INTRODUCTION:

Nanoparticles are defined as particulate dispersions or solid particles with a size in the range of 10-1000nm. The drug is dissolved, entrapped, encapsulated or attached to a nanoparticle matrix. Depending upon the method of preparation, nanoparticles, nanospheres or nanocapsules can be obtained. Nanocapsules are systems in which the drug is confined to a cavity surrounded by a unique polymer membrane, while nanospheres are matrix systems in which the drug is physically and uniformly dispersed. In recent years, biodegradable polymeric nanoparticles, particularly those coated with hydrophilic polymer such as poly (ethylene glycol) (PEG) known as long-circulating particles, have been used as potential drug delivery devices because of their ability to circulate for a prolonged period time target a particular organ, as carriers of DNA in gene therapy, and their ability to deliver proteins, peptides and genes. ^1-4

The major goals in designing nanoparticles as a delivery system are to control particle size, surface properties and release of pharmacologically active agents in order to achieve the site-specific action of the drug at the therapeutically optimal rate and dose regimen. Though liposomes have been used as potential carriers with unique advantages including protecting drugs from degradation, targeting to site of action and reduction toxicity or side effects, their applications are limited due to inherent problems such as low encapsulation efficiency, rapid leakage of water-soluble drug in the presence of blood components and poor storage stability. On the other hand, polymeric nanoparticles offer some specific advantages over liposomes. For instance, they help to increase the stability of drugs/proteins and possess useful controlled release properties.^{5, 6}

Drug delivery systems based on nanoparticles have proved to be a great route for targeting malignant brain tumors where the conventional therapy is not as much effective. Enhanced permeability and retention (EPR) is the unique property of nanoparticles to accumulate and interact with the tumor cells ⁷Platelets plays a vital role in the development of cardiovascular diseases so the antiplatelet agents are considered as the necessary components for the curing such diseases. Therefore, the interaction of nanoparticles and the vascular pathway becomes an essential part of the management and prevention of cardiovascular disease. Among all metallic nanoparticles the gold nanoparticles proved to be the safest and much less toxic agents for drug delivery and for hyperthermic agents for the cancer treatment. ⁸

Nanotechnology induced advance approaches in the field of biomedical sciences specially related to the cancer therapy and for diagnostic applications regarding efficient drug delivery and reduced side effects as compared to the conventional drugs, which have been used for cancer treatment. Main properties of nanoparticles to be an effective drug delivery agent includes monodispersity, lack of cytotoxicity and simple mechanism of interaction with desired ligands. One the basis of these characteristics many nanoparticles have been synthesized and used in cancer treatment, drug delivery systems and imaging such as dendrimers, quantum dots, polymer gels, gold nanoparticles, ZnO, or Fe2O3 ⁹. Various chemical and physical methods have been adapted for the synthesis of nanoparticles which are quite expensive and the chemicals used are harmful to the environment. To overcome these problems green synthesis is emerging field of research of current era. Inorganic nanoparticles have particular application in molecular imaging as contrast agent such as magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), ultrasound and optical imaging. ¹⁰

Gold Nanoparticle:

Properties of gold nanoparticles are different from its bulk form because bulk gold is yellow solid and it is inert in nature while gold nanoparticles are wine red solution and are reported to be anti-oxidant. Inter particle interactions and assembly of gold nanoparticles networks play key role in the determination of properties of these nanoparticles ¹¹. Gold nanoparticles exhibit various sizes ranging from 1 nm to 8 μm and they also exhibit different shapes such as spherical, sub-octahedral, octahedral, decahedral, icosahedral multiple twined, multiple twined, irregular shape, tetrahedral, nanotriangles, nanoprisms, hexagonal platelets and nanorods. (Figure 1).

Figure 1: Various shapes of gold nanoparticles

Among all these shapes triangular shaped nanoparticles show attractive optical properties as compared to the spherical shaped nanoparticles. Using of single active substance from plant extract in the synthesis of gold nanoparticles is an important bio synthesis technique to purify gold nanoparticles and to investigate about their medical uses. Gold nanoparticles have been widely used in the field of radiation medicine as radiation enhancer.¹² Those also provide therapeutic enhancement in radiation therapy due to the efficient and targeted drug delivery to the tumor site. Gold nanoparticles have various applications as platform nanomaterials for biomolecular ultrasensitive detection, killing cancer cells by hyperthermal treatment, labeling for cells and proteins and delivering therapeutic agents within cells.

Fluorescent nanoparticles or nanoprobes based on gold nanoparticles have good biocompatibility for molecular imaging of many enzymes and metabolites which is necessary for cellular functions in cancer. Gold nanorods have gained much attention in recently few past years due to their specific optical and chemical property and hence used for biological applications. ¹³

Advantages of Gold Nanoparticle:

Gold nanoparticles mediated drug delivery systems have many advantages over other nanocarriers as well as to conventional drugs. Gold nanoparticles have been widely used as a cancer antigen and in tumor therapies.¹⁴ Some advantages are listed here;

(i) Gold nanoparticles have unique optical [16], physical and chemical properties due to their size and shape.⁹

(ii) Gold nanoparticles have high surface area which provide dense drug loading; ¹⁵

(iii) These particles are biocompatible [1] and are readily available for conjugation with small biomolecules such as proteins, enzymes, carboxylic acid, DNA, and amino acids. ¹⁶

(iv)Gold nanoparticles have controlled dispersity.¹⁷

(v) Due to small size and uniform dispersion they can easily reach to the targeted site with blood

Flow.¹⁸

(vi) They are non-cytotoxic to the normal cells. ¹⁹

(vii) Gold nanoparticles are easily synthesized by various methods. ²⁰

Types of gold nanoparticles ²¹

Gold nanorods

Gold nanoshells

Gold nanocages

Gold nanosphere

Gold Nanorods:

These are synthesized by template method. These are prepared by electrochemical deposition of gold within the pores of nanoporous polycarbonate template membranes. Goldnanorods diameter is according to the diameter of pore of the template membrane

Gold Nanoshells:

Surface plasmon resonance peaks (ranging from visible to near I.R. region) is used for the designing and fabrication of gold nanoshells. The core of gold nanoshells is made up of silica and outer surface is made up of gold. Gold controls the thickness of the shell.

Gold Nanocage:

Through galvanic replacement reaction between truncated silver nanocubes and aqueous. HAuCl gold nanocage is synthesized.

Gold Nanospheres:

These are synthesized by reduction of an aqueous HAuCl₄by using citrate as reducing agent. Through citrate /gold ratio the size of nanospheres can be controlled . By two phase ratio the size of nanospheres can be affected by thiol/gold molar ratios.

APPLICATIONS:

· Old Nanoparticles for the Delivery of Protein, Peptides and Nucleic acid:

These can be employed as a carrier for delivery of peptides, proteins and nucleic acid like DNA due to their tunable size.²²Gold nanoparticles are functionalized with cationic⁴° ammonium group, can bind DNA plasmid through helectrostatic interactions and protect DNA from enzymatic digestion. Gold nanoparticles can work as a carrier for peptides and proteins, have reported that the cationic tetra alkyl ammonium functionalized GNP’s recognise the cell surfacereceptor.²³

Gold nanoparticles act as a carrier of insulin. Chitosan coated gold nanoparticles easily adsorb insulinon their surface and the transmucosal delivery of insulinis enhanced.²⁴

· Photo Physical Property of GNPs for Delivery of Drug:

GNPs cause local heating when irradiated with light in 800 to 1200 nm. They cause the photo thermal destruction of tumours. GNPs are doped into the shells of capsules containing the drug. When the light irradiated on it then the shells rupture and the drug release²⁵

· In vivo Targeting Using Gold Nanoparticles:

It can bedone by using two approaches²⁶

Active Targeting:

It depends on the recognition of ligands on the gold nanoparticles surface by cell surface receptors. ²⁷

Passive Targeting:

It depends on the extravasations of vectors through leaky blood vessels in unhealthy tissue.²⁸

· Gold nanoparticles are used for identifying the different classes of bacteria. At present time identification of bacteria is done by expensive machine. So GNPs are used for identification of different bacterial classes that will be beneficial for cancer diagnosis²⁹

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Received on 23.01.2016 Accepted on 15.02.2016

Asian J. Pharm. Res. 6(1): January -March, 2016; Page 45-48

DOI: 10.5958/2231-5691.2016.00008.3