INTRODUCTION

NANOPARTICLES

Nanoparticles are particles between 1 and 100 nanometres in size with a surrounding interfacial layer. The interfacial layer is an integral part of nanoscale matter, fundamentally affecting all of its properties. The interfacial layer typically consists of ions, inorganic and organic molecules. Organic molecules coating inorganic nanoparticle are known as stabilizer, capping and surface ligands or passivating agents. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties.

TYPES OF NANOPARTICLES:

Nanoparticles can be classified into different types according to the size, morphology, physical and chemical properties. Some of them are carbon -based nanoparticles, ceramic nanoparticles, metal nanoparticles, semiconductor nanoparticles, polymeric nanoparticles and lipid -based nanoparticles.

Carbon-based nanoparticles:

Carbon-based nanoparticles include two main materials: carbon nanotubes (CNTs) and fullerenes. CNTs are nothing but graphene sheets rolled into a tube. These materials are mainly used for the structural reinforcement as they are 100 times stronger than steel. CNTs can be classified into single -walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). CNTs are unique in a way as they are thermally conductive along the length and non conductive across the tube.

Ceramic Nanoparticles:

Ceramic nanoparticles are inorganic solids made up of oxides, carbides,carbonates and phosphates. These nanoparticles have high heat resistance and chemical inertness. They have applications in photocatalysis,photodegradation of dyes, drug delivery and imaging. These nanoparticles have been used effectively as a drug delivery system for a number of diseases like bacterial infections, glaucoma, cancer etc.

Metal Nanoparticles:

Metal nanoparticles are prepared from metal precursors. These nanoparticles can be synthesized by chemical, electrochemical or photochemical methods. In chemical methods, the metal nanoparticles are obtained by reducing the metal -ion precursors in solution by chemical reducing agents.These nanoparticles have the application in research areas, detection and imaging of biomolecules and environmental applications. For example, gold nanoparticles are used to coat the sample before analysing in SEM. This is usually done to enhance the electronic stream, which helps us to get high quality SEM images.

Semiconductor Nanoparticles:

Semiconductor nanoparticles have properties like those of metals and non-metals.They are found in the periodic table in groups II -VI, III - V or IV-VI. These particles have wide bandgaps, which on tuning show different properties. They are used in photocatalysis, electronic devices, photo -optics and water splitting applications. Some examples of semiconductor nanoparticles are GaN, GaP, InP, InAs from group 13-15 and ZnO, ZnS, CdS, CdSe, CdTe are 12-16group semiconductors and silicon and germanium are from group 14 and CuS are 11-16 group semiconductors.

Polymeric Nanoparticles:

Depending upon the method of preparation, these have structures shaped like nanocapsular or nanospheres. A nanosphere particle has a matrix like structure whereas the nano capsular particle has core shell morphology. Some of the merits of polymeric nanoparticles are controlled release, protection of drug molecules, ability to combine therapy and imaging, specific targeting and many more.

Lipid-Based Nanoparticles:

Lipid nanoparticles are generally spherical in shape with a diameter ranging from 10 to 100 nm. It consists of a solid core made of lipid and a matrix containing soluble lipophilic molecules.The external core of these nanoparticles is stabilized by surfactants and emulsifiers. These nanoparticles have applications in the biomedical field as a drug carrier and delivery and RNA release in cancer therapy.