Nanobiotechnology lecture 3
- 1. Process of self assembly and self organization Based on molecular recognition, relatively simple building blocks recognize each other, associate with one another and then associate with other molecules to finally form a well organized functional entity. Central to all biological systems as all living cells evolve from simple building blocks which spontaneously associate into complex networks and structures.
- 2. Organization of bacterial S- layers S-layers are bacterial cell surface structures found in all archaea and many bacterial species. Archaea are extremophiles (halophiles and thermophiles), phylogenetically different from bacteria, having some similarities to eukaryotes in aspects of transcription and translation. S-layers have evolved to such stable and well organized form through evolution of billion of years.
- 3. S-layers are composed of single protein or glycoprotein species that assemble into ordered layer which completely covers the cell surface. These layers have morphology, symmetry and thickness in the order of nano range in their natural distribution. These efficient biological self assembling systems may be used for making stable nano devices.
- 5. Self organization of viruses Another self assembly for nanotechnological applications is the spontaneous template assisted formation of viral shells. The most investigated example is that of tobacco mosaic virus (TMV) which was shown invitro as the first macromolecular structure of self assembly. Incubation of viral purified coat proteins and its RNA spontaneously self assemble and formed virus particles. These structures are rod like, hollow cylinder with 300nm length and inner diameter of 4 nm. Each viral particle contains 2000 protein subunits, arranged as a right handed helix.
- 6. The RNA molecule is retained in the helix. TMV self assembly starts by binding of protein bilayer disk to a site on the RNA. It results the protein subunits to undergo through a coordinated rearrangement to yield a helical nucleoprotein complex. TMV viral nanoparticles resemble to inorganic or carbon nanotubes, however they are formed spontaneously by self assembly at the mild conditions. TMV nanoparticles have many applications in metallization.
- 9. Self organization of Phospholipid memberanes 2-D layers closed in space to form closeed- cage spheroid structures. Phospholipid is an amphiphilic molecule having phosphate head as hydrophilic part and aliphatic tail as hydrophobic part. Upon transfer to aqous solution, phospholipid undergoes through a spontaneous association into bilayer structures. Aliphatic parts of each layer point towards each other while the hydrophobic heads point to the bulk water or to inside part of the closed structure.
- 11. Phospholipis layers can be manipulated at the nano scale in the form of tubular structures, hexagonal shapes and spherical shapes. Small lipid vesicles known as liposomes are well studied nanoparticles used for drug delivery.
- 12. Carbon nanotubes: Key building blocks for future nanotechnological application Elongated variants of the C60 fullerenes. Resembles graphite sheets wrapped around into elongated cylinders with or without capping at their ends. Their length to width ratio is extremely high. Can be formed in a single shell called as single walled nanotubes (SWNTs) Or in multiwall fashion known as multiwalled nanotubes (MWNTs) They have unique mechanical and electrical properties
- 13. Have ten time more tensile strength than steel. Thus are suitable candidate materials for development of ultra strong materials like in construction of car and aviation industries. Can be used as a source of fabrics and clothing for making lightweight bulletproof fabrics. Can be used in assembly of an ultra strong cable in construction of space elevator. Being very small and highly conductive carbon nanotubes can be used as molecular wires, conductive composites and interconnects.
- 14. Graphene A single layer of carbon which is one atom thick is called graphene. It has high thermal and electrical conductivity and is mechanically very strong yet strechable material. Being transparent and very conductive it can be used in liquid crystal displays and solar cells etc.
- 15. The inorganic nanomaterials The noncarbon nanotubes made by inorganic material which resemble like the carbon fullerene structures. Tungsten, molebdenum etc can form 2D layer rearrangements as evidenced in graphite structures for making nanotube. The structures that have formed in a cage fashion can be rolled to form fullerene like structures. For instance the nano particles of the layered WS2 compound can form closed cage structures that are similar in their molecular organization to carbon fullerenes.
- 16. Used in many industrial and technological applications. as a solid lubricant Increases the life span and efficiency of motors and other power tools with motor parts Used as additives for motor oil. Used as lubricants of medical and dental devices.
- 17. Quantum Dots The nano objects consist of semiconductor materials surrounded by a shell composed of ZnS or CdS. Also called as nanocrystals and have dimensions of few nm to a few tens of nanometers. Serve as a cage for electrons and the molecular diameters of these structures reflect the number of electrons they contain. The size may depends from a single electron to a collection of several thousands.
- 18. Quantum dot behave like a giant atom. Energy levels in a given quantum dot become quantized due to confinement of electrons. The band gap b/w the two energetic states determines the energy of a photon that is being emitted by the transition b/w the two states The energy can be either in the visible or the infrared region depending on the specific band gap