**2.1 Physicochemical methods**

NPs can be produced through two main approaches including top-down approach which is the production of NPs by making smaller and smaller structures by etching the bulk agents and bottom-up approaches which is the building up of NPs from atoms [6]. Physical, chemical, biological, and in some cases hybrid technique are the main ways of NP production. The physical methods of NP production include methods like laser ablation, high-energy irradiation, spray pyrolysis, and ion implantation, and the chemical one includes chemical reduction technique, sonochemical method, solgel process, microemulsion method, and electrochemistry. The biological method which is also called green NP biosynthesis involves application of plants extracts, microorganisms, enzymes, and even some agricultural wastes for NP production. Although the physical and chemical methods resulted in bulk amount of NPs a few times, application of chemical agents during the NP production in coordination with production of environmentally dangerous compounds simultaneously with NP production limited their applications [10]. For instance, thermolysis which is a chemical method for dissociation of organometallic precursors is performed at high temperatures by using organic solvents. Also in some cases, surfactant is added to the reaction medium for reducing coalescence of particles [11]. Chemical reduction technique is an adopted chemical method which used a wide range of reducing agents such as sodium borohydride, hydroxylamine, and N,N-dimethylformamide for production of zerovalent ions. Wave-assisted chemical method used ultrasonic waves in coordination with surfactant or reducing agent for production of NPs. The formation of micro cavities with high temperatures upon ultrasonic induction can start chemical reduction of substrates. The physical NP production methods are mainly energy intensive and need special devices. For instance, milling process is a way by which metallic microparticles are crush using high-energy ball mills. The gas-phase process or aerosol process which is divided into four main types (including flame reactor, plasma reactor, laser reactor and hot wall reactor, and chemical gas-phase deposition) is a particular way for the production of NPs like fullerenes and carbon nanotubes. All types of these methods need special devices and are mainly high energy consuming. NP production by wet chemical synthesis takes place at low temperature and is one of the most employed methods for NP production. Limitations in increasing batch reactor because of limited mixing and low heat transfer are mentioned as the main disadvantage of wet chemical synthesis method. The main advantages and disadvantages of NP production by physicochemical methods are summarized in **Table 1**.

### **2.2 Green NP production methods**

Green technology using biological systems like plants, microorganisms, and enzymes is rising fast as an alternative method for conventional chemical and

**5**

*Nanoparticle Synthesis, Applications, and Toxicity DOI: http://dx.doi.org/10.5772/intechopen.87973*

Gas condensation • Production of ultrafine

Laser ablation • High-purity NP

Solgel • Simple method

Chemical reduction • Cost-effective

alloys

production

of materials • Uses low temperature

Chemical vapor deposition and chemical vapor condensation

(CVD and CVC)

**Table 1.**

physical. In contrast to physiochemical methods which mainly lead to environmental toxicity, the biological NP production methods are known as eco-friendly and nontoxic protocols [16]. The biologically produced NPs' special features including high catalytic activity, low toxicity contaminations, high stability, and plausible biocompatibility and biodegradability make them distinctive from NPs produced from other methods. The microorganism's related NP productions are classified into intracellular and extracellular synthesis methods [17]. In an intracellular way, ions of interest are transported into the microbial cell and then reduced in the presence of enzymatic processes, while the metal ions are entrapped and reduced at microorganism's surface in an extracellular way [18]. Microbial NP production regarding the ability of the majority of bacteria and fungi in tolerating ambient conditions of varying temperatures, pH, salt concentrations, and pressures makes this approach a safe, cost-effective, and environmental method. Several microbial species have been isolated from different environments and used for production of various NPs. Compared to microbial production method, plant NP production is more desirable because it does not need any special and multistep processes, it has faster production rate, and it has easy scaling up procedure and because of its cost-effectiveness [19]. Investigations have revealed that metals bioaccumulated in plants which sometimes are called phytomining are mainly in the form of NPs. For instance, high level of silver NP accumulation in *Brassica juncea* and *Medicago sativa* [20], gold NP production in *M. sativa* [21], and copper NP accumulation in *Iris pseudacorus* [22] has been reported. This type of NP production has several disadvantages including heterologous size and morphology of NPs, difficult extraction and isolation procedure, and low production yield [21]. The alternative approach is in vitro production method which is based on reduction of ions using plant extracts. This method is more controllable through making change in plant extract and ion concentration, time of reaction, temperature, and pH of reaction medium. The production rate of this method is much faster and easier than in vivo method [23, 24]. For example, the

*The main physicochemical methods of NP production and their corresponding advantages and disadvantages.*

**Method Advantages Disadvantages Ref.**

nanocrystalline metals and

• Production of large range

• Good production rate

• High pure NPs production • High temperature of

procedure (above 300°C) • Uses of chemical agents

• Need for special devices • Extremely slow

• Need special devices • Difficult to control size, agglomeration, and crystal structures

• Using chemical agents • Undesirable agents production

• The cost of materials may

• Application of toxic

• Hazardous by product formation

be high

agents

[12]

[13]

[14]

[15]

[11]

*Nanoparticle Synthesis, Applications, and Toxicity DOI: http://dx.doi.org/10.5772/intechopen.87973*


#### **Table 1.**

*Applications of Nanobiotechnology*

**2. NP production methods**

**2.1 Physicochemical methods**

attributes of NPs and their corresponding biological effects. For instance, it is shown that although the positive charge of NPs enhances the efficacy of gene delivery, and imaging, it also enhances the cytotoxicity of corresponding constructs [9]. In this chapter we briefly introduce the main way of NP production and their applications in biological and medical studies. Also the mechanism of cytotoxicity

NPs can be produced through two main approaches including top-down approach which is the production of NPs by making smaller and smaller structures by etching the bulk agents and bottom-up approaches which is the building up of NPs from atoms [6]. Physical, chemical, biological, and in some cases hybrid technique are the main ways of NP production. The physical methods of NP production include methods like laser ablation, high-energy irradiation, spray pyrolysis, and ion implantation, and the chemical one includes chemical reduction technique, sonochemical method, solgel process, microemulsion method, and electrochemistry. The biological method which is also called green NP biosynthesis involves application of plants extracts, microorganisms, enzymes, and even some agricultural wastes for NP production. Although the physical and chemical methods resulted in bulk amount of NPs a few times, application of chemical agents during the NP production in coordination with production of environmentally dangerous compounds simultaneously with NP production limited their applications [10]. For instance, thermolysis which is a chemical method for dissociation of organometallic precursors is performed at high temperatures by using organic solvents. Also in some cases, surfactant is added to the reaction medium for reducing coalescence of particles [11]. Chemical reduction technique is an adopted chemical method which used a wide range of reducing agents such as sodium borohydride, hydroxylamine, and N,N-dimethylformamide for production of zerovalent ions. Wave-assisted chemical method used ultrasonic waves in coordination with surfactant or reducing agent for production of NPs. The formation of micro cavities with high temperatures upon ultrasonic induction can start chemical reduction of substrates. The physical NP production methods are mainly energy intensive and need special devices. For instance, milling process is a way by which metallic microparticles are crush using high-energy ball mills. The gas-phase process or aerosol process which is divided into four main types (including flame reactor, plasma reactor, laser reactor and hot wall reactor, and chemical gas-phase deposition) is a particular way for the production of NPs like fullerenes and carbon nanotubes. All types of these methods need special devices and are mainly high energy consuming. NP production by wet chemical synthesis takes place at low temperature and is one of the most employed methods for NP production. Limitations in increasing batch reactor because of limited mixing and low heat transfer are mentioned as the main disadvantage of wet chemical synthesis method. The main advantages and disadvantages of NP production by physicochemical methods are summarized in

Green technology using biological systems like plants, microorganisms, and enzymes is rising fast as an alternative method for conventional chemical and

induction and the main ways of detecting this toxicity are explained.

**4**

**Table 1**.

**2.2 Green NP production methods**

*The main physicochemical methods of NP production and their corresponding advantages and disadvantages.*

physical. In contrast to physiochemical methods which mainly lead to environmental toxicity, the biological NP production methods are known as eco-friendly and nontoxic protocols [16]. The biologically produced NPs' special features including high catalytic activity, low toxicity contaminations, high stability, and plausible biocompatibility and biodegradability make them distinctive from NPs produced from other methods. The microorganism's related NP productions are classified into intracellular and extracellular synthesis methods [17]. In an intracellular way, ions of interest are transported into the microbial cell and then reduced in the presence of enzymatic processes, while the metal ions are entrapped and reduced at microorganism's surface in an extracellular way [18]. Microbial NP production regarding the ability of the majority of bacteria and fungi in tolerating ambient conditions of varying temperatures, pH, salt concentrations, and pressures makes this approach a safe, cost-effective, and environmental method. Several microbial species have been isolated from different environments and used for production of various NPs. Compared to microbial production method, plant NP production is more desirable because it does not need any special and multistep processes, it has faster production rate, and it has easy scaling up procedure and because of its cost-effectiveness [19]. Investigations have revealed that metals bioaccumulated in plants which sometimes are called phytomining are mainly in the form of NPs. For instance, high level of silver NP accumulation in *Brassica juncea* and *Medicago sativa* [20], gold NP production in *M. sativa* [21], and copper NP accumulation in *Iris pseudacorus* [22] has been reported. This type of NP production has several disadvantages including heterologous size and morphology of NPs, difficult extraction and isolation procedure, and low production yield [21]. The alternative approach is in vitro production method which is based on reduction of ions using plant extracts. This method is more controllable through making change in plant extract and ion concentration, time of reaction, temperature, and pH of reaction medium. The production rate of this method is much faster and easier than in vivo method [23, 24]. For example, the

#### *Applications of Nanobiotechnology*

extract of *Tectona grandis* seeds was used for reduction of AgNO3 to 10–30 nm Ag NPs with significant antibacterial properties [25], whereas Au NPs with an average size of about 3 nm have been synthesized using leaf extract of *Ziziphus zizyphus* [26]*.* Various plant extracts have been used for production of NPs from different ions with diverse sizes and shapes [27]. **Table 2** summarizes some examples of NP production through a biological way.


#### **Table 2.**

*Some examples of biologically produced NPs and their corresponding special characteristics.*

**7**

**3.3 Biosensor**

*Nanoparticle Synthesis, Applications, and Toxicity DOI: http://dx.doi.org/10.5772/intechopen.87973*

With respect to special properties of NPs discussed before, they have various applications. Here we investigate some of these applications with special look at

NPs are of great interest for being used as a device for site-specific drug delivery with optimum dosage drug release. Current NP-based drug delivery approaches focused mainly on enhancing drug shelf life though improving drug uptake efficiency [46]. NP-based drug carriers are able to cross the blood-brain barrier and tight junctions of the skin epithelial tissue [47]. Also they improve hydrophobic molecule solubility and increase stability of biological therapeutic agents.

NPs enabled us to deliver drugs by various routes including nasal mucosa and oral administration, aerosol method, and topical vaccination. The aerosol technology is used for respiratory disorder drug delivery. Target drug delivery approaches using magnetic NPs are widely being used for cancer therapy, gene therapy, MRI, and cell sorting [48, 49]. For instance, Fe3O4, γ-Fe2O3, and super magnetic iron oxide NPs (SPIONs) are the main NPs used for site-specific drug delivery. The surface properties and particular shape of fullerenes and carbon nanotubes make them attractive for drug delivery. These particles are such small that can pass through cell

membrane and deliver agents like DNA and protein into the cells [50, 51].

tions and finally lead to acute microbial death [56, 57].

The prevalence of antibiotic-resistant bacteria species becomes a threat for human health. NPs with significant antibacterial properties and no bacterial resistance are the best alternative for common antibiotics [52]. Ag NPs are the leading NP-based antibacterial agents with significant bactericidal effects on both Gram-negative and Gram-positive bacteria [53]. Every day various NPs with different physicochemical properties and bactericidal activities have been developed, and their mechanism of action and potential side effects are under investigations. Also application of common antibiotics such as ampicillin, chloramphenicol, and kanamycin in the presence of NPs demonstrated the positive effects of this combination. Previous studies showed that NPs can be used as a vehicle for antibiotic delivery. The attachment of NPs to the bacterial surface and induction of damages are reported as the main mechanism bacterial death with NPs [54, 55]. Interaction of NPs with bacterial cell membrane and disruption of its normal function are the most common way of NP bacterial killing. NPs are also able to hindrance bacterial biofilm formation. Furthermore, NPs are able to produce different types of ROS species. For example, Mg NPs are able to produce O2<sup>−</sup>, and ZnO NPs produce H2O2 and OH. These ROS species interact with bacterial cells and cause acute stress reac-

The optical and electronic properties of NPs make them suitable for biosensor application. The size, type of ion, and shape of NPs are critical parameters affecting SPR peaks and line widths of sensor. The noble metals like Au, Ag, and Pt NPs showed special physicochemical features which make them the most popular components of NP-based biosensors [58]. NPs have different roles in any types

**3. NP biomedical applications**

their uses in biomedical fields.

**3.1 Drug delivery**

**3.2 Antibacterial agent**
