Nanoparticles:
Particles between 1 and 100 nanometres (nm) in size with a surrounding interfacial layer are known as nanoparticles.
Nanoparticles are generally de?ned as:
“Particulate matter with at least one dimension that is less than 100 nm”. (SCENIHR 2005).
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Synthesis of nanoparticles:
The nanoparticles are synthesised by chemical, physical and biological methods. The property of the nanoparticles and efficacy of synthesis vary with procedure of synthesis. The chemical methods have been found to synthesize the nanoparticles more efficiently than other methods.
The commercial synthesis of nanoparticles is largely done by chemical methods. There are different chemical methods to synthesize the nanoparticle. Some of the important chemical methods are:
Chemical reduction method
colloidal method
sonochemical method
Chemical reduction method:
This method to synthesize copper nanoparticles In the chemical reduction methods, a copper salt is reduced by a reducing agent such as sodium borohydride (Aslam et al., 2002), ascorbate (Wang et al., 2006), polyol (Park et al., 2007), isopropyl alcohol with Cetyl Trimethyl Ammonium Bromide (CTAB) (Athawale et al., 2005) as well as glucose. Chemical reduction of copper salts using ascorbic acid (Vitamin C) is a new and green approach in which ascorbic acid is used both as the reduction and capping agent (Umer et al., 2012)
Microemulsion/colloidal method:
Microemulsion is a good technique for the synthesis of nanoparticles in which two immiscible fluids such as water in oil (W/O) or oil in water (O/W) or water in supercritical carbon dioxide (W/Sc. CO2) become a thermodynamically stable dispersion with the aid of a surfactant.Purely metallic nanoparticles (Cu, Ag, Co, Al), oxides (TiO2, SiO2), metal sulphides (CdS, ZnS) and various other nanomaterials are prepared using this technique (Cason et al., 2001).
Sonochemical method:
In the sonochemical process, powerful ultrasound radiations of 10-20 kHz are applied to molecules to enhance the chemical reaction (Suslick et al., 1991). This method, initially proposed for the synthesis of iron nanoparticles (Suslick et al., 1996), is now a days, used to synthesize different metals and metal oxides (Pol et al., 2003).
Nanotechnology:
Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is about 1 to 100 nanometers. Conversion of macromaterials in to nano size particles (1-100 nm) gives birth to new characteristics and the material behaves differently. The nanoparticles (NPs) have a high surface to volume ratio that increases their reactivity and possible biochemical activity (Dubchak et al., 2010)
Applications of nanotechnology in pests and plant diseases management:
Today use of chemicals such as pesticides, fungicides and herbicides is the fastest and cheapest way to control pests and diseases. Also biological control methods are very expensive currently. Uncontrolled use of pesticides has caused many problems such as: adverse effects on human health and adverse effects on pollinating insects. Intelligent use of chemicals on the nano scale can be a suitable solution for this problem. These materials are used into the part of plant that was attacked by disease or pest. Also these carriers in nano scale has self-regulation, this means that the medication on the required amount only be delivered into plant tissue. Nanotechnology helps to agricultural sciences and reduce environmental pollution by production pesticides and chemical fertilizers by using the nano particles. Nano materials including polymeric nano particles, iron oxide nano particles and gold nano particles which can be easily synthesized and exploited as pesticide . (Sharon et al., 2010). Diseases are one of the major factors limiting crop productivity. The problem with the disease management lies with the detection of the exact stage of prevention. Among the different diseases, the viral diseases are the most difficult to control, as one has to stop the spread of the disease by the vectors. But, once it starts showing its symptoms, pesticide application would not be of much use. Therefore, detection of exact stage such as stage of viral DNA replication or the production of initial viral protein is the key to the success of control of diseases particularly viral diseases (Prasanna, 2007)
The most simple and obvious way is direct application of nanoparticles in the soil on seeds or foliage to protect plants from pathogen invasion. In this way, the NPs may suppress the pathogens in a way comparable to chemical pesticides. When nanoparticles are to be applied directly in soil, their effects on non-target organisms especially the mineral fixing/solubilizing microorganisms will be of great significance. Hence, to reckon the scope and application of nanoparticles in plant disease management, the effects can be discussed through two major point of views i.e direct effect of NPs on pathogens and use of nanomaterials in formulating the pesticides i.e., nanopesticides. In view of ultra-small size of the particle and their very high degree of reactivity/sensitivity, the NPs may also prove very effective in the diagnosis of plant pathogens/diseases.
Effect of nanoparticles on the pathogens/microorganisms:
Nanoparticles because of ultra-small size, even smaller than a virus particle and high reactivity, may affect the activity of microorganisms. The silver has been generally found non injurious to microorganisms. However, silver NPs inhibited the colonization of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumonia. Nanoparticles have definite effect on the colonization of bacteria and fungi.
Effect of nanoparticles on bacteria:
Antibacterial activity of zinc nanoparticles against P. aeruginosa has been reported by Jayaseelan et al. (2012). The study showed that the ZnO NPs proved to be a novel antimicrobial material. The antibacterial activity of the synthesized Ag NPs/PVP against three different groups of bacteria-Staphylococcus aureus, E. coli, P. aeruginosa as well as against spores of Bacillus subtilis has been studied (Bryaskova et al., 2011). The antibacterial activities of CuO NPs has also been reported against S. aureus, Bacillus subtilis, P. aeruginosa and E. coli (Azam et al., 2012). Guzman et al. (2009) found that silver nanoparticles showed high antimicrobial and bactericidal activity against gram positive bacteria such as E. coli, P. aureginosa and S. aureus.
Effect of nanoparticles on plant pathogenic fungi:
The nanoparticles have also been found suppressive to fungi.
Singh et al. (2013) reported that among nanoforms of 15 micronutrients, CuSo4 and Na2B4O7 were found most effective in controlling rust disease of field peas. Microelements such as manganese and zinc also suppressed the damping off and charcoal rot diseases in sunflower (Abd El-Hai et al., 2009). The Ag NPs/PVP were tested for fungicidal activity against different yeasts and molds such as Candida albicans, C. krusei, C. tropicalis, C. glabrata and Aspergillus brasiliensis. Fungicidal effect of zinc oxide nanoparticles (ZnO NPs) against two postharvest pathogenic fungi, Botrytis cinerea and Penicillium expansum, have been reported.
