Metallic Nano Particle Nanotechnology is a vast area

Metallic � Nano. Particle

�Nanotechnology is a vast area at an interface many disciplines like biology, physics, engineering). It deals with miniaturize-sized particles with at least one dimension ranging from 1 to 100 nm

The synthesis of metallic NPs mainly takes into account two different approaches named as “top-down” and “bottom -up”. The top-down process is the breaking down of a system or a molecule to generate NPs whereas the bottom-up approach means to assemble or piece together the single atoms or molecules to build up nanostructures

Stable and monodisperse NPs � are synthesized by using -physical methods � -chemical methods. � �

For the synthesis of metal NPs, it is a critical step to determine Size, shape and morphology NPs through characterization by using - high-through put instruments. -Various factors such as temperature, incubation time, concentration

�The metallic NPs are categorized �into different types such as metal NPs �(silver, gold, copper, platinum), metal oxide NPs(copper/cuprous, zinc, titanium), magnetic NPs (iron, nickel, cobalt, manganese) and �

These potential features of metal NPs make them applicable in -wide spectrum of biomedical areas including A-imaging for disease diagnosis B-targeted drug delivery, C-cancer treatment, D-gene therapy, E- wound healing/ F-tissue repair and tissue engineering

Synthesis of Metal and � Metal Oxide NPs �

These nanomaterials � are mainly synthesized � by the use of -chemical methods � physical methods. �

The employmentof alternative biogenic route for the NPs synthesis by using biological entities of unicellular living organisms such as bacteria, fungi, actinomycetes plant parts has seeked apparent attention of the scientists

�The formation of NPs being �intracellular � extracellular �can easily be manipulated by controlling various � A-process � B-parameters like: � substrateconcentration, � p. H, � temperature � and many more �

�The metal NPs hold a variety of uses �in the pharmaceutical sector, �catalysis �sensor

Several methods used for the � formation NPs include : � electrochemical, � sonochemical, � -thermal decomposition � laser ablation, � chemical reduction, � polyol and microemulsion � method. �

These methods are described below in � detail with suitable examples of each type of � NPs. � The synthesis of semiconductor � nanocrystal can be categorized into two basic types, � 1 - synthesis in aqueous media � 2 - synthesis in organic media. � 3 -using biological agents for the synthesis of � NP

Electrochemical Synthesis �This method involves the passing and conduction �of electric current through an electrolytic solution �resulting in chemical changes. In an electrochemical �method, two electrodes of metal made �as anode and cathode are dipped in the electrolytic �solution containing metal salt and a stabilizer �and electric voltage is applied over the �electrodes (Ibrahim et al. 2013).

Electrochemical Synthesis

�In this process, a �constant electric current flows into the electrolytic �cell leading to the dissociation of metal �salt solution due to its ionization.

�Oxidation �occurs and metal sheet is dissolved at the anode while the reduction of intermediate salt takes place at �cathode �. Metal is removed from the �anode terminal and gets deposited onto cathode �plate.

At the end of electrolysis process, � metal atoms in the form of NPs are carefully � collected from cathode �. (terminal). �

The surfactants like poly � (N-vinylpyrrolidone) (PVP) can be � used forsynthesis of Ag. NPs in the aqueous phase. By � adding anionic surfactants to the � electrolyte at an optimum level, the particle size distribution can be improved.

The highly pure Ag. NPs of different sizes can be obtained by just an alteration in the current density. The surfactants like poly (N-vinylpyrrolidone) (PVP) can synthesis of Ag. NPs in the aqueous phase.

By adding anionic surfactants to the electrolyte at an optimum level, the particle size distribution can be improved

The highly pure Ag. NPs of � different sizes canbe obtained by just an alteration in current � density. �

PVP as a stabilizer favours � to formation of monodisperse � Ag. NPs and decreases the deposition of silver on � cathode. . �

Electrochemical method possesses � certain advantages over chemical methods as it leads � tothe formation of size and shape-controlled highly pure metal NPs. The significant features of electrochemical methods are : 1 -its ease of operation, � 2 -high productivity of NPs � 3 - absence of any undesired side products. �

Sonochemical Method �

This method has been used for the synthesis � of metal NPs by the reduction of metal salt solution in the aqueous � phase. A sonochemical reaction � results from the �

acoustic cavitation produced by � ultrasonic waves and implosion of bubbles � A pulse of high energy is given to � produce heavy nuclei �

ultrasonic energy which in turn � lead to sudden release of. The water molecules generate � free radical species through the � production of ultrasound in the aqueous phase. � Generated H+ � ions cause the reduction of metal � ions according to the following equations: � H 2 O H ++ OH � -

What wants to be oxidized?

Metal salt solution reduced to metallic NPs by � the high temperature and pressure applied � during this process. The transient temperature and fast � cooling rates are necessary for the formation of particles in the sonochemical process.

This method aims at controlling the � particle size and morphology of NPs within a � much narrow size distribution. � The productivity and properties of synthesized material depend upon the ultrasonic power) and frequency, � dissolved gas, � type of � solvent and � temperature of � the solution � ( � �

Laser Ablation � �It is a physical technique to generate NPs and is characterized by the absence of any counter-ion �contamination and surface active molecules. �There are two main problems. �

faced by researchers while using laser � ablation method. � - Firstly, due to post-ablation � agglomeration, the particles coalesce with each other � and form large clusters. � - Secondly, at higher laser � fluence, large fragments are formed � which limit the formation of small clusters �

The advantages of laser � ablation technique involve no use of chemical reagents and � simplicity The method is quite fast � and effective and does not require several � reaction steps as well as long processing time to � carry out the reaction �

Chemical method for the � synthesis of NPs

Chemical Reduction Chemical method for the synthesis of NPs has � been greatly employed. This method is relatively � simple and easy to perform the synthesis of � stable NPs in solution. �

Metal precursors, reducing agents and stabilizing agents are three basic components used in any chemical method. For the synthesis of monodisperse and uniform-sized NPs, all the nuclei should be formed at the same time to acquire the same subsequent growth.

The only disadvantage of chemical � reduction synthesis method is that it � involves the use of some toxic chemicals which may � cause harm to the users as well as environment. � Moreover, the process is quiet costly as it takes � into account the utility of expensive chemical �

Biological Synthesis �

Biological Synthesis Recent trend has adopted the use of � bacteria, fungus, actinomycetes, plant � and plant parts for the synthesis of metal and � metal oxide NPs. Biological approach is environmental � friendly, non-toxic and relatively cheap. �

Also, this � approach does not involve the use of any � harmful chemicals as well as no energy intensive � process is required for the synthesis purpose �

Bacteria-Mediated Synthesis � The use of micro-organisms for the NPs synthesis � purpose is found to be easy, economical � and eco-friendly. � s �

Ag. NPs have been synthesized intracellularly and extracellularly using Bacillus strain CS 11. For this, Ag. NO 3 solution was added to the nutrient broth-containing bacterial biomass

and incubated for 72 h at room temperature in the presence of light. The change in colour of the medium from pale yellow to brown has indicated the formation of Ag. NP �

The biosynthesis of Au. NPs has been � reported from Pseudomonas aeruginosa � and Rhodopseudomonas capsulate whereby the cell free � supernatant of these two strains is mixed with � hydrogen tetrachloroaurate, �

indicating the colour � change of solution to purple or � red wine, further confirming the formation of � Au. NPs. The p. H of the solution is the deciding factor � for the shape and size of NPs. �

At p. H 4 and 7, nanoplates and � spherical NPs of size range 10– 20 � nm have been formed, respectively � Cubic Au. NPs were developed � when a filamentous cyanobacterium, � Plectonema boryanum �

The mechanism for the � bioreduction of silver ion to Ag. NPs is still � unclear. � Although, it is considered that some � enzymes like nitrate reductase secreted � by the microbes are responsible for the reduction �

Ag. NPs can also be synthesized by � adding Ag. NO 3 solution to the � supernatant of bacterial cultures of Bacillus subtilis, � Lactobacillus

The extracellular � metabolites excreted by the � cultures reduce the silver ions into Ag. NPs in the � presence of light

acidophilus, Klebsiella � pneumoniae, Escherichia coli, � Enterobacter cloacae and � Staphylococcus aureus, etc. �

Fungus-Mediated Synthesis � The use of fungal species has also been � reported for the formation of Ag. NPs. ). �

The fungus mediated � formation of Ag. NPs is based on the � mechanism that the fungal cells trap Ag ions � on its surface followed by the reduction with the � help of released enzymes. �

The fungal species � Aspergillus terreus has also been reported � earlier leading to formation of Ag. NPs by � extracellular nicotinamide adenine dinucleotide � dehydrogenase (NADH)-dependent reductase enzyme �

Extracellular biosynthesis of � Ag. NPs by the use of Fusarium oxysporum is � based on the reduction of metal ions by � nitrate-dependent reductase enzyme and shuttle � quinone process Fungi produce �

large amounts of Ag. NPs as compared to � bacteria due to the secretion of a large � number of proteins by a fungus. � Phanerochaete chrysosporium � (fungal mycelium) � was treated with HAu. Cl 4 under ambient � conditions to form Au. NPs within 90 min by � the

protein secreted by fungus itself. � The extracellular � and intracellular production of Au. NPs was � due to the secretion of enzymes lacase and � ligninase by fungus, respectively Fungi �

F. oxysporum and Verticiilium species � were able to form iron oxides mainly Fe 3 O 4 � by hydrolyzing the precursor ions � extracellularly

Plant-Mediated Synthesis � A variety of plant parts and their extracts have � been used to synthesize Ag. NPs. � The sun-dried � mass of Cinnamomum camphora leaf � extract has been reported to form spherical Ag. NPs. � The polyol component and the water- � soluble heterocyclic

compounds present in the leaf extract � could be responsible for the reduction of � silver ions and their stabilization � The extracellular enzymatic synthesis of � Ag. NPs has been obtained when geranium ( � P. graveolens) � leaf extract was exposed to Ag. NO 3 solution. �

The terpenoids, proteins and other � bio-organic compounds in leaf broth � were the causal agents for the reduction of Ag ions and their stabilization

ﺫ Thanks � for � your attention �