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Green Synthesis, Characterization and Applications of Nanoparticles
Автор: Elsevier Science
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Green Synthesis, Characterization and Applications of Nanoparticles shows how eco-friendly nanoparticles are engineered and used. In particular, metal nanoparticles, metal oxide nanoparticles and other categories of nanoparticles are discussed. The book outlines a range of methodologies and explores the appropriate use of each. Characterization methods include spectroscopic, microscopic and diffraction methods, but magnetic resonance methods are also included as they can be used to understand the mechanism of nanoparticle synthesis using organisms. Applications covered include targeted drug delivery, water purification and hydrogen generation.
This is an important research resource for those wishing to learn more about how eco-efficient nanoparticles can best be used. Theoretical details and mathematical derivations are kept to a necessary minimum to suit the need of interdisciplinary audiences and those who may be relatively new to the field.
Explores recent trends in growth, characterization, properties and applications of nanoparticles Gives readers an understanding on how they are applied through the use of case studies and examples Assesses the advantages and disadvantages of a variety of synthesis and characterization techniques for green nanoparticles in different situations
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There has been a great deal of development in the field of nanoparticle synthesis and characterization in recent years. Green synthesis methods have attracted the scientific community throughout the globe due to environmental and sustainability concerns. Different characterization methods have come into practice in view of the wide range of nanoparticle applications. This collection, Green Synthesis, Characterization, and Applications of Nanoparticles, is an attempt to present a holistic view. Metal nanoparticles, metal oxide nanoparticles, and other categories of nanoparticles constitute the subject matter. Water purification, hydrogen generation, targeted drug delivery, and biomedical applications have been addressed in detail. This volume has 21 chapters written by eminent experts from different laboratories/countries highlighting the recent trends. The interdisciplinary character of this collection has emerged in a natural way. We hope that the readers will come across new challenges and future lines of action in the area of green synthesis of nanoparticles, their characterization, and applications.
We express our heartfelt gratitude to all the expert contributors for their valuable and informative chapters. We also thank the anonymous reviewers of this book project for their constructive suggestions. We sincerely thank Simon Holt, the acquisitions editor for the Micro and Nano Technologies series at, Elsevier, and Naomi Robertson, the editorial project manager, who not only gave us an opportunity to present this work, but also extended their constant support from the start of this project to its publication.
Green synthesis of nanoparticles: A greener approach for a cleaner future
Gaurav Pal; Priya Rai; Anjana Pandey Department of Biotechnology, MNNIT Allahabad, Allahabad, Uttar Pradesh, India
Nanotechnology, the study of matter at the nanoscale (i.e., between 1–100 nm), has opened up novel dimensions in the field of biotechnology and nanomedicine, along with various other important applications such as drug delivery, electronics, cosmetics, and biosensors. Nanoparticles of varied shapes and sizes can be synthesized by using physical, chemical, or biological pathways. However, exploiting physical and chemical routes lead to high energy consumption, low yield, high cost, and environmental damage by employing harsh reducing agents. The biological pathways involve the use of microorganisms (bacteria, fungi, yeast, algae, etc.) or plants, and using microorganisms is riskier because of the pathogenicity issue; it also requires maintenance of large cultures. Therefore, synthesis of nanoparticles with greener methods is preferred. In this chapter, we present a generalized view of green synthesis for the generation of nanoparticles involving plants or their parts as a cost-effective, simpler, and eco-friendly approach. The various factors affecting the green synthesis of nanoparticles are also considered and explained.
Green synthesis; Nanoparticles; Nanomedicine; Phytocompounds; Quantum confinement
1Introduction
2Approaches Involved in the Green Synthesis of Nanoparticles
2.1Approaches for Nanoparticle Synthesis
2.2What Is a Nanoparticle?
2.3Types of Nanoparticles
3Methods of Nanoparticle Generation
3.1Physical Approach
3.2Chemical Approach
3.3Biological Methods
4Green Synthesis of Nanoparticles
4.1Bacteria-Mediated Nanoparticle Generation
4.2Fungi-Mediated Nanoparticle Generation
4.3Actinomycetes-Mediated Nanoparticle Generation
4.4Yeast-Mediated Nanoparticle Generation
4.5Algae-Mediated Nanoparticle Generation
4.6Biomolecular Templates for Engineering Nanoparticles
4.7Plant-Mediated Nanoparticle Generation
5Factors Affecting Green Synthesis of Nanoparticles
5.1ph of the Reaction Medium
5.2Reaction Temperature
5.3Method of Production or Technique Used
5.4Pressure
5.5Time
6Conclusion
Rapid progressions and technological innovations in the field of science and technology have generated immense interest among the research community across the globe to explore novel aspects of nanotechnology. Nanotechnology can be defined as the manipulation of matter such that any one of its dimensions falls in the nanoscale range (i.e., 1–100 nm) [1]. Particles generated at the nanoscale have varied unique properties (optical, magnetic, electrical, etc.) because of their very large specific surface area, high surface energy, and quantum confinement [2]. Due to these exclusive physicochemical properties, nanoparticles find endless applications in medicine [3], cosmetics [4], electronics [5], the food industry [6], and the chemical industry [7]. Metallic nanoparticles can be generated through various routes comprised of physical, chemical, and biological pathways [8]. These various physicochemical and biological pathways for nanoparticle synthesis fall under two distinct categories: a top-down approach and a bottom-up approach.
The top-down approach involves processes in which nanoparticles are generated via size reduction, whereas in the bottom-up approach, nanoparticles are generated from small entities such as atoms and molecules [9].
The commonly used physical methods for the synthesis of nanoparticles are laser ablation [10], inert gas condensation [11], electric arc discharge [12], and the radiofrequency (RF) plasma method [13]. These physical methods require a lot of time to achieve thermal stability, consuming a lot of energy while raising the environmental temperature around the source material, along with occupying large spaces in the case of tube furnaces [14]. Therefore, the physical synthesis pathway is not suitable for the generation of nanoparticles. The major disadvantage with the chemical synthesis of nanoparticles is that it employs harsh reducing agents such as sodium borohydride, sodium citrate, etc., and organic solvents [15]. These chemical reagents pose toxicity issues along with environmental issues [16]. Due to the aforesaid reasons, the biological synthesis pathways are preferred over physical and chemical synthesis methods for the generation of nanoparticles. The biological synthesis method for the generation of nanoparticles involves the use of bacteria [17], fungi [18], algae [19], and plants [20]. In addition to being slow, the pathogenicity issue and the maintenance of large-scale cultures are major drawbacks associated with the use of microorganisms for the generation of nanoparticles [21,22].
Green synthesis of nanoparticles involves the use of plant or plant parts for the bioreduction of metal ions into their elemental form in the size range 1–100 nm [2]. The process of green synthesis is more efficient, simpler, and economical, and can easily be scaled up to perform larger operations [8]. Also, there is no need to maintain large-scale cultures, and the process does not pose a biohazard problem as in the case of microorganism-mediated synthesis of nanoparticles [23,24]. Different nanoparticles such as silver [25], gold [26], palladium [27], iron [28], and zinc oxide [29] have easily been synthesized through green synthesis. The agents responsible for the bioreduction of metallic ions are the phytocompounds present in the plant extracts such as polyphenols, terpenoids, and polyols [30]. The nanoparticles so generated possess remarkable antimicrobial [31], antioxidant [32], and catalytic [33] properties derived from the phytocompounds that reduce them into nanoparticles. These properties have resulted in a broad range of nanoparticle applications such as drug delivery [34], the enzyme industry [35], cosmetics [36], the food industry [37], and pharmaceuticals [38]. Other potential aspects of nanoparticles are currently being explored by the research community across the globe.
2 Approaches involved in the green synthesis of nanoparticles
The term nanotechnology is defined by Tokyo Science University Professor Norio Taniguchi as follows: Nanotechnology deals with the processing of separation, consolidation, and deformation of materials by one atom or by one molecule [39]. In simpler words, it is the science of manipulating matter on a molecular and atomic scale. Richard Feynman first introduced the concept of nanotechnology in 1959, which is considered the beginning of advanced nanotechnology [40]. The synthesis of nanoscale materials and the exploration of their unique physicochemical properties are examples of the rapid growth of the novel frontiers of this upcoming technology. As a result of these advancements nanotechnology, this field has gained enormous impulsion in diversified areas such as electronics [41], biomedical applications [42], the food industry [43], the chemical industry [44], the pharmaceutical industry [45], environmental health [46], the space industry [47], mechanics [48], and optics [49]. The development and utilization of nanomaterials has provided a more reliable and sustainable alternative solution to different technological and environmental challenges in various fields such as solar energy harvesting [50], drug delivery [51], catalysis [52], waste water treatment [53], and hydrogen generation [54].
The research community throughout the world is continuously engaged in developing eco-friendly techniques to produce products that are environmentally amiable and nontoxic, as well as highly effective, via the employment of green nanotechnology and biotechnology [55,56]. Nanomaterials synthesized through green technology in a one-step procedure are environmentally friendly with enhanced stability and remarkable properties and dimensions, thereby eliminating the need for high temperature, pressure, pH, etc., during synthesis [57].
Synthesis of nanomaterials can be achieved by using either the top-down or bottom-up approach. All the physical, chemical, and biological methods of synthesis of nanoparticles follow one of these two approaches (Fig. 1).
Fig. 1 Different types of processes for the synthesis of nanoparticles.
2.1 Approaches for nanoparticle synthesis
All the different methods of nanoparticle generation follow one of the two approaches: top-down approach or bottom-up approach.
2.1.1 Top-down
In this approach, the appropriate bulk material breaks down to fine particles through the use of suitable lithographic techniques such as grinding, sputtering, and milling [58].
2.1.2 Bottom-up
This approach involves nanoparticle generation through the self-assembly of atoms into new nuclei, which further grow into a particle possessing nanoscopic dimensions and employing various chemical and biological methods [59].
2.2 What is a nanoparticle?
Nanoparticles are materials with nanoscopic dimensions (i.e., in the range of 1–100 nm) falling in the transitional zone between individual molecules and their bulk counterparts [60,61]. Due to their size, they embrace exceptional physicochemical properties including a large specific surface area, high energy, and quantum internment [23,62,63]. Nanoparticles exhibit diverse chemical natures and can be metallic (silver, gold, copper, zinc, etc.), or comprised of metal oxide, silicates, polymers, organics, or carbon. In addition to their diverse chemical nature, nanoparticles can be produced in different morphologies such as spheres [64], cylinders [65], sheets [66], or tubes [67]. This amazing morphological and chemical diversity of nanoparticles results in shape dependent upon on the type of medium from which they are created, as well as the number of bioactive compounds present in the medium [68].
2.3 Types of nanoparticles
Nanoparticles can be of different types, such as metallic, metal oxide-based, alloy-based, and magnetic, as well as others.
2.3.1 Metallic nanoparticles
Such nanoparticles can be described as nanometals in nanoscopic dimensions (i.e., between 1-100 nm in size). Faraday (1857) first recognized the existence of metallic nanoparticles in solution [69], whereas Mie (1908) gave the quantitative description of the color-changing behavior of nanoparticles in solution [70]. The important characteristics of metallic nanoparticles include:
✓ Large surface-area-to-volume ratio
✓ Large surface energies
✓ Specific electronic structure (i.e., local density of states [LDOS]) provided by their transition between molecular and metallic states
✓ Plasmon excitation
✓ Quantum confinement
Different types of metallic nanoparticles have been synthesized, primarily of silver [71], gold [72], copper [73], palladium [74], and platinum [75]. Silver is the nanoparticle most widely preferred and synthesized via green synthesis because of its unique antibacterial property along with its easy reduction from monovalent silver to metallic silver [76]. Silver also exhibits the highest efficiency of plasmon excitation [77]. Silver enjoys wide-ranging applications in areas such as medicine [78], textiles [79], water treatment [80], and catalysis [81]. Likewise, gold nanoparticles are also of considerable importance but to a lesser extent than their silver counterparts. Other metallic nanoparticles have been reportedly synthesized in the literature, but in very low numbers.
2.3.2 Metal oxide nanoparticles
Synthesizing this type of nanoparticle involves connecting the metal centers with oxo (M-O-M) or hydroxo (M-OH-M) bridges, therefore producing metal-oxo or metal-hydroxo polymers in solution [82].
2.3.3 Alloy nanoparticles
Generating alloys by combining different elements can greatly extend the range of metallic nanoparticles' properties. In most cases, the synergistic effects of alloying result in enhancement of specific properties [83]. By varying the composition and atomic ordering, as well as the size of the clusters, their physical and chemical properties can be easily tuned, which has generated much interest in alloy nanoparticles [84]. Nanoalloys may also display properties very distinct from their bulk counterparts, leading to a number of applications in the field of electronics, engineering, and catalysis [85].
2.3.4 Magnetic nanoparticles
These nanoparticles consist of two types of components: a magnetic component, such as iron, nickel, or cobalt, and a chemical component with a specific functionality [86]. Due to the presence of the magnetic component, these nanoparticles can easily be magnetically manipulated [87]. As these nanoparticles possess a range of attractive properties, they have applications in catalysis [88], medical diagnostics [89], and tissue-specific targeting [90].
3 Methods of nanoparticle generation
Nanoparticles can be generated in three ways: physical, chemical, and biological.
3.1 Physical approach
The most commonly used methods in the physical approach to nanoparticle generation include laser ablation [91], high-energy ball milling (HEBM) [92], electrospraying [93], evaporation-condensation [94], and laser pyrolysis [95]. Other physical approaches include an arc discharge method [96], metal sputtering [97], atomization [98], and annealing [99]. Various nanoparticles such as silver, gold, lead sulfide, and fullerene have been successfully synthesized using evaporation-condensation methods [100]. These physical approaches are more advantageous than chemical approaches because of the absence of solvent contamination in the prepared thin films and the uniformity of synthesized nanoparticle distribution [96,101]. It has been demonstrated that silver nanoparticles could be synthesized via a small ceramic heater with a local heating source [10]. The vapor cools at a suitably rapid rate because the temperature gradient in the vicinity of the heater surface is very steep compared with that of a tube furnace. This makes the formation of small nanoparticles in a high concentration possible. This physical method can be useful as a nanoparticle generator for long-term experiments for inhalation toxicity studies and as a calibration device for nanoparticle measurement equipment [102]. Silver nanoparticles could be synthesized via laser ablation of metallic bulk materials in solution [103–110]. Silver nanoparticles are prepared via subdivision of bulk silver metal, usually by laser ablation methods [111,112]. The ablation efficiency and the characteristics of produced nanosilver particles depend upon many factors, such as the wavelength of the laser impinging the metallic target, the duration of the laser pulses (in the femto-, pico-, and nanosecond regimes), the laser fluence, the ablation time duration, and the effective liquid medium, with or without the presence of surfactants [21,23,113,114]. One important advantage of the laser ablation technique compared with other methods for production of metal colloids is the absence of chemical reagents in solution. Therefore, pure and uncontaminated metal colloids for further applications can be prepared with this technique [115].
3.2 Chemical approach
The most commonly used chemical methods include the sol-gel method, the microemulsion technique, hydrothermal synthesis, polyol synthesis, and chemical vapor synthesis. Chemical reduction with organic and inorganic reducing agents such as NaBH4 is the most common approach for the synthesis of silver nanoparticles. Other important reducing agents include sodium citrate, hydroquinone, gallic acid, and elemental hydrogen. Generally, these reactions are carried out in solution, and the product has colloidal characteristics. For this reason, the common term used for the overall phenomenon is coprecipitation, which involves the concurrence of different phenomena: reduction, nucleation, growth, coarsening, and/or agglomeration [116]. The aforementioned reducing agents reduce silver ions (Ag+) and lead to the formation of metallic silver (Ag⁰), which is followed by agglomeration into oligomeric clusters [103–105]. These clusters eventually lead to the formation of metallic colloidal silver particles [117–120]. The presence of surfactants comprising functionalities (e.g., thiols, amines, acids, and alcohols) for interactions with particle surfaces can stabilize particle growth and protect particles from sedimentation, agglomeration, or loss of their surface properties. A large quantity of nanoparticles can be synthesized using a chemical reduction method, but the major disadvantages are that reagents are toxic and the byproducts generated are not eco-friendly.
3.3 Biological methods
The biological methods include synthesis of nanoparticles using bacteria, fungi, or plants. The primary requirements of green synthesis of silver nanoparticles are silver metal ion solution and a reducing biological agent. In most cases, reducing agents or other constituents present in the cells act as stabilizing and capping agents, so there is no need to add capping and stabilizing agents from outside. The reducing agents are widely distributed in biological systems. The AgNPs have been synthesized using different organisms belonging to four out of five kingdoms of living organisms, that is, monera (prokaryotic organisms without true nucleus), protista (unicellular organisms with true nucleus), fungi (eukaryotic, saprophyte/parasite), and plantae (eukaryotic, autotrophs) [118].
4 Green synthesis of nanoparticles
As discussed earlier, nanoparticles can be generated in various ways (physical, chemical, or biological routes), but generating nanoparticles through physical and chemical pathways results in toxicity issues as well as environmental concerns. The physical pathway (for example, the use of a tube furnace) requires a large amount of space and generates a large amount of heat, raising the environmental temperature around the source material, in addition to being very time consuming. The major drawback to the chemical method of nanoparticle generation is its use of toxic solvents and chemicals, which could cause a great deal of harm to our already suffering environment. Therefore, the need for a different alternative in nanoparticle generation was felt across the globe, which led to the development of the green nanotechnology (or green nanobiotechnology) concept. Green nanotechnology is simple, cost-effective, and environment friendly, and has gained a lot of importance in the recent past. A large number of nanoparticles generated with green nanotechnology have successfully been used in various applications.
Green nanotechnology can be defined, in general, as the use of biological routes like bacteria, fungi, or plants for the synthesis of nanomaterials (or nanoparticles) with the aid of various biotechnological techniques. The nanoparticles so generated are free of toxic chemicals and are eco-friendly. We will discuss various biological routes for the synthesis of nanoparticles in detail.
4.1 Bacteria-mediated nanoparticle generation
Bacteria are potent biofactories for the synthesis of metallic nanoparticles such as silver and gold, because they are known to produce various inorganic materials either intra- or extracellularly. Silver is well known for its biocidal properties. However, some bacteria are resistant to silver [121], and they can accumulate silver on their cell wall to as much as 25% of their dry weight biomass, suggesting their potential use in the industrial recovery of silver from ore materials [122]. The first evidence of bacteria synthesizing silver nanoparticles was established using the Pseudomonas stutzeri AG259 strain isolated from a silver mine [123].
The most widely accepted mechanism of silver biosynthesis is the presence of the nitrate reductase enzyme, which converts nitrate into nitrite. In in vitro synthesis of silver using bacteria, the presence of alpha-nicotinamide adenine dinucleotide phosphate reduced form (NADPH)-dependent nitrate reductase removes the downstream processing step required in other cases [124]. A study reported intracellular E. coli DH5α-mediated synthesis of gold nanoparticles from chloroauric acid with mostly spherical morphology, along with some triangular and quasihexagonal morphologies, deposited on the cell surface, realizing the direct electrochemistry of hemoglobin and other proteins [125]. In contrast, extracellular synthesis of magnetite nanoparticles 10–50 nm in size was reportedly achieved under anaerobic conditions using Geobacter metallireducens GS-15, a nonmagnetotactic bacterium that was isolated from Potomac Riversediments [126]. Similarly, crystalline ferromagnetic Co3O4 nanoparticles 5–7 nm in size were extracellularly synthesized using a metal-tolerant marine bacterium, Brevibacterium casei, using cobalt acetate as precursor [127].
4.2 Fungi-mediated nanoparticle generation
Fungi are used to synthesize metallic nanoparticles because fungi exhibit tolerance and metal bioaccumulation ability, high binding capacity, and intracellular intake similar to that of bacteria [103–105]. Various fungi such as Fusarium sp. [128], Colletotrichum sp. [129], and Phaenerocheate chrysosporium [130] have been used for nanoparticle generation. Nanoparticle generation using fungi is more advantageous than using other microorganisms because fungi grow more quickly and are simpler to handle and fabricate in a laboratory process than bacteria. Fungal mycelial mesh can also withstand various conditions such as flow pressure and agitation in bioreactors or other reaction compartments. The nanoparticle synthesis mechanism in fungi is different in that fungi secrete large amounts of enzymes used to reduce silver ions that induce the formation of metallic nanoparticles [131]. These extracellular enzymes like naphthoquinones and anthraquinones are said to facilitate reduction. Considering the example of F. oxysporum, it is believed that the NADPH-dependent nitrate reductase and a shuttle quinine extracellular process are responsible for nanoparticle formation [132].
The first synthesis involving fungus-mediated approaches for the metal nanoparticle was performed in the beginning of the 20th century, and AgNPs with a diameter of 25 ± 12 nm were synthesized using the fungus Verticillium [119,120]. Verticillium luteoalbum was used for intracellular gold nanoparticle generation, in which morphology, as well as the size of the gold nanoparticles, varied according to pH changes in the medium [133,134]. The extract of saprophytic straw mushroom fungus, Volvariella volvacea, was used in extracellular, fungus-mediated nanoparticle biosynthesis, resulting in the production of gold, silver, and silver-gold nanoparticles [135].
4.3 Actinomycetes-Mediated nanoparticle generation
Actinomycetes are a member of the phylum Actinobacteria sharing various characteristics with fungi and are responsible for the production of at least two-thirds of the total antimicrobial compounds currently in use [136]. However, much research is needed in the field of nanoparticle generation using actinomycetes. Scientists have reported the formation of monodisperse spherical gold nanoparticles with an average size of 8 nm by using a new extremophilic actinomycete, Thermomonospora sp., which was stable for almost 6 months. Proteins responsible for nanoparticle stabilization were confirmed to be present on the nanoparticles' surface using Fourier-Transform Infrared Spectroscopic (FTIR) analysis [103–105]. Intracellular accumulation of gold nanoparticles 5–15 nm in size was reported from an alkalotolerant actinomycete, Rhodococcus sp., and the particles were found to be accumulated on the cell wall and cell membrane as Ag⁰ [103–105]. Similarly, silver nanoparticles are reported to have been synthesized by various actinomycetes such as Streptomyces sp. [137], Thermoactinomyces sp. [138], and Rhodococcus sp. [139]. The synthesized nanoparticles were applied in various biomedical applications and successfully tested for their antimicrobial ability against various pathogens [140].
4.4 Yeast-Mediated nanoparticle generation
Yeast, a unicellular eukaryotic microorganism, has been used mainly for the synthesis of semiconductors. Monodispersed, spherical, peptide-bound CdS quantum crystallites 20 Å in size were synthesized using yeast Candida glabrata, and Schizosaccharomyces pombe produced wurtzite hexagonal CdS crystals in mid-log phase 1–1.5 nm in size [141]. Similarly, Torulopsis sp. was used for the successful intracellular production of PbS nanocrystallites with a dimension of 2–5 nm in its vacuoles, and the produced nanoparticles were used in the fabrication of an ideal diode[142,143]. Silver-tolerant yeast strain MKY3 has been used for the extracellular synthesis of silver nanoparticles. In its log phase, the strain synthesized silver nanoparticles 2–5 nm in size when challenged with 1 mM soluble silver, and the particles were separated based on differential thawing of the sample. The formation of silver nanoparticles was confirmed by optical absorption, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy [142,143].
4.5 Algae-Mediated nanoparticle generation
Many studies have reported the use of algae for the synthesis of nanoparticles. A blue-green alga, Spirulina platensis has reportedly been used in protein-mediated gold nanoparticle synthesis, resulting in the formation of uniform-sized gold nanoparticles with an average size of approximately 5 nm. These were used for antibacterial assays against Bacillus subtilis and Staphylococcus aureus [144]. Sargassum wightii, a brown seaweed, has been reported to synthesize stable, well-dispersed gold nanoparticles of the size range 8–12 nm, as confirmed by UV-visible spectrum, transmission electron spectroscopy, and x-ray diffraction analysis [145]. Similarly, silver nanoparticles were also synthesized using Sargassum wightii and were tested for their antibacterial potential [146]. Gold nanoparticles, EPS-gold, and silica-gold bionanocomposites have been synthesized with diatoms such as Navicula atomus and Diadesmis gallica [147].
4.6 Biomolecular templates for engineering nanoparticles
Various biomolecules such as nucleic acids, cell membranes, and viruses are reportedly used as templates for the generation of nanoparticles. DNA, with its strong affinity toward transition metal ions, acts as an excellent biomolecular template. Studies have reported the synthesis of gold nanoparticles when DNA hydrogel was made and cross-linked, followed by incorporation of transition metal ions such as gold in to DNA macromolecules. Bioreduction of Au³ + ions into Au⁰ atoms took place in this process, and metal clusters developed on the DNA chain into Au nanoparticles, which were further applied in catalytic activities [148]. Using DNA as the template, a highly stable, wire-like cluster of silver nanoparticles was synthesized, which was then used as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate [149]. In a study, DNA was used as a template, and an electroless photolytic method was devised for the synthesis of gold nanostructures. The nanoclusters have a size of 10−40 nm, and the nanostructure have a diameter of 40−70 nm with resistivity comparable to that of pure metal. The gold nanostructures were continuous, as revealed by electrical characterization, and exhibited Ohmic behavior with very low contact resistance with the electrodes [150]. Continuous and electrically conductive nanowires of Au, Pd, and CdS have reportedly been synthesized through fast, electroless, UV-irradiation/microwave-assisted methods using DNA as both a reducing agent and a capping agent. These nanowires were proposed for use as the building blocks of various nanodevices, sensors, and other optoelectronic applications [150–153]. Similarly, biological membranes have also been utilized as templates to synthesize and engineer nanoparticles, exploiting the membranes' ultrafine pores. Gold nanoparticles were synthesized using a rubber membrane made from Hevea brasiliensis acting as a preservative in the reduction of Au+ 3 in a solution at a temperature of 80°C [154]. Alternatively, nanoparticles of uniform size and morphology could also be synthesized using viruses as templates, utilizing the hollow spaces in their center [155]. Tobacco mosaic virus (TMV) was exploited as a template for the synthesis of iron oxides through oxidative hydrolysis, CdS and PbS cocrystallization, and SiO2 synthesis using sol-gel condensation [156]. Likewise, an M13 bacteriophage was used for the synthesis of quantum dots of ZnS and CdS [157,158].
4.7 Plant-Mediated nanoparticle generation
Using plants for the production assembly of silver nanoparticles has drawn attention in recent years because its rapid, ecofriendly, nonpathogenic, and economic protocol provides a single-step technique for the biosynthetic process. The reduction and stabilization of silver ions by a combination of biomolecules (such as proteins, amino acids, polysaccharides, terpenes, alkaloids, phenolics, saponins, and vitamins) which are already established in the plant extracts, provides the easiest and cheapest way to produce silver nanoparticles [159] (Fig. 2).
Fig. 2 Schematic diagram depicting green synthesis of silver nanoparticles.
The major advantages of using plant extracts for silver nanoparticle synthesis is that they are easily available, safe, nontoxic in most cases, have a broad variety of metabolites that can aid in the reduction of silver ions, and are quicker in synthesis than microbes. Because of photochemicals, plant-assisted reduction is the main mechanism considered for this process. The relatively high levels of the steroids, saponins, carbohydrates, and flavonoids act as reducing agents and phytoconstituents as the capping agents, which provide stability to the silver nanoparticles [160]. A list of nanoparticles synthesized using green synthetic methods has been summarized in Table 1.
The kinetics of plant-mediated nanomaterial synthesis are much higher than in other biosynthetic methods comparable to chemical nanoparticle synthesis. Silver nanoparticles have been synthesized using a variety of medicinal plants such as Oryza sativa, Helianthus annus, Saccharum officinarum, Sorghum bicolor, Aloe vera, Zea mays, Basella alba, and Capsicum annuum, and have been used in various pharmaceutical as well as biological applications [182]. The aqueous extract of Alternanthera dentate was used for the rapid synthesis of silver nanoparticles 50–100 nm in size. The extracellular silver nanoparticles were synthesized within 10 min and exhibited antibacterial activity against Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia, and Enterococcus faecalis [183]. Gold nanoparticles 20–25 nm in size were synthesized showing spherical, triangular, hexagonal, and rod-shaped morphologies using Cymbopogon citratus leaf extract, and were found to boost the predation efficiency of copepod Mesocyclops aspericornis against malaria and dengue mosquitoes [184]. Copper oxide nanoparticles were synthesized extracellularly through a colloid-thermal synthesis process using a medicinal plant, Euphorbia nivulia, and the particles were proposed to be stabilized by the terpenoids and peptides present within the latex. The antibacterial activity of the particles was also assessed [174]. In a study, indium oxide (In2O3) nanoparticles were synthesized using indium acetylacetonate a solution extracted from the Aloe vera plant, and the particles were characterized for their structural, morphological, and optical properties [185]. Zinc oxide nanoparticles with hexagonal wurtzite structure were synthesized from a zinc hyperaccumulator plant, Sedum alfredii, with a mean size of 53.7 nm [186]. Furthermore, iron oxide nanoparticles were synthesized using alfalfa with four different pH values in the solution, and aggregates 1–10 nm in size were obtained. It was proposed that the size of the nanoparticles could be controlled in the region of 1–4 nm under optimal pH conditions [187].
5 Factors affecting green synthesis of nanoparticles
Various factors, such as pH, temperature, and reaction time, control the synthesis and stabilization of nanoparticles synthesized by biological entities. Some of the factors that influence biogenic nanoparticle synthesis are:
5.1 pH of the reaction medium
The pH of the reaction medium plays an important role in the generation of nanoparticles [133]. Different hydrogen ion concentrations lead to differences in the size and shape of the nanoparticles. It was also observed that larger particles are produced at lower acidic pH values than at higher pH values [187a,188]. Large rod-shaped Au nanoparticles (25–85 nm) were formed from Avena sativa at pH 2, whereas relatively smaller nanoparticles (5–20 nm) were formed at pH 3 and 4 [189]. Similarly, more spherical silver nanoparticles were synthesized using Cinnamon zeylanicum bark extract at higher pH values (pH 5 and above) [190].
5.2 Reaction temperature
Temperature plays a very stimulating role in the synthesis of metallic nanoparticles by specifically affecting the shapes and sizes of the resulting nanoparticles. When gold nanoparticles were synthesized using Cymbopogon flexosus leaf extract, it was observed that lower reaction temperatures resulted in the formation of nanotriangles, whereas more spherical nanoparticles were synthesized along with the nanotriangles at higher reaction temperatures [191].
5.3 Method of production or technique used
Nanoparticles are synthesized through different methods ranging from physical and chemical to biological synthetic procedures, and each of these procedures have specific positive and negative aspects. Because they are ecofriendly and nontoxic, nanoparticles synthesized through biological routes are considered to be far superior to those synthesized via other synthetic routes [192].
Pressure also plays an important role in the synthesis of metallic nanoparticles as it affects the shape and size of the nanoparticles synthesized [193]. Studies suggest that, when ambient pressure conditions are provided, the reduction of metal ions through phytochemical agents take place at a faster rate than normal [194].
5.5 Time
The time duration of incubation for nanoparticle reaction media incubation greatly affects the quality and morphology of the nanoparticle [195]. Time variations also influence the properties of the synthesized nanoparticles as do light exposure, the synthesis method used, and storage conditions [196,197]. Long nanoparticle incubation may result in aggregation or shrinkage, which might cause a reduction in the nanoparticles' potential [198].
In recent years, green biotechnology has emerged as a major tool for the production of nanoparticles that are environment-friendly, nontoxic, and cost-effective. Nanobiotechnology holds immense potential with enormous areas of applications yet to be explored. Using green synthesis, we can synthesize different varieties of nanoparticles that can further be applied in a diversity of applications. Synthesis of nanoparticles using greener methods is affected by various factors such as pH, temperature, and incubation time, which must be taken into consideration to obtain an optimal result. This chapter provides brief information about various approaches and methods in the synthesis of nanoparticles, with special emphasis on green nanoparticle synthesis and the factors governing nanoparticle formation. More advancement and investigation in the field of green nanotechnology would surely help expand our knowledge base and improving our understanding of the principles of green nanoparticle synthesis and the factors affecting that synthesis, which will further determine more efficient applications of nanoparticles in different areas of interest.
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Goodreads appetizer: When two people make beautiful music together onstage, can their love survive once the curtain falls? Linnea Larson is willing to do anything to keep her family's Minneapolis dinner theatre from going under. Anything, that is, besides accepting a date from the Hollywood hunk her father hired to inject a dose of star power into their production of Guys & Dolls. It's a toss up whether his greatest claim to fame is playing a superhero on screen, or a super stud off screen. Neither fact convinces her he's got what it takes to share her stage. And thanks to a life long pact with her best friend, she never dates actors.
Luke Powell has fame, fortune, and an endless string of women, but also a lingering dissatisfaction with his picture perfect life. Looking for a change, he escapes to his theatrical roots. What he finds are wary cast mates, a nervous best friend convinced the show will ruin Luke's career, and an adorable costar who stubbornly refuses to go out with him. Suddenly singing and dancing aren't the only challenges he'll tackle over the summer. Far from the spotlights of Hollywood, can he find happiness in the footlights of a tiny theatre?
Despite Luke dragging her into his daily paparazzi nightmare, Linnea can't deny her mounting attraction to his irresistible charm. And even if she's crazy enough to chance getting involved, their fling would have a guaranteed expiration date. He's leaving at the end of the run, and she's tied to her family's theatre. Why risk the inevitable heartbreak? Their job is to act like they're in love, but will they decide it's worth the leap to fall in love for real?
My Thoughts: Act Like We're in Love is a wonderful contemporary romance. It is sweet, it is fresh, it is funny and very importantly: it is very well written!
The story is set in Minneapolis showing the life of a local (musical) theatre company whose routine is quite shaken up by an international movie star being cast in their latest production.
Linnea is the heroine, whose parents own the theatre. The theatre is going through some difficult times and to save its precarious financial situation the director of the company (Linnea's father) casts Luke a world famous action movie star to play the lead in their new production of Guys and Dolls. Most of the company is simply surprised and excited to finally meet and work with such a celebrity, but Linnea is quite hostile. First of all she is a bit hurt that her parents instead of discussing the theatre's situation with her chose to remedy it this way, secondly she truly fears that even if Luke is a good movie actor he won't be able to be a good stage actor and will endanger their production.
All characters, be it main or supporting are well created and interesting, Christi Barth gives them flesh and some characteristics even if they just pass through a scene. But the main four characters: Linnea, Luke, Wes (Luke's manager and good friend, also romantical hero for Ingrid) and Ingrid (dancer of the company, best friend of Linnea) are truly well developed (I even resented Wes and Ingrid some of their showtime, I would have loved to see more of Luke and Linnea, but that is just a personal preference :-p), fresh and three dimensonal.
Luke is so much more than a cardboard Hollywood movie star, and Linnea shows endearing vulnerability besides being a gorgeous and talented actress/singer. And then when these two get together, not spraks but fireworks fly! The chemistry between Luke and Linnea is so potent, the very first scene they meet, you will feel all tingly, Christi Barth does an amazing job conveying this extraordinarily powerful attraction and chemistry between these two! Every one of their interaction is full of life, teasing banter or sweet innuendos.
The romance is sweet and interesting, I loved how Christi Barth included other characters and aspects of the H/H's life and not focused only on developing the romance. I particularly enjoyed reading about the daily life of the company and how they prepare for the premiere, all these behind the scenes glimpses were executed with finesse keeping the reader enthralled in the story and loving the discovery of the mechanism of the theatre.
"Hey Sky, your mission doll's looking for you."
Luke loved getting to this point in the rehearsal process, when everyone called you by your character name. When the show took you so deep, you lived and breathed it. Almost as if the character you played was more real than you.
"Nathan and Adelaide have been engaged for fourteen years at the start of the show. Can you imagine? I can't keep a woman for fourteen months. " Stu barked out a laugh, and his self-deprecating grin encouraged the circle of men to join in on the joke.
"A gentleman never tells." Luke's voice dropped to a whisper. "But when I run out of fingers, I just stop counting for the night." A roar of masculine approval filled the hallway.
"Enough talk. I'm going to kiss you now," he whispered in her ear. "If you like it, i'll keep going. All night." Then he licked the rim down to the lobe, and gently bit down.
"I want my hands on you, Linnea. I'm going to discover you. What makes you happy, what makes you moan, what makes your eyes roll back in your head. Mostly I'm going to discover how good we are together." He levered himself up to look her square in the eyes. "If you don't feel the same way, you'd better stop me right now."
"Wow" she said and instantly regretted it.
I can only echo that: Wow... doesn't it give you those good kind of shivers?
He picked up the pace, his long legs eating up the pavement. Temper pushed him faster till Linnea practically trotted beside him to keep from being dragged along. She flat-out pissed him off. Couldn't she see how difficult this was for him? Did he really have to spell it out?
"Listen to me. I don't care whether Mom wants to see you - which, by the way, she does. Don't you get it? I want her to meet you. It's important. Not to be polite. Not to torture you as payback for your parents breathing down my neck every day. But because you both matter to me, damn it!"
"Linnea, [...] how can you believe when I kiss you it's anything less than the best moment of my day?"
Verdict: Act Like We're in Love is an amazing contemporary romance! If you like your romance with an interesting background story, three dimensional quirky supporting characters and charismatic, powerful main characters, if you like your romance to be sweet, sensual yet funny, then Act Like We're in Love is the novel for you!
"When you see a guy reach for the stars in the sky, you can bet that he's doing it for some doll."


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Oklahoma vs Baylor Picks and Odds
Baylor's Davion Mitchell (45) plays against Washington in an NCAA college basketball game Sunday, Nov. 29, 2020, in Las Vegas. (AP Photo/John Locher)
The No. 2 Baylor Bears (9-0, 2-0 Big 12) travel to Norman to take on the Oklahoma Sooners (6-2, 2-1 Big 12) Wednesday, Jan. 6, at 9:00 pm ET
The Bears are coming off a hard-fought 76-65 road victory Saturday against Iowa State, while the Sooners got a season-high 29 points from Umoja Gibson in a 75-71 win over No. 9 West Virginia Saturday
Read below for odds, analysis, and our best bet for this matchup
The No. 2 Baylor Bears (9-0, 2-0 Big 12) will try to remain undefeated Wednesday, Jan. 6 when they host the dangerous Oklahoma Sooners (6-2, 2-1 Big 12) in Waco. Tip is set for 9:00 p.m. ET inside the Ferrell Center.
Head coach Scott Drew's club scratched out a 76-65 road win over Iowa State Saturday in a game that saw the nation's best 3-point shooting team held without a 3-pointer in the first half for the first time all season. But junior guard Jared Butler came alive in the second half, scoring a game-high 21 to help the Bears
Meanwhile, Lon Kruger's squad knocked off No. 9 WVU 75-71 Saturday thanks to eight 3-pointers from junior guard Umoja Gibson on his way to a season-high 29 points. The victory was the Sooners' third straight over the Mountaineers and marked the fourth time in the last seven outings OU has beaten a ranked opponent. But Baylor is still a pretty big favorite over Oklahoma Wednesday.
Oklahoma vs #2 Baylor Odds
Oklahoma +11.5 (-110) +610 O 151.5 (-106)
Baylor -11.5 (-110) -900 U 151.15 (-114)
Odds taken Jan. 5 at FanDuel
Baylor got a scare Saturday in Ames, but passed its first major conference test with flying colors. The second-ranked Bears had been dominant this season through their first eight games, outscoring opponents by a national-best 32.8 points per game on average. But pesky Iowa State wouldn't go away at Hilton Coliseum.
Butler hit a dagger 3 from the left wing with just over a minute left as Baylor escaped with an 11-point win.
The Bears have been ranked No. 2 all season in the AP poll and have been rated anywhere between No. 1 and No. 3 by KenPom through the first six weeks of the 2020-21 campaign. This is a team that has legitimate national championship aspirations, even with its relatively soft strength of schedule (287th out of 340 Division I teams). But the Bears beat then-No. 5 Illinois 82-69 on Dec. 2 and had completely blown out most of its opponents prior to the somewhat-narrow victory over the Cyclones.
But Drew knows Big 12 play is where his team will prove its worth this season. The conference possesses five teams in the top-20 in KenPom's ratings — including the surprising Texas Longhorns at No. 6. The Bears have four players averaging in double-digits, including Butler at 16 points per game. Baylor got a wake-up call of sorts at Iowa State. It will be interesting to see how the program responds Wednesday.
2021 Naismith College Basketball Player of the Year Odds Tracker
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Our selection as finalists was formally recognised at the Telstra Business Awards Gala Dinner which was held on Friday 27 July at the Hyatt Hotel.
Check out all the photos from the night on our Facebook Page.
Directors of Nexis Accountants & Business Advisors, Domenic Stramandinoli and Scott Hammond were ecstatic with the selection.
"Being selected as a finalist is such a great honour and an indication of all of the hard work all our staff have put in over the years," said Stramandinoli.
The Telstra Business Awards are the most prestigious and coveted awards of their kind and 2012 marks the 20th year anniversary of the awards.
The Telstra Business Awards program celebrates the country's entrepreneurs and innovators. It offers a unique chance for small to medium businesses to be recognised for their hard work, commitment and of course, success.