Water, an elixir of life has now become a source to carry much water borne illness. Bacterial and neurotoxic algal growth in drinking water bodies affects human health. Unclean household water tanks and public water supply system supports many harmful water borne illness through the microbes, Vibrio cholera, Salmonella typhi, Salmonella paratyphi, Staphyllococcus aureus, E. coli and other enteric pathogens. Further many fresh water bodies are also contaminated with microbes. Algal growth and bacterial contaminants in our household water tanks clog the water taps, affect health and promote several waterborne diseases. To find out a safe solution for this menace, green synthesized silver nanoparticles were tried. Algal blooms in water bodies reduce dissolved oxygen content and prevent solar penetration. This leads to eutrophication and challenges to aquatic cultivable species. Some algal bloom decolorizes the water and the consumption of the water with their spores cause many neurological problems. Harmful algal blooms known as red tides, blue green algae or Cyanobacteria, or other harmful algal blooms were reported to cause toxic water bodies and affect human health, aquatic ecosystem and economy. Hence it is imperative to protect the drinking water sources and aquaculture ponds from algal bloom and water borne pathogens. The chemical methods of disinfecting the water bodies lead to other eco-induced harmfulness in human beings. So a safe, non toxic, eco friendly agent is needed to contain pathogenic microbes and algae in water bodies. In this direction the green synthesized silver nanoparticles are good choice    . Hence in the present study, silver nano particles were prepared using Bamboo leaves and the potential of green synthesized AgNPs was tested against water borne bacterial pathogens and algae causing harmful algal bloom (HAB) in water.
2. Materials and Methods
Fresh leaves of, Bambusa vulgaris were collected from Anna university, Chennai campus, and washed several times with water to remove the dust particles and then air dried to remove the residual moisture and ground to powder form. The plant extract was prepared by mixing 1% of plant material with isopropanol (50 ml) in a 250 ml of (Borosil, India) conical flask. Then the solution was incubated for 2 days at room temperature. The supernatant was separated and filtered with filter paper. Then the solution was used for the reduction of silver ions Ag(+) silver nanoparticles Ag(−).
Firstly a 10 ml solution of AgNO3 (1 mM) is prepared in a beaker and also 5 ml of bamboo extract solution was prepared. Then 5 ml of AgNO3 was mixed with the bamboo extracts solution. The solution was kept undisturbed for 6 hours. A change in the colour of the solution was observed and the solution turned pale yellowish green colour. The optical absorption spectra of silver nanoparticle were recorded using a UV-Vis PG-T90; initially base line adjustments are performed. The sample was taken in cuvettes with water as the solvent and placed in the setup and the absorption spectra are recorded in the wavelength range 200 - 900 nm. The prepared particle were analysed by X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods  . Prepared particle were screened against bacterial pathogens by standard methods  .
UV visible spectroscopy: UV-Visible spectroscopy was performed in spectrophotometer using distilled water as blank. The spectroscopy was performed for absorbance between the range of 200 - 900 nm. In green synthesized solution the peak was observed at 422 nm (Figure 1). Silver nanoparticle showed the peak between the range of 390 - 430 nm and this indicates the presence of silver nanoparticles in our sample (Figure 2).
Microscope analysis: The particles synthesized are spherical in shape. They are smallest in size and are monodispersed in nature as analyzed by SEM (Figure 3) and TEM (Figure 4, Figure 5). Also the agglomeration which is due to the surface charge of the nanoparticles was observed. The nanoparticles are square shaped and are present in different size. This method has modified the shape of the AgNPs which has same size (Figure 6).
Antimicrobial activity of silver nanoparticles: The antimicrobial activity of Ag nanoparticles was investigated against Escherichia coli, Staphylococcus aureus and Vibrio cholera (Table 1). In these tests, Muller Hinton agar plates were used and Ag nanoparticles of various concentrations were supplemented in liquid systems. The results showed that E. coli were inhibited at a low concentration of Ag nanoparticles, whereas the growth-inhibitory effects on S. aureus were mild. Disruption of algal cell is more pronounced in green synthesized silver nano particle treatment and algal cell wall got ruptured (Figures 7-9).
Figure 1. UV-Vis-Spectrum of Ag nanoparticle (Green synthesis).
Figure 2. X-ray diffraction of synthesized nanoparticles.
Figure 3. SEM images of green synthesised AgNPs.
Figure 4. TEM image for Green synthesized AgNPs.
Figure 5. TEM image of Green synthesized AgNPs.
Figure 6. Particle size analyzer graphs of green synthesised AgNPs.
Table 1. Antimicrobial activity of AgNPS.
Figure 7. SEM image of algae (control).
Figure 8. SEM image showing control (a) and AgNPs treated A. chlordae with broken and clumbed cells ((b), (c)).
Figure 9. Ruptured cell wall of algae due to treatment with AgNPs.
Nanoscience is revolutionizing many aspects of bioscience today. For the safe environmental approach, nanoparticles are synthesized using plant extracts and used in various medical applications. In the present study silver nanoparticles (AgNPs) were prepared. The morphology and size of the AgNPs were studied using UV, TEM, SEM, XRD, EDAX and PSA. Using the extracts of the leaves of the bamboo leaves the AgNPs were prepared and tested for antibacterial and anti algal bloom activities. The study showed that the green synthesized AgNPs have good antibacterial activities. The water borne pathogens E. coli, V. cholerae, Salmonella typhii and S. aureus tested against AgNP3 showed high inhibition for Salmonella typhii (18 nm) at a dose of 50 µl and little less (16 nm) for V. cholerae. The study indicates a good antibacterial activity. The silver ions in the AgNPs were reported to damage the cell membranes in bacterial cell and affecting the membrane functions and cell physiology  .
The action of silver ion AgNPs on the membrane or cell boundary was confirmed by its action against the cell wall of the two species of algae chosen. SEM study confirmed the damage to cell boundary. Of the two micro algae chosen cell wall rupture is more prominent in Algoriphagus chordae than Dictyosphaerium pulchellum. Aharodnik et al.,  reported that AgNPs damages cell membraene and plasma in bacteria by cell wall tearing, causing exhaustion of the intracellular adenosine triphosphate. Algal bloom in water bodies particularly in aquaculture ponds and drinking water source cause several harmful effects. Algal bloom not only alters the physico-chemical quality of water but also affects its utility by releasing toxins, hazardous to human health  . From the results of the present study it is evident that biogenic synthesis of silver nanoparticles using bamboo leaves are potential water cleaning agent.
Authors are very much thankful to the Management and Principal of Prathyusha Engineering college, Chennai for providing facility to carry out this work in lab.