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Highly sensitive colorimetric detection of lead using maleic acid functionalized gold nanoparticle Nalin Ratnarathorn, Orawon Chailapakul, Wijitar Dungchai
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S0039-9140(14)00852-2 http://dx.doi.org/10.1016/j.talanta.2014.10.024 TAL15163
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Talanta
Received date: 5 August 2014 Revised date: 6 October 2014 Accepted date: 10 October 2014 Cite this article as: Nalin Ratnarathorn, Orawon Chailapakul, Wijitar Dungchai, Highly sensitive colorimetric detection of lead using maleic acid functionalized gold nanoparticle, Talanta, http://dx.doi.org/10.1016/j.talanta.2014.10.024 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Highly Sensitive Colorimetric Detection of Lead Using Maleic Acid Functionalized Gold Nanoparticle
Nalin Ratnarathorn,a Orawon Chailapakul,b Wijitar Dungchaia,*
a
Department of Chemistry, Faculty of Science, King Mongkut’s University of Technology
Thonburi, Prachautid Road, Thungkru, Bangkok, 10140, Thailand b
Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials,
Chulalongkorn University, Patumwan, Bangkok, 10330, Thailand
Corresponding author: Dr. Wijitar Dungchai E-mail: [email protected] Fax: +66-02-470-8840 Tel: +66-02-470-9553
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Abstract
Highly sensitive colorimetric detection for Pb2+ has been developed using maleic acid (MA) functionalized GNP. The –COOH on MA was used to modify GNP surface whereas the other –COOH functional group have strong affinity to coordination behavior of Pb2+ allowing the selective formation more than other ions. MA-GNPs solution changed from red to blue color after the addition of Pb2+ due to nanoparticle aggregation. The different optical absorption and discriminate of particle size between the MA-GNPs solution with and without Pb2+ were characterized by UV-Visible spectroscopy and transmission electron microscopy (TEM), respectively. The color intensity as a function of Pb2+ concentration gave a linear response in the range of 0.0–10.0 µgL-1 (R2 = 0.990). The detection limit was found at 0.5 µgL-1 by naked eye and can be completed the analysis within 15 min. The MA-GNPs aggregated with Pb2+ showed high selectivity when was compared to other metal ions (As3+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) and anions (Cl-, NO3- and SO42-). Our proposed method was also applied for the determination of Pb2+ in real drinking water samples from 5 sources. The result of real water samples were not statistically significant different from the standard methods at the 95% confidence level (pair t-test method). Moreover, we evaluated our proposed method for the determination of trace Pb2+ concentration in real breast milk samples. The recoveries were acceptable and ranged from 101–104% for spiked Pb2+ in real breast milk samples. Thus, MA-GNP colorimetric sensing provides a simple, rapid, sensitive, easy-to-use, inexpensive and low detection limit for the monitoring of Pb2+.
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Keywords: Colorimetric sensing, Gold nanoparticle, Lead
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1. Introduction The present food and drinking water are often contaminated with harmful substances for humans, either as part of the production process, natural or caused by the additives added to it. Lead (Pb2+) is a major environmental pollutant and ranks second in the list of toxic substances that cause renal malfunction and damage to the brain and kidneys [1]. It has also been classified as carcinogenic agents by the World Health Organization (WHO) and International Agency for Research on cancer. Moreover, the long-term exposure to low concentrations of these metals causes adverse health effects. Therefore, WHO controlled level of lead in drinking water is not over 10 ugL-1 [2]. Several methods have been used for the detection of lead such as atomic absorption spectrometry (AAS) [3–5], inductively coupled plasma mass spectrometry (ICP/MS) [6], inductively coupled plasma atomic emission spectroscopy (ICP/AES) [7], electrochemical method [8] and X-ray fluorescence spectrometry [9]. Although, these methods can detect lead sensitively and accurately, but there are limits in their complicated sample preparation processes, expensive, and required any specialized as well as sophisticated instrumentation [10]. Colorimetric sensors for Pb2+ determination attract much attention for their conveniences of visual observation and simple operations. They allow the direct analysis by the naked eyes without costly instruments compared with other methods. In recent year,gold nanoparticles (GNPs) have been widely used for colorimetric assays because their extinction coefficients are high relative to common organic compound [11-13].
GNPs have been
extensively employed as colorimetric sensors for the detection of small concentrations of toxic metals such as arsenic, cadmium, cobalt, nickel and lead [14-16]. Kim et al. used GNPs capped with 11-mercaptoundecanoic acid to be capable of detecting Pb2+ through the coordination between the carboxylic groups and Pb2+[17]. Moreover, Lu and co-workers reported a colorimetric sensor for Pb2+ detection using DNA-functionalized GNPs [18]. In
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2010, GNPs capped with gallic acid (GA–GNPs) for the detection of Pb2+ has been reported. Huang and co-workers have also demonstrated the aggregation of GA–GNPs in aqueous solutions and its minimum detectable concentration for Pb2+ in drinking water is 10 nM or 2.1 ugL-1 [12].
The detection limits of GA-GNPs are lower than the maximum allowable
contamination level of Pb2+ in drinking water (WHO). However, the European Food Safety Authority (EFSA) reported that even using a low concentration of Pb2+ in drinking water (2.1 ugL-1), adverse effect children’s intelligence development can be observed[19-20]. In the absence of a safe exposure limit of children to Pb2+ and because of its ability to accumulate in the body for a long time, a great interest in the evaluation of the adverse effects of Pb2+ in low concentrations has emerged. Moreover, Human Health State of the Science in Canada has studied the trace Pb2+ concentration in breast milk because it is good biomarkers of maternal and infant exposure to Pb2+. The Pb2+ level in human milk was found in the range from 0.025 to 15.8 ugL-1 in 210 mothers cross Canada [21-22]. Therefore, a highly sensitive, selective, simple and rapid method for the detection and quantification of trace Pb2+ is still required not only for the acceptance criteria of food safety but also toxicology. Maleic acid, which has two carboxylic groups (HO2CCH=CHCO2H), should be suitable for the modification of nanoparticles surface. In the previous reports, GNPs was modified by thiol compounds such as glutathiol [10], cysteine [23], alkyl phosphate [24] and 11-mercaptoundecanoic acid [25] for the determination of Pb2+ in micromole level but maleic acid functionalized GNPs has been not investigated for the colorimetric detection of Pb2+. Thus, the aim of this work was to develop the highly sensitive, selective, simple and rapid colorimetric sensor for trace Pb2+ determination using maleic acid modified GNPs. Maleic acid is easy to modify on GNPs surface within 1 h. MA-GNPs solution changed from red to blue color after the addition of Pb2+ and can be observed by the naked eye. The pH effect and
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the reaction time were studied in this work. The low limits of detection for Pb2+ at sub ugL-1 level with a short analysis time of 15 min were obtained by our proposed assay. Finally, our developed method was successfully applied for determination of trace levels of Pb2+in drinking water samples and the human breast milk samples. 2.Experimental 2.1 Chemicals and Materials All chemicals used in experiment were analytical reagent (AR) grade and solutions were prepared using high pure water with a resistance of 18 M: cm-1. Dithiothreitol (DTT), glutathione (Glu), homocysteine (Hcy), L-cysteine (L-cys), maleic acid (MA), metal ions (As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, Zn2+using atomic absorption grade), KCl, KNO3 and K2SO4 were bought from Sigma-Aldrich (St.Louis, Missouri). Whatman No.1 filter paper was bought from Cole-Parmer (Vernon Hills, IL). All glassware was thoroughly cleaned with freshly prepared 1:1 HCl/HNO3 and rinsed with high pure water prior to use. All metal ions stock solutions were prepared in 50 mM phosphate buffer pH 5.8. 2.2 Instrumentation UV–Visible absorption spectra were recorded in a quartz cuvette (1-cm pathlength) using a UV–Visible spectrometer (Lambda 35, Perkin Elmer Instruments, USA).
Size
distribution of particles was recorded by Transmission Electron Microscope (TEM, TECNAI T20 G2, FEI, Netherland).
Photographic results were recorded using a digital camera
(PowerShot S95, 10.1 Megapixels, Canon). An atomic absorption spectrometer (AAS) with a hollow cathode lamp and standard air/acetylene flame (Analyst 300, Perkin Elmer Instruments, USA) was used for atomic absorbance measurements. A hollow cathode lamp was used under the following operations conditions: wavelength: 283.3 nm; slit-width: 0.7H nm; lamp current: 10 mA.
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2.3 Synthesis of GNPs 100 mL of HAuCl4 (0.01%) was added into a 250 mL Erlenmeyer flask and then boiled. After that, 3.5 mL of trisodium citrate (1%) was added and further rapidly stirred for 15 min. We continually stirred for 30 min without heating. The solution was cooled to room temperature which was stored in the refrigerator 4 oC before further use [15]. The MA-GNPs solution was prepared using self-assembly of the organic compound on the GNP surface. A red of GNP solution (a 20 nm in diameter) was first prepared from GNPs stock solution. Then, 0.20 mL of 0.01 M MA was added into 0.40 mL of GNP solution to generate MA-GNPs. Organic compound was self-assembled on to the surface of GNPs by incubating the GNPs with the MA solutions for 1 h at room temperature. After this step, the GNP aggregation was characterized using UV–Visible Spectrometry. 2.4 Detection of lead 0.60 mL of MA-GNP solution in the eppendrof was mixed with 0.40 mL of metal ion solutions (As3+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) and anions solutions (KCl, KNO3 and K2SO4) in 50 mM phosphate buffer at pH 5.8. For background (Bg), 0.40 mL of buffer was mixed 0.60 mL of MA-GNP solution (Bg-MAGNPs). Then, the mixture was incubated for 15 min at the room temperature and analysis by the spectrometer and TEM. 2.5 Sample preparation for Transmission Electron Microscopy (TEM) Transmission electron microscope (TEM) measurements were performed on TECNAI T20 G2 instrument which operated at an accelerating voltage of 120 kV and the 25000X magnification. The sample solutions for TEM studies were prepared by placing a drop of GNPs, MA-GNPs, Bg-MA-GNPs and Pb2+-MA-GNPs on a formvar coated copper grid. The
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films on the TEM grids were allowed to dry for 1 h. The size of nanoparticle studies was performed in aqueous solution by Center of Nanoimaging, Mahidol University. 2.6 Applications To evaluate the utility of our proposed method, the Pb2+ in the drinking water samples from five different sources was quantified. Our method was validated against AAS. Prior to analysis by AAS, pre-concentration was carried out on all samples. 1.5 L of sample was mixed with 1 mL of 0.1 M HCl and then heated to evaporate excess water until 5.0 mL of samples remained. For AAS, samples were adjusted to a final volume of 10 mL with deionized water. For our proposed method, 0.60 mL of MA-GNP solution in the eppendrof was mixed with 0.40 mL of the water sample without any pretreatment. Then, the mixture was incubated for 15 min at the room temperature and analysis by spectrometer. For testing of trace levels of Pb2+ in the human breast milk, the sample was divided two parts. The first was analyzed by our method without spiking Pb2+ and the second was spiked with the standard Pb2+ solution at 10.0, 25.0 and 50.0 µgL-1 to obtain the final concentration at 1.0, 2.5 and 5.0 µgL-1, respectively. Prior to analysis, spiked samples were precipitated the protein by adding 0.75 mL of sample with 0.15 mL of 10% w/v TCA (Tri chloroacetic acid). After that, samples were stored at 4 0C for 15 minutes and then subjected to centrifugation at 14,500 rpm for 10 minutes. The precipitate was removed from the supernatant and kept only supernatant for analysis. 3. Results and discussion 3.1 Characterization of GNP aggregation Maleic acid has two carboxylic groups (HO2CCH=CHCO2H) so one carboxylic group should be suitable for the modification of nanoparticles surface and the other carboxylic group can capture Pb2+ in aqueous solution as shown in scheme 1. In this experiment, the
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color of solution change from dark pink to blue after adding 1.0 ugL-1 of Pb2+ in the MAGNPs solution (Fig. 1). MA-GNPs in the presence and absence of Pb2+ were characterized by UV-Vis Spectroscopy and Transmission Electron Microscope (TEM). A characteristic band of MA-GNPs was observed at approximate 520 nm. After the addition of Pb2+, the wavelength at 520 nm decreased and a new red-shifted change at 600 nm (Fig. 1), so Pb2+ can induce aggregation of MA-GNPs. To confirm the mechanism of the interaction between MA-GNPs and Pb2+, the solution of GNPs, MA-GNPs, Bg-MA-GNPs and Pb2+-MA-GNPs were analyzed by TEM as shown in Fig. S1. The prepared GNPs were dispersed an average particle size under a20 nm in diameter, whereas the nanoparticles remain isolated and randomly distributed in the absence of Pb2+ ions (Fig. S1 a-c). Upon addition of Pb2+into MA-GNPs, the solution turned blue color. TEM studies clearly indicate that Pb2+ induces aggregation of nanoparticles (Fig. S1 d). Possible mechanism is the obstructive aggregation of MA-GNPs in the absence of Pb2+ due to the electrostatic repulsion against van der Waals attraction of carboxylic of MA on the GNPs surface [13]. After the addition Pb2+, the other – COOH group of MA can binds with Pb2+ and it is specificity than other metals (Fig. 1) because of the coordination number of Pb2+ more over the other metal cations. Other metal cations interact only with lesser numbers of ligands, leaving the nanoparticles isolated; hence, no spectral change and no color of solution change were observed under the experimental conditions [26].
3.2 Selectivity Study We investigated the change in values of absorption ratio (A600/520) for MA-GNPs that measured after 15 minupon the addition of the metal ions. The concentration of other metal ions was studied for 15 minat higher than 100 times of Pb2+ concentration (1.0 ugL-1 of Pb2+ and 0.1 mgL-1 of As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+ and Zn2+). Most
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interference levels in this study were higher than the permissible limit in the drinking water by WHO (For example; 0.003, 0.05 and 0.02 mgL-1 for Cd2+, Co2+ and Ni2+, respectively). Moreover, interference effect of anions at the levels containing in drinking-water (250.0 mgL1
Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42- by WHO, 2004) was studied. The result
showed that the color of solution didn’t change to blue color after the addition of anions and other metal ions as shown in Fig. 1. The absorbance ratio (A600/520) of MA-GNPs with different metal ions and anions is shown in Fig. 2. Only Pb2+ can be observed a significant A600/520 value.
Possible mechanism is the unique coordination behavior of Pb2+ as
[Xe]4f145d106s2 electronic configuration. It appears as a borderline acid, able to bind to wide families of ligands within very flexible bond length and geometry so it allows the formation of a stable supramolecular complex. Other metal cations interact only with lesser numbers of ligands, leaving the nanoparticles isolated because of the rigid coordination geometry or may result from other factors e.g., the change in particle geometry. Hence, no spectral and color change were observed under the experimental conditions [2627]. On the aforementioned results, MA-GNPs can be utilized to detect Pb2+ with high selectivity. GNPs surface can be typically modified by carboxylic, amino, and thiols group to achieve selective cross-linking (and thus aggregation) therefore we also investigated the effect of cross-linking group in this part. DTT, Hcy, L-Cys and Glu were studied due to the active group in their molecules. All modified GNPs synthesized by our method showed an absorbance at 520 nm wavelength and observed a red solution. After adding 1.00 ugL-1 various metals including Pb2+, As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+ and Zn2+ in the solution of DTT-GNPs, Hcy-GNPs and L-Cys-GNPs at pH 5.8, the color of the solution for all metals changes from red to violet and spectra shifts from 520 nm to 600 nm (Fig. S2 a-c). Whereas, Glu-GNPs (Fig. S2 d) showed no change occurs, the absorption
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spectrum is still intact. Therefore, Glu-GNPs, DTT-GNPs, Hcy-GNPs and L-Cys-GNPs gave no specificity to Pb2+ under this condition. 3.3 Effect of pH and reaction time We investigated the colorimetric response of MA-GNPs with Pb2+ at different pH (5.8, 6.4, 7.4 and 8.0). Only MA-GNPs with Pb2+at pH 5.8 showed the color change and higher absorbance ratio (A600/520) than buffer (Bg). While at pH 6.4, 7.4 and 8.0 show no significant difference of the absorbance ratio (A600/520) and color solution between presence and absence of Pb2+ (Fig. 3). Additionally, Bg-MA-GNPs slightly change color at low pH ( 600 nm).
The value is not in a linear range.
Consequently, the concentration of
Pb2+ranging from 0.0 – 10.0 µgL-1 made this assay suitable for the determination of Pb2+ in aqueous solution. Compared with the other colorimetric methods based on nanoparticles (Table 2), our method has the higher sensitivity and more rapid. 3.5 Analytical Applications To validate our assay for the determination of Pb2+ in real samples, drinking water samples from 5 sources were analyzed by our assay and the traditional method (Atomic Absorption Spectroscopy, AAS) as shown in Table 3. The data were then compared by a paired t-test. Our results were not statistically significant different from the standard methods
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at the 95% confidence level (t-test value = 0.67, t critical value = 2.31). Moreover, we also evaluated the utility of our method by analysis low level of Pb2+ in human breast milk samples. We found that Pb2+ in the human breast milk samples were not detectable under our detection limit (0.5 µgL-1). Thus, known amounts of Pb2+ were spiked into milk samples to get the final concentration at 1.0, 2.5 and 5.0 µgL-1. It was found the level of Pb2+ at 1.09+0.20, 2.93+0.62, and 5.06+0.29 µgL-1, respectively (n=7) and the percentage recovery in the range 101-105 %. Therefore, the MA-GNPs can be used to measure the low amount of Pb2+ in real samples. It is an easy to measure without the need for analyze complex or expensive, used of less levels and does not require expert analysis.
4. Conclusions In summary, a simple, rapid, highly sensitive, easy-to-use, inexpensive, and portable alternative point-of-measurement monitoring for Pb2+ using MA-GNPs colorimetric assay has been developed. The Pb2+-induced MA-GNPs aggregation results in a marked red shift in the UV-Vis absorption spectra and a visible color change from red to blue. The detection limit of this method by the detection of naked eye is 0.5 ugL-1 which lower than other GNPs colorimetric probs. Furthermore, Pb2+ was clearly distinguish able color change from the other heavy metal ions under the optimum conditions at the critical level of Pb2+ in drinking water prescribed by WHO. Finally, our method was successfully applied to analysis of Pb2+ in water samples and the human breast milk samples. Therefore, this method should be applicable to detect low level of Pb2+ in drinking water and some biological samples.
Acknowledgements
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Orawon Chailapakul and Wijitar Dungchai gratefully acknowledge the financial support from Thailand Research Fund through TRF Senior Research Scholar (RTA5780005).
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(1997) 1997-1080.
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[12] K.W. Huang, C.J. Yu, and W.L. Tseng, Biosens. Bioelectron. 25 (2010) 984–989. [13] Z. Chen, Z. Wang, J. Chen, S. Wang, X. Huang, Analyst. 137 (2012) 3132-3137. [14]J.R. Kalluri, T. Arbneshi, S.A. Khan, A. Neely, P. Candice, B. Varisli, M. Washington, S. McAfee, B. Robinson, S. Banerjee, A.K. Singh, D. Senapati, P.C. Ray, Angew. Chem. Int. Ed. 48 (2009) 1–5 [15] M. Zhang, Y.Q. Liux, B.C., Ye, Analyst. 137 (2012) 601-607. [16] X.K. Li, Z.X. WANG, Chem. Res. Chinese Universities. 2 (2010) 194-197. [17] Y. Kim, R.C. Johnson, J.T. Hupp, Nano Lett. 1 (2001) 165–167. [18] J. Liu, Y. Lu, J. Am. Chem. Soc. 127 (2005) 12677-12683. [19] Lead Standard in Drinking Water, The SCHER. (2011). [20] EFSA Panel on Contaminants in the Food Chain (CONTAM), EFSA Journal 8 1147. Available online: http://www.efsa.europa.eu/en/efsajournal/pub/1570.htm. [21] The Minister of Health, Final Human Health State of the Science Report on Lead. (2013). Available online: http://www.hc-sc.gc.ca/ewh-semt/pubs/contaminants/dhhssrl-rpecscepsh/index-eng.php [22]G.A.K. Koyashiki1, M.M.B. Paoliello, P.B. Tchounwou, Rev. Environ. Health. 25 (2010) 243–253. [23] Y.P. Zhanga, J. Chena, L.Y. Baib, X.M. Zhoub, L.M. Wang, J. Chin. Chem. Soc. 57 (2010) 972-975. [24] S.K. Kim, S. Kim, E.J. Hong, M.S. Han, Korean Chem. Soc. 31 (2010) 38063808. [25] C. Fan, S. He, G. Liu, L. Wang, S. Song, Sensors. 12 (2012) 9467-9475. [26] K. Yoosaf, B.I. Ipe, C.H. Suresh, K.G. Thomas, J. Phys. Chem. C. 111 (2007) 1283912847.
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[27] L.S., Livny, J.P., Glusker, C.W., Bock, Inorganic Chemistry. 37 (1998) 1853-1867. [28] H. Wei, B. Li, J. Li, S. Dong E. Wang, Nanotechnology. 19 (2008) 1-5. [29] N. Ding, Q. Cao, H. Zhao, Y. Yang , L. Zeng, Y. He, K. Xiang, G. Wang, Sensors. 10 (2010) 11144-11155. [30] Y. Guo, Z. Wang, W. Qu, H. Shao, X. Jiang Biosens. Bioelectron. 26 (2011) 4064–4069.
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Figure captions Scheme 1 Schematic of aggregating process of MA-GNPs induced by adding Pb2+ Figure 1 UV–visible spectra of MA-GNPs solutions with cations (1.0 ugL-1 of Pb2+ and 0.1 mgL-1 of other cations) and anions ( 250.0 mgL-1 Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42following Guidelines for drinking-water quality by WHO, 2004)
Figure 2 The values (A600/520) of MA-GNPs upon the addition of 1.0 ugL-1 Pb2+ and 0.1 mgL1
of other cations and 250.0 mgL-1 Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42-. The error
bars represent standard deviations based on three independent measurements.
Figure 3 Effect of pH 0.6 µL of MA-GNPs mixed 0.4 µL of Pb2+(1.0 ugL-1) in phosphate buffer pH 5.8, 6.4, 7.4 and 8.0 for 15 min. Error bar at n = 3 Figure 4 Effect of reaction time between 0-60 minute (0.6 µL of MA-GNPs mixed 0.4 µL of Pb2+(1.0 ugL-1) in phosphate buffer pH 5.8) Error bar at n = 3 Figure 5 UV–visible spectra of MA-GNP solutions with various concentrations of Pb2+ in the range from 0.0 to 10.0 ugL-1 at 15 min.
Table 1 Nanoparticles optical assays for the detection of Pb2+
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Table 2 Levels of Pb2+ in drinking water samples were measured using our method and AAS.
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Table 1
Probe unit
LOD
Linear range
Real sample
Time
Ref.
(min) DNAzyme and GNPs
103.6µgL- N/Aa
N/Aa
20
[28]
N/Aa
30
[12]
N/Aa
[26]
Drinking water
N/Aa
[29]
N/Aa
N/Aa
N/Aa
[30]
N/Aa
N/Aa
[16]
N/Aa
15
[24]
Drinking water
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Our
1
Gallic acid–GNPs
2.1µgL-1
2.1-207.2 µgL-1
Gallic acid–GNPs or Gallic N/Aa
6.2-62.2 mgL- N/Aa
acid-AgNPs
1
Gallic acid–GNPs
5.2 µgL-1
10.4 -207.2 µgL-1
Papain-GNPs
41.4 µgL1
Cysteine-alanine-leacine-
20.7 µgL-
20.7 µgL-1-
asparagine-asparagine-
1
6.2 mgL-1
GNPs
10.4-41.4 mgL-1
Alkyl Phosphate-GNPs
Maleic acid-GNPs
621.6
0.0 -2.1 mgL-
µgL-1
1
0.5 µgL-1
0.0-10.0 µgL-
21 1
and milk
a = Not available
Water samples
Concentration of Pb2+ (µgL-1) AAS
Our method
Sample 1
6.74+0.02
6.42+0.51
Sample 2
7.71+0.03
7.95+1.38
Sample 3
7.90+0.01
9.21+0.77
method
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Sample 4
7.74+0.03
8.68+0.79
Sample 5
10.20+0.06
11.42+0.04
Table 2
The standard deviation of water samples at n = 5
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Highly Sensitive Colorimetric Detection of Lead Using Maleic acid Functionalized Gold nanoparticles
Nalin Ratnarathorn,a Orawon Chailapakul,b Wijitar Dungchaia,*
Highlights x Our colorimetric sensing provides highly sensitive detection for Pb2+ (0.5 PgL-1). x
The GNP modified with maleic acid has strong affinity to Pb2+.
x Our method can be used for the determination of Pb2+ within 15 min. x Our method was successfully applied for the Pb2+ determination in milk samples.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Highly sensitive colorimetric detection of lead using maleic acid functionalized gold nanoparticle Nalin Ratnarathorn, Orawon Chailapakul, Wijitar Dungchai
www.elsevier.com/locate/talanta
PII: DOI: Reference:
S0039-9140(14)00852-2 http://dx.doi.org/10.1016/j.talanta.2014.10.024 TAL15163
To appear in:
Talanta
Received date: 5 August 2014 Revised date: 6 October 2014 Accepted date: 10 October 2014 Cite this article as: Nalin Ratnarathorn, Orawon Chailapakul, Wijitar Dungchai, Highly sensitive colorimetric detection of lead using maleic acid functionalized gold nanoparticle, Talanta, http://dx.doi.org/10.1016/j.talanta.2014.10.024 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Highly Sensitive Colorimetric Detection of Lead Using Maleic Acid Functionalized Gold Nanoparticle
Nalin Ratnarathorn,a Orawon Chailapakul,b Wijitar Dungchaia,*
a
Department of Chemistry, Faculty of Science, King Mongkut’s University of Technology
Thonburi, Prachautid Road, Thungkru, Bangkok, 10140, Thailand b
Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials,
Chulalongkorn University, Patumwan, Bangkok, 10330, Thailand
Corresponding author: Dr. Wijitar Dungchai E-mail: [email protected] Fax: +66-02-470-8840 Tel: +66-02-470-9553
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Abstract
Highly sensitive colorimetric detection for Pb2+ has been developed using maleic acid (MA) functionalized GNP. The –COOH on MA was used to modify GNP surface whereas the other –COOH functional group have strong affinity to coordination behavior of Pb2+ allowing the selective formation more than other ions. MA-GNPs solution changed from red to blue color after the addition of Pb2+ due to nanoparticle aggregation. The different optical absorption and discriminate of particle size between the MA-GNPs solution with and without Pb2+ were characterized by UV-Visible spectroscopy and transmission electron microscopy (TEM), respectively. The color intensity as a function of Pb2+ concentration gave a linear response in the range of 0.0–10.0 µgL-1 (R2 = 0.990). The detection limit was found at 0.5 µgL-1 by naked eye and can be completed the analysis within 15 min. The MA-GNPs aggregated with Pb2+ showed high selectivity when was compared to other metal ions (As3+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) and anions (Cl-, NO3- and SO42-). Our proposed method was also applied for the determination of Pb2+ in real drinking water samples from 5 sources. The result of real water samples were not statistically significant different from the standard methods at the 95% confidence level (pair t-test method). Moreover, we evaluated our proposed method for the determination of trace Pb2+ concentration in real breast milk samples. The recoveries were acceptable and ranged from 101–104% for spiked Pb2+ in real breast milk samples. Thus, MA-GNP colorimetric sensing provides a simple, rapid, sensitive, easy-to-use, inexpensive and low detection limit for the monitoring of Pb2+.
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Keywords: Colorimetric sensing, Gold nanoparticle, Lead
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1. Introduction The present food and drinking water are often contaminated with harmful substances for humans, either as part of the production process, natural or caused by the additives added to it. Lead (Pb2+) is a major environmental pollutant and ranks second in the list of toxic substances that cause renal malfunction and damage to the brain and kidneys [1]. It has also been classified as carcinogenic agents by the World Health Organization (WHO) and International Agency for Research on cancer. Moreover, the long-term exposure to low concentrations of these metals causes adverse health effects. Therefore, WHO controlled level of lead in drinking water is not over 10 ugL-1 [2]. Several methods have been used for the detection of lead such as atomic absorption spectrometry (AAS) [3–5], inductively coupled plasma mass spectrometry (ICP/MS) [6], inductively coupled plasma atomic emission spectroscopy (ICP/AES) [7], electrochemical method [8] and X-ray fluorescence spectrometry [9]. Although, these methods can detect lead sensitively and accurately, but there are limits in their complicated sample preparation processes, expensive, and required any specialized as well as sophisticated instrumentation [10]. Colorimetric sensors for Pb2+ determination attract much attention for their conveniences of visual observation and simple operations. They allow the direct analysis by the naked eyes without costly instruments compared with other methods. In recent year,gold nanoparticles (GNPs) have been widely used for colorimetric assays because their extinction coefficients are high relative to common organic compound [11-13].
GNPs have been
extensively employed as colorimetric sensors for the detection of small concentrations of toxic metals such as arsenic, cadmium, cobalt, nickel and lead [14-16]. Kim et al. used GNPs capped with 11-mercaptoundecanoic acid to be capable of detecting Pb2+ through the coordination between the carboxylic groups and Pb2+[17]. Moreover, Lu and co-workers reported a colorimetric sensor for Pb2+ detection using DNA-functionalized GNPs [18]. In
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2010, GNPs capped with gallic acid (GA–GNPs) for the detection of Pb2+ has been reported. Huang and co-workers have also demonstrated the aggregation of GA–GNPs in aqueous solutions and its minimum detectable concentration for Pb2+ in drinking water is 10 nM or 2.1 ugL-1 [12].
The detection limits of GA-GNPs are lower than the maximum allowable
contamination level of Pb2+ in drinking water (WHO). However, the European Food Safety Authority (EFSA) reported that even using a low concentration of Pb2+ in drinking water (2.1 ugL-1), adverse effect children’s intelligence development can be observed[19-20]. In the absence of a safe exposure limit of children to Pb2+ and because of its ability to accumulate in the body for a long time, a great interest in the evaluation of the adverse effects of Pb2+ in low concentrations has emerged. Moreover, Human Health State of the Science in Canada has studied the trace Pb2+ concentration in breast milk because it is good biomarkers of maternal and infant exposure to Pb2+. The Pb2+ level in human milk was found in the range from 0.025 to 15.8 ugL-1 in 210 mothers cross Canada [21-22]. Therefore, a highly sensitive, selective, simple and rapid method for the detection and quantification of trace Pb2+ is still required not only for the acceptance criteria of food safety but also toxicology. Maleic acid, which has two carboxylic groups (HO2CCH=CHCO2H), should be suitable for the modification of nanoparticles surface. In the previous reports, GNPs was modified by thiol compounds such as glutathiol [10], cysteine [23], alkyl phosphate [24] and 11-mercaptoundecanoic acid [25] for the determination of Pb2+ in micromole level but maleic acid functionalized GNPs has been not investigated for the colorimetric detection of Pb2+. Thus, the aim of this work was to develop the highly sensitive, selective, simple and rapid colorimetric sensor for trace Pb2+ determination using maleic acid modified GNPs. Maleic acid is easy to modify on GNPs surface within 1 h. MA-GNPs solution changed from red to blue color after the addition of Pb2+ and can be observed by the naked eye. The pH effect and
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the reaction time were studied in this work. The low limits of detection for Pb2+ at sub ugL-1 level with a short analysis time of 15 min were obtained by our proposed assay. Finally, our developed method was successfully applied for determination of trace levels of Pb2+in drinking water samples and the human breast milk samples. 2.Experimental 2.1 Chemicals and Materials All chemicals used in experiment were analytical reagent (AR) grade and solutions were prepared using high pure water with a resistance of 18 M: cm-1. Dithiothreitol (DTT), glutathione (Glu), homocysteine (Hcy), L-cysteine (L-cys), maleic acid (MA), metal ions (As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, Zn2+using atomic absorption grade), KCl, KNO3 and K2SO4 were bought from Sigma-Aldrich (St.Louis, Missouri). Whatman No.1 filter paper was bought from Cole-Parmer (Vernon Hills, IL). All glassware was thoroughly cleaned with freshly prepared 1:1 HCl/HNO3 and rinsed with high pure water prior to use. All metal ions stock solutions were prepared in 50 mM phosphate buffer pH 5.8. 2.2 Instrumentation UV–Visible absorption spectra were recorded in a quartz cuvette (1-cm pathlength) using a UV–Visible spectrometer (Lambda 35, Perkin Elmer Instruments, USA).
Size
distribution of particles was recorded by Transmission Electron Microscope (TEM, TECNAI T20 G2, FEI, Netherland).
Photographic results were recorded using a digital camera
(PowerShot S95, 10.1 Megapixels, Canon). An atomic absorption spectrometer (AAS) with a hollow cathode lamp and standard air/acetylene flame (Analyst 300, Perkin Elmer Instruments, USA) was used for atomic absorbance measurements. A hollow cathode lamp was used under the following operations conditions: wavelength: 283.3 nm; slit-width: 0.7H nm; lamp current: 10 mA.
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2.3 Synthesis of GNPs 100 mL of HAuCl4 (0.01%) was added into a 250 mL Erlenmeyer flask and then boiled. After that, 3.5 mL of trisodium citrate (1%) was added and further rapidly stirred for 15 min. We continually stirred for 30 min without heating. The solution was cooled to room temperature which was stored in the refrigerator 4 oC before further use [15]. The MA-GNPs solution was prepared using self-assembly of the organic compound on the GNP surface. A red of GNP solution (a 20 nm in diameter) was first prepared from GNPs stock solution. Then, 0.20 mL of 0.01 M MA was added into 0.40 mL of GNP solution to generate MA-GNPs. Organic compound was self-assembled on to the surface of GNPs by incubating the GNPs with the MA solutions for 1 h at room temperature. After this step, the GNP aggregation was characterized using UV–Visible Spectrometry. 2.4 Detection of lead 0.60 mL of MA-GNP solution in the eppendrof was mixed with 0.40 mL of metal ion solutions (As3+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) and anions solutions (KCl, KNO3 and K2SO4) in 50 mM phosphate buffer at pH 5.8. For background (Bg), 0.40 mL of buffer was mixed 0.60 mL of MA-GNP solution (Bg-MAGNPs). Then, the mixture was incubated for 15 min at the room temperature and analysis by the spectrometer and TEM. 2.5 Sample preparation for Transmission Electron Microscopy (TEM) Transmission electron microscope (TEM) measurements were performed on TECNAI T20 G2 instrument which operated at an accelerating voltage of 120 kV and the 25000X magnification. The sample solutions for TEM studies were prepared by placing a drop of GNPs, MA-GNPs, Bg-MA-GNPs and Pb2+-MA-GNPs on a formvar coated copper grid. The
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films on the TEM grids were allowed to dry for 1 h. The size of nanoparticle studies was performed in aqueous solution by Center of Nanoimaging, Mahidol University. 2.6 Applications To evaluate the utility of our proposed method, the Pb2+ in the drinking water samples from five different sources was quantified. Our method was validated against AAS. Prior to analysis by AAS, pre-concentration was carried out on all samples. 1.5 L of sample was mixed with 1 mL of 0.1 M HCl and then heated to evaporate excess water until 5.0 mL of samples remained. For AAS, samples were adjusted to a final volume of 10 mL with deionized water. For our proposed method, 0.60 mL of MA-GNP solution in the eppendrof was mixed with 0.40 mL of the water sample without any pretreatment. Then, the mixture was incubated for 15 min at the room temperature and analysis by spectrometer. For testing of trace levels of Pb2+ in the human breast milk, the sample was divided two parts. The first was analyzed by our method without spiking Pb2+ and the second was spiked with the standard Pb2+ solution at 10.0, 25.0 and 50.0 µgL-1 to obtain the final concentration at 1.0, 2.5 and 5.0 µgL-1, respectively. Prior to analysis, spiked samples were precipitated the protein by adding 0.75 mL of sample with 0.15 mL of 10% w/v TCA (Tri chloroacetic acid). After that, samples were stored at 4 0C for 15 minutes and then subjected to centrifugation at 14,500 rpm for 10 minutes. The precipitate was removed from the supernatant and kept only supernatant for analysis. 3. Results and discussion 3.1 Characterization of GNP aggregation Maleic acid has two carboxylic groups (HO2CCH=CHCO2H) so one carboxylic group should be suitable for the modification of nanoparticles surface and the other carboxylic group can capture Pb2+ in aqueous solution as shown in scheme 1. In this experiment, the
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color of solution change from dark pink to blue after adding 1.0 ugL-1 of Pb2+ in the MAGNPs solution (Fig. 1). MA-GNPs in the presence and absence of Pb2+ were characterized by UV-Vis Spectroscopy and Transmission Electron Microscope (TEM). A characteristic band of MA-GNPs was observed at approximate 520 nm. After the addition of Pb2+, the wavelength at 520 nm decreased and a new red-shifted change at 600 nm (Fig. 1), so Pb2+ can induce aggregation of MA-GNPs. To confirm the mechanism of the interaction between MA-GNPs and Pb2+, the solution of GNPs, MA-GNPs, Bg-MA-GNPs and Pb2+-MA-GNPs were analyzed by TEM as shown in Fig. S1. The prepared GNPs were dispersed an average particle size under a20 nm in diameter, whereas the nanoparticles remain isolated and randomly distributed in the absence of Pb2+ ions (Fig. S1 a-c). Upon addition of Pb2+into MA-GNPs, the solution turned blue color. TEM studies clearly indicate that Pb2+ induces aggregation of nanoparticles (Fig. S1 d). Possible mechanism is the obstructive aggregation of MA-GNPs in the absence of Pb2+ due to the electrostatic repulsion against van der Waals attraction of carboxylic of MA on the GNPs surface [13]. After the addition Pb2+, the other – COOH group of MA can binds with Pb2+ and it is specificity than other metals (Fig. 1) because of the coordination number of Pb2+ more over the other metal cations. Other metal cations interact only with lesser numbers of ligands, leaving the nanoparticles isolated; hence, no spectral change and no color of solution change were observed under the experimental conditions [26].
3.2 Selectivity Study We investigated the change in values of absorption ratio (A600/520) for MA-GNPs that measured after 15 minupon the addition of the metal ions. The concentration of other metal ions was studied for 15 minat higher than 100 times of Pb2+ concentration (1.0 ugL-1 of Pb2+ and 0.1 mgL-1 of As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+ and Zn2+). Most
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interference levels in this study were higher than the permissible limit in the drinking water by WHO (For example; 0.003, 0.05 and 0.02 mgL-1 for Cd2+, Co2+ and Ni2+, respectively). Moreover, interference effect of anions at the levels containing in drinking-water (250.0 mgL1
Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42- by WHO, 2004) was studied. The result
showed that the color of solution didn’t change to blue color after the addition of anions and other metal ions as shown in Fig. 1. The absorbance ratio (A600/520) of MA-GNPs with different metal ions and anions is shown in Fig. 2. Only Pb2+ can be observed a significant A600/520 value.
Possible mechanism is the unique coordination behavior of Pb2+ as
[Xe]4f145d106s2 electronic configuration. It appears as a borderline acid, able to bind to wide families of ligands within very flexible bond length and geometry so it allows the formation of a stable supramolecular complex. Other metal cations interact only with lesser numbers of ligands, leaving the nanoparticles isolated because of the rigid coordination geometry or may result from other factors e.g., the change in particle geometry. Hence, no spectral and color change were observed under the experimental conditions [2627]. On the aforementioned results, MA-GNPs can be utilized to detect Pb2+ with high selectivity. GNPs surface can be typically modified by carboxylic, amino, and thiols group to achieve selective cross-linking (and thus aggregation) therefore we also investigated the effect of cross-linking group in this part. DTT, Hcy, L-Cys and Glu were studied due to the active group in their molecules. All modified GNPs synthesized by our method showed an absorbance at 520 nm wavelength and observed a red solution. After adding 1.00 ugL-1 various metals including Pb2+, As3+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+ and Zn2+ in the solution of DTT-GNPs, Hcy-GNPs and L-Cys-GNPs at pH 5.8, the color of the solution for all metals changes from red to violet and spectra shifts from 520 nm to 600 nm (Fig. S2 a-c). Whereas, Glu-GNPs (Fig. S2 d) showed no change occurs, the absorption
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spectrum is still intact. Therefore, Glu-GNPs, DTT-GNPs, Hcy-GNPs and L-Cys-GNPs gave no specificity to Pb2+ under this condition. 3.3 Effect of pH and reaction time We investigated the colorimetric response of MA-GNPs with Pb2+ at different pH (5.8, 6.4, 7.4 and 8.0). Only MA-GNPs with Pb2+at pH 5.8 showed the color change and higher absorbance ratio (A600/520) than buffer (Bg). While at pH 6.4, 7.4 and 8.0 show no significant difference of the absorbance ratio (A600/520) and color solution between presence and absence of Pb2+ (Fig. 3). Additionally, Bg-MA-GNPs slightly change color at low pH ( 600 nm).
The value is not in a linear range.
Consequently, the concentration of
Pb2+ranging from 0.0 – 10.0 µgL-1 made this assay suitable for the determination of Pb2+ in aqueous solution. Compared with the other colorimetric methods based on nanoparticles (Table 2), our method has the higher sensitivity and more rapid. 3.5 Analytical Applications To validate our assay for the determination of Pb2+ in real samples, drinking water samples from 5 sources were analyzed by our assay and the traditional method (Atomic Absorption Spectroscopy, AAS) as shown in Table 3. The data were then compared by a paired t-test. Our results were not statistically significant different from the standard methods
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at the 95% confidence level (t-test value = 0.67, t critical value = 2.31). Moreover, we also evaluated the utility of our method by analysis low level of Pb2+ in human breast milk samples. We found that Pb2+ in the human breast milk samples were not detectable under our detection limit (0.5 µgL-1). Thus, known amounts of Pb2+ were spiked into milk samples to get the final concentration at 1.0, 2.5 and 5.0 µgL-1. It was found the level of Pb2+ at 1.09+0.20, 2.93+0.62, and 5.06+0.29 µgL-1, respectively (n=7) and the percentage recovery in the range 101-105 %. Therefore, the MA-GNPs can be used to measure the low amount of Pb2+ in real samples. It is an easy to measure without the need for analyze complex or expensive, used of less levels and does not require expert analysis.
4. Conclusions In summary, a simple, rapid, highly sensitive, easy-to-use, inexpensive, and portable alternative point-of-measurement monitoring for Pb2+ using MA-GNPs colorimetric assay has been developed. The Pb2+-induced MA-GNPs aggregation results in a marked red shift in the UV-Vis absorption spectra and a visible color change from red to blue. The detection limit of this method by the detection of naked eye is 0.5 ugL-1 which lower than other GNPs colorimetric probs. Furthermore, Pb2+ was clearly distinguish able color change from the other heavy metal ions under the optimum conditions at the critical level of Pb2+ in drinking water prescribed by WHO. Finally, our method was successfully applied to analysis of Pb2+ in water samples and the human breast milk samples. Therefore, this method should be applicable to detect low level of Pb2+ in drinking water and some biological samples.
Acknowledgements
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Orawon Chailapakul and Wijitar Dungchai gratefully acknowledge the financial support from Thailand Research Fund through TRF Senior Research Scholar (RTA5780005).
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Figure captions Scheme 1 Schematic of aggregating process of MA-GNPs induced by adding Pb2+ Figure 1 UV–visible spectra of MA-GNPs solutions with cations (1.0 ugL-1 of Pb2+ and 0.1 mgL-1 of other cations) and anions ( 250.0 mgL-1 Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42following Guidelines for drinking-water quality by WHO, 2004)
Figure 2 The values (A600/520) of MA-GNPs upon the addition of 1.0 ugL-1 Pb2+ and 0.1 mgL1
of other cations and 250.0 mgL-1 Cl-, 45.0 mgL-1 NO3- and 200.0 mgL-1 SO42-. The error
bars represent standard deviations based on three independent measurements.
Figure 3 Effect of pH 0.6 µL of MA-GNPs mixed 0.4 µL of Pb2+(1.0 ugL-1) in phosphate buffer pH 5.8, 6.4, 7.4 and 8.0 for 15 min. Error bar at n = 3 Figure 4 Effect of reaction time between 0-60 minute (0.6 µL of MA-GNPs mixed 0.4 µL of Pb2+(1.0 ugL-1) in phosphate buffer pH 5.8) Error bar at n = 3 Figure 5 UV–visible spectra of MA-GNP solutions with various concentrations of Pb2+ in the range from 0.0 to 10.0 ugL-1 at 15 min.
Table 1 Nanoparticles optical assays for the detection of Pb2+
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Table 2 Levels of Pb2+ in drinking water samples were measured using our method and AAS.
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Table 1
Probe unit
LOD
Linear range
Real sample
Time
Ref.
(min) DNAzyme and GNPs
103.6µgL- N/Aa
N/Aa
20
[28]
N/Aa
30
[12]
N/Aa
[26]
Drinking water
N/Aa
[29]
N/Aa
N/Aa
N/Aa
[30]
N/Aa
N/Aa
[16]
N/Aa
15
[24]
Drinking water
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Our
1
Gallic acid–GNPs
2.1µgL-1
2.1-207.2 µgL-1
Gallic acid–GNPs or Gallic N/Aa
6.2-62.2 mgL- N/Aa
acid-AgNPs
1
Gallic acid–GNPs
5.2 µgL-1
10.4 -207.2 µgL-1
Papain-GNPs
41.4 µgL1
Cysteine-alanine-leacine-
20.7 µgL-
20.7 µgL-1-
asparagine-asparagine-
1
6.2 mgL-1
GNPs
10.4-41.4 mgL-1
Alkyl Phosphate-GNPs
Maleic acid-GNPs
621.6
0.0 -2.1 mgL-
µgL-1
1
0.5 µgL-1
0.0-10.0 µgL-
21 1
and milk
a = Not available
Water samples
Concentration of Pb2+ (µgL-1) AAS
Our method
Sample 1
6.74+0.02
6.42+0.51
Sample 2
7.71+0.03
7.95+1.38
Sample 3
7.90+0.01
9.21+0.77
method
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Sample 4
7.74+0.03
8.68+0.79
Sample 5
10.20+0.06
11.42+0.04
Table 2
The standard deviation of water samples at n = 5
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Highly Sensitive Colorimetric Detection of Lead Using Maleic acid Functionalized Gold nanoparticles
Nalin Ratnarathorn,a Orawon Chailapakul,b Wijitar Dungchaia,*
Highlights x Our colorimetric sensing provides highly sensitive detection for Pb2+ (0.5 PgL-1). x
The GNP modified with maleic acid has strong affinity to Pb2+.
x Our method can be used for the determination of Pb2+ within 15 min. x Our method was successfully applied for the Pb2+ determination in milk samples.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
