Green Synthesis and Characterization of Silver Nanoparticles Using Bauhinia Variegate Leaves Aqueous Extract

Nanotechnology has become one of the most talented technologies useful in all areas of science. Metal nanoparticles produced by nanotechnology have received global attention due to their widespread claims in the biomedical and physiochemical fields. Recently, synthesizing metal nanoparticles using plants has been extensively studied and has been recognized as a green and efficient way for further exploiting microorganisms as convenient manufactories. The current study designed to investigate the ability of Bauhinia variegate aqueous extract in the bio reduction of silver salt during the nanoparticle synthesis and evaluation of UV–visible spectroscopy as well as Transmission Electron Microscopy (TEM) of the synthetized nanoparticles.


Introduction
Silver nanoparticles (Nps) have showed to be most effective because of its good antimicrobial efficacy against bacteria, viruses and other eukaryotic micro-organisms [1]. Silver is one of the basic elements that make up our planet. It is a rare, but naturally occurring element, marginally harder than gold and very ductile and flexible.
Pure silver has the uppermost electrical and thermal conductivity of all metals and has the lowermost contact resistance. Silver can be present in four different oxidation states: Ag0, Ag2+, Ag3+. The former two are the most plentiful ones, the latter are unstable in the aquatic environment [2,3]. Metallic silver itself is insoluble in water, but metallic salts such as AgNO3 and Silver chloride are soluble in water [4]. Metallic silver is used for the surgical prosthesis and splints, fungicides and coinage. Soluble silver compounds such as silver slats, have been used in treating mental illness, epilepsy, nicotine addition, gastroenteritis and infectious diseases including syphilis and gonorrhea [5].
Although acute toxicity of silver in the environment is dependent on the availability of free silver ions, investigations have shown that these concentrations of Ag+ ions are too low to lead toxicity [6]. Metallic silver appears to pose minimal risk to health, whereas soluble silver compounds are more readily absorbed and have the potential to produce adverse effects [7]. The wide variety of uses of silver allows exposure through various routes of entry into the body. Ingestion is the primary route for entry for silver compounds and colloidal silver proteins. Dietary intake of silver is estimated at 70-90μg/day. Since silver in any form is not thought to be toxic to the immune, cardiovascular, nervous or reproductive system, it is not considered to be carcinogenic [8], therefore silver is relatively non-toxic [9].

Biosynthesis of Nps From Bauhinia Variegate Aqueous Extract
The broth solution of fresh leaves was prepared by taking 10 g of thoroughly washed and finely cut leaves in a 300mL Erlenmeyer flask along with 100mL of sterilized double-distilled water and then boiling the mixture for 5 min before finally decanting it. The extract was filtered with Whatman filter paper no. 1 and stored at −15°C; it could be used within 1 week. The filtrate was treated with aqueous 1 mM AgNO 3 (21.2mg of AgNO 3 powder in 125mL Milli-Q water) solution in an Erlenmeyer flask and incubated at room temperature. Eighty-eight milliliters of an aqueous solution of 1 mM silver nitrate was reduced using 12 mL of leaf extract at room temperature for 10 min, resulting in a brown-yellow solution indicating the formation of AgNPs [17].

UV-Visible Spectroscopy
To examine the optical properties of nanoparticles UV-Vis spectroscopy is used aacording to the method described by Abbas [18]. In Figure 4, Bauhinia variegate synthetized nanoparticles (BVL-SNPs) spectrum is observed in the figure characteristic absorption peak of the sample is noted that is 395nm and band gap is 3.26 eV.
The supporting point is that there is no other peak is observed in whole a spectrum that means BVL-SNPs has successfully formed.

Transmission Electron Microscopy (TEM)
TEM analysis was performed on the analytical electron microscope (Jeol JEM 2100F) with a Field Emission Gun (FEG) operating at 200 kV. The samples were prepared by a simple colloid dropping on amorphous carbon film supported on cupper (Cu) grids. The electron dose used during all process was kept between 150 and 250 e/A2. s [19].

Results and Discussion
Qualitative analysis for the formation of silver nanoparticles can easily be followed using spectrophotometer.  [20]. Nanoparticles with smaller size can have promising applications in biomedicine due to the advantage of increased surface area [21]. Silver nanoparticles are being increasingly utilized in blood-contacting biomedical applications and devices. As with any new technology, thorough preclinical evaluation is necessary to ensure patient safety [22].    Biogenic synthesis is useful not only because of its reduced environmental impact [15] compared with some of the physicochemical production methods as well as it results in production of large quantities of nanoparticles that are free of contamination and have a well-defined size and morphology [22].
The ability of plant extracts to reduce metal ions has been known since the early 1900s, although the nature of the reducing agents involved was not well understood. In view of its simplicity, the use of live plants or whole plant extract and plant tissue for reducing metal salts to nanoparticles has attracted considerable attention within the last 30-years [23,24]. Typically, a plant extract-mediated bio reduction involves mixing the aqueous extract with an aqueous solution of the relevant metal salt. The reaction occurs at room temperature and is generally complete within a few minutes. In view of the number of different chemicals involved, the bio reduction process is relatively complex. Nanoparticles are already used in numerous applications [25] including in vitro diagnostics, but their use in medicine is mostly on an experimental basis. Drugs bound to nanoparticles have been claimed to have advantages compared with the conventional forms of the drugs [26]. The size of the drug nanoparticle and its surface characteristics can be modified to achieve the desired delivery characteristics [20].
In synthesis of silver nanoparticles using a Bauhinia variegate leaf extract, the particles formed rapidly, and a stable size of 20-30nm was achieved. The nanoparticles are quite polydispersity and a layer of the organic material surrounding the synthesized Ag nanoparticles could explain the good dispersion of these nanoparticles in solution. Generally, the Ag nanoparticles synthesized by means of aqueous extracts are dispersed finely though some of them were renowned to be agglomerated.

Volume 29-Issue 5
Particularly, the mainstream of the particles in the TEM images are not in physical contact with each other but appeared separated by the organic layer. Therefore, TEM images evidently indicate the coating of Ag nanoparticles with an organic layer. The presence of several polyphenolic components including flavonoids and terpenoids facilitated the reduction of Ag ions and also stabilized the surface of the resultant Ag nanoparticles [27].

Conclusion
The use of plant extracts is cheap, simply scalable, and environmentally harmless to yield metallic nanoparticles. It is predominantly suitable to make nanoparticles applicable as therapeutic agents. The synthesis of a plant extract can offer controlled sized and morphological nanoparticles. Nanoparticles in medicine, for example, are used in bandages as antimicrobial agents. Targeted drug delivery and clinical diagnosis technologies are being developed.