Biosynthesis has emerged as an option for obtaining nanometric materials due to the need to use more environmentally-friendly synthesis methods.
To synthesize silver nanoparticles (Ag NPs) with aqueous Crataegus gracilior Phipps (tejocote) bark extract as precursor.
Ag NPs were synthesized with AgNO3 and aqueous Crataegus gracilior bark extracts, and later characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). In addition, their size distribution and zeta potential were obtained.
The presence of Ag NPs reached maximum values at concentrations of 10 % (w/v). Mostly spherical nanoparticles were found in the range of 20 to 50 nm in size. FTIR confirmed the stabilization of the nanoparticles through their interactions with functional groups of carbohydrates and proteins. XRD and TEM results were explained by their face-centered cubic (FCC) structure with a size of 26 nm, a mean hydrodynamic diameter of 108 nm and polydispersity index of 0.24. The zeta potential values in the dispersions were -21.9 ± 5.11 mV, denoting colloidal stability.
Limitations of the study:
The characteristics of the nanoparticles obtained are only valid under the following synthesis conditions: 10 % (w/v) solids and pH 10.
A non-reported plant material was used, capable of acting as a reducing and passivating agent of silver nanoparticles.
Biosynthesis of Ag NPs with tejocote extract is an efficient, low-cost and environmentally-friendly method.
Crataegus spp., a Mexican plant commonly known as tejocote, has medicinal, industrial and ornamental uses (Nieto-Ángel, Pérez-Ortega, Núñez-Colín, Martínez-Solís, & González-Andrés, 2009). The Crataegus gracilior plant extract contains a high percentage of pectin, which is composed mainly of D-galacturonic acid and, in less proportion, D-galactose, L-arabinose, D-xylose and L-rhamnose. In Ag NP synthesis, pectin forms polymer networks in which silver nanoparticles are embedded, also acting as a reducing agent and silver ion protector (Krivorotova et al., 2016; Zahran, Ahmed, & El-Rafie, 2014; Zainudin, Wong, & Hamdan, 2018). To our knowledge, however, this has never been addressed in the literature. Therefore, the objective of the present study was to synthesize Ag NPs using aqueous Crataegus gracilior bark extract as precursor.
Materials and methods
Ag NPs were synthesized using silver nitrate (AgNO3, > 99.8 %, Sigma-Aldrich®, USA) as precursor and aqueous tejocote bark extracts as reducing and passivating agent. Deionized water (18 MΩ·cm-1; Easypure II, Thermo ScientificTM, Spain) was used throughout the experiments and sodium hydroxide (NaOH) was used to adjust the pH.
For the synthesis, 100 mL of aqueous tejocote bark extract were placed in a round-bottomed flask, where the pH was adjusted with 0.1M HCl and 0.1 M NaOH. Then, the solution was heated to 75 °C under constant stirring. When the desired temperature was reached, 10 mL of 0.1 M AgNO3 were added. The final mixture was stirred for 30 min at the same temperature. Preliminary analyses were conducted at solid concentrations of 1, 5, and 10 % (w/v) and pH0 6, 8, and 10. Samples with a 10 % solid concentration and pH 10 contained the smallest and most stable nanoparticles.
Characterization of nanoparticles
Ultraviolet-visible spectroscopy (UV-Vis). Optical absorption spectra for Ag NP suspensions were obtained using a Cary 50 spectrophotometer (Varian®, USA). Ag NP suspensions were diluted at a 5:1 ratio with deionized water (18 μΩ·cm-1) prior to analysis. Deionized water was used as a reference.
Fourier-transform infrared spectroscopy (FTIR). The Ag NP suspension was centrifuged at 13 000 rpm (Sigma 2-16, Sigma Laborzentrifugen GmbH®, Germany) and subsequently dried at room temperature. Dried powdered plant material and Ag NPs were separately mixed with KBr at a 1:10 ratio to form pellets. The spectra were recorded using a spectrometer (Spectrum One, Perkin Elmer®, USA), with a 4 000 to 400 cm-1 frequency range.
Transmission Electron Microscopy (TEM). Ag NPs were examined in a JEM-2010 microscope (JEOL®, Japan) operating at 200 kV and 115 μA, for which a single drop of the colloidal solution was placed on a 200-mesh carbon-coated copper grid (Electron Microscopy Sciences, USA). Additionally, the selected area electron diffraction (SAED) was obtained at a wavelength of 0.0025 nm and a camera length of 20 cm. Average size and size distribution values were obtained by analyzing 150 particles, using PhotoImpact 11 software (Ulead Systems®, USA).
X-ray diffraction (XRD). It was performed in a D8 Advance diffractometer (Bruker®, Germany). The patterns were recorded by CuKα (1.54 A°) with a cupper monochromator. The scanning of Ag NPs was done in a region of 2θ from 5 to 90° at 0.05°/10 s.
Determination of zeta potential and size distribution. The hydrodynamic diameter and polydispersity index of the nanoparticles were determined by dynamic light scattering (DLS) and zeta potential (ZS ZEN3600, Malvern Instruments®, UK). Measurements were performed in triplicate, with each measurement conducted using 1 mL of suspension at room temperature (25 °C). The calculations of electrophoretic mobility were automatically converted into zeta potential values, based on the Smoluchowski model; ten readings were obtained to calculate the average electrical charge.
Results and discussion
UV-Vis. After the addition of AgNO3 to the extract solution, the color of the solution changed from colorless to brown indicating the formation of silver nanoparticles. It is highly possible that pectin, hydrolysable tannins, polyphenols and flavonoids present in the tejocote extract have acted as reducing agents to produce Ag0. Maximum absorbance values for Ag NP with tecojote extracts suspensions were obtained (10 % w/v) at 500 nm.
The position and shape of the absorption band for a surface plasmon depend on particle size and shape: increases in size cause the absorption band to shift towards higher wavelengths (Slistan-Grijalva et al., 2008). Based on the spectral signals obtained (Mitra & Bhaumik, 2007), nanoparticles obtained with the tejocote extracts presented an average size ≤ 30 nm (Figure 1).
FTIR analysis. Shown in Figure 2 are the FTIR spectra of the precursors (AgNO3 and tejocote extract) and Ag NPs. The spectrum of tejocote extract denotes absorption bands at 1 045 cm-1 and 1 115 cm-1 (corresponding to CO vibrations), 3 417 cm-1 (amide A, NH stretching and OH bending and stretching), 1 619 cm-1 (amide I, C=O stretching), 1 520 cm-1 (amide II, bending vibrations of NH and CN stretching), and 1 254 cm-1 (amide III, bending vibrations of NH (Hayashi & Mukamel, 2008). FTIR spectra for AgNO3 revealed an intense absorption band at 1 376 cm-1, characteristic of the Ag+NO3- ion pair.
On the other hand, in the spectrum of the silver nanoparticles, the absorption bands corresponding to the amide groups shifted to lower wavenumber values. These changes on the position bands may be due to the interactions of proteins that are possibly bound to Ag NPs through the amine groups. Additionally, the band intensity of the ion pair Ag+NO3- decreased and shifted to a higher wavenumber value. This peak, centered at 1 385 cm-1, is characteristic of the NO3- ion in free form, and the absorption band displacement is caused by a change in the electronic environment of the anion, as a result of the separation of its counterpart Ag+ (Cho & So, 2006).
TEM. Figure 3a shows the Ag NPs embedded in a polymer network at tejocote concentrations of 10 %. Dark areas corresponded to Ag NPs and light areas to different compounds present in the plant extract. Ag NPs showed an average diameter of 30 nm and a spherical morphology, although the magnification showed an ovoid shape. Figure 3b exemplifies an electron diffraction pattern of the Ag NPs. High magnification evidenced a face-centered cubic (FCC) structure, a spatial group of Fm-3m (225), and a lattice parameter a = 4.09 Å.
XRD. Results obtained by TEM and calculations using the Scherrer equation were best explained by an average size of 26 nm. Figure 4 shows the X-ray diffraction pattern obtained for Ag NPs. Five Bragg reflections are observed in the diffractogram at 2θ angles centered at 38.0°, 44.0° 64.4°, 77.32°, and 81.34° corresponding to planes (111), (200), (220), (311), and (222) respectively, from the FCC of the Ag with spatial group Fm-3m (225), according to the diffraction analysis PDF-04-0783. The diffractogram indicates the presence of nanometric-size crystals without preferential direction for growth.
Nanoparticle size distribution and zeta potential. According to the DLS analysis, the particles obtained are a polydisperse mixture with a mean hydrodynamic diameter of 108 nm and a polydispersity index of 0.24. On the other hand, the colloidal solution of Ag NPs had a zeta potential value of -21.9 ± 5.11 mV, indicating good NP stability. This stability mainly depends on the surface charge; hence particles with a similar surface charge repel each other due to electrostatic repulsion forces (Khan, Mukherjee, & Chandrasekaran, 2011). According to Sun et al. (2014), a suspension with an absolute zeta potential lower than 20 mV is considered unstable, and its constituent particles will tend to precipitate, whereas an absolute zeta potential greater than 20 mV is indicative of a stable solution.
Biosynthesis of Ag NPs was performed using AgNO3 and aqueous tejocote (Crataegus gracilior) bark extracts as precursors, achieving an efficient, low-cost and environmentally-friendly synthesis. FTIR results confirmed the stabilization of Ag NPs by interacting with organic components in the extract, primarily carbohydrates and proteins. TEM showed that Ag NPs were mostly spherical, with an average size of 30 nm. Additionally, electron diffraction patterns confirmed an FCC structure.
The authors thank the Consejo Nacional de Ciencia y Tecnología (CONACyT) and the Secretaría de Investigación y Posgrado del Instituto Politécnico Nacional (SIP-IPN) for the funding provided.
Bankar, A., Joshi, B., Kumar, A. R., & Zinjarde, S. (2010). Banana peel extract mediated novel route for the synthesis of silver nanoparticles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 368(1-3), 58-63. doi: 10.1016/j.colsurfa.2010.07.024
Basavaraja, S., Balaji, S. D., Lagashetty, A., Rajasab, A. H., & Venkataraman, A. (2008). Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium semitectum. Materials Research Bulletin, 43(5), 1164-1170. doi: 10.1016/j.materresbull.2007.06.020
Bradley, J. S., Schmid, G., Shevchenko, E. V., & Weller, H. (2004). Synthesis of metal nanoparticles. In: Schmid, G. (Ed), Nanoparticles: From theory to application (pp. 185-238). Germany: Wiley-VCH. doi: 10.1002/3527602399
Cho, J. W., & So, J. H. (2006). Polyurethane-silver fibers prepared by infiltration and reduction of silver nitrate. Materials Letters, 60(21-22), 2653-2656. doi: 10.1016/j.matlet.2006.01.072
Cruz, D., Falé, P. L., Mourato, A., Vaz, P. D., Serralheiro, M. L., & Lino, A. R. (2010). Preparation and physicochemical characterization of Ag nanoparticles biosynthesized by Lippia citriodora (Lemon Verbena). Colloids and Surfaces B: Biointerfaces, 81(1), 67-73. doi: 10.1016/j.colsurfb.2010.06.025
Hayashi, T., & Mukamel, S. (2008). Two-dimensional vibrational lineshapes of amide III, II, I and A bands in a helical peptide. Journal of Molecular Liquids, 141(3), 149-154. doi: 10.1016/j.molliq.2008.02.013
He, S., Guo, Z., Zhang, Y., Zhang, S., Wang, V., & Gu, N. (2007). Biosynthesis of gold nanoparticles using the bacteria Rhodopseudomonas capsulata. Materials Letters, 61(18), 3984-3987. doi: 10.1016/j.matlet.2007.01.018
Kaviya, S., Santhanalakshmi, J., Viswanathan, B., Muthumary, J., & Srinivasan, K. (2011). Biosynthesis of silver nanoparticles using citrus sinensis peel extract and its antibacterial activity. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 79(3), 594-598. doi: 10.1016/j.saa.2011.03.040
Khan, S. S., Mukherjee, A., & Chandrasekaran, N. (2011). Impact of exopolysaccharides on the stability of silver nanoparticles in water. Water Research, 45(16), 5184-5190. doi: 10.1016/j.watres.2011.07.024
Krivorotova, T., Cirkovas, A., Maciulyte, S., Staneviciene, R., Budriene, S., Serviene, E., & Sereikaite, J. (2016). Nisin-loaded pectin nanoparticles for food preservation. Food Hydrocolloids, 54(49-56). doi: 10.1016/j.foodhyd.2015.09.015
Kumar, B., Smita, K., Cumbal, L., & Debut, A. (2017). Green synthesis of silver nanoparticles using Andean blackberry fruit extract. Saudi Journal of Biological Sciences, 24(1), 45-50. doi: 10.1016/j.sjbs.2015.09.006
Luo, C., Zhang, Y., Zeng, X., Zeng, Y., & Wang, Y. (2005). The role of poly(ethylene glycol) in the formation of silver nanoparticles. Journal of Colloid and Interface Science, 288(2), 444-448. doi: 10.1016/j.jcis.2005.03.005
Mahendran, G., & Ranjitha-Kumari, B. D. (2016). Biological activities of silver nanoparticles from Nothapodytes nimmoniana (Graham) Mabb. fruit extracts. Food Science and Human Wellness, 5(4), 207-218. doi: 10.1016/j.fshw.2016.10.001
Mitra, A., & Bhaumik, A. (2007). Nanoscale silver cluster embedded in artificial heterogeneous matrix consisting of protein and sodium polyacrylate. Materials Letters, 61(3), 659-662. doi: 10.1016/j.matlet.2006.05.039
Narayanan, K. B., & Sakthivel, N. (2008). Coriander leaf mediated biosynthesis of gold nanoparticles. Materials Letters, 62(30), 4588-4590. doi: 10.1016/j.matlet.2008.08.044
Nieto-Ángel, R., Pérez-Ortega, S. A., Núñez-Colín, C. A., Martínez-Solís, J., & González-Andrés, F. (2009). Seed and endocarp traits as markers of the biodiversity of regional sources of germplasm of tejocote (Crataegus spp.) from Central and Southern Mexico. Scientia Horticulturae, 121(2), 166-170. doi: 10.1016/j.scienta.2009.01.034
Petica, A., Gavriliu, S., Lungu, M., Buruntea, N., & Panzaru, C. (2008). Colloidal silver solutions with antimicrobial properties. Materials Science and Engineering: B, 152(1-3), 22-28. doi: 10.1016/j.mseb.2008.06.021
Raja, S., Ramesh, V., & Thivaharan, V. (2017). Green biosynthesis of silver nanoparticles using Calliandra haematocephala leaf extract, their antibacterial activity and hydrogen peroxide sensing capability. Arabian Journal of Chemistry, 10(2), 253-261. doi: 10.1016/j.arabjc.2015.06.023
Slistan-Grijalva, A., Herrera-Urbina, R., Rivas-Silva, J. F., Ávalos-Borja, M., Castillón-Barraza, F. F., & Posada-Amarillas, A. (2008). Synthesis of silver nanoparticles in a polyvinylpyrrolidone (PVP) paste, and their optical properties in a film and in ethylene glycol. Materials Research Bulletin, 43(1), 90-96. doi: 10.1016/j.materresbull.2007.02.013
Sondi, I., & Salopek-Sondi, B. (2004). Silver nanoparticles as antimicrobial agent: a case study on E. Coli as a model for Gram-negative bacteria. Journal of Colloid and Interface Science, 275(1), 177-182. doi: 10.1016/j.jcis.2004.02.012
Sun, Q., Cai, X., Li, J., Zheng, M., Chen, Z., & Yu, C. (2014). Green synthesis of silver nanoparticles using tea leaf extract and evaluation of their stability and antibacterial activity. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 444(5), 226-231. doi: 10.1016/j.colsurfa.2013.12.065
Vigneshwaran, N., Ashtaputre, N. M., Varadarajan, P. V., Nachane, R. P., Paralikar, K. M., & Balasubramanya, R. H. (2007). Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus. Materials Letters, 61(6), 1413-1418. doi: 10.1016/j.matlet.2006.07.042
Zahran, M. K., Ahmed, H. B., & El-Rafie, M. H. (2014). Facile size-regulated synthesis of silver nanoparticles using pectin. Carbohydrate polymers, 111, 971-978. doi: 10.1016/j.carbpol.2014.05.028
Zainudin, B. H., Wong, T. W., & Hamdan, H. (2018). Design of low molecular weight pectin and its nanoparticles through combination treatment of pectin by microwave and inorganic salts. Polymer Degradation and Stability, 147, 35-40. doi: 10.1016/j.polymdegradstab.2017.11.011