NANO TECHNOLOGY

NANO TECHNOLOGY
(NANO TECHNOLOGY OF CHIP DESIGNING THROUGH BIOLOGY)

ABSTRACT
Nano technology is slowly creeping into electronic chips shrinking them to infinitesimal units. So far it was discovered that carbon in the form of carbon Nano tubes only could be used to achieve this technology. The design and fabrication of carbon nano tube based chips requires ultra high precision equipment working in dangerous and expensive industrial environments where one slightest flaw results in an adverse outcome. For such a vital situation biotechnology stands with promising solutions. It solves using simple biological molecules and microbes, which can themselves, assemble electronic materials and build Nano scale circuits. They can even self-correct while growing the materials. Biotechnological approach first involves selection of the Peptides that recognize a particular semiconductor material like gallium arsenide or indium phosphide and even one crystallographic face versus another with a very high specificity. These peptides are used to engineer a special virus called Bacteriophage. These engineered viruses are reproduced by a cyclic process called Directed evolution. By engineering the virus’s structure, it acts as template for making Nano transistors, Nano wires and Quantum dots. Here Nano transistors formed are of FET type. Quantum dots are basic functional blocks in circuits. By regular arrangements of these quantum dots, Nano wires are formed. Using these tools Nano circuits are made. Using a property of virus called Self-assembly, which states that when viruses are separated from water, they form multi layer films lining up shoulder-to-shoulder forming liquid crystal. This biological approach revolutionizes the field of chip design and fabrication as the chips can be designed at ordinary room temparatures in aqueous, nontoxic conditions than that of other nano wire fabrication methods. This revolution result in high-density quantum flash memories, foldable display screens using viral films, nano robots, micro computers in body for diagnosis and treatment and quantum era bringing super fast quantum computers and quantum communication systems at very low cost.

BIOTECHNOLOGY’S ASSURANCE FOR NANOTECHNOLOGY
The explorations and necessities in science and technology are gradually wiping off the barriers and amalgamating different sectors of science, which appear to be un-correlated. One such ground breaking and innovative exploration is chip designing using biotechnology. If this becomes a success there would be major break through in the field of nano technology.
With the speed and accuracy of the circuits increasing, the complexity of the circuits increases with crumbling the size of chips. This increases the need for ultra high precision and sophisticated equipment, which is very expensive and laborious. Even though the equipment is used, the efficiency of the systems is uncertain when compared with the investment over it. Hence there is a need to look for an alternative approach, which promotes Nano technology. Biotechnology has some promising solutions for this.


INTRODUCTION
Living creatures produce the most complex molecular structures known to science. Crafted over ages by natural selection, these 3-dimensional arrangements of atoms manifest a precision and fidelity, not to mention minuteness far beyond the capabilities of current technologies. Under the direction of Genes encoded in DNA, cells construct proteins that put together the fine structures necessary for life. By altering the genetic codes of these cells, they can be used for various applications. This briefly illustrates biology’s promise in furthering Nano technology, the manufacture of circuits and devices only billionths of a meter in size.
Genetic engineers are evolving nano technology tools by picking the best molecules among the variants found in large populations over several generations. It was discovered that a special type of virus could be used for achieving this. By implementing mainly two processes on the virus, they can be used in developing tools and circuits at nano scale. The processes are 1) Directed evolution 2) Self-assembly
ROLE OF PEPTIDES IN THIS APPROACH
In this approach peptides play an important role in the fabrication of chips from viruses. Peptides are small proteins made of short chain of amino acids. There are a billion different peptides from which some peptides possess special property of affinity towards certain materials of interest. Peptides that have a high affinity for some particular semiconductor material are selected. Here initially, peptides having affinity towards materials like zinc sulphide and gold are considered and used to genetically engineer the virus.

DESCRIPTION AND ENGINEERING OF VIRUS
The virus used here is a special type of virus called bacteriophage. It gets its name form its property of afflicting bacteria, which is used here to amplify its population. It resembles a very fat, rocket shaped pencil, with a major protein coat of one type of peptide along its painted shaft and another type as minor protein coat on the five tentacle like structures at the “eraser” end, -each controlled by its own genes. It has a length of 880 nanometers and a width of 6.6 nanometers. Inside the major protein coat there is a single strain of DNA, which controls the nature of virus. The DNA consists of three genes and the gene-3 is the peptide that is present on the minor protein coat. So we have a billion different viruses that are all genetically similar, except that they differ from each other based on a small peptide on each end. The reason for selecting bacteriophage is not only due to their physical structure but also due to their property of multiplying and modifying rapidly in the lab. When a solution contains all the one billion possible viruses with random peptide insert at the ends of them, the solution is termed as phage library. Usually water is used as the solution to act as a medium for the viruses.



The peptide coats can be independently genetically engineered with different peptides of interest, which ultimately changes the physical and adhering properties of virus towards certain materials, which is a vital property used in the chip-designing process.

DIRECTED EVOLUTION
Directed evolution is used to describe the techniques for the iterative production, evaluation and selection of variants of a biological sequence. It mimics the process of natural selection.
Directed evolution basically involves testing the phage library, selecting the specific engineered viruses and amplifying the population of engineered viruses retaining the original properties, which are desired.


TARGETING PURE SEMICONDUCTOR CRYSTALS
First the phage library, of the peptide, which has affinity towards the substance of interest, is selected. Then the phage library is exposed to the substance of interest, such as a wafer of Zinc sulphide. Those viruses whose minor protein coats have a natural affinity for the material, with their eraser ends stick to the wafer. Then the chip is washed with dilute acid or a chemical bath. Phages that do not bind well to the wafer are washed away and the remaining phages that are sticking to the wafer are removed by a process called PH-Elution. The removed phage population is amplified by infecting with bacteria. Again the produced viruses are poured back onto the chip and subjected to a more stringent i.e. more acidic or basic wash. After several cycles of such washes in which the wash becomes stronger and stronger, the viruses sticking to the wafer are those whose peptide coats have a tight fit to the semiconductor crystal. Similarly several rounds of directed evolution are performed to pick out viruses that bind to crystals of Gallium arsenide and Indium phosphide, the two semi conductors employed in high frequency communications chips. The produced viruses act as versatile templates in the fabrication of chips.

FOUNDATION FOR NANO CIRCUITS, NANO WIRES & NANO RINGS
The viruses can, not only stick to the semiconductor materials, but also can grow nano scale semiconductor crystals over them. Consider first the viruses, which are engineered on some locations on the major protein coat with the peptide, which has affinity towards the semiconductor of interest. Now these, when mixed with precursor chemicals containing the semiconductor’s elemental ingredients, the virus’s engineered peptides act as a template, hustling atoms into the same crystal structure to which the peptides were engineered to bind. The result is an organic and inorganic hybrid with viral particles of 7nm wide, 800nmlong, and 2 to 3nm semiconductor crystals wherever an engineered peptide is found. If the entire protein coat is engineered with the peptide, semiconductor crystals are formed all over the shaft of the virus. These crystals are called Quantum dots and these are the fundamental components of nano scale circuits. The core of the quantum dot is usually contained with zinc sulphide, which has a higher electronic band gap. This improves the confinement of the electron-hole pairs and helps in conduction. After the formation of quantum dots all over the shaft, the virus is subjected to a process called annealing which removes the virus’s organic framework. High-temperature annealing removes the organic materials of virus, leaving the inorganic quantum dots to collapse into the space formerly occupied by the virus to form a single crystal, which results in solid Nano wire. Varying the length of the virus before the start of the process can produce Nano wires of variable lengths.
By suitable peptide engineering, Viruses can be selected to form quantum dots of the semiconductors Zinc sulphide and cadmium sulphide and the magnetic materials cobalt-platinum and iron-platinum from which corresponding Nano wires are made.
For making a Nano ring initially two different genetic modifications are done to the bacteriophage, one at the eraser end and one at the pencil tip end. Then the two ends are linked together with another molecule to form a Nano ring. Then similar procedure as that of a nano wire using precursor chemicals of cobalt. Finally resulting tiny magnetic rings of cobalt particles smaller than 100 nanometers. They find applications in storing magnetic information at a high speed only at room temperature.





CONSTRUCTION OF NANO TRANSISTOR
Transistor fabrication is another important part in the process of chip designing. The transistors used in conventional chip designing are of FET type, which are highly efficient. The present biological approach also has a solution to design FET transistors at Nano scale.
For the construction of the transistor, initially the virus is engineered at the tip of the major protein coat and minor protein coat ends with a peptide, which has affinity towards the Gold. The middle portion of the shaft is engineered with peptide having affinity towards the desired semiconductor whose channel is to be formed. A Silicon wafer is patterned in desired form, so that it has exposed source and drain electrodes of gold with a gate electrode between them buried under a layer of insulation. Now the virus suspension would be poured onto the wafer. Due to the affinity of peptide, the gold seeking ends of the virus would find and bind to the electrodes forming a viral bridge between source and drain, across the gate. Then semiconductor precursor chemicals like zinc sulphide, which should form the channel, would be added. The semiconductor crystals are nucleated over the shaft wherever an engineered peptide is found. As the shaft is completely engineered, it result in formation of a semiconductor coat of 10 nm diameter on the virus turning the virus’s coat into a nano wire. For making a working transistor, the virus is annealed by a blast of heat, leaving only the nano wire bonded to the gold electrodes, yielding a nano transistor.



FORMATION OF LIQUID CRYSTAL FILMS
The virus possesses one peculiar property, which can be used in making viral films. This property of virus is called Self-assembly, which states that, “When virus are separated from water, they form multi layer films lining up shoulder to shoulder in liquid crystal”. These liquid crystal films are optically transparent and can be modified. The properties of the films like transparency mainly depend on the precursor chemicals. Films containing Zinc sulphide are crystal clear and used in many applications related to display and memory technology.




APPLICATIONS
The applications of this approach are very fascinating and give a motivating and breaking edge to all the future end technologies. The applications are-

High speed quantum flash memories
Flash memories can be fabricated by this approach in two ways. One way is through nano rings of magnetic materials forming high density magnetic memory, other is by viral films with magnetic material quantum dots on them giving rise to high density quantum flash memories.
The Nano rings formed of cobalt particles could be utilised for data storage. The cobalt nano particles, used to form the rings, have magnetic north and south poles and join up when brought together. Once formed into rings a collective magnetic state known as flux closure occurs. That is within the ring there is strong magnetic force, or flux, but there is a zero net magnetic effect on the outside. This results in cheaper and faster higher density magnetic data storage.
The viral films formed due to the property of self-assembly are designated with quantum dots of magnetic materials. Later the viral arrays are turned to Nano wires. The result is that, each quantum dot is joined with a Nano wire. When each Nano wire is systematically patterned and with each quantum dot acting as a storage for 1-bit memory, 30GB memory space can be accommodated with in 1 sq cm.

Quantum computer era
The Nano tools and circuits designed under this approach lead to strong foundation for quantum computer era. Quantum computers are the next generation computers, which will harness the power of atoms and molecules to perform memory and processing tasks. Ordinary digital computers work by manipulating bits that exist in one of two states: a 0 or a 1. Quantum computers aren't limited to two states; they encode information as quantum bits, or qubits. A qubit can be a 1 or a 0, or it can exist in a superposition that is simultaneously both 1 and 0 or somewhere in between. Qubits represent atoms that are working together to act as computer memory and a processor. As the quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers.
Quantum computers perform certain calculations billions of times faster than any silicon-based computer They have the potential to store and process enormous amounts of information, immensely more than can be handled by today’s computers. They can factor very large numbers, perform cryptography, and drive science in large-scale modeling projects such as simulation of materials properties.

Quantum communication systems
Quantum communications detector system can be designed on a single 1 mm chip. It is the receiver for quantum communications system, which is a calibration tool for single photon sources, used to evaluate quantum communication protocols and the security of quantum cryptographic systems. It offers much higher efficiency, lower noise than conventional detectors and eliminates false positive results. The quantum communications detector system not only indicates the arrival of photon at destination but also determines how many photons arrive simultaneously and produces an electrical signal proportional to the absorbed energy from the photon. Quantum communications techniques offer greatly improved security of data communications by making crimes physically impossible.

Display technology
The present day’s image technologies used in computer screen are based upon pixels or tiny dots of light given out by materials used in them like LCD, LED, or phosphors on which our eyes cannot focus accurately. This results in many disorders relating to vision. These can be avoided by using displays made of crystallized nano wires of viral films. The quality and resolution are very high than any other present day technologies.
By using fluid containing the designed viral films with format as the ink, processes such as ink-jet printing or soft lithography can be used for manufacturing flexible display devices such as roll-up computer or TV screens at very low costs. Using this approach, displays having ability to serve as the human interface for information technology systems and new image-generation technology for thumbnail-sized high quality displays at a low cost can be achieved.

Nano robots and micro scopic computers in medicine
Micro scopic computers designed by this approach can be programmed to coordinate microscopic nano robots in human body, which patrol inside the body. As the disease causing parasites continue to mutate and produce new diseases, and human natural immune systems could not cope with the new mutated parasites, the nano robots under the directions of micro computers installed in side the body act as nano cell sentinel. When ever the microcomputer tracks a foreign invader with a different DNA track than that of the person’s, it commands the cell sentinels to destroy. Armed with the knowledge of the person’s DNA, the nano cell sentinels under the directions of micro scopic computers, can form immunity to not only of common cold but also any dangerous mutation that takes place in the body.

CONCLUSION
With all these research going on, the future circuit will self-assemble with the fidelity, for example to match the gate voltages on each of millions of transistors in a circuit. Researchers are shifting towards living cells, trying to engineer varieties that can construct and manipulate many types of material, as cell’s genes, unlike those of virus, can encode complex instructions that can be executed in a real time. With a microbe like that, Biology could not just be used to build circuits, but also to diagnose and repair them.
Nano technology achieved using biotechnology will change the very face of the world without consuming natural resources and leaving no pollutants. This future end technology is the gateway through which man can bring the innovations, which now felt to be fictious and hyperbolic, into existence. So Nano technology through Biotechnology is one choice for a safe and healthy world.
REFERENCE

Books:
“Selection of peptides with semi conductor binding specificity for directed nanocrystal assembly” by S.R. WHALEY.
Web sites:
http://web.ukonline.co.uk/webwise/spinneret/genes/dna.htm
www.bio.davidson.edu/courses/Molbio/MolStudents/spring2003/watson/phage.htm
http://cmbi.bjmu.edu.cn/www-learn/labmeeting/labmeeting_006.pdf
http://pubs.acs.org/cen/topstory/8202/8202notw1.html
http://www.vlsi.wpi.edu/webcourse/ch02/ch02.html
http://www.science.org.au/sats2003/belcher.htm
http://www.eetimes.com/at/news/OEG20040204S0014
http://www.zyvex.com/nano.htm
Magazines:
IEEE SPECTRUM
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