Nanomaterials: Novel Preparation Routes, Characterizations, and Applications
JUHI SAXENA1 and ANUPAM JYOTI2*
JDr. B. Lai Institute of Biotechnology, Malviya Industrial Area, Jaipur, India
2Amity Institute of Biotechnology, Amity University Rajasthan, Jaipur, India
Nanotechnology is a multidisciplinary area as it finds diverse applications in biomedicine, catalysis, molecular detection, and many more. Scientists are facing challenges in obtaining nanoparticles (NPs) with high mono- dispersity, specific composition, and size. In the context of this, several research groups have exploited the synthesis of NPs by the biological system over non-biological systems due to many reasons. This chapter intends to present the biosynthesis of NPs involving the use of bacteria, yeast, fungi, and plants. Furthermore, we discussed the different characterization methods and overviewed on potential applications of nanomaterials in different fields.
Nanotechnology is a modem era of technology that influences all aspects of human life. Scientists are interested in the synthesis of nanoparticles (NPs) with high mono-dispersity, specific composition, and size, which form the core part of the nanomaterials . Several methods, including physical, chemical, and biological approaches, have been employed for the synthesis of NPs. The physical and chemical approaches are complicated, outdated, costly, and produce hazardous toxic wastes that are harmful to the environment and human health. Biogenic synthesis utilizing enzymes secreted by bacteria, fungi, yeast, and plants for NPs synthesis are gaining more importance . NPs have important applications in therapeutics as it fights against pathogenic microbes and hence have essential to clinical application. NPs kill the microbes by penetrating the cell wall, damaging the cell membrane, interacting with respiratory enzymes, inhibiting various signaling pathways, producing excessive free radicals, and damaging the DNA .
BIOLOGICAL SYNTHESIS OF NANOPARTICLES (NPS)
The biological synthesis of NPs is preferred over physical and chemical means because of its cost-effectiveness, rapid synthesis, the option of size and shape control, less toxic, and eco-friendly approach. In general, extracts of different biological sources like bacteria, fungi, yeast, and plants containing natural reducing agents are added to metal ion solutions and observed for a color change that results in NPs synthesis (Figure 2.1). In addition, these biomolecules also confer stability to NPs.
FIGURE 2.1 Schematics of nanoparticle synthesis from biological sources.
NANOPARTICLE (NP) SYNTHESIS BY BACTERIA
In previous years, the synthesis of NPs using bacteria has gained immense importance. Bacteria secrete various enzymes, including nitrate reductase that reduces metallic salts into NPs. In doing this, the size of metal reduced, and hence, surface area to volume ratio increases. Several bacterial species, including Escherichia coli , Ureibacillus thermosphaericus , Staphylococcus aureus , Corynebacterium strain SH09 , Bacillus cereus  and many more have been shown to synthesize NPs. The understanding of natural processes will apparently help in the discovery of an entirely new and unexplored methodology of metal NP synthesis.
NANOPARTICLE (NP) SYNTHESIS BY PLANT EXTRACTS
NPs synthesis by plants is gaining importance as it provides a single step biosynthesis process. Plants offer a simple source of NP synthesis, which is free from any toxicants. Stability of NPs is an important issue, which is resolved by plant-mediated synthesis as it provides natural capping agent. Furthermore, plant-mediated NP synthesis is a cost-effective and environment-friendly approach. Plants secrete reductase enzyme extracel- lularly that helps in the reduction of metal ions into NPs hence synthesized extracellularly. Primarily gold and silver nanoparticles (AgNPs) have been shown to synthesize by plant extracts. NP synthesis furthermore carried out using Azadirachta indica , Mirabilis jalapa , Murraya koenigii , Cardiospermum helicacabum , Aloe vera , and many more.
NANOPARTICLE (NP) SYNTHESIS BY FUNGI
Biological production of NPs by fungi is catching attention from the researchers nowadays. Different species of fungi like [14, 15] Fusarium solani , Pleurotus sajorcaju , Fusarium semitectum , Alter- naria altemata , Fusarium acuminatum , Penicillium fellutanum , Penicillium brevicompactum , Aspergillus clavatus , and Sclerotinia sclerotiorum  have been known for synthesis of NPs. Fungi have an upper edge in NP synthesis over other sources because of higher bioaccumulation, comparatively economic, effortless synthesis method, an excellent source of various extracellular enzymes, and simple downstream processing and biomass handling. There are various reasons onto which fungi can be preferred over bacteria and plants in NP synthesis :
- 1. Large Seeretor of Protein: Fungi have the capacity to produce large amounts of extracellular enzymes that helps in the reduction of metal ions into NPs.
- 2. Ease in Isolation: Being simple nutritional requirements fungi are easy to isolate and subculture that further helps in NPs synthesis.
- 3. Extracellular Synthesis: Being an excellent seeretor of enzymes outside the cell, fungi synthesize NP extracellularly that is helpful in easier downstream processing.
NANOPARTICLE (NP) SYNTHESIS BY YEAST
Yeast has also been shown to synthesize NPs with simple downstream processing. Biosynthesis of NPs using Candida glabrata and Schizosac- charomyces pombe , Rhodosporidium diobovatum , Saccharo- myces cerevisiae, and Cryptococcus humicola has been documented .
There are various attributes for NP characterization. These include size, morphology, and surface charge. A range of diverse techniques like spectroscopy techniques (UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy), microscopy techniques (scanning electron microscopy, transmission electron microscopy (ТЕМ)), x-ray based characterization techniques [x-ray photoemission spectroscopy (XPS), energy dispersive x-ray analysis (EDX), and particles size analyzer (dynamic light scattering (DLS)] are handful to characterize NPs (Figure 2.2).
1. UV-vis spectroscopy: This technique characterizes NPs based on the color they produce. There is free movement of electrons in metallic NPs. Hence, when the oscillation of electrons of NPs is in resonance with the light wave, oscillations result in a unique color and produces surface plasmon resonance (SPR) absorption band .
FIGURE 2.2 Characterization techniques of nanoparticles.
- 2. Fourier Transform Infrared (FTIR): In this technique, NPs are analyzed by observing the atomic vibrations when exposed to electromagnetic radiation in the wavelength ranging from 4000-400 cm-1. This provides the information which can assist molecular interaction studies such as hydrogen bonding, conformational changes, amino acid functionalization and also confirm the secondaiy structure of the proteins on the basis of the absorption of amide bonds .
- 3. Transmission Election Microscopy (ТЕМ): It is a powerful and teclmique for determining the structure and absolute size of NPs. Samples prepared for the ТЕМ analysis must be veiy thin and able to bear up the high vacuum present inside the instrument. These samples are fixed with uranyl acetate, and a beam of electrons is transmitted through ultra-thin sample results in surface characteristics .
- 4. Scanning Electron Microscopy (SEM): It provides three-dimensional images of the NPs. For SEM characterization, dried powder form of NP is taken and then mounted on a sample holder followed by coating with gold. Furthermore, a beam of electron scans the sample, and the surface characteristics of the sample are obtained from the secondaiy electrons emitted from the sample surface .
- 5. X-Ray Photoemission Spectroscopy (XPS): It is a quantitative spectroscopic teclmique that is used to estimate the elemental composition .
- 6. Energy Dispersive X-Ray Analysis (EDX): It is a useful technique performed along with SEM. In this technique, an electron beam strikes with the surface of the specimen results in X-ray to be emitted from the material. The energy of these emitted X-rays depends on the type of elements present in the material.
- 7. Dynamic Light Scattering (DLS): It is the fastest method of determining particle size. DLS is used to determine the size of NPs in colloidal suspensions. When a monochromatic light hits a solution of NPs in Brownian motion, it causes a change in the wavelength of incoming light due to the Doppler shift. This change is related to the size of the particle .
Nanomaterials with their unique properties have been exploited the most in various industrial sectors; however, evaluation of their biological, as well as environmental toxicity, is a major area of concern. In vivo and in vitro models, including plant, microbial systems, animals, primary cells, and cell lines have been tested for increasing accumulation nanomaterials in environmental systems . Nanomaterial for their therapeutic applications should have no or less cytotoxicity. Following administration, any exogenous agent interacts with blood cells, which are independent from the route of administration, therefore the interaction with blood components needed to be studied for cytotoxicity studies . Hemolysis assay can be employed for estimating toxicity on red blood cells. The assay revealed safe rates of RBC lysis of under 5% (1.1 to 4.6%) . Mechanistically, NPs produce reactive oxygen species and led to genotoxicity . NPs have also been reported to induce an inflammatory response through the activation of various cytokines .
NPs find diverse applications in various fields such as cosmetics, agriculture, pharmaceuticals, food and beverages, polymers, etc.  (Figure 2.3).
1. Anti-Bacterial: Emergence of multi-drug resistant bacterial strains is increasing day by day and representing a major threat. NPs, especially silver NP, are remarkable in killing both Gramnegative and Gram-positive bacterial pathogens. Mechanistically,
NPs enter to the bacterial cells by perforation in the cell wall, degrading membrane proteins, inhibiting signaling molecules, damaging DNA, and producing excessive free radicals.
- 2. Biosensors: Being specific electrochemical properties, NPs are instrumental in biosensor development. These biosensors are highly specific and sensitive and generate a response in a quick time. NPs provide a platform for biomolecules to adhere. The physicochemical properties of NPs are suitable for designing new sensing devices.
- 3. Disease Diagnosis: NPs have also found applications in the diagnosis of biomedical disorders. Presently, imaging techniques using iron oxide nanoparticles (IONPs) are used for the diagnosis of diseases.
FIGURE 2.3 Applications of nanotechnology.
- 4. Drug Delivery System: One of the important applications of NPs is in delivering the drug. NPs cany the drug and deliver it at the site of alignment. NPs improve important features, including solubility, stability, kinetic property, availability, and enhancing their efficacy.
- 5. Cosmetics: NPs are widely used in cosmetics. Zinc oxide and titanium dioxide NPs are used in various products, including sunscreens, cosmetics, sanitizer, and toothpaste.
- 6. Wound Healing: NPs are used in healing wounds as compared to standard silver sulfadiazine ointment.
- 7. Catalysis: NPs have remarkable biocatalytic properties. Metal NPs are used in the immobilization of enzymes for enhancing enzymatic activity.
- 8. Vegetable and Food Preservation: NPs have been shown to improve the shelf life of vegetables and fruits when added into sodium alginate thin film.
- • Fourier transform infrared
- • nanoparticles
- • scanning electron microscopy
- • surface plasmon resonance
- • transmission electron microscopy
- • x-ray photoemission spectroscopy
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