Nanotechnology: A Brief Introduction

The term ‘Nanotechnology’ was first defined in 1974 by Norio Taniguchi of the Tokyo Science University as the study of manipulating matter on an atomic and molecular scale. The definition of nanotechnology is based on the prefix ‘nano’ which is from the Greek word meaning ‘dwarf’. Technically the word ‘nano’ means one billionth of something. A nanometer is one billionth of a meter. The word nanotechnology is generally used when referring to materials with the size of 1 to 100 nanometers (nm). Nanotechnology is a new branch of science that deals with the generation and alteration of materials to nanosize. Materials with a particle size less than 100 nm at least in one dimension are generally classified as nanomaterials. These materials display different properties from bulk materials due to their size. These differences include physical strength, chemical reactivity, electrical conductance, magnetism and optical effects. Therefore, nanotechnology is the manipulation or self-assembly of individual atoms or molecule or molecular cluster into structures to create materials and devices with new or vastly different properties. Nanosensors and monitoring system enabled by nanotechnology will have a large impact on future precision methodologies. Hence, nanotechnology employs materials (NPs) having one or more dimension in the order of 100 nm or less.

Nanomaterials (NMs) of inorganic and organic origin are used for nanoparticles (NPs) synthesis by a variety of physical and chemical methods. The techniques for making nanoparticles are generally involved either a top-down approach or a bottom-up approach. In top-down approach, size reduction is achieved by various chemical and physical treatments such as milling, high pressure homogenization and sonication while in bottom-up synthesis, the nanostructure building blocks of the nanoparticles are formed first and then assembled to produce the final particle.

Among inorganic materials, metal oxide nanoparticles such as ZnO, TiO_2, AgO, MgO are of particular interest as they are physically and optically stable with tunable optical properties. Metallic nanomaterials are very interesting materials with unique electronic and electrocatalytic properties depending on their size and morphology and include the utilization of nanostructured materials with specific forms like quannologytum dots (QDs). Other inorganic materials such as montmorillionite and other clay nanoparticles have a structure of stacked platelets with one dimension of the platelet in the nanometer scale. Nano-clays have a high aspect ratio that provide more interactive surface when exfoliated and dispersed well. Organic materials such as carbon nanotubes, lipids and polymers are versatile materials with multiple applications.

Carbon nanotubes (CNTs) are hollow cylindrical tubes composed of one, two or several concentric graphite layers capped by fullerenic hemisphere, which are referred to as single-, double-, and multi-walled CNTs. The unique electronic, metallic and structural characteristics make CNTs an important class of materials. The possibility of electron transfer reaction due to their structure dependent metallic character and their high surface area provides ground for unique biochemical sensing system. Solid lipid nanoparticles are delivery systems that comprise of aqueous dispersion of solid lipids or dry powder such as triglycerides, steroids, waxes, long chain fatty acids and emulsifiers prepared by high pressure homogenization. Polymeric nanoparticles made from natural and synthetic polymers by wet synthetic routes are widely used due to their stability and ease of surface modification. Nanoparticles prepared from biopolymers or natural sources possess merits such as available from replenishable agricultural (cellulose, starch, pectin) or marine (chitin and chitosan) resources, biocompatibility, biodegradability and other ecological safety. Chitosan is one of the most promising NMs due to its excellent biocompatibility, complete biodegradiability and non-tixic nature. The degradation products of chitosan are harmless natural metabolites. It is obtained by the deacetylation of chitin, the second most abundant natural polymer after cellulose, which is found in the shells of crustaceans (crabs and shrimp), the cuticles of insects, and the cell walls of fungi. It is suitable for electrochemical sensors due to its transparent nature. Quantum dots (QDs) are inorganic nanocrystals, approximately 1-100 nm in size, with unique properties of broad excitation, narrow size-tunable emission spectra, high photochemical stability and negligible photoleaching. They have been widely used, mainly as alternative to fluorophores,  for the development of optical biosensors to detect ions, organic compounds and biomolecules such as nucleic acids, proteins, amino acids, enzymes, carbohydrates.  Dendrimers are known as organic macromolecules with tridimensional (3D) and highly defined structure functionality. The capability of these dendrimeric structures to stabilize and maintain the integrity of metallic nanoparticles has been reported.

Nanoparticles are generally characterized by their size, shape surface area, and disparity. The common techniques of characterizing nanoparticles are scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-visible spectrophotometery, X-ray diffraction (XRD), dynamic light scattering (DLS), energy dispersive spectroscopy (EDS).

Some nanomaterials and their applications

Nanomaterials

Applications

Inorganic Metal nanoparticles           AgO, TiO2, ZnO, CeO2; Fe2O3,          FePd, Fe-Ni; Silica; CdTe, CdSe   Clay         Montmorillonite layerd double hydroxides Organic  Carbon nanotubes,           nanofibres  Lipids       Liposomes       Lippolyplexes       Solid lipid nanoparticles Poymeric       Natural         Cellulose, Starch, Gelatin, Albumin         Chitin, Chitosan      Synthetic        Dendrimers        Polyethylene oxide        Polyethylene  glycol        Polylactides

Delivery of biomolecules (proteins, peptides, nucleic acids), biosensors, diagnostic techniques, pesticide degradation Delivery of pesticides, fertilizers, plant growth promoting hormones Biocatalysts, sensing, Delivery of DNA  and pesticides, essential oils Biocompatible, biodegradable Delivery of DNA/RNA Delivery of pesticides and DNA/RNA