**Abstract**

Nanotechnology which deals with the synthesis and characterization of dispersed or solid particles in nano-metric range has emerged out to be a novel approach due to its ample applications in biomedical fields. The advancements in the field of nanotechnology and substantial evidences in biomedical applications have led the researchers to explore safe, ecofriendly, rapid and sustainable approaches for the synthesis of colloidal metal nanoparticles. This chapter illustrates superiority of biogenic route of synthesis of nanoparticles over the different approaches such as chemical and physical methods. In biogenic route, plants and microorganisms like algae, fungi, yeast, actinomycetes etc. act as "bio-factories" which reduce the metal precursors and play a crucial role in the synthesis of nanoparticles with distinct morphologies. Thus, the need of hazardous chemicals is eliminated and a safer and greener approach of nanoparticles synthesis can be adopted. This chapter also outlines the effect of optimization of different parameters mainly pH, temperature, time and concentration of metal ions on the nanoparticle synthesis. It is evident that the optimization of various parameters can yield nanoparticles with desired properties suitable for respective biomedical applications.

**Keywords:** colloidal metal nanoparticles, biogenic synthesis, biomedical applications, optimization, nanobiotechnology

## **1. Introduction**

Ever since the origin of human civilization as early as 500 BC, nanomaterials (NMs) have been used for a range of applications, biomedicinal formulations being a crucial one [1]. Due to small size ranging from 1 to 100 nm, high aspect ratio, distinguished magnetic, optical, electrical, mechanical properties as compared with bulk materials of their same kind, MNs are being widely explored for their possible range of biomedical applications. In addition, ease of synthesis, control over size and morphology have revolutionized the field of nanobiotechnology [2]. The convergence of nanotechnology and biotechnology has led to the emergence of innovative and powerful field that explores the possibility of utilizing various NMs for biomedical applications [2]. The manipulations of macro materials resulting

in unique properties of NMs have attracted biomedical researchers to utilize these properties in pharmaceutical fields such that the NMs would play a momentous role and indeed add to the functionality of original compound [3]. The NMs and nanobiomaterials are being extensively used in biomedical field for diagnostics, imaging, drug delivery and as prostheses and implants due to their superior biocompatibility to artificial polymeric materials [4]. The metallic and non-metallic nanoparticles (NPs) used extensively in biomedicines are derived from sources such as bulk metals, non-metals, chemicals, plants and microbes. Owing to well-defined and tunable size, shape, molecular weight and uniform dispersity of lipids and proteins based NMs, they are used for the fabrication of nanocarriers such as liposomes, micelles and dendrimers for drug and gene delivery [5–7]. Depending upon the type of NMs, the pharmaceutical ingredient can be either encapsulated or attached onto the surface of such nanocarriers in such a way that, irrespective of the water solubility, the pharmaceutical ingredient can be delivered to the target site and protected against degradation [2]. Presently, almost 175 exclusive nanomedicinal products for the treatment of cancer and infectious diseases are at different stages of clinical trials soon to be launched into the market [8]. Concurrently, surgical blades, suture needles, contrast-enhancing agents for magnetic resonance imaging, bone replacement materials, wound dressing materials, anti- microbial textiles, *in vitro* molecular diagnostic chips, microcantilevers, and microneedles are already out in the market [9].

The capsules PillCamESo and PillCam Colon, sized as that of a normal pill act as a substitute for the traditional endoscopy technique. These contain a flashlight and a camera which is swallowed by the patient and the images of the gastrointestinal system are captured and sent wirelessly for further diagnostic purposes [10]. Similarly, 'microbots' structurally similar to flagella equal to half the human hair diameter are fabricated using computer chip technology. These comprise a magnetic head and can be controlled via an external magnetic field which delivers medicine to destroy tumors [11, 12]. Microbots can also relieve diabetes patients from the pain to test their blood multiple times every day and the inconvenience of self-testing to ensure stable blood-glucose levels. These could be used to retrieve data from varied locations of the body at the same time allowing continuous blood sugar level monitoring [2, 13]. The field of nanobiotechnology has also assisted insulin delivery systems to detect fluctuations in blood glucose levels and spontaneously modulate the adequate insulin release thereby maintaining normoglycemiea [14, 15]. A major drawback of non-specific drug delivery associated with conventional delivery system for cancer therapies can be overcome by using various NMs using metal NPs. To this end, metal NPs can be surface functionalized by attaching specific targeting moiety and imaging agents to target the cancerous cells [16]. This approach enables and enhances the efficiency in terms of not only timely detection of the cancerous cells but also treatment of tumors via targeted and specific release of drugs to yield maximum effectiveness with lower cytotoxicity to healthy cells [2]. In addition, nanobiotechnology has also contributed a solution for the treatment of a significant worldwide problem of hard tissue repair and regeneration by means of artificial bone scaffolds which mimic natural bone composition and structure [17, 18]. The use of biomimetics nano-assembly technology and additive manufacturing techniques make the scaffolds, cells and growth factors mimic the natural bone [19, 20]. Such scaffolds can also be used to deliver growth factors by acting as an alternative to extracellular matrix and other bioactive factors including small molecules, cytokines, peptides, proteins and genes [21, 22] to achieve controlled release and enhanced osteoblast proliferation and differentiation for stimulation of bone regeneration [23, 24].

**5**

growing day-by-day.

activities, etc. [23, 51–53].

*Optimization of Biogenic Synthesis of Colloidal Metal Nanoparticles*

**2. Colloidal metal nanoparticles as important nanomaterials** 

In general terms, colloidal systems are heterogeneous systems in which very fine particles of one matter are scattered through another substance. Former is referred as "Dispersed Phase" while later as "Dispersion Medium" and both can be present in either of solid, liquid or gas states. Dispersed phase is completely insoluble in dispersion medium [25]. Colloidal NPs, as also called nanocolloids or solid colloidal particles, resemble a normal colloidal system where NPs act as dispersed phase. Being dispersed in the solvent medium, NPs are embroiled in some lively motions such as Brownian motions [26, 27]. As a consequence of their dominant characteristics over bulk correspondents the colloidal NPs, play vital role in number of applications [28]. The unique properties such as tunable size, configuration, structural arrangement, formulation, crystallinity and dimensions can deeply rectify the features of colloidal NPs according to the applications [29]. Colloidal NPs can be employed in prospective applications in the wide range of sectors including electronics, coatings, catalysis, packaging, biomedicine, biotechnology etc. In addition, the uses of colloidal NPs in biomedical field are increasing incredibly as they are being administrated with elegant attributes for healthier reactions with the biological circumstances and cope with on-demand requirements of *in vivo* diagnosis and therapies [30]. To boot, the fine size of NPs not only allows them to pass through the tissues or cells but also accesses them easily to target organs engrossing the novel

Magnetic NPs specifically iron oxide NPs are principally studied and utilized for their peculiar physicochemical, biological and magnetic features [32], remarkably stability, least perilous, significant magnetic vulnerability, severe saturation magnetism and biocompatibility [33]. Similarly, other magnetic NPs such as alloy, also known as bimetallic NPs of iron-cobalt (Fe-Co), iron-platinum (Fe-Pt) have high magnetic properties, super paramagnetism, high curie temperature [34, 35]. The exceedingly reported and mostly scrutinized uses of magnetic and bimetallic NPs are for target specific drug delivery [36, 37], in magnetic resonance imaging

Metallic NPs are the matter of curiosity that has been mesmerizing experts due to their extraordinary optical, electronic properties accompanied by its massive potential in nanotechnology. Nobel metal NPs of gold, silver, platinum, palladium, etc. have been used since ancient times for medicinal intents. Chemical inertness, ability to resist corrosion and oxidation even in moist air wholly justifies their uptake for biomedical applications [42]. Negative charge on the surface of gold NPs presents easy functionalization with organic compounds that offers further interactions with antibodies, drugs moieties or ligands for *in vitro* or *in vivo* drug delivery [43]. Likewise, silver NPs embrace distinct characteristics of being chemical inactivity, catalytic activity, high thermal and electrical conductive [44, 45]. The astonishing antimicrobial activity of silver NPs leads its utility in textile industries, wound healing dressings and as disinfectants [46, 47]. The employability of other metal NPs in bioimaging [48], biosensors [49], photothermal therapies [50] are

Metal oxide NPs such as titanium dioxide (TiO2) and zinc oxide (ZnO) NPs are markedly used in paints, coatings, food coloring, beauty products, sunscreens etc. Equating with other metal oxide NPs, ZnO confers minimal toxicity to living cells so that there is increase in biomedical applications namely in diabetes treatment, wound healing, anti-inflammation treatment, anti-aging products, antibacterial

*DOI: http://dx.doi.org/10.5772/intechopen.94853*

biomedical applications at cellular level [31].

[38, 39] and to treat hyperthermia magnetically [40, 41].

**for various applications**

*Colloids - Types, Preparation and Applications*

in the market [9].

in unique properties of NMs have attracted biomedical researchers to utilize these properties in pharmaceutical fields such that the NMs would play a momentous role and indeed add to the functionality of original compound [3]. The NMs and nanobiomaterials are being extensively used in biomedical field for diagnostics, imaging, drug delivery and as prostheses and implants due to their superior biocompatibility to artificial polymeric materials [4]. The metallic and non-metallic nanoparticles (NPs) used extensively in biomedicines are derived from sources such as bulk metals, non-metals, chemicals, plants and microbes. Owing to well-defined and tunable size, shape, molecular weight and uniform dispersity of lipids and proteins based NMs, they are used for the fabrication of nanocarriers such as liposomes, micelles and dendrimers for drug and gene delivery [5–7]. Depending upon the type of NMs, the pharmaceutical ingredient can be either encapsulated or attached onto the surface of such nanocarriers in such a way that, irrespective of the water solubility, the pharmaceutical ingredient can be delivered to the target site and protected against degradation [2]. Presently, almost 175 exclusive nanomedicinal products for the treatment of cancer and infectious diseases are at different stages of clinical trials soon to be launched into the market [8]. Concurrently, surgical blades, suture needles, contrast-enhancing agents for magnetic resonance imaging, bone replacement materials, wound dressing materials, anti- microbial textiles, *in vitro* molecular diagnostic chips, microcantilevers, and microneedles are already out

The capsules PillCamESo and PillCam Colon, sized as that of a normal pill act as a substitute for the traditional endoscopy technique. These contain a flashlight and a camera which is swallowed by the patient and the images of the gastrointestinal system are captured and sent wirelessly for further diagnostic purposes [10]. Similarly, 'microbots' structurally similar to flagella equal to half the human hair diameter are fabricated using computer chip technology. These comprise a magnetic head and can be controlled via an external magnetic field which delivers medicine to destroy tumors [11, 12]. Microbots can also relieve diabetes patients from the pain to test their blood multiple times every day and the inconvenience of self-testing to ensure stable blood-glucose levels. These could be used to retrieve data from varied locations of the body at the same time allowing continuous blood sugar level monitoring [2, 13]. The field of nanobiotechnology has also assisted insulin delivery systems to detect fluctuations in blood glucose levels and spontaneously modulate the adequate insulin release thereby maintaining normoglycemiea [14, 15]. A major drawback of non-specific drug delivery associated with conventional delivery system for cancer therapies can be overcome by using various NMs using metal NPs. To this end, metal NPs can be surface functionalized by attaching specific targeting moiety and imaging agents to target the cancerous cells [16]. This approach enables and enhances the efficiency in terms of not only timely detection of the cancerous cells but also treatment of tumors via targeted and specific release of drugs to yield maximum effectiveness with lower cytotoxicity to healthy cells [2]. In addition, nanobiotechnology has also contributed a solution for the treatment of a significant worldwide problem of hard tissue repair and regeneration by means of artificial bone scaffolds which mimic natural bone composition and structure [17, 18]. The use of biomimetics nano-assembly technology and additive manufacturing techniques make the scaffolds, cells and growth factors mimic the natural bone [19, 20]. Such scaffolds can also be used to deliver growth factors by acting as an alternative to extracellular matrix and other bioactive factors including small molecules, cytokines, peptides, proteins and genes [21, 22] to achieve controlled release and enhanced osteoblast proliferation and differentiation for

**4**

stimulation of bone regeneration [23, 24].
