Nanoparticles are metal particles in the size range of 1-100nm and form building blocks of nanotechnology. Nanotechnology is a multidisciplinary science comprising various aspects of research and technology .Metal nanoparticles like gold, silver and platinum have gained considerable attention in recent times due to a wide variety of potential applications in biomedical, optical, and electronic fields.

The wide range of applications of nanoparticles is due to their unique optical, thermal, electrical, chemical and physical properties that are due to a combination of the large proportion of high energy surface atoms compared to the bulk solid. Nanoparticles are of great scientific interest as they bridge the gap between bulk materials and atomic or molecular structures.

The various applications of nanomaterials in biology or medicine are:

Fluorescent biological labels: - Highly luminescent semiconductor quantum dots (zinc sulfide-capped cadmium selenide) have been covalently coupled to biomolecules for use in ultrasensitive biological detection. In comparison with organic dyes such as rhodamine, this class of luminescent labels is 20 times as bright, 100 times as stable against photobleaching, and one-third as wide in spectral linewidth. These nanometer-sized conjugates are water-soluble and biocompatible. Complementary bioconjugates based on antibody-antigen interactions have been developed from luminescent CdTe nanoparticles.

Drug and biomolecule delivery: - Drug delivery system provides positive attributes to a free drug by improving solubility, in vivo stability and biodistribution. A recent study has reported on the therapeutic ability of a novel cyclodextrin -covered gold nanoparticle carrier for noncovalent encapsulation of an anti-cancer drug.

Gold NPs could possibly be employed in the delivery of the diatomic therapeutic agents like singlet oxygen or nitric oxide. Gold nanoparticles chemically modified with primary amine groups have been developed as intracellular delivery vehicles for therapeutic small interfering RNA(si RNA).Functionalized gold nanoparticles have been demonstrated as carriers of insulin.

Nanobots and Nanostars:- Chemists at New York University (NYU) have developed DNA-based nanobots to target cancer cells. The nanorobots have been given the shape of a star to beat the problem associated with the deliver of drugs.

Bio detection of pathogens: - The Bead ARray Counter (BARC) is a multi-analyte biosensor that uses DNA hybridization, magnetic microbeads, and giant magnetoresistive (GMR) sensors to detect and identify biological warfare agents. The current prototype is a table-top instrument consisting of a microfabricated chip (solid substrate) with an array of GMR sensors, a chip carrier board with electronics for lock-in detection, a fluidics cell and cartridge, and an electromagnet. DNA probes are patterned onto the solid substrate chip directly above the GMR sensors, and sample analyte containing complementary DNA hybridizes with the probes on the surface. Labeled, micron-sized magnetic beads are then injected that specifically bind to the sample DNA. A magnetic field is applied, removing any beads that are not specifically bound to the surface. The beads remaining on the surface are detected by the GMR sensors, and the intensity and location of the signal indicate the concentration and identity of pathogens present in the sample. The current BARC chip contains a 64-element sensor array, however, with recent advances in magnetoresistive technology, chips with millions of these GMR sensors will soon be commercially available, allowing simultaneous detection of thousands of analytes. Because each GMR sensor is capable of detecting a single magnetic bead, in theory, the BARC biosensor should be able to detect the presence of a single analyte molecule.

Detection of proteins :- An ultrasensitive method for detecting protein analytes has been developed. The system relies on magnetic microparticle probes with antibodies that specifically bind a target of interest and nanoparticle probes that are encoded with DNA that is unique to the protein target of interest and antibodies that can sandwich the target captured by the microparticle probes. Magnetic separation of the complexed probes and target followed by dehybridization of the oligonucleotides on the nanoparticle probe surface allows the determination of the presence of the target protein by identifying the oligonucleotide sequence released from the nanoparticle probe. Because the nanoparticle probe carries with it a large number of oligonucleotides per protein binding event, there is substantial amplification and PSA can be detected at 30 attomolar concentration. Alternatively, a polymerase chain reaction on the oligonucleotide bar codes can boost the sensitivity to 3 attomolar. Comparable clinically accepted conventional assays for detecting the same target have sensitivity limits of approximately 3 picomdar, six orders of magnitude less sensitive than what is observed with this method.

Probing of DNA structure :- Semiconductor nanoparticles, also known as quantum dots, are receiving increasing attention for their biological applications. These nanomaterials are photoluminescent and are being developed both as dyes and as sensors. These quantum dots can be used to detect different intrinsic DNA structures. Structural polymorphism in DNA may serve as a biological signal in vivo, highlighting the need for recognition of DNA structure in addition to DNA sequence in biotechnology assays.

Tissue engineering :- Tissue engineering is based on the creation of new tissues in vitro followed by surgical placement in the body or the stimulation of normal repair in situ using bioartificial constructs or implants of living cells introduced in or near the area of damage. Though it is mainly concerned with using human material, either from the patient themselves (autologous) or from other human sources (allogeneic), material from other mammalian sources have also been applied in humans (xenogeneic).

The involvement of microelectronics or nanotechnology in creating a truly bioartificial tissue or organ that can take the place of one that is terminally diseased, such as an eye, ear, heart, or joint has been envisaged. Implantable prosthetic devices and nanoscaffolds for use in the growing of artificial organs are goals of nanotechnology researchers. Nanoengineering of hydroxyapatite for bone replacement is reasonably advanced.

Nanofibers are fibres with diameters of less than 1,000 nm. The various medical applications include materials used in implants, tissue engineering and artificial organ components and materials for wound dressings. Researchers have also found its applications in regeneration of human tissue, bone and cartilage.

Tumour destruction via heating (hyperthermia):- Magnetic cationic liposomes (MCLs) that contained magnetic nanoparticles as heating mediator for applying them to local hyperthermia have been developed.

Separation and purification of biological molecules and cells: Ferromagnetic iron dextran particles covalently coupled to Protein A from Staphylococcus aureus are used to indirectly label antigen sites on human red blood cells and thymocytes for visualization by scanning and transmission electron microscopy. Cells labeled with these immunospecific ferromagnetic particles are quantitatively retained by a simple permanent magnet and could be separated from unlabeled cells.

Phagokinetic studies: - The uptake of colloidal semiconductor nanocrystals by a large range of eukaryotes is directly correlated with the cell motility, as has been shown by comparing the motions of cancerous and healthy human breast cells. The nanocrystals are more photochemically robust than organic dyes and provide a powerful tool for studying the processes of cell motility and migration-behaviors that are responsible for metastases of primary cancers.

Future Directions
As it stands now, the majority of commercial nano particle applications in medicine are geared towards drug delivery. In bio sciences, nanoparticles are replacing organic dyes in the applications that require high photo-stability as well as high multiplexing capabilities. There are some developments in directing and remotely controlling the functions of nano-probes, for example driving magnetic nanoparticles to the tumor and then making them either to release the drug load or just heating them in order to destroy the surrounding tissue. The major prerequisite in further development of nano-materials is to make them multifunctional and controllable by external signals and more research should be oriented in this direction for further development in the field of nanomedicine.

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About Author / Additional Info:
Smitha M.S.
Assistant Professor at AIMB(Amity Institute of Microbial Biotechnology)