This article was downloaded by: [New York University] On: 15 June 2015, At: 20:26 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles a
a
b
a
M.I. Hernández-Castillo , O. Zaca-Morán , P. Zaca-Morán , A. Orduña-Diaz , R. Delgadoa
a
Macuil & M. Rojas-López a
Instituto Politécnico Nacional, CIBA-Tlaxcala, Tepetitla, Tlax, México
b
Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias, Pue, México Published online: 11 Jun 2015.
Click for updates To cite this article: M.I. Hernández-Castillo, O. Zaca-Morán, P. Zaca-Morán, A. Orduña-Diaz, R. Delgado-Macuil & M. RojasLópez (2015) Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 50:8, 584-589, DOI: 10.1080/03601234.2015.1028841 To link to this article: http://dx.doi.org/10.1080/03601234.2015.1028841
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Environmental Science and Health, Part B (2014) 50, 584–589 Copyright © Taylor & Francis Group, LLC ISSN: 0360-1234 (Print); 1532-4109 (Online) DOI: 10.1080/03601234.2015.1028841
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles 1 1 1, P. ZACA-MORAN 2, A. ORDUNA-DIAZ e M. I. HERNANDEZ-CASTILLO , O. ZACA-MORAN , 1 1 R. DELGADO-MACUIL and M. ROJAS-LOPEZ 1
Downloaded by [New York University] at 20:26 15 June 2015
2
Instituto Polit ecnico Nacional, CIBA-Tlaxcala, Tepetitla, Tlax, M exico Benem erita Universidad Aut onoma de Puebla, Instituto de Ciencias, Pue, M exico
The absorption of pesticide endosulfan on the surface of gold nanoparticles results from the formation of micrometric structures (1–10 mm) with irregular shape because of the aggregation of individual particles. Such aggregation of gold nanoparticles after absorption of pesticide shows a surface-enhanced Raman scattering (SERS) spectrum, whose intensity depends on the concentration of endosulfan. In addition, the discoloration of the colloidal solution and a diminishing of the intensity of the surface plasmon resonance absorption from individual particles were observed by UV-visible spectroscopy. At the same time, a second band between 638 and 700 nm confirms the formation of aggregates of gold nanoparticles as the concentration of endosulfan increases. Finally, we used the SERS intensity of the S O stretching vibration at 1239 cm¡1 from the SO3 group as a measure of concentration of pesticide endosulfan. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form. Keywords: Gold nanoparticles, endosulfan, aggregation, SERS.
Introduction Endosulfan(6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3 benzodioxathiepine-3-oxide) is a broad spectrum organochlorine pesticide, which is also one of the most stable substances detected in the environment throughout the world. Nowadays, the presence of residues of endosulfan and their metabolites in different matrixes such as food, water and soil represents one of the major issues for environmental chemistry.[1] Endosulfan exists as two diasteromers a-endosulfan and b-endosulfan,[2] and it is typically applied to crops as a 70:30 isomeric ratio of a:b. Fish are very susceptible to endosulfan toxicity at a level of 1–20 ng/L, although degradation of endosulfan by oxidation or hydrolysis caused by biological systems as Anabaena species has been reported.[3] Besides that exposure of endosulfan for long periods results in serious harm to the human nervous system, respiratory tract
Address correspondence to M. Rojas L opez, Centro de Investigaci on en Biotecnología Aplicada, Instituto Politecnico Nacional, Carretera Estatal Santa Ines Tecuexcomac Km. 1.5, Tepetitla, Tlaxcala Z.P. 90700, Mexico; E-mail: marlonrl@ yahoo.com.mx; [email protected] [email protected] Received October 30, 2014. Color versions of one or more figures in this article can be found online at www.tandfonline.com/lesb.
and cardiovascular system.[4] Endosulfan develops its toxicity mainly on the nerve cell membranes by inhibiting the transport of cations as Ca2C, KC, NaC and Mg2C across the membranes.[5–7] On the other hand, the nanotechnology has represented a viable alternative to study and remove different organic pollutants such as pesticides from solution or soil.[8–10] and also for the development of sensor devises.[11,12] Especially, metallic nanoparticles present the optical phenomenon called the surface plasmon resonance (SPR), when a beam of light impinges them due the oscillating electric field, which causes the conduction electrons to oscillate coherently.[13] This strong SPR absorption allows that nanoparticles are useful for many applications such as biological sensing.[10,14] Other important property of metallic nanoparticles is the capacity to enhance the intensity of adsorption and scattering signals.[15] The surface enhanced Raman scattering (SERS) phenomenon can be observed in molecular species adsorbed on metal surface of gold nanoparticle, providing information about the orientation and on the conformation of the adsorbed species.[16,17] Although the adsorption of endosulfan on gold nanoparticles (AuNPs) has been reported previously,[9] there is few information on morphological and structural properties of the aggregates formed by the adsorption of endosulfan on AuNPs. In this form, SERS spectroscopy can be applied to investigate the chemical processes undergone by these
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles substances in the environment. In this paper, we have studied the adsorption of a-endosulfan on gold nanoparticles as well as the formation of aggregates through UV-visible absorption, scanning electron microscopy (SEM) and Raman spectroscopy taking advantage of the SERS phenomena.
Materials and methods
Downloaded by [New York University] at 20:26 15 June 2015
Reagents Gold (III) chloride HAuCl4 (99.99%) was purchased from Sigma Aldrich (Mexico), and sodium citrate (C6H5Na3O7) was purchased from J. T. Baker (Mexico). a-Endosulfan (6,7,8,9,10,10-hexachloro-5,5a,6,9,9a-hexahydro-6,9-methane-2,4,3-benzodioxathiepyne-3-oxide) was purchased from Aldrich and used as received. Stock solution of a-endosulfan in ethanol was prepared to a final concentration of 10¡3 M. All the reagents employed were of analytical grade. Sample preparation Colloidal gold nanoparticles were prepared by using Gold (III) chloride HAuCl4 as precursor agent and sodium citrate as reducing agent, employing the Turkevich method or also called citrate reduction method.[18–20] A total of 20 mL of Gold (III) chloride solution was added to 200mL of deionized water. Then, before the mixture began to boil, 3 mL of sodium citrate solution at 1% was rapidly added, finally the resulting mixture was shaken for 30 min. The resulting colloid showed a red color. On the other hand, stock solution of endosulfan (4 ppm) was prepared in 2propanol. To continue, the endosulfan solution was mixed with the gold nanoparticle solution in water to get the final concentrations at 2, 20, 50, 100 and 200 ppm. To carry out UV-visible absorption measurements, the samples were deposited directly onto a quartz cell of 1 cm optical path length. Sample preparation for Raman and SEM measurements were made by immobilizing 3 mL of each sample on monocrystalline silicon substrates by allowing to dry at room temperature.
585
Results and discussion Gold nanoparticles (AuNPs) were synthesized by the citrate reduction method,[18,19] and the conditions of preparation have been reported elsewhere.[20] The average size of AuNPs was near 15–20 nm of diameter. Figure 1 shows the UV-visible absorption spectra of colloidal solutions of AuNPs exposed to several concentrations of endosulfan (2, 20, 50, 100 and 200 ppm) after 9 h of reaction. The inset of Figure 1 shows TEM image of the typical appearance of gold nanoparticles used in this work. Starting from the UV-visible absorption of the AuNPs (SPR) centered near 520 nm; then we had no change in the SPR signal for adsorption of endosulfan at 2 ppm and a little diminishing in intensity at 20 ppm. However, for the next concentrations (50, 100 and 200 ppm), we can observe two things: the diminishing of the intensity of the SPR signal which is associated to individual gold nanoparticles; and also the presence of a second band centered between 638 and 700 nm, which is due to the aggregated state of AuNPs formed during the adsorption of endosulfan into the surface of the particles. It can be seen that for higher concentrations of endosulfan, the absorption of the aggregates suffers a shift to lower energies and also a diminishing in the intensity of the optical absorption. The last suggests the formation of structures of major size compared with the individual size of the AuNPs. Figure 2 shows the exponential dependence of the intensity of the SPR absorption from AuNPs (520 nm) with the concentration of endosulfan. UV-visible spectra of AuNPs were recorded immediately after mixing with endosulfan, and for 9 and 21 h of reaction. This dependence is associated with the diminishing of the number of individual
Instrumentation UV-visible spectra were recorded by using an Evolution 606 Thermo Scientific spectrophotometer in the interval 190–900 nm, using the line 785 nm as source of excitation which was provided by a diode laser with a power of 10 mW at the sample. The resolution was set at 4 cm¡1, and 100 scans were applied for each sample. SEM micrographs were taken in an environmental scanning electron microscope Vega Tescan digital microscopy imaging, operating in high-vacuum mode. The acceleration voltage was 20 kV and a secondary electrons detector was employed.
Fig. 1. UV-visible spectra of gold nanoparticles exposed to several concentrations of a-endosulfan. The inset shows a TEM picture of the typical appearance of the particles used in this work (15–20 nm). The exposition time was 9 h.
Downloaded by [New York University] at 20:26 15 June 2015
586
Fig. 2. Intensity of the surface plasmon resonance (SPR) absorption from AuNPs as a function of the concentration of endosulfan: (a) 0, (b) 2, (c) 20, (d) 50, (e) 100 and (f) 200 ppm).
AuNPs available to absorb at 520 nm, by the effect of the adsorption of endosulfan in the AuNPs, which takes them to form aggregates. For long periods of time and large concentrations of endosulfan, the attenuation of the SPR
Hernandez-Castillo et al. intensity does not suffer a lot of changes. The inset of Fig. 2 shows the change of color of the colloidal solutions from pure colloidal AuNPs (red) to a-ES/AuNP 200 ppm (colorless). Figure 3 shows SEM images of the aggregates formed by the absorption of a-endosulfan (50 and 200 ppm, respectively) on gold nanoparticles at two scales 100 and 20 mm. An aliquot of the colloidal solution that has reacted with endosulfan during 9 h was put on a monocrystalline silicon substrate to be let dry later. From the SEM images, we can observe aggregates with a maximum size of 1 mm for 50 ppm, and near 10 mm for 200 ppm. In fact, the size and shape of these structures are variable, which cause broadening of the UV-visible absorption in the interval (638–700 nm). These aggregates are formed during the reaction between AuNPs and endosulfan and they are the reason why the intensity of the SPR absorption of gold nanoparticles (at 520 nm) diminishes as the concentration of endosulfan increases. The micrometric structures observed in SEM images were obtained after 9 h of reaction between a-endosulfan and AuNPs. These colloidal solutions were deposited on monocrystalline silicon substrates to be analyzed after by Raman spectroscopy. Figure 4 shows the Raman spectrum of a standard of a-endosulfan (highly concentrated) which was deposited on a monocrystalline silicon
Fig. 3. SEM images of the aggregates formed by the interaction of AuNPs with a-endosulfan at 50 ppm (a) 100 mm and (b) 20 mm, and at 200 ppm (c) 100 mm and (d) 20 mm.
587
Downloaded by [New York University] at 20:26 15 June 2015
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles
Fig. 4. Raman spectrum of the pesticide a-endosulfan (a), SERS spectrum of gold nanoparticles (AuNP) (b), and SERS spectrum of a-ES/AuNP.
substrate. It depicts many intense bands shown in Table 1, which are associated to vibrations of several groups of their chemical structure among them C Cl, C C, C H, S O and CHC. The SERS spectrum of gold
nanoparticles (control) shows vibration modes at 1374, 1449 and 1558 cm¡1, which are assigned to the symmetric stretching vibrations from the carboxylate group,[21] whereas the peak at 1595 cm¡1 is assigned to the asymmetric stretching vibration of the same group. This is because the gold nanoparticles are stabilized with citrate groups after the synthesis process. In the same Figure is depicted the SERS spectrum of a-ES/AuNP at 200 ppm, which is caused by the microstructures observed in Figure 3. The peaks at 258, 302, 282 and 395 cm¡1 are associated with vibrations of C Cl (being the last peak linked to CHC), whereas the peaks at 430, 572, 600 and 712 cm¡1 arise from the skeletal deformations of endosulfan.[22] The peak at 1005 cm¡1 can be associated to the stretching vibration of C H, whereas the peak at 1239 arises from the S-O stretching vibration of SO3 of endosulfan.[22] The peaks at 853 and 1125 cm¡1 are not identified. However the intense peak of the SERS spectrum of a-ES/AuNP at 1373 cm ¡1 is associated to the C-H wagging and twisting motions of the structure of endosulfan, whereas the peak at 1446 cm¡1 can be assigned to an in-plane deformation of CH2 group. Finally, the band at 1580–1600 cm¡1 can be associated to the stretching CHC mode of endosulfan. Table 1 summarizes the Raman frequencies of a standard
Table 1. Raman and SERS frequencies (cm¡1) of a-ES and a-ES adsorbed on AuNPs (a-ES/AuNP). Raman a-ES[22]
Raman a-ES (this work)
315m
242s 289s 314s
345s 375s 400vs
346s 374s 401vs
467w 539w 587m 621w 676w
467w 538m 588m 622m 675w 697w 751s 785w 858w 912m 966m 1004w 1032m 1094w 1189m 1231w 1257w 1378w 1451w 1603m
750s 784w 911m 966w 1029w 1093w 1187m 1228w 1254w 1450w 1604m
n: stretching; d: in-plain deformation.
SERS a-ES/AuNP[22]
SERS a-ES/AuNP (this work)
Assignments
258w 302w 315m 335m 351w 374w 400s
n:
382s 395s 430w
n:
(C
(C
Cl)
Cl) linked to C
480w 564w
695w
572w 600w
Skeletal deformations
712s —
853s n:
(C
H)
1005s –
1125s 1181w 1240w
1239s 1370s 1446w 1580m
n:
(SO3)
— d(CH2) n: (CHC)
C
Downloaded by [New York University] at 20:26 15 June 2015
588
Fig. 5. SERS spectra of gold nanoparticles (AuNP) with several concentrations of a-ES (2, 20, 50, 100 and 200 ppm) adsorbed on their surface.
of a-ES and also with the SERS frequencies of a-ES/ AuNP (200 ppm) adsorbed on the surface of the gold nanoparticles. Thus, Raman spectroscopy (Fig. 4) suggests that the micrometric structures observed in Figure 3 are constituted by aggregates of gold nanoparticles with endosulfan adsorbed on their surface. Figure 5 shows the SERS spectra of gold nanoparticles with a-endosulfan adsorbed on their surface for several concentrations of this pesticide. The SERS intensity increases with the a-endosulfan concentration (2– 200 ppm). This enhancement of the intensity of scattering is favored when the proximity of each a-ES/AuNP particles is considerable, that is the case of the formation of aggregates.
Hernandez-Castillo et al. The linear dependence between the SERS intensity of the a-endosulfan adsorbed on gold nanoparticles (a-ES/ AuNP) with the concentration is depicted in Figure 6. In this case, we have used the SERS intensity of the S-O stretching vibration at 1239 cm¡1 from the SO3 group as a representative measure of the endosulfan concentration. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form, only by depositing an aliquot of 3 mL of the colloidal solution after the reaction on a monocrystalline silicon substrate, let dry the aliquot and acquire the SERS spectrum. However, if the polluted sample includes a great number of unknown compounds, then it is necessary to functionalize the gold nanoparticles. Guerrini et. al.[22] reported the use of bis-acridinium lucigenin, which functionalizes the metallic surface of silver nanoparticles, acting as a chemical assembler to selectively adsorb endosulfan. In our case, the SERS intensity is directly associated with the concentration of endosulfan due to the proximity of a-ES/AuNP structures by the formation of aggregates.
Conclusion We have analyzed morphological, optical and vibration properties of colloidal solutions obtained after the absorption of pesticide a-endosulfan (2, 20, 50, 100 and 200 ppm) on gold nanoparticles. The absorption of endosulfan on the AuNPs generates a discolouration of the colloidal solution and a diminishing of the intensity of the SPR absorption from individual AuNPs observed by UVvisible spectroscopy. The diminishing of the intensity of AuNPs is accompanied by the observation of another new band located in the interval 638–700 nm. This band is associated with the optical absorption of the aggregates formed during the adsorption of endosulfan (a-ES/ AuNP). As the concentration of pesticide increases, this band (from aggregates) suffers a shift to low energies, suggesting that the aggregates increase their size. SEM images confirm the formation of structures of micrometric size, and these sizes increase as the pesticide concentration does (~10 mm for 200 ppm). SERS spectra reveal that these micrometric structures are formed by aggregates of a-ES/ AuNP, and their intensity depends directly on the concentration of endosulfan. The last methodology could be used as a practical technique to sense the amount of endosulfan adsorbed by gold nanoparticles.
References
Fig. 6. Linear dependence between the SERS intensity of the adsorption of a-endosulfan on gold nanoparticles (a-ES/AuNP) with the concentration of a-endosulfan.
[1] Bootharaju, M.S.; Pradeep, T. Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles. Langmuir. 2012, 28, 2671–2679. [2] Schmidt, W.F.; Hapeman, C.J.; McConnell, L.L.; Mookherji, S.; Rice, C.P.; Nguyen, J.K.; Qin, J.; Lee, H.; Chao, K.; Kim, M.S. Temperature-dependent Raman spectroscopic evidence of and
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles
[3]
[4]
[5]
[6]
Downloaded by [New York University] at 20:26 15 June 2015
[7]
[8]
[9]
[10]
[11]
[12]
molecular mechanism for irreversible isomerization of b-endosulfan to a-endosulfan. J. Agric. Food Chem. 2014, 62, 2023–2030. Lee, S.E.; Kim, J.S.; Kennedy, I.R.; Park, J.W.; Kwon, G.S.; Koh, S.C.; Kim, J.E. Biotransformation of an organochlorine insecticide endosulfan by Anabaena species. J. Agric. Food Chem. 2003, 51, 1336–1340. Koch, R.B. Inhibition of animal tissue ATP ase activities by chlorinated hydrocarbon pesticides. Chem. Biol. Interact. 1969, 1, 199–209. Folmar, L.C. In vitro inhibition of rat brain ATPase, pNPPase, and ATP-32Pi exchange by chlorinated-diphenyl ethanes and cyclodiene insecticides. Bull. Environ. Contam. Toxicol. 1978, 19, 481–488. Luo, M.; Bodnaryk, R. P. The effect of insecticides on (Ca2C C Mg2C)-ATPase and the ATP-dependent calcium pump in moth brain synaptosomes and synaptosome membrane vesicles from the bertha armyworm. Pesticide Biochem. Phys. 1988, 30, 155–165. Saxena, P.N.; Gupta, V.D. Role of molecular geometry, valence charge distribution and vibrational modes in bioactivity of cyclodiene insecticides. J. Appl. Toxicol. 2005, 25, 39–46. Dejun, X.; Haibing, L. Colorimetric detection of pesticides based on calixarene modified silver nanoparticles in water. Nanotechnology. 2008, 19, 1–6. Sreekumaran, N.A.; Tom, R.T.; Pradeep, T. Detection and extraction of endosulfan by metal nanoparticles. J. Environ. Monit. 2003, 5, 363–365. Sreekumaran, N.A.; Tom, R.T.; Rajeev Kumar, V.R.; Subramaniam, C.; Pradeep, T. Chemical interactions at noble metal nanoparticle surfaces-calalysis. Sensors and Devices. Cosmos 2007, 3, 103–124. Evanoff, D.D.; Chumanov, G. Synthesis and optical properties of silver nanoparticles and arrays. Chem. Phys. Chem. 2005, 6, 1221–1231. Ansary, A.E.; Faddah, L.M. Nanoparticles as biochemical sensors, Nanotechnology, Science and Applications 2010, 3, 65–76.
589
[13] Haes, A.J.; Zou, S.; Schatz, G.C.; Van Duyne, R.P. Nanoscale optical biosensor: short range distance dependence of the localized surface plasmon resonance of noble metal nanoparticles. J. Phys. Chem. B. 2004, 108, 6961–6968. [14] Sannomiya, T.; V€ or€ os, J. Single plasmonic nanoparticles for biosensing, Trends in Biotechnology. 2011, 29, 343–351. [15] Nie, S.; Emory, S.R. Probing single molecules and single nanoparticles by Surface-Enhanced Raman Scattering, Science. 1997, 275, 1102–1106. [16] Lopez, M.R.; Guerrini, L.; García, J. V.; Sanchez, S. Vibrational analysis of herbicide diquat: A normal Raman and SERS study on Ag nanoparticles, Vibr. Spectrosc. 2008, 48, 58–64. [17] S anchez, S.; Domingo, C.; García, J.V.; Azn arez, J.A. SurfaceEnhanced Vibrational Study (SEIR and SERS) of dithiocarbamate pesticides on gold films. Langmuir. 2001, 17, 1157–1162. [18] Turkevich, J.; Stevenson, P.C.; Hillier, J. A study of the nucleation and growth process in the synthesis of colloidal gold. Faraday Soc. 1951, 11, 55–75. [19] Kimling, J.; Maier, M.; Okenve, B.; Kotaidis, V.; Ballot, H.; Plech, A. Turkevich method for gold nanoparticle synthesis revisited. J. Phys. Chem. B. 2006, 110, 15700–15707. [20] Rios-Corripio, M.A.; García-Perez, B.E.; Jaramillo-Flores, M.E.; Gayou, V.L.; Rojas-L opez, M. UV-Visible intensity ratio (aggregates/single particles) as a measure to obtain stability of gold nanoparticles conjugated with protein A. J. Nanopart. Res. 2013, 15, 1624, 1–7. [21] Wai Mak, J.S. Thesis: Raman characterization of colloidal nanoparticles using hollow-core photonic crystal fibers. University of Toronto (2011). Chap. 5, pp. 59–109. [22] Guerrini, L.; Aliaga, A.E.; Carcamo, J.; Gomez-Jeria, J.S.; Sanchez-Cortes, S.; Campos-Vallette, M.M.; Garcia-Ramos, J.V. Functionalization of Ag nanoparticles with the bis-acridinium lucigenin as a chemical assembler in the detection of persistent organic pollutants by surface-enhanced Raman scattering. Anal. Chim. Acta 2008, 624, 286–293.
Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles a
a
b
a
M.I. Hernández-Castillo , O. Zaca-Morán , P. Zaca-Morán , A. Orduña-Diaz , R. Delgadoa
a
Macuil & M. Rojas-López a
Instituto Politécnico Nacional, CIBA-Tlaxcala, Tepetitla, Tlax, México
b
Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias, Pue, México Published online: 11 Jun 2015.
Click for updates To cite this article: M.I. Hernández-Castillo, O. Zaca-Morán, P. Zaca-Morán, A. Orduña-Diaz, R. Delgado-Macuil & M. RojasLópez (2015) Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 50:8, 584-589, DOI: 10.1080/03601234.2015.1028841 To link to this article: http://dx.doi.org/10.1080/03601234.2015.1028841
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Environmental Science and Health, Part B (2014) 50, 584–589 Copyright © Taylor & Francis Group, LLC ISSN: 0360-1234 (Print); 1532-4109 (Online) DOI: 10.1080/03601234.2015.1028841
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles 1 1 1, P. ZACA-MORAN 2, A. ORDUNA-DIAZ e M. I. HERNANDEZ-CASTILLO , O. ZACA-MORAN , 1 1 R. DELGADO-MACUIL and M. ROJAS-LOPEZ 1
Downloaded by [New York University] at 20:26 15 June 2015
2
Instituto Polit ecnico Nacional, CIBA-Tlaxcala, Tepetitla, Tlax, M exico Benem erita Universidad Aut onoma de Puebla, Instituto de Ciencias, Pue, M exico
The absorption of pesticide endosulfan on the surface of gold nanoparticles results from the formation of micrometric structures (1–10 mm) with irregular shape because of the aggregation of individual particles. Such aggregation of gold nanoparticles after absorption of pesticide shows a surface-enhanced Raman scattering (SERS) spectrum, whose intensity depends on the concentration of endosulfan. In addition, the discoloration of the colloidal solution and a diminishing of the intensity of the surface plasmon resonance absorption from individual particles were observed by UV-visible spectroscopy. At the same time, a second band between 638 and 700 nm confirms the formation of aggregates of gold nanoparticles as the concentration of endosulfan increases. Finally, we used the SERS intensity of the S O stretching vibration at 1239 cm¡1 from the SO3 group as a measure of concentration of pesticide endosulfan. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form. Keywords: Gold nanoparticles, endosulfan, aggregation, SERS.
Introduction Endosulfan(6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3 benzodioxathiepine-3-oxide) is a broad spectrum organochlorine pesticide, which is also one of the most stable substances detected in the environment throughout the world. Nowadays, the presence of residues of endosulfan and their metabolites in different matrixes such as food, water and soil represents one of the major issues for environmental chemistry.[1] Endosulfan exists as two diasteromers a-endosulfan and b-endosulfan,[2] and it is typically applied to crops as a 70:30 isomeric ratio of a:b. Fish are very susceptible to endosulfan toxicity at a level of 1–20 ng/L, although degradation of endosulfan by oxidation or hydrolysis caused by biological systems as Anabaena species has been reported.[3] Besides that exposure of endosulfan for long periods results in serious harm to the human nervous system, respiratory tract
Address correspondence to M. Rojas L opez, Centro de Investigaci on en Biotecnología Aplicada, Instituto Politecnico Nacional, Carretera Estatal Santa Ines Tecuexcomac Km. 1.5, Tepetitla, Tlaxcala Z.P. 90700, Mexico; E-mail: marlonrl@ yahoo.com.mx; [email protected] [email protected] Received October 30, 2014. Color versions of one or more figures in this article can be found online at www.tandfonline.com/lesb.
and cardiovascular system.[4] Endosulfan develops its toxicity mainly on the nerve cell membranes by inhibiting the transport of cations as Ca2C, KC, NaC and Mg2C across the membranes.[5–7] On the other hand, the nanotechnology has represented a viable alternative to study and remove different organic pollutants such as pesticides from solution or soil.[8–10] and also for the development of sensor devises.[11,12] Especially, metallic nanoparticles present the optical phenomenon called the surface plasmon resonance (SPR), when a beam of light impinges them due the oscillating electric field, which causes the conduction electrons to oscillate coherently.[13] This strong SPR absorption allows that nanoparticles are useful for many applications such as biological sensing.[10,14] Other important property of metallic nanoparticles is the capacity to enhance the intensity of adsorption and scattering signals.[15] The surface enhanced Raman scattering (SERS) phenomenon can be observed in molecular species adsorbed on metal surface of gold nanoparticle, providing information about the orientation and on the conformation of the adsorbed species.[16,17] Although the adsorption of endosulfan on gold nanoparticles (AuNPs) has been reported previously,[9] there is few information on morphological and structural properties of the aggregates formed by the adsorption of endosulfan on AuNPs. In this form, SERS spectroscopy can be applied to investigate the chemical processes undergone by these
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles substances in the environment. In this paper, we have studied the adsorption of a-endosulfan on gold nanoparticles as well as the formation of aggregates through UV-visible absorption, scanning electron microscopy (SEM) and Raman spectroscopy taking advantage of the SERS phenomena.
Materials and methods
Downloaded by [New York University] at 20:26 15 June 2015
Reagents Gold (III) chloride HAuCl4 (99.99%) was purchased from Sigma Aldrich (Mexico), and sodium citrate (C6H5Na3O7) was purchased from J. T. Baker (Mexico). a-Endosulfan (6,7,8,9,10,10-hexachloro-5,5a,6,9,9a-hexahydro-6,9-methane-2,4,3-benzodioxathiepyne-3-oxide) was purchased from Aldrich and used as received. Stock solution of a-endosulfan in ethanol was prepared to a final concentration of 10¡3 M. All the reagents employed were of analytical grade. Sample preparation Colloidal gold nanoparticles were prepared by using Gold (III) chloride HAuCl4 as precursor agent and sodium citrate as reducing agent, employing the Turkevich method or also called citrate reduction method.[18–20] A total of 20 mL of Gold (III) chloride solution was added to 200mL of deionized water. Then, before the mixture began to boil, 3 mL of sodium citrate solution at 1% was rapidly added, finally the resulting mixture was shaken for 30 min. The resulting colloid showed a red color. On the other hand, stock solution of endosulfan (4 ppm) was prepared in 2propanol. To continue, the endosulfan solution was mixed with the gold nanoparticle solution in water to get the final concentrations at 2, 20, 50, 100 and 200 ppm. To carry out UV-visible absorption measurements, the samples were deposited directly onto a quartz cell of 1 cm optical path length. Sample preparation for Raman and SEM measurements were made by immobilizing 3 mL of each sample on monocrystalline silicon substrates by allowing to dry at room temperature.
585
Results and discussion Gold nanoparticles (AuNPs) were synthesized by the citrate reduction method,[18,19] and the conditions of preparation have been reported elsewhere.[20] The average size of AuNPs was near 15–20 nm of diameter. Figure 1 shows the UV-visible absorption spectra of colloidal solutions of AuNPs exposed to several concentrations of endosulfan (2, 20, 50, 100 and 200 ppm) after 9 h of reaction. The inset of Figure 1 shows TEM image of the typical appearance of gold nanoparticles used in this work. Starting from the UV-visible absorption of the AuNPs (SPR) centered near 520 nm; then we had no change in the SPR signal for adsorption of endosulfan at 2 ppm and a little diminishing in intensity at 20 ppm. However, for the next concentrations (50, 100 and 200 ppm), we can observe two things: the diminishing of the intensity of the SPR signal which is associated to individual gold nanoparticles; and also the presence of a second band centered between 638 and 700 nm, which is due to the aggregated state of AuNPs formed during the adsorption of endosulfan into the surface of the particles. It can be seen that for higher concentrations of endosulfan, the absorption of the aggregates suffers a shift to lower energies and also a diminishing in the intensity of the optical absorption. The last suggests the formation of structures of major size compared with the individual size of the AuNPs. Figure 2 shows the exponential dependence of the intensity of the SPR absorption from AuNPs (520 nm) with the concentration of endosulfan. UV-visible spectra of AuNPs were recorded immediately after mixing with endosulfan, and for 9 and 21 h of reaction. This dependence is associated with the diminishing of the number of individual
Instrumentation UV-visible spectra were recorded by using an Evolution 606 Thermo Scientific spectrophotometer in the interval 190–900 nm, using the line 785 nm as source of excitation which was provided by a diode laser with a power of 10 mW at the sample. The resolution was set at 4 cm¡1, and 100 scans were applied for each sample. SEM micrographs were taken in an environmental scanning electron microscope Vega Tescan digital microscopy imaging, operating in high-vacuum mode. The acceleration voltage was 20 kV and a secondary electrons detector was employed.
Fig. 1. UV-visible spectra of gold nanoparticles exposed to several concentrations of a-endosulfan. The inset shows a TEM picture of the typical appearance of the particles used in this work (15–20 nm). The exposition time was 9 h.
Downloaded by [New York University] at 20:26 15 June 2015
586
Fig. 2. Intensity of the surface plasmon resonance (SPR) absorption from AuNPs as a function of the concentration of endosulfan: (a) 0, (b) 2, (c) 20, (d) 50, (e) 100 and (f) 200 ppm).
AuNPs available to absorb at 520 nm, by the effect of the adsorption of endosulfan in the AuNPs, which takes them to form aggregates. For long periods of time and large concentrations of endosulfan, the attenuation of the SPR
Hernandez-Castillo et al. intensity does not suffer a lot of changes. The inset of Fig. 2 shows the change of color of the colloidal solutions from pure colloidal AuNPs (red) to a-ES/AuNP 200 ppm (colorless). Figure 3 shows SEM images of the aggregates formed by the absorption of a-endosulfan (50 and 200 ppm, respectively) on gold nanoparticles at two scales 100 and 20 mm. An aliquot of the colloidal solution that has reacted with endosulfan during 9 h was put on a monocrystalline silicon substrate to be let dry later. From the SEM images, we can observe aggregates with a maximum size of 1 mm for 50 ppm, and near 10 mm for 200 ppm. In fact, the size and shape of these structures are variable, which cause broadening of the UV-visible absorption in the interval (638–700 nm). These aggregates are formed during the reaction between AuNPs and endosulfan and they are the reason why the intensity of the SPR absorption of gold nanoparticles (at 520 nm) diminishes as the concentration of endosulfan increases. The micrometric structures observed in SEM images were obtained after 9 h of reaction between a-endosulfan and AuNPs. These colloidal solutions were deposited on monocrystalline silicon substrates to be analyzed after by Raman spectroscopy. Figure 4 shows the Raman spectrum of a standard of a-endosulfan (highly concentrated) which was deposited on a monocrystalline silicon
Fig. 3. SEM images of the aggregates formed by the interaction of AuNPs with a-endosulfan at 50 ppm (a) 100 mm and (b) 20 mm, and at 200 ppm (c) 100 mm and (d) 20 mm.
587
Downloaded by [New York University] at 20:26 15 June 2015
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles
Fig. 4. Raman spectrum of the pesticide a-endosulfan (a), SERS spectrum of gold nanoparticles (AuNP) (b), and SERS spectrum of a-ES/AuNP.
substrate. It depicts many intense bands shown in Table 1, which are associated to vibrations of several groups of their chemical structure among them C Cl, C C, C H, S O and CHC. The SERS spectrum of gold
nanoparticles (control) shows vibration modes at 1374, 1449 and 1558 cm¡1, which are assigned to the symmetric stretching vibrations from the carboxylate group,[21] whereas the peak at 1595 cm¡1 is assigned to the asymmetric stretching vibration of the same group. This is because the gold nanoparticles are stabilized with citrate groups after the synthesis process. In the same Figure is depicted the SERS spectrum of a-ES/AuNP at 200 ppm, which is caused by the microstructures observed in Figure 3. The peaks at 258, 302, 282 and 395 cm¡1 are associated with vibrations of C Cl (being the last peak linked to CHC), whereas the peaks at 430, 572, 600 and 712 cm¡1 arise from the skeletal deformations of endosulfan.[22] The peak at 1005 cm¡1 can be associated to the stretching vibration of C H, whereas the peak at 1239 arises from the S-O stretching vibration of SO3 of endosulfan.[22] The peaks at 853 and 1125 cm¡1 are not identified. However the intense peak of the SERS spectrum of a-ES/AuNP at 1373 cm ¡1 is associated to the C-H wagging and twisting motions of the structure of endosulfan, whereas the peak at 1446 cm¡1 can be assigned to an in-plane deformation of CH2 group. Finally, the band at 1580–1600 cm¡1 can be associated to the stretching CHC mode of endosulfan. Table 1 summarizes the Raman frequencies of a standard
Table 1. Raman and SERS frequencies (cm¡1) of a-ES and a-ES adsorbed on AuNPs (a-ES/AuNP). Raman a-ES[22]
Raman a-ES (this work)
315m
242s 289s 314s
345s 375s 400vs
346s 374s 401vs
467w 539w 587m 621w 676w
467w 538m 588m 622m 675w 697w 751s 785w 858w 912m 966m 1004w 1032m 1094w 1189m 1231w 1257w 1378w 1451w 1603m
750s 784w 911m 966w 1029w 1093w 1187m 1228w 1254w 1450w 1604m
n: stretching; d: in-plain deformation.
SERS a-ES/AuNP[22]
SERS a-ES/AuNP (this work)
Assignments
258w 302w 315m 335m 351w 374w 400s
n:
382s 395s 430w
n:
(C
(C
Cl)
Cl) linked to C
480w 564w
695w
572w 600w
Skeletal deformations
712s —
853s n:
(C
H)
1005s –
1125s 1181w 1240w
1239s 1370s 1446w 1580m
n:
(SO3)
— d(CH2) n: (CHC)
C
Downloaded by [New York University] at 20:26 15 June 2015
588
Fig. 5. SERS spectra of gold nanoparticles (AuNP) with several concentrations of a-ES (2, 20, 50, 100 and 200 ppm) adsorbed on their surface.
of a-ES and also with the SERS frequencies of a-ES/ AuNP (200 ppm) adsorbed on the surface of the gold nanoparticles. Thus, Raman spectroscopy (Fig. 4) suggests that the micrometric structures observed in Figure 3 are constituted by aggregates of gold nanoparticles with endosulfan adsorbed on their surface. Figure 5 shows the SERS spectra of gold nanoparticles with a-endosulfan adsorbed on their surface for several concentrations of this pesticide. The SERS intensity increases with the a-endosulfan concentration (2– 200 ppm). This enhancement of the intensity of scattering is favored when the proximity of each a-ES/AuNP particles is considerable, that is the case of the formation of aggregates.
Hernandez-Castillo et al. The linear dependence between the SERS intensity of the a-endosulfan adsorbed on gold nanoparticles (a-ES/ AuNP) with the concentration is depicted in Figure 6. In this case, we have used the SERS intensity of the S-O stretching vibration at 1239 cm¡1 from the SO3 group as a representative measure of the endosulfan concentration. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form, only by depositing an aliquot of 3 mL of the colloidal solution after the reaction on a monocrystalline silicon substrate, let dry the aliquot and acquire the SERS spectrum. However, if the polluted sample includes a great number of unknown compounds, then it is necessary to functionalize the gold nanoparticles. Guerrini et. al.[22] reported the use of bis-acridinium lucigenin, which functionalizes the metallic surface of silver nanoparticles, acting as a chemical assembler to selectively adsorb endosulfan. In our case, the SERS intensity is directly associated with the concentration of endosulfan due to the proximity of a-ES/AuNP structures by the formation of aggregates.
Conclusion We have analyzed morphological, optical and vibration properties of colloidal solutions obtained after the absorption of pesticide a-endosulfan (2, 20, 50, 100 and 200 ppm) on gold nanoparticles. The absorption of endosulfan on the AuNPs generates a discolouration of the colloidal solution and a diminishing of the intensity of the SPR absorption from individual AuNPs observed by UVvisible spectroscopy. The diminishing of the intensity of AuNPs is accompanied by the observation of another new band located in the interval 638–700 nm. This band is associated with the optical absorption of the aggregates formed during the adsorption of endosulfan (a-ES/ AuNP). As the concentration of pesticide increases, this band (from aggregates) suffers a shift to low energies, suggesting that the aggregates increase their size. SEM images confirm the formation of structures of micrometric size, and these sizes increase as the pesticide concentration does (~10 mm for 200 ppm). SERS spectra reveal that these micrometric structures are formed by aggregates of a-ES/ AuNP, and their intensity depends directly on the concentration of endosulfan. The last methodology could be used as a practical technique to sense the amount of endosulfan adsorbed by gold nanoparticles.
References
Fig. 6. Linear dependence between the SERS intensity of the adsorption of a-endosulfan on gold nanoparticles (a-ES/AuNP) with the concentration of a-endosulfan.
[1] Bootharaju, M.S.; Pradeep, T. Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles. Langmuir. 2012, 28, 2671–2679. [2] Schmidt, W.F.; Hapeman, C.J.; McConnell, L.L.; Mookherji, S.; Rice, C.P.; Nguyen, J.K.; Qin, J.; Lee, H.; Chao, K.; Kim, M.S. Temperature-dependent Raman spectroscopic evidence of and
Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles
[3]
[4]
[5]
[6]
Downloaded by [New York University] at 20:26 15 June 2015
[7]
[8]
[9]
[10]
[11]
[12]
molecular mechanism for irreversible isomerization of b-endosulfan to a-endosulfan. J. Agric. Food Chem. 2014, 62, 2023–2030. Lee, S.E.; Kim, J.S.; Kennedy, I.R.; Park, J.W.; Kwon, G.S.; Koh, S.C.; Kim, J.E. Biotransformation of an organochlorine insecticide endosulfan by Anabaena species. J. Agric. Food Chem. 2003, 51, 1336–1340. Koch, R.B. Inhibition of animal tissue ATP ase activities by chlorinated hydrocarbon pesticides. Chem. Biol. Interact. 1969, 1, 199–209. Folmar, L.C. In vitro inhibition of rat brain ATPase, pNPPase, and ATP-32Pi exchange by chlorinated-diphenyl ethanes and cyclodiene insecticides. Bull. Environ. Contam. Toxicol. 1978, 19, 481–488. Luo, M.; Bodnaryk, R. P. The effect of insecticides on (Ca2C C Mg2C)-ATPase and the ATP-dependent calcium pump in moth brain synaptosomes and synaptosome membrane vesicles from the bertha armyworm. Pesticide Biochem. Phys. 1988, 30, 155–165. Saxena, P.N.; Gupta, V.D. Role of molecular geometry, valence charge distribution and vibrational modes in bioactivity of cyclodiene insecticides. J. Appl. Toxicol. 2005, 25, 39–46. Dejun, X.; Haibing, L. Colorimetric detection of pesticides based on calixarene modified silver nanoparticles in water. Nanotechnology. 2008, 19, 1–6. Sreekumaran, N.A.; Tom, R.T.; Pradeep, T. Detection and extraction of endosulfan by metal nanoparticles. J. Environ. Monit. 2003, 5, 363–365. Sreekumaran, N.A.; Tom, R.T.; Rajeev Kumar, V.R.; Subramaniam, C.; Pradeep, T. Chemical interactions at noble metal nanoparticle surfaces-calalysis. Sensors and Devices. Cosmos 2007, 3, 103–124. Evanoff, D.D.; Chumanov, G. Synthesis and optical properties of silver nanoparticles and arrays. Chem. Phys. Chem. 2005, 6, 1221–1231. Ansary, A.E.; Faddah, L.M. Nanoparticles as biochemical sensors, Nanotechnology, Science and Applications 2010, 3, 65–76.
589
[13] Haes, A.J.; Zou, S.; Schatz, G.C.; Van Duyne, R.P. Nanoscale optical biosensor: short range distance dependence of the localized surface plasmon resonance of noble metal nanoparticles. J. Phys. Chem. B. 2004, 108, 6961–6968. [14] Sannomiya, T.; V€ or€ os, J. Single plasmonic nanoparticles for biosensing, Trends in Biotechnology. 2011, 29, 343–351. [15] Nie, S.; Emory, S.R. Probing single molecules and single nanoparticles by Surface-Enhanced Raman Scattering, Science. 1997, 275, 1102–1106. [16] Lopez, M.R.; Guerrini, L.; García, J. V.; Sanchez, S. Vibrational analysis of herbicide diquat: A normal Raman and SERS study on Ag nanoparticles, Vibr. Spectrosc. 2008, 48, 58–64. [17] S anchez, S.; Domingo, C.; García, J.V.; Azn arez, J.A. SurfaceEnhanced Vibrational Study (SEIR and SERS) of dithiocarbamate pesticides on gold films. Langmuir. 2001, 17, 1157–1162. [18] Turkevich, J.; Stevenson, P.C.; Hillier, J. A study of the nucleation and growth process in the synthesis of colloidal gold. Faraday Soc. 1951, 11, 55–75. [19] Kimling, J.; Maier, M.; Okenve, B.; Kotaidis, V.; Ballot, H.; Plech, A. Turkevich method for gold nanoparticle synthesis revisited. J. Phys. Chem. B. 2006, 110, 15700–15707. [20] Rios-Corripio, M.A.; García-Perez, B.E.; Jaramillo-Flores, M.E.; Gayou, V.L.; Rojas-L opez, M. UV-Visible intensity ratio (aggregates/single particles) as a measure to obtain stability of gold nanoparticles conjugated with protein A. J. Nanopart. Res. 2013, 15, 1624, 1–7. [21] Wai Mak, J.S. Thesis: Raman characterization of colloidal nanoparticles using hollow-core photonic crystal fibers. University of Toronto (2011). Chap. 5, pp. 59–109. [22] Guerrini, L.; Aliaga, A.E.; Carcamo, J.; Gomez-Jeria, J.S.; Sanchez-Cortes, S.; Campos-Vallette, M.M.; Garcia-Ramos, J.V. Functionalization of Ag nanoparticles with the bis-acridinium lucigenin as a chemical assembler in the detection of persistent organic pollutants by surface-enhanced Raman scattering. Anal. Chim. Acta 2008, 624, 286–293.
