was confirmed by UV−vis absorbance, fluorescence emission, Fourier transform infrared (FTIR), and cyclic voltammetry (CV) analytical techniques. The fully characterized Cu(II)-Au@ONPs were then investigated for their sensing ability for the detection of various analytes, and the selective sensing ability of Cu(II)-Au@ONPs toward quinalphos was confirmed by the protocol available in the literature.10−12 To prove the utility of the developed sensor under solid state, we then coated Cu(II)-Au@ONPs nanomaterial onto the silica and
INTRODUCTION Water pollution by poisonous chemicals is one of the most serious problems for conservation of the ecosystem and for safe drinking water. Organophosphates are widely used for the protection of crops from pests in the agriculture sector.1 The wide use of pesticides tends to contaminate almost all types of environmental resources and cause severe health problems.2 Among these, quinalphos is extensively hazardous and causes severe problems that range from permanent nerve damage to death in the human population.3,4 Thus, serious efforts are underway toward the detection and removal of quinalphos from natural resources. Sophisticated high-performance liquid chromatography, gas chromatography, NMR, and photodegradation techniques are available; however, high operation costs and hectic operational procedures make these techniques less useful.5 Hence, the development of a rapid, simple, and reliable method is a prerequisite for the detection of toxic analytes. In due course, extensive research has already provided us highly efficient tools such as ligand−metal complexes, quantum dots, carbon dots, and multiple forms of a metal−organic framework for the detection of these toxic entities.6 However, because of their several advantages, viz., high surface area, ideal photophysical behavior, high sensitivity, and their utility in aqueous condition, nanomaterials have emerged as one of the ideal tools for the development of sensors.7,8 Considering these facts, we also intend to develop a nanomaterial-based sensor for © XXXX American Chemical Society
Received: September 24, 2018 Accepted: December 11, 2018 Published: December 11, 2018 A
DOI: 10.1021/acsanm.8b01624 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials Scheme 1. Synthesis of Polymer P1
Figure 1. TEM images of (A) ONPs and (B) Au@ONPs showing the characteristic morphology.
Figure 2. (A) UV−vis absorption, (B) fluorescence, and (C) IR spectra and (D) CV of P1, ONPs, and Au@ONPs.
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found selective sensing of quinalphos through an emissive color
RESULT AND DISCUSSION
Development of a Hybrid Nanomaterial of Polymer P1 with Gold. The polymer P1 was synthesized by a multistep synthetic procedure and characterized (Scheme S1 and Figures S1−S3). Organic compounds often tend to agglomerate in an aqueous environment because of their poor solubility. Thus, as a way to overcome the solubility issue, we have fabricated the ONPs of P1 via a reprecipitation method (section S2 in the
change under solid state. The beads were further used to remove quinalphos from water samples through a cartridge-based device. Thus, Cu(II)-Au@ONPs can be considered as a multifunctional material with sensing and water purification abilities. B
DOI: 10.1021/acsanm.8b01624 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials
Figure 3. (A) Emission response of the Cu(II)-Au@ONPs complex at different pH values. (B) Emission response of Cu(II)-Au@ONPs in water upon the addition of different phosphates. (C) Enhancement in the emission profile of Cu(II)-Au@ONPs upon the successive addition of quinalphos from 5 nM to 0.13 μM at pH 7.4 ± 0.5. The inset showed the calibration curve for the emission response with the quinalphos concentration. (D) Plot of 1/ΔI versus 1/[C] for determination of the binding constant of quinalphos with Au@ONPs. (E) Upon illumination with light of 365 nm, emission color change of coated silica. Row 1: compound, ONPs, Au@ONPs. Row 2: Au@ONPs coated with (Cu2+, Hg2+, Ni2+, Pb2+, Ca2+, Cd2+, Zn2+, Co2+, Al3+, Fe3+, Na+, and K+). Row 3: Au@ONPs coated with (CN−, F−, Cl−, Br−, I−, HSO4−, NO3−, AcO−, HClO4−, SCN−, S2−, and H2PO4−). Row 4: Au@ONPs coated with (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12). Row 5: Cu(II)-Au@ONPs coated with (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12); 1 = dichlorvos, 2 = profenophos, 3 = ethion, 4 = triazophos, 5 = quinalphos, 6 = phorate, 7 = phosphemedon, 8 = ATP, 9 = ADP, 10 = AMP, 11 = NAD, and 12 = NADH. (F) Solid fluorescence intensity of coated silica beads of Cu(II)-Au@ONPs at different concentrations of quinalphos.
Supporting Information).13 The TEM images of ONPs clearly revealed the formation of well-organized, spherical nanostructures, and the size range was found to be less than 40 nm (Figure 1A). These ONPs were then trapped inside the gold covering as per section S2 in the Supporting Information to produce Au@ ONPs. The TEM image of Au@ONPs revealed its spherical shape, and the particle size was found to be more than 50 nm, i.e., greater than ONPs (Figure 1B). Finally, the size ranges of ONPs and Au@ONPs were again confirmed from DLS studies. The hydrodynamic sizes revealed by DLS were found to be 70 and 95 for ONPs and Au@ONPs, respectively (Figure S4). Spectroscopic and Electrochemical Properties of the Nanomaterial. To further characterize the fabricated nanomaterial, the photophysical and electrochemical properties of P1, ONPs, and Au@ONPs have been studied (Figure 2). The UV−vis absorption spectrum of P1 in dimethyl sulfoxide (DMSO) reveals a strong peak at 380 nm, and upon ONPs
fabrication, the same peak got shifted to 385 nm. However, in the case of Au@ONPs, the 380 nm specific band got compromised, and a couple of characteristic bands at 300 and 570 nm were obtained (Figure 2A). Similarly, the fluorescence profile of P1 in DMSO revealed a weak emission profile at 425 nm, whereas in ONPs, an intense fluorescence peak at 397 nm was observed. In the case of Au@ONPs, a strong emission peak at 405 nm was observed (Figure 2B and section S3 in the Supporting Information). These results engrain in us the Au@ONPs interaction, thus representing the photophysical properties of Au@ONP nanoparticles. Subsequently, as a way to further confirm the Au@ ONPs binding interaction, FTIR studies of P1, ONPs, and Au@ ONPs were also investigated. Significant shifting in the ONPassociated FTIR signals upon the incorporation of a gold solution was observed. Therefore, the existence of bonding between ONPs and gold entities to form Au@ONPs was C
DOI: 10.1021/acsanm.8b01624 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
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ACS Applied Nano Materials
Figure 4. (A) 31P NMR of quinalphos and Cu(II)-Au@ONPs + quinalphos. (B) Binding scheme of quinalphos with Cu(II)-Au@ONPs.
upon Cu(II)-Au@ONPs addition, the same peak got shifted toward the 61.041 ppm value. The observed shift can also be considered to be an additional proof, showing the existence of binding interactions within the Cu(II)-Au@ONPs−quinalphos system. Moreover, the observed upfield shift indicated shielding within the quinalphos-associated electronic system (Figure 4A). The literature-based reports clearly revealed the high binding ability of gold toward sulfur, and thus binding of P1 toward gold within Au@ONPs via a sulfur linkage is also justified.14 Initially, gold got established on the surface of ONPs via a sulfur linkage, producing Au@ONP hybrid nanoparticles. Additional functionalities within gold in association with slightly exposed P1 functionalities within Au@ONPs tend to provide its firm binding toward Cu2+ to produce Cu(II)-Au@ONPs. Upon surface association, the electrochemical properties of Cu2+ also got tuned favorably and tuned Cu2+ in association with P1 functionalities and created active sites for the selective binding and detection of quinalphos entities (Figure 4B). Real-Time Application. Water samples were collected from various sources, and a known amount of quinalphos was spiked into it. The quantitative determination of spiked quinalphos samples was done using the developed sensor, and reliable results were obtained (Table S1 and section S7 in the Supporting Information). Furthermore, silica-coated Cu(II)Au@ONPs were used to develop a water purification cartridge for removing quinalphos from water samples (section S8 in the Supporting Information). Using this cartridge, we have successfully eliminated more than 80% quinalphos from spiked water samples. Therefore, Cu(II)-Au@ONPs engineered by us are multifunctional materials with sensing as well as water purification properties and found to be comparatively better than the reported materials (Tables S2 and S3).
confirmed from these studies (Figure 2C). Similarly, the comparative electrochemical behavior of P1, ONPs, and Au@ ONPs was also explored by CV studies. Herein also, significant variation in oxidation−reduction peaks in case of P1, ONPs and Au@ONPs were observed. Therefore, the formation and characterization aspects of Au@ONPs were explored by these studies (section S3 in the Supporting Information). Recognition Properties of Cu(II)-Au@ONPs and SolidState Sensing Behavior. The binding ability of Au@ONPs against various analytes was investigated by UV−vis absorption and emission spectroscopy techniques. Among all of the investigated analytes, only Cu2+ showed binding toward the Au@ONPs through significant fluorescence changes. Therefore, Cu2+ binding to Au@ONPs and the formation of triplelayered Cu(II)-Au@ONPs were confirmed from all of these observation (details in section S4 in the Supporting Information). Similarly, the Cu(II)-Au@ONPs so prepared were also evaluated for their binding behavior against various analytes. Initially, the fluorescence properties of Cu(II)-Au@ ONPs alone at different pH values were explored, and the emission profile was found to be constant at the pH 6−11 range; therefore, a pH of 7.4 ± 0.5 was selected for the studies. Among all of the analytes, only quinalphos has revealed a significant enhancement in the fluorescence profile of Cu(II)-Au@ONPs (Figure 3). Considering these facts, the quinalphos sensing ability of Cu(II)-Au@ONPs was further confirmed and a detection limit of 2.4 nM was also established (sections S4 and S5 in the Supporting Information). Finally, to explore the applicability of Cu(II)-Au@ONPs under solid state, their silica-coated beads were prepared as per section S6 in the Supporting Information. Upon incubation of silica beads with different analytes for 2 h, a distinctive solid-state greenish-yellow emission only in the case of quinalphos was observed at 365 nm of illumination wavelength (Figure 3E). The solid-state emission profile of Cu(II)-Au@ONPs with increasing concentration of the quinalphos was found to be linear within a broad concentration range (Figure 3F). Therefore, the quinalphos sensing capability of Cu(II)-Au@ONPs under an aqueous as well as solid state was confirmed by these observations. Mechanism of Sensing of Quinalphos. The excessively changed fluorescence behavior of Cu(II)-Au@ONPs upon quinalphos addition confirmed its binding ability toward quinalphos. 31P NMR can be considered highly useful toward exploring such binding mechanisms. The obtained 31P NMR of quinalphos alone and in the presence of Cu(II)-Au@ONPs is presented in Figure 4A. The 31P NMR peak corresponding to 31 P NMR of quinalphos alone was observed at 61.529 ppm, and
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CONCLUSION We have successfully designed noble polymer P1 and its ONPs under aqueous conditions. The ONPs were used to produce organic−inorganic nanohybrids (Au@ONPs). The surfaces of the Au@ONPs were finally decorated with Cu2+ to produce Cu(II)-Au@ONP-based triple-layered hybrid nanomaterials. The Cu(II)-Au@ONPs revealed exceptional binding as well as sensing ability toward selective quinalphos detection under aqueous conditions. The real sample analysis studies further revealed its actual applicability toward quinalphos detection. Silica coating of Cu(II)-Au@ONPs was also done, and the solid materials so obtained revealed exceptional quinalphos detection and water purification potential. The water purification cartridges, engineered containing the above silica-coated Cu(II)-Au@ONPs, actually showed exceptional quinalphos D
DOI: 10.1021/acsanm.8b01624 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
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ACS Applied Nano Materials
Detection of Cyproheptadine and Thiabendazole. ACS Sustainable Chem. Eng. 2018, 6, 3723−3732. (11) Raj, P.; Singh, A.; Kaur, K.; Aree, T.; Singh, A.; Singh, N. Fluorescent chemosensors for selective and sensitive detection of phosmet/chlorpyrifos with octahedral Ni2+ complexes. Inorg. Chem. 2016, 55, 4874−4883. (12) Kaur, A.; Kaur, G.; Singh, A.; Singh, N.; Kaur, N. Polyamine Based Ratiometric Fluorescent Chemosensor for Strontium Metal Ion in Aqueous Medium: Application in Tap Water, River Water, and in Oral Care. ACS Sustainable Chem. Eng. 2016, 4, 94−101. (13) Allouche, J., Synthesis of organic and bioorganic nanoparticles: an overview of the preparation methods. Nanomaterials: A Danger or a Promise?; Springer, 2013; pp 27−74. (14) Manea, F.; Houillon, F. B.; Pasquato, L.; Scrimin, P. Nanozymes: Gold-nanoparticle-based transphosphorylation catalysts. Angew. Chem., Int. Ed. 2004, 43, 6165−6169.
trapping abilities, and by using them, more than 80% of quinalphos removal was done from contaminated water samples. Therefore, the multifunctional material engineered by us was found to be highly useful for a wide range of sensing and water purification applications.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.8b01624.
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Details of material design, graphs and comparison tables, experimental section, tables, equations, and device fabrication (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Narinder Singh: 0000-0002-8794-8157 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS R.R. acknowledges DST-SERB, India, for a National PostDoctoral Fellowship (PDF/2017/002440). N.S. and P.T. are thankful to DST-Conacyt for an Indian−Mexican joint project (Projec DST/INT/Mexico/P-05/2016).
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DOI: 10.1021/acsanm.8b01624 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
