Abstract
The current study was aimed to synthesis and characterization of silver (AgNPs) & gold (AuNPs) nanoparticles using Callistemon citrinus leaf extract, and to evaluate their in vitro antioxidant, antimicrobial, cytotoxic activities as well as their total phenolic content (TPC). Silver and gold were synthesized and characterized via UV-vis absorbance spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses. The antioxidant activity was evaluated using dot-blot and DPPH staining, and via phosphomolybdenum assays. Also, the in vitro antimicrobial activity was evaluated via disc agar plate method. The cytotoxic activity was evaluated via brine shrimp lethality test (BSLT), and TPC was estimated via Folin-Ciocalteu’s assay. The transmission electron microscopy (TEM) analysis showed that the sizes of the synthesized AgNps ranged from 8-14 nm with maximum UV/vis absorbance at 450nm. Also, the synthesized AuNPs exhibited an average size of 5.8 to 8.84nm with maximum UV/vis absorbance at 535nm. Moreover, the results revealed that TPC of the tested extracts was ranged from 548.85 to 123.30 mg gallic acid equivalent (GAE)/g dry extract. The total antioxidant capacity (TAC) was ranged from 643.90 to 147.96 mg ascorbic acid equivalent/g dry extract. Furthermore, there is a promising antimicrobial activity against four strains with inhibition zones ranged from 8.5 to 15.5mm, Penicillin G was used as positive control at concentration of 100 μg/disc. In terms of LC50 the n-butanol extract (63.09 μg/ml) was the most potent cytotoxic, followed by EtOAc (100.0 μg/ml). In, conclusion the leaves of Callistemon citrinus showed a noticeable antioxidant, antimicrobial & cytotoxic activities and the ability to produce AgNPs and AuNPs.
Highlights
Nanotechnology is an interesting field concerned by the green biosynthesis of nanoparticles (Mc Donell et al, 1999; Govindaraju and Tamilselvan, 2010)
Abdelhady et al (2011) reported that the total phenolic content of in the phosphomolybdenum assaythe nBuOHextract was the most potent antioxidant of total antioxidant capacity (TAC) (804.87 ± 1.20mg ascorbic acid equivalent/g dry extract), followed by ethyl acetate, defatted 85% MeOH, aqueous extracts of TAC (510.56 ± 1.15, 492.67 ± 1.55, 252.02 ± 0.75, respectively), the weak activity was recorded with the remaining fractions CH2Cl2 (175.58 ± 0.90), and pet. ether (110.56 ± 0.85) mg ascorbic acid equivalent/g dry extract)(Table 1)
In Vitro Antimicrobial Activity The different extracts of C. citrinus were tested for their in vitro antimicrobial activity against five pathogenic microbial strains including Gram +ve and Gram -ve bacteria and fungi i.e., Pseudomonas aeruginosa with inhibition zones ranged from 18.0 to 7.5mm, Staphylococcus aureus with inhibition zones ranged from 17.5 to 7.5mm, Methicillin-resistant Staphylococcus aureus with inhibition zones ranged from 18.5 to 7.5mm,Candida albicans with inhibition zones ranged from 21.5 to 8.5mm,however85% MeOH of flower part only showed a moderate activity against Aspergillus niger with inhibition zone 9.5mm (Table 2)
Summary
Nanotechnology is an interesting field concerned by the green biosynthesis of nanoparticles (Mc Donell et al, 1999; Govindaraju and Tamilselvan, 2010). The green biosynthesis of metal nanoparticles using medicinal plants extracts is a vital issue of research due to their importance in the different fields especially drug delivery (Chaudhuri et al, 2016). Numerous reports are available on the use of medicinal plants in the green biosynthesis of nanoparticles especially silver AgNPs and gold AuNPs. most plants usually contain polyphenolic secondary metabolites viz., phenolic acids, flavonoids, and anthraquinones which act as strong reducing agents useful in the synthesis of nanoparticles (Siemieniec and Kruk, 2013). During the biosynthesis of silver and gold nanoparticles such polyphenolic compounds undergo keto-enol form conversion, which led to the reduction of AuCl4- ion to Au0 metal, and the conversion of Ag+ ion to Ag0 metal (Siemieniec and Kruk, 2013; Abdel-Aziz et al, 2014).
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