**1. Introduction**

Nanotechnology can regulate and manipulate objects at the individual level of atoms and particles. Physicist Richard Feynman previously envisioned the hypothetical utilization of nanotechnology in 1959, and indeed, the term "Nanotechnology" was coined by Norino Taniguchi. When a parameter is stated as a measure of 10−9 meters of SI units, it is called "nano" [1].

Dimensionality, shape, composition, homogeneity, and aggregation are used to classify nanoparticles. The shape and syllable structure of nanoparticles plays a significant role in their function and harmful impacts on the environment and people. Nanoparticles can be classified into one, two, and three-dimensional nanoparticles. One-dimensional nanoparticle includes thin flicks used in electronics and sensor devices. Two-dimensional nanoparticles are high in carbon nanotubes absorption capacity and constancy. Three-dimensional nanoparticles are dendrimer quantum points. On top of that, morphology may be the basis of nanoparticles flat, spherical, and crystal in structure. They may be in a single form or the arrangement of compounds. Nanoparticles can be supplementary classified oxide nanoparticles, sulfide nanoparticles, and magnet nanoparticles [2, 3].

Various physical, chemical, and biological strategies are generally utilized to synthesize nanoparticles. Integrated nanoparticles are considered unfavorable due to high capital cost, energy requirements, anaerobic conditions, utilization of toxicity generation of furnaces, and harmful waste. Nanoparticles are less biodegradable, and utilizing toxic chemicals for synthesis, and the absence of sustainability have restricted their utilization in medical applications. Therefore, the development of ecologically safe, economical, and biological compatibility events for the assembly of nanoparticles is preferred. The fabrication of nanoparticles by natural resources is economical and alternate for physical and chemical methods. The latest advances were made in developing nanotechnology collection of Nano-sized particles. These nanoparticles are considered building blocks for developing optoelectronic electronics and numerous biochemical and chemical sensors [2, 4].

Development of ecologically safe, economical, and biological compatibility procedures for the assembly of nanoparticles is preferred. The synthesis of nanoparticles by biological means is low-priced. For the fabrication of nanoparticles, biological synthesis, including microbes, has been exploited worldwide. Bacteria, fungi, and yeasts are chosen for synthesis due to their rapid growth rate, easy cultivation, and ability to grow ambient temperature, pH, and pressure environments. Because of their adaptation to a toxic metal environment, eco-friendly microorganisms have the inherent ability to integrate nanoparticles by following the reduction mechanism through internal and external-external routes. Microbes trap metal ions from the location and convert them into the basic form using their enzymes [2].

Nanomedicine utilizes nanoscale structures to diagnose, treat, and prevent diseases in improving human health. Nanomaterials are comparable to cellular elements, including nano quantity proteins; thus, they can target chosen sites without contacting other cellular machinery. Now scientists aim to integrate the modernity of nanomedicine with conventional molecular tools and biotechnology to develop advanced therapies for the treatment of disease and tissues repair, novel drug delivery systems, rapid and ultrasensitive analytic tools such as biosensors, biopharmaceuticals, surgical aids compatible biomaterials [2, 5].

Arthropods are extremely dangerous vectors of pathogens and parasites, which may hit epidemics or pandemics in the increasing world population of humans and animals [6]. Among them, mosquitoes (Diptera: Culicidae) represent a huge threat for millions of people worldwide, vectoring important diseases, including malaria, dengue, yellow fever, filariasis, Japanese encephalitis and Zika virus [7]. Furthermore, Culicidae transmits key pathogens and parasites that dogs and horses are very susceptible to, including dog heartworm, West Nile virus, and Eastern

#### *Bacterial Silver Nanoparticles: Method, Mechanism of Synthesis and Application in Mosquito… DOI: http://dx.doi.org/10.5772/intechopen.104144*

equine encephalitis [8, 9]. Unfortunately, no treatment is available for most of the arboviruses vectored by mosquitoes, with special reference to dengue. A promising interface between nanotechnology and arthropod control recently opened new routes to manage vector and pest populations [10].

Now the researcher is strongly promoting the development of nano-based insecticides. Nanobiotechnology is a new discipline in nanosciences that emerged from the interface between nanotechnology and biotechnology. This crossbreeding performance is green and environmentally friendly, biocompatible, inexpensive, and a great alternative to traditional chemical approaches in the pest control industry [11]. Among the bio-based insecticides, microbial insecticides are essential for improving the toxicity of mosquito larvae, causing less harm to non-target species, and reducing environmental risks. Therefore, microbially mediated nano metallic synthesis has proven to be an environmentally friendly and efficient source, and bacteria have been reported to be effective reducing agents in synthesizing silver and gold nanoparticles (NPs). In this synthesis method, several metabolites of microorganisms can be used, which simultaneously promote the reduction and stabilization of nanoparticles and the adhesion and formation of a layer of biomolecules on their surface, the corona, which increases their biocompatibility. In this context, the current work was aimed to study the method, mechanism of synthesize of silver nanoparticles using bacteria, characterize the silver nanoparticles and assess its larvicidal effectiveness against mosquito vectors.

#### **2. Synthesis of silver nanoparticle**

The specific mechanism for synthesizing nanoparticles using biological agents has not yet been developed, as diverse biological agents react inversely with metal ions. The composition of nanoparticles contains different biological molecules. In addition, the mechanism for intracellular and extracellular synthesis of nanoparticles differs in other biological agents (**Figure 1**). The cell wall of microorganisms plays a vital role in the endogenous synthesis of nanoparticles. The cell wall interacts electronically with the positively charged metal ions as it is negatively charged. Enzymes inside the cell wall biodegrade metal ions into nanoparticles, which eventually propagate through the cell wall in small volumes [12].

#### **2.1 Biosynthesis of metal nanoparticles using bacteria**

Many reports proved that bacteria is an excellent organic apparatus for the fabrication of metal nanoparticles—for instance, Streptomyces sp. M25 was isolated from a soil sample of Western Ghats and is used to synthesize silver nanoparticles [13]. The bacterial sample was inoculated into 100 ml of YEM broth and incubated in the rotary shaker for 5 days. 10 g bacterial mass was mixed with the 100 ml 1 Mm AgNO3. The reaction mixture was kept in a rotary shaker for 24 h. The color change is the primary confirmation of the synthesis of Ag NPs. The same solution was centrifuged, and the Ag NP was collected from the supernatant. The reaction mixer was further subjected to spectrometric UV-VIS spectrophotometer, Transmission electron microscopy, X-ray diffraction (XRD), and further characterization. The result showed that the size of the Ag NPs is 10-35 nm [13].

*Bacillus safensis* LAU 13 is the gram-positive spore-forming bacteria isolated from the waste dumpsite, and it was used for the biosynthesis of silver nanoparticles using


**Figure 1.**

*Schematic flow diagram for intracellular and extracellular synthesis of nanomaterials.*

the supernatant of *B. safensis* LAU 13. 1 mM of AgNO3 was diluted into the 40 ml of distilled water and add 1 ml of the supernatant of *B. safensis* LAU 13. The synthesized silver nanoparticle is spherical shaped, having a size of 5–95 nm, and it is confirmed by UV-VIS spectrophotometer, Fourier transform infrared spectroscopy, and Transmission electron microscope. Bio synthesized silver nanoparticles were used for bioassay against first instar Anopheles larvae in 10–100 μg/ml [14].

## **2.2 Mechanism of bacterial silver nanoparticle synthesis**

All the bacteria cannot reduce the metal ions. The capability of the reduction mechanism depends upon the bacterial defense mechanism. If the bacteria are exposed to the metal environment, metal ions like Ag + enter the cell and bind to the bacterial DNA. Silver particles have a positive charge, and DNA is contrarily charged. It changed the nature of DNA, resulting in a loss of structure and replication ability. Ag + binds with protein, especially thiol-containing proteins, and inhibits the function of proteins. The reductase enzyme of bacteria reacts metal (active Ag + − inactive Ag0) into inactive and is not lead to cell death. Most of the reductase enzymes are NADPH dependent, and bacteria can have or secrete this cofactor NADH dependent enzyme. The quantity of reductase enzymes varies between microorganisms. Extracellular and intracellular reductions do the defense mechanism. Extracellular means the bacteria can release the reductase enzyme to the external environment and reduce the metal ions. Intracellular implies the removal of metal ions by reductase that takes place inside the cell. If the bacteria do not have a reductase mechanism, they will die [12].
