Abstract
Silver nanoparticles (AgNPs) were biologically synthesized in an eco-friendly manner using aqueous leaf extract of Origanum majorana plant and silver nitrate (AgNO3) solution. Size, shape, and crystallinity of the biosynthesized AgNPs were determined by using a transmission electron microscope (TEM). Zeta potential analyzer was used to prove the stability of the metallic nanoparticles, while Fourier transform infrared spectroscopy was used to identify the bioreducing and capping agents. AgNPs were electrochemically investigated using cyclic voltammetry (CV), while the optical properties of the metallic nanoparticles were studied using UV-Vis and fluorescence spectroscopies. According to TEM images, AgNPs are spherical with an average size of 35 nm. TEM also refers to the presence of mono and polycrystalline AgNPs. The value of zeta potential (−39 mV) proved the stability of AgNPs caused by capping molecules of O. majorana plant. CV studies showed that AgNPs were electrochemically investigated at 0.39 mV. AgNPs showed a surface plasmon resonance peak at 440 nm, while the emission peak was detected at 466 nm. These nanoparticles are promising for many industrial and medical applications.
1 Introduction
Nanochemistry is defined as a field that deals with the synthesis of nanostructures studying their size- and shape-dependent physical and chemical features [1]. Synthesis of metal nanoparticles is regarded as an important aspect of nanochemistry research. Silver nanoparticles (AgNPs) exhibit more preferred properties than other metal nanoparticles like gold, copper, and palladium [2]. AgNPs have unusual catalytic, chemical, magnetic, optical, electronic, photo electrochemical, and biological labeling criteria [3, 4]. There are a variety of physical and chemical ways to synthesize silver nanoparticles including electrochemical, laser ablation, γ-radiation, photochemical, and chemical reduction methods [5]. Bioreduction using fungi [6], bacteria [7], cyanobacteria [8], or plant biomass [9] is an alternative to chemical and physical methods for the production of AgNPs in an eco-friendly manner. The green synthesis process of AgNPs involves mainly the selection of nontoxic solvent, nontoxic reducing agent, and environmentally benign capping substances [10]. Previous studies investigated Plectranthus amboinicus [5], Myrmecodia pendan [11], Boerhaavia diffusa [2], Caesalpinia coriaria [12], Origanum vulgare [13], and Iresine herbstii [14] extracts for the biosynthesis of AgNPs. Origanum majorana of Lamiaceae family is mainly distributed in the Mediterranean region [15]. The antioxidant activity of O. majorana was documented [16]. To the best of our knowledge, this is the first study directed towards Egyptian O. majorana plant extract as a reducing and capping agent for the biosynthesis of AgNPs. The work has been done as part of our ongoing project of synthesis of metal nanoparticles [17, 18]. In the present study, a green method has been used for the synthesis of AgNPs employing aqueous leaf extract of O. majorana followed by characterization of their electrochemical and optical properties.
2 Materials and methods
2.1 Materials
Fresh leaves of O. majorana were collected from the Research Centre of the Medicinal and Aromatic Plants, El- Kanater, El- Qalyoubeyah, Egypt during 2013. It was authenticated by Prof. Dr. Zaki Turki, Department of Botany, Faculty of Science, El-Menoufia University where voucher specimen NO B15 was kept at the Botany Department Herbarium. The leaves were washed by distilled water to remove dust, shade-dried for 3 weeks, then powdered using grinding mill. Silver nitrate (99.8% pure) was purchased from Cambrian chemicals (Oakville, ON, Canada).
2.2 Biosynthesis of silver nanoparticles
The aqueous extract was obtained by heating a mixture of 2.5 g of the obtained powder and 400 ml of distilled water in a bath for 5 min at 60°C. The extract was kept in refrigerator at 4°C for a week then filtered using Whatman No 42 filter paper. Some 7 ml of the prepared extract was added to 165 ml aqueous solution of 2 mm silver nitrate. The mixture was heated for 1 h at 60°C using a water bath. Finally, the obtained solution was centrifuged at 6000 rpm for 45 min and kept till further use.
2.3 Characterization of the AgNPs
A transmission electron microscope (TEM) [JEM-2100 (JEOL), Tokyo, Japan] was used to determine the size, shape, and crystallinity of the nanoparticles. A small aliquot of the nanoparticles suspension was left in the ultrasonic apparatus for 25 min. A drop from the aqueous suspension was placed on a copper grid coated with carbon film. The specimen was placed in an oven to dry at ambient temperature prior to further examination. A sample from AgNPs suspension was subjected to Fourier transform infrared (FT-IR) spectroscopy (IR100/IR 200 Spectrometer, VA, USA) and measured at a wavelength of 4000–400 cm−1. The stability of the formed nanoparticles was determined via zeta potential analyzer (ZetaPALS, Brookhaven, Holtsville, NY, USA).
2.4 Electrochemical properties of AgNPs
Cyclic voltammetry (CV) (MF-9002 BASi Epsilon, West Lafayette, IN, USA) was used in the electrochemical measurement of the biosynthezied AgNPs. Three-electrode system was used to perform the CV measurement. The electrodes used were glassy carbon as the working electrode, Pt wire as the counter electrode, and silver/silver chloride as the reference electrode. The supporting electrolyte was pH 7.4 phosphate buffer solution (PBS, Sigma Aldrich, USA). We mixed 3 ml of AgNPs with 7 ml of pH 7.4 PBS before the electrochemical analysis.
2.5 Optical properties of AgNPs
An ultraviolet visible (UV-Vis) spectrophotometer (UV-2450, Shimadzu, Tokyo, Japan) and a spectrofluorophotometer (RF-5301PC, Shimadzu, Tokyo, Japan) were used to study the optical properties of the biosynthesized AgNPs. The UV-Vis spectrophotometer was used to monitor the absorption or surface plasmon resonance (SPR) peak of the AgNPs. A diluted aliquot of the nanoparticles suspension was subjected to the apparatus at the wavelength of 200–800 nm. The fluorescence phenomenon of AgNPs was monitored using spectrofluorophotometer.
3 Results and discussion
3.1 Biosynthesis of silver nanoparticles
The biosynthesis of AgNPs was indicated visually by the observation of color change from yellow to brown (Figure 1). The UV-Vis spectra of the AgNPs have a strong band in the visible region ranging from 350 to 550 nm [11]. Figure 2 exhibits UV-Vis absorption peak of the biosynthesized AgNPs at 440 nm confirming the formation of AgNPs. The absorption peaks that appeared in the region of 410–450 nm were attributed to the formation of the spherical silver nanoparticles [19, 20].
3.2 Characterization of the AgNPs
Supporting the UV-Vis spectroscopy predictions, TEM images (Figure 3A–C) show that AgNPs are spherical with a small percentage of elongated particles where the particle sizes are in the range of 25–50 nm (average size of 35 nm). Figure 3D shows the diffraction pattern of the metallic nanoparticles which reveals that the nanoparticles are crystalline in nature. The diffraction rings refer to the presence of polycrystalline nanoparticles while diffraction dots refer to the single crystals.
The FT-IR spectroscopy was used to identify the functional groups present in the AgNPs suspension and could be responsible for the metal ion (Ag+) reduction and nanoparticles stability [11, 21]. Figure 4A shows the FT-IR spectrum of the biosynthesized AgNPs. The broad band at 3395 cm−1 is due to N–H and O–H stretching modes. Peaks at 2922 and 2861 cm−1 correspond to C–H stretching. The peak at 1639.97 cm−1 can be attributed to carbonyl stretch of amides originated from the plant proteins [20]. The stretching frequency of N–H band is broad in nature due to its involvement in the coordination within AgNPs [10]. We observed a negative zeta potential (−39 mV) of the biosynthesized AgNPs (Figure 4B). Metallic nanoparticles with zeta potentials more positive than +30 mV or more negative than −30 mV are considered stable [22]. In this study, the biosynthesized AgNPs showed stability exceeded 6 months. Zeta potential of the nanoparticles depends on many parameters including the pH and the electrolyte concentration of the suspension [3]. The stability of our biosynthesized AgNPs using O. majorana is higher than the stability of AgNPs biosynthesized by other plants such as Ambrosia maritima [17], Calendula officinalis [18], O. vulgare [13], Phytolacca decandra, Gelsemium sempervirens, Hydrastis canadensis, and Thuja occidentalis [10] which were reported previously.
These highly stable AgNPs could be used in many applications. They can be used as coating material of pipes and reservoirs in water treatment plant to resist the formation of biofilm which have many drawbacks including corrosion of the metals [17].
3.3 Electrochemical properties
The green synthesized AgNPs were electrochemically detected based on the Faradaic charge transfer when AgNPs strike an electrode [23]. The cyclic voltammogram was shown in Figure 5. The AgNPs were detected at 0.39 mV at a scan rate of 100 mV S−1. The anodic peak current was 24 μA at this potential. The anodic peak was resulted from the oxidation of metal nanoparticles at the glassy carbon electrode. The contribution to the Faradic current due to the side reactions is little as the concentration is extremely low compared to AgNPs concentration [22]. There is a reduction of the formed Ag+ ions in every cycle which lead to the nucleation of silver nanoparticles at the glassy carbon electrode and the metallic nanoparticles surfaces [24].
3.4 Optical properties
The attractive optical properties of AgNPs make them applicable in photonics, optical limiting, optical devices, and optical signal processing [4, 25, 26]. Silver nanoparticles exhibit interesting optical properties related to SPR resulting from the collective oscillation of the surface electrons in metal nanoparticles [27]. This oscillation is due to the interaction of metal electrons and the incident light at the interface between metal and a dielectric medium [28]. The SPR band of the biosynthesized AgNPs was shown in Figure 2. For the nanoparticles, the maximum absorbance intensity and bandwidth of the SPR band depend on the medium and other the surroundings [29]. The fluorescence phenomenon of the excited electron at a wavelength of 340 nm was observed in Figure 6. The fluorescence spectrum was shifted to higher wavelength (466 nm) compared to the corresponding absorption spectrum. As a consequence, AgNPs can be used in the construction of optical sensors based on the special optical properties [30]. These nanoparticles can be embedded in glass or deposited on the top of antireflection layer of the solar cell to reduce the light reflection [17].
4 Conclusion
We documented a green synthesis of AgNPs with O. majorana plant. The AgNPs were indicated visually and confirmed by UV-Vis spectrophotometer. TEM ensured that the nanoparticles are spherical and in the size range of 25–50 nm. The diffraction pattern clarified that there is single and polycrystalline metal nanoparticles. FT-IR spectroscopy data showed that AgNPs are capped by protein molecules. CV was used in the electrochemical characterization of AgNPs using a glassy carbon as a working electrode. The optical properties are studied through UV-Vis spectrophotometer and spectrofluorophotometer.
About the authors
Moustafa Zahran earned his Bachelor’s degree in chemistry (2012) and his Master’s degree in organic chemistry (2016) from El-Menoufia University, Shebin El-Kom, Egypt. His research focused on the green synthesis of metallic nanoparticles using plant extracts studying their electrochemical and optical properties. He has published a paper entitled “Spectral characterisation of the silver nanoparticles biosynthesised using Ambrosiamaritima plant.”
Maged El-Kemary is a professor of photo- and nanochemistry, Chemistry Department, Faculty of Science, Kafrelsheikh University. He obtained his Bachelor’s degree (1981), Master’s degree (1987) and PhD degree (1991) in chemistry from Tanta University, Tanta, Egypt. He is an editorial board member of the International Journal of Materials and Chemistry and Nanoscience and Nanotechnology Research. Currently, he is the president of KafrelSheikh University.
Shaden Khalifa is a certified Swedish physician with a Bachelor’s degree in medical and surgical sciences. She has completed her Master’s degree in biomedical science at Uppsala University and her PhD at Karolinska Institute, Stockholm, Sweden. Shaden spent 2 years as visiting researcher at Keio University, Japan. Dr. Shaden has published 20 papers in reputed journals, most of which are within the area of tissue engineering and regenerative medicine.
Hesham El-Seedi is working in the area of natural products chemistry. He is a former fellow of the Japanese Society of Promotion of Science as a visiting assistant professor, Department of Chemistry, Faculty of Science and Technology, Keio University, Japan. He worked in internationally recognized laboratories including Kunglia Tekniska högskola (KTH), Stockholm, Sweden, Uppsala Biomedical Center, Uppsala University, Sweden, University of Malaya, and Menoufia University, Egypt.
References
[1] Zuo Y, Chen G, Zeng G, Li Z, Yan M, Chen A, Guo Z, Huang Z, Tan Q. J. Hazard. Mater. 2015, 285, 236–244.10.1016/j.jhazmat.2014.12.003Search in Google Scholar PubMed
[2] Kumar PPNV, Pammi SVN, Kollu P, Satyanarayana KVV, Shameem U. Ind. Crops Prod. 2014, 52, 562–566.10.1016/j.indcrop.2013.10.050Search in Google Scholar
[3] Sharma VK, Yngard RA, Lin Y. Adv. Colloid Interface Sci. 2009, 145, 83–96.10.1016/j.cis.2008.09.002Search in Google Scholar PubMed
[4] Ara MHM, Javadi Z, Sirohi RS. Optik 2011, 122, 1961–1964.10.1016/j.ijleo.2010.11.025Search in Google Scholar
[5] Ajitha B, Reddy YK, Reddy PS. Spectrochim. Acta Part A 2014, 128, 257–262.10.1016/j.saa.2014.02.105Search in Google Scholar PubMed
[6] Devi LS, Bareh DA, Joshi SR. Proc. Natl Acad. Sci. India Sect. B Biol. Sci. 2014, 84, 1091–1099.10.1007/s40011-013-0185-7Search in Google Scholar
[7] Morsy FM. Arch. Microbiol. 2015, 197, 645–655.10.1007/s00203-015-1098-zSearch in Google Scholar PubMed
[8] Husain S, Sardar M, Fatma T. World J Microbiol Biotechnol 2015, 31, 1279–1283.10.1007/s11274-015-1869-3Search in Google Scholar PubMed
[9] Mubarak Ali D, Thajuddin N, Jeganathan K, Gunasekaran M. Colloids Surf. B Biointerfaces 2011, 85, 360–365.10.1016/j.colsurfb.2011.03.009Search in Google Scholar PubMed
[10] Das S, Das J, Samadder A, Bhattacharyya SS, Das D, Khuda-Bukhsh AR. Colloids Surf. BBiointerfaces 2013, 101, 325–336.10.1016/j.colsurfb.2012.07.008Search in Google Scholar PubMed
[11] Zuas O, Hamim N, Sampora Y. Mater. Lett. 2014, 123, 156–159.10.1016/j.matlet.2014.03.026Search in Google Scholar
[12] Jeeva K, Thiyagarajan M, Elangovan V, Geetha N, Venkatachalam P. Ind. Crops Prod. 2014, 52, 714–720.10.1016/j.indcrop.2013.11.037Search in Google Scholar
[13] Sankar R, Karthik A, Prabua A, Karthik S, Shivashangari KS, Ravikumar V. Colloids Surf. B Biointerfaces 2013, 108, 80–84.10.1016/j.colsurfb.2013.02.033Search in Google Scholar PubMed
[14] Dipankar C, Murugan S. Colloids Surf. B Biointerfaces 2012, 98, 112–119.10.1016/j.colsurfb.2012.04.006Search in Google Scholar PubMed
[15] Lukas B, Schmiderer C, Mitteregger U, Novak J. Food Chem. 2010, 121, 185–190.10.1016/j.foodchem.2009.12.028Search in Google Scholar
[16] Shan B, Cai YZ, Sun M, Corke H. J. Agric. Food Chem. 2005, 53, 7749–7759.10.1021/jf051513ySearch in Google Scholar PubMed
[17] El-Kemary M, Zahran M, Khalifa SAM, El-Seedi HR. Micro. Nano Lett. 2016, 11, 311–314.10.1049/mnl.2015.0572Search in Google Scholar
[18] El-Kemary M, Ibrahim E, A-Ajmi MF, Khalifa SAM, Alanazi AD, El-Seedi HR. Int. J. Electrochem. 2016, 11, 10795–10805.10.20964/2016.12.88Search in Google Scholar
[19] Zaheer Z, Rafiuddin. Colloids Surf. B Biointerfaces 2012, 90, 48–52.10.1016/j.colsurfb.2011.09.037Search in Google Scholar PubMed
[20] Suriyakalaa U, Antony JJ, Suganya S, Siva D, Sukirtha R, Kamalakkannan S, Pichiah PBT, Achiraman S. Colloids Surf. B Biointerfaces 2013, 102, 189–194.10.1016/j.colsurfb.2012.06.039Search in Google Scholar PubMed
[21] Sripriya J, Anandhakumar S, Achiraman S, Antony JJ, Siva D, Raichur AM. Int. J. Pharm. 2013, 457, 206–213.10.1016/j.ijpharm.2013.09.036Search in Google Scholar PubMed
[22] Raut RW, Mendhulkar VD, Kashid SB. J. Photochem. Photobiol. B 2014, 132, 45–55.10.1016/j.jphotobiol.2014.02.001Search in Google Scholar PubMed
[23] Zhou Y, Rees NV, Compton RG. Angew. Chem. Int. Ed. Eng. 2011, 50, 4219–4221.10.1002/anie.201100885Search in Google Scholar PubMed
[24] Giovanni M, Pumera M. Electroanalysis 2012, 24, 615–617.10.1002/elan.201100690Search in Google Scholar
[25] Luo C, Zhang Y, Zeng X, Zeng Y, Wang Y. J. Colloid Interface Sci. 2005, 288, 444–456.10.1016/j.jcis.2005.03.005Search in Google Scholar PubMed
[26] Faraji N, Yunus WMM, Kharazmi A, Saion E. Optik (Stuttg) 2014, 125, 2809–2812.10.1016/j.ijleo.2014.01.011Search in Google Scholar
[27] Mulvaney P. Langmuir 1996, 12, 788–800.10.1021/la9502711Search in Google Scholar
[28] Cyrankiewicz M, Wybranowski T, Kruszewski S. Acta Phys. Pol. A 2014, 125, 11–15.10.12693/APhysPolA.125.A-11Search in Google Scholar
[29] Lah NAC, Johan MR. Appl. Surf. Sci. 2011, 257, 7494–7500.10.1016/j.apsusc.2011.03.067Search in Google Scholar
[30] Wang G-L, Zhu X-Y, Jiao H-J, Yu-Ming Dong, Wu X-M, Li Z-J. Anal. Chim. Acta 2012, 747, 92–98.10.1016/j.aca.2012.08.019Search in Google Scholar PubMed
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