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NATURAL PRODUCTS FOR THE OPTIMIZATION OF SHAPE OF SILVER NANO PARTICLE AND ITS APPLICATION IN DNA SENSING
The silver nanoparticle synthesized by soluble starch is an approach towards green chemistry which is efficient, bio-compatible, non-toxic and foremost inexpensive. The soluble starch acts as reducing as well as stabilizing agent for the synthesized nano particle and stabilizes nano silver over a period of three months. For the synthesis of nano silver, the starch solution is prepared in deionized water, when the solution becomes clear it is divided into two parts. Silver nitrate solution was added to both and DNA solution was also added to both parts but in different concentrations. Change in color was noticed. The methods like UV-Vis, X-ray diffraction (XRD) and photo luminiscence analysis are done for the characterization of the structure of the nano silver synthesized. The present research work is focused on DNA sensing as its application is widespread as in the fields of pharmacy and biomedicine. The DNA-nano silver conjugation has enormous catalytic and optical properties which has a comprehensive coverage in detecting, manipulating and delivering genes.
Keywords: green chemistry, soluble starch, silver nano particle, DNA sensing.
Nano particles have a wide range of applications in the areas of chemistry, biomedical sciences, physics, nanotechnology. The silver nano particles synthesized have profound applications in the field of optics, electronics, drug delivery and pharmaceuticals. Over the past few decades, there is a great concern between scientists over the use of non toxic methodologies to produce nanoparticles. As the synthetic methods used to produce the nano particles have high toxic effects and pose a threat to the environment and have biological risks. So, to reduce the risk and production of non toxic products for the preparation of nano particles led to the concept of “green chemistry”. It is a concept which reduce the toxicity to the smallest degree and adopt sustainable development. Natural products are being used for the synthesis of silver nanoparticles which have widespread applications for therapeutics and biomedical purposes.
Until recently, the scientists are using natural materials like soluble starch for the production of silver nano particle. It is called “sweet nano chemistry”. It is an effort towards the strategy of green chemistry, in neither any hazardous chemical is used nor does it pose any threat to the environment. It is a very fast, reliable and safe approach. Previously, the bacteria and other micro-organisms were used as reducing agents for nano particles, but they used to contaminate the nanoparticle. Now, the soluble starch, albumin, Azadirachta indica (neem), Aloe vera are being used for the reduction and synthesis of nano silver. These materials also stabilize the silver nano particle.
The current protocol used in this paper is the production of nano silver by soluble starch which is totally a green synthesis for the production of nano silver. The potato is used which is highly rich in starch content. Moreover, the starch also acts as the reducing as well as the stabilizing agent for the silver nano particle produced. The alkali dissolved in the starch acts as reducing agent for the silver ions and as a stabilizing agent for the nano silver formed. The chemical reduction is a three step process. The first step is the reduction of the silver salt by a reducing agent i.e. AgNO3 is basically used. In the second step, the silver atoms which are neutral in nature are formed which progress towards the formation of nano silver. The third step is the stabilization of the nano particle synthesized which otherwise can agglomerate and form masses.
The starch is used as the capping agent to synthesize the nano particle. The starch nano particles will perform a dual role:as a reducing agent for silver ions and a capping agent for the silver nano particles formed with the production of starch-silver nano particles. The use of highly sophisticated techniques for the characterization, and assessment of the nano structural features of the formed nano silver by UV-Vis Spectroscopy, Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) Spectroscopy is done.
MATERIALS AND METHODS:
In this protocol, 1.0 g of soluble starch was dissolved in 100 ml of deionized water and was boiled in a microwave oven. After it completely dissolved, it was cooled and was divided into two parts. Separately DNA solution was prepared of different concentration (0.05 mM and 0.10 mM) and was added to the starch solutions in two different conical flasks. Then 20 mL solution with a concentration of 0.25 mM silver nitrate(AgNo3) was added to starch solutions in both the flasks.0.6 mL of 10 mM NaBH4 was added at once to both the flasks and stirred vigorously with a magnetic stirrer for 30s. After 30s, stirring was stopped. Then the nano particles were characterized by UV-VIS absorption spectroscopy and AFM was done.AFM confirms the shape of the nanoparticles.
RESULT AND DISCUSSION:
In case of silver nanoparticles,the two bands that is conduction and valence are lying close to each other in which electrons move freely which gives rise to a Surface Plasmon Resonance(SPR) absorption band. This band arises due to oscillations of electrons of silver nanoparticles in resonance with light waves.
We can see two different peaks in case of two different concentrations of DNA. Sharp peak is seen around 502nm wavelength for dna concentration of 0.10mM whereas for dna concentration of 0.05mM the maximum absorbance lies around 500nm. When there is a decrease in concentration of DNA it increases the number of free electrons. Two different peaks generally arise due to varying size and size distribution of particles and also due to two different concentrations of DNA.
There is no extinction peak beyond 700nm for 0.6mL sodium borohydride. This saturation indicates that conversion of Ag2+ to Ag0+ by sodium borohydride is complete. This might result when electron injection into silver nanoparticles by sodium borohydride reaches a saturation point.
In our work starch solution first acts as a reducing agent which reduces the silver ions.In the second step the starch solution acts as a capping agent for the silver nanoparticles.The silver nanoparticles are stabilized by the help of sodium borohydride.
UV-Vis is used to confirm the size of silver nanoparticles. AFM results awaited which will confirm the shape of the particle.
The main tool we used for the analysis of the nano particle formation is the UV-Vis spectroscope, depends upon the surface Plasmon resonance [SPR]. Excitation of the localized surface plasmon causes strong light scattering by an electric field at a wavelength where
resonance occurs; as a result strong band appears. When the extract is mixed in the AgNO3
solution, the solution first becomes yellowish after 2-3 mins and then turns brown after reaction completion (15 mins),which indicate the nanosilver particle formation. The formation of the nanosilver starts with the addition of the soluble starch which increases rapidly after 1 min and starts stabilizing after 10 min. No change in peak was observed after 20 min, i.e., all silver ions were consumed within 20 min.
In this paper, we have demonstrated the application of green chemistry principles in the synthesis of nanosilver particle. The particles produced here are expected to be stable and comparable in size to those produced via conventional physiochemical methods. The use of environment friendly and easily available source that is soluble starch form boiled potato offers numerous benefits ranging from environmental safety to ready integration of these nanomaterials to biologically relevant systems. This combination of solvent and renewable reactants represents a wide range of possibilities for the further development of green nanoparticles syntheses in laboratory. We are expecting a uniform, high surface areas and tunable pore sizes onto the GC electrode facilitate its manipulation for sensor preparation and DNA sensing application. This nanosilver synthesized in laboratory may be a promising candidate for electronic systems, catalysis, fuel cells and nano devices and for sensing purposes of nucleic acids [DNA/RNA] .
We thank VIT University providing support and encouragement which enabled us to complete the project successfully. Also we would like to thank the School of Biosciences and Technology, VIT University, for having provided us with the calf thymus DNA and silver nitrate.
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