INTRODUCTION:
The development marks a big stride in the quest to produce the electronic circuit that replace the current silicon semi-conductors, which will reach a memory capacity barrier sometime in the next decade.
The need for speed has prompted miniaturization of the conventional silicon wafers used in computer processors in prompted researchers to look for materials that could surpass the existing speed limits.
Living organisms have millions of supercomputers-DNA molecules-in their body. DNA resembles a computer hard drive in the way it stores data. Data transfer using DNA molecules is much faster than in even the fastest supercomputers.
DNA molecules posses 3 main advantages over current silicon chips:
· They are cheap in use.
· They do not use toxic compounds.
· They are abundantly available.
Adlema, a computer scientist, discovered computing potential of DNA. He successfully performed experiments to solve well-known capabilities of DNA molecules in solving complex mathematical problems, logic gates, etc which forms basis of all computer calculations.
Using bio-electronic circuits, the achievements will be significant step towards building a new generation of chips, computers and smart gadgets. It is 1000 times more powerful than the currently used silicon based circuits. It uses less electricity and their potential remains beyond our imagination. Its commercial application is not expected a decade or more.
This technology could be used someday to deliver the processing power of desktop computers, wristwatches, mobile phones or ultra-thin wearable computing systems. Thus, it overcomes the limitations of silicon based memory device in dealing with data.
Bio-electronic Circuits:
“THE BEGINNIG OF THE END FOR SILICON CHIP”
This is radically a different approach of how chips and computers are made. The new chips will totally change the industry’s logic and manufacturing techniques.
Bio-electronic circuits consist of elements, which can be reconfigured into memory chips for electronically storing and retrieving information. These elements are made from protein specially fabricated so that the signal exchange mechanism in organism can be applied to electronic circuits.
Key to development is a molecular – scale optical diode, consisting of two metal electrodes and two thin layers of protein that bridge the current flow between them. Incredibly small, device can handle immense amount of data. The devices will be building blocks for terabit-level memory chips, which researchers and corporations world-wide are racing to be the first to build.
Biochemist researchers are now studying ways to combine the two thin layers into one, which would result in a more powerful memory capacity. A joint project is underway between Tokyo University of Japan and Durham University of Britain to create a single structure of optical diode.
Chips in commercial use today can store up to 1 gigabit of data per square inch. Devices at that 10 gigabit-level have reportedly been developed but have not yet come out of the laboratory.
Molecular–level chips provide an alternative, and means of going beyond the limitations of currently lithographically made chips.
How electronic circuits work with use of DNA?
We show that an electric field can drive single-stranded RNA and DNA molecules through a 2.6-nanometer diameter ion channel in a lipid bilayer membrane. Because the channel diameter can accommodate only a single strand of RNA or DNA, each polymer traverses the membrane as an extended chain that partially blocks the channel. The passage of each molecule is detected as a transient decrease of an ionic current whose duration is proportional to polymer length. Channel blockades can therefore be used to measure polynucleotide length. With further improvements, the method could provide direct, high-speed detection of the sequence of the basis in single molecules of DNA or RNA.
Experiment for implementing Read-Write-Erase Functions:
An Italian research team has developed an optical control method that alters the structure of Green Fluorescent Protein (GFP), which allows the fabrication of single-bimolecular optical toggle switches, offering the possibility of biological devices.
The biologically engineered photo physical properties of the GFP enable to laser beams of different wavelengths to optically control the shift between bright and dark states. The molecule used is a mutation of an enhanced GFP, which glows at room temperature and is commonly used as an optical marker in biology.
A 476 nm laser beam excites the molecule into fluorescing bright state. After a few seconds’ excitation at 476 nm, blinking and photo bleaching into a long-lasting dark state were observed. But conversion back to the original normal glowing state can be achieved by laser irradiation at 350 nm. The normal glowing and dark states thus encode a binary bit that can be stored and manipulated in the protein.
One possible implementation is to exploit photo conversion, using irradiation at 350 nm, from the dark to the normal glowing state as the write function.
Fluorescent emission following excitation at 476 nm of the normal glowing state could be considered as the read function. With photo bleaching from the normal glowing state to dark state also takes care of erase function.
This is an important characteristic of this memory device. Since emission can now be detected at the single molecule level, the use of these GFPs can lead to nano-devices in which the memory cell is composed of just one protein.
In addition, the reading-writing-erasing processes that we demonstrated occur at room temperature. Therefore the active element of design is Protein.
Experiment regarding Memory Cell:
The electrical switching and memory phenomena are observed in molecular thin film sandwich between two metal electrodes which are called memory cell. Memory cell can be used for creating digital and analog memory chips such as DRAM, SRAM, EPROM and so on.
A layer of copper conductor with a chromium sublayer is evaporated through a mask onto a cleaned glass slide. Over the copper conductors, the molecular film was produced.
Aluminium conductors are then evaporated through a mask on to the molecular film orthogonally to the copper ones, producing the memory cell active areas of 100*100 micron2 (Fig. 1a).
In order to get active areas of the memory cell of 2*2 micron2 and under, we use a different type of memory cell. Electrode thickness was approximately 0.5 micron, while the molecular film was in range from 0.1-0.5 micron.
Memory cell is characterized by current voltage measurement. Series of resistor is used to limit current in the transition to ON state.
Result:
Electric switching phenomena in our molecular thin films, as in other works are characterized by the existence of two stable states, a high impedance state (OFF state) and a low impedance (ON state).
Switching from the OFF state to ON state occurs when an increasing electrical field exceeds a threshold value. A transition from ON state to the OFF state takes place when an electrical field of different polarity is applied.
Molecular Memory:
The molecular switch consists of two interlocked rings of atoms. When a voltage bias is applied, the one molecule does a half-turn, the red and the green molecules shown in the diagram are reversed, and the switch is “closed”.
The HAIR-THICK switches can be turned ON and OFF time after time, offering the possibility of random-access memory – a key facility of computers that allows users to store and manipulate information. The basis of the tiny switch is a molecule called a catename.
A pulse electricity will remove one electron causing one ring to flip or rotate around the other. This turns the switch ON. Putting electron back turns the switch OFF. This gives us a basis of read only memory.
Nanopore Technology:
Figure shows principles and components of a high-speed device for sequencing single molecules of DNA. A channel in a membrane separates two solution filled compartments, labeled “-“ and “+”. Ion flow through the open channel (top) in response to a voltage applied across the membrane. When DNA, which is negatively charged, is added to the “-” compartment (bottom), the negatively charged DNA molecules are pulled, one at a time, into and through the channel. Ionic current is reduced during the time the channel is occupied by the DNA.
A revolutionary technology for probing, eventually sequencing, individual DNA molecules using single-channel recording techniques has been conceived. This technology is based on very high speed method that:
1. Translates the characteristics to sequence of a polynucleotide into electronic signals.
2. Has the potential to sequence of DNA at unprecedented speeds.
3. Can probe very long stretches of DNA or RNA.
4. Is a high throughput, single molecule technique compatible with high levels of nanofabrication.
HP MAPS MOLECULAR MEMORY
Building electronic components like computer memory out of individual molecules would yield extraordinarily powerful and cheap computers. But figuring out how to mass-produce the devices is a tremendous challenge.
Assuming the devices can be built, another monumental challenge remains: how do you talk to them? The wires in today's semiconductor devices are about 100 times too large to fit molecular devices.
Researchers at Hewlett-Packard Company have found a random chemical process that bridges the gap.
The researchers' proposed molecular memory unit is a grid of tiny wires, each about two nanometers in diameter. A nanometer, which is one millionth of a millimeter, is about 10 carbon atoms long. A single molecule at each junction of the nanowires is an electrically activated switch whose on and off states represent the ones and zeros of computing. On one side the tiny wires extend past the grid.
To connect the memory unit to the outside world, the researchers plan to randomly sprinkle nanometer-size gold particles on the sections of the nanowires that extend past the grid and then lay down a set of larger wires on the gold particles at right angles to the nanowires. This second set of wires, each about 200 nanometers in diameter, is large enough to make a connection to the macroscopic world.
The red dots in this diagram of a molecular memory array represent gold nanoparticles that connect nanowires, represented by the black lines, to larger wires, represented by the blue and yellow bars. The random distribution of the gold nanoparticles gives each nanowire a unique address.
By using the right concentration of gold particles, the researchers can ensure that half of the junctions between the larger wires and nanowires hold individual particles. "There's a purely random, 50-50 chance that a nanowire is connected to a big wire by a dot," said Philip Kuekes, a computer architect and senior scientist at HP Labs.
Some of the junctions the larger wires make with a single nanowire will have connections and others won't. For instance, a nanowire connected randomly to 10 larger wires might have connections at the first, second, fourth, seventh and ninth, but not the third, fifth, sixth, eighth and tenth larger wires. If a connection represents a one hand no connection a zero, this particular string of junctions would represent the binary number 1101001010. "So there's a random binary number. That's a unique address for the nanowire," said Kuekes.
In order to read or write to a memory array of nanowire junctions, you have to be able to identify each junction, which holds one bit of data. The binary numbers of the two
nanowires that intersect at a junction combine to make a unique address for the junction.
If it were possible to assign addresses directly to the nanowires, 10 larger wires would be sufficient to name 1,000 nanowires because 210 is 1,024. But because the addresses are assigned randomly, many of them are duplicated. Increasing the size of the addresses by adding more larger wires reduces the number of duplicated addresses, said Kuekes.
The trick is finding the balance between getting as few duplicated addresses as possible and keeping the number of larger wires manageable. The HP researchers found that four times the log of the number of nanowires is optimal, said Kuekes. The log of a number is how many times you have to multiply 10 to get the number. For example, the log of 1,000 is three because 103 equals 1,000. By this formula, 12 larger wires can address 1,000 nanowires, 16 can address 50,000 nanowires, 23 can address 500,000 nanowires, 24 can address a million nanowires and 36 can address a billion nanowires.
To find all the unique nanowire addresses, the HP researchers came up with a computer algorithm that measures electrical resistance as the larger wires are switched on and off. Because each nanowire crosses a unique sequence of larger wires, it has a unique electrical signature. The process essentially builds a map of the nanowire grid, said Kuekes.
Figuring out how to exchange information between molecular scale devices and conventional electronic devices is perhaps the most fundamental molecular electronics problem, said Tom Jackson, a professor of electrical engineering at
One problem is that simply connecting the nanowires to the larger wires with gold nanoparticles would yield fixed connections that could not be turned on and off, making it impossible to electrically identify each nanowire,
These parallel wires are about 10 atoms wide and the spaces between them about 50 atoms wide. Grids of nanowires are slated to serve s the foundations of Hewlett- Packard's molecular memory devices.
Putting a molecular switch on each nanoparticle and then forming connections between the nanowires and larger wires without crushing the molecular switches is a major but not insurmountable challenge,
Researchers at Hewlett-Packard and the
The researchers' ultimate goal is to pack 100 gigabits, or 100 billion bits, into one square centimeter of chip space using the molecular memory technology, he said. That's at least 1,000 times more than is possible using standard semiconductor technology, he said.
The molecular memory addressing system could be used in practical devices in five to ten years, according to Kuekes. Beginning in five years the technology could be used in niche products that require very low-power, very high-density memory, he said. The molecular memory technology should match the data capacity of standard semiconductor memory in nine or 10 years, he added.
Applications:
The Defense Advanced Research Project Agency’s (DARPA) UltraScale Computing effort seeks to explore, expand, and enable advancements in biological computing. Currently it is focusing on 4 major areas:
1. HYBRID COMPUTATION:
Two way communication channels that transducer electrical/optical/magnetic signals to chemical processes will be bioengineered. Large numbers of organically based computational computer assets to solve computationally hard problems in drastically reduced elapsed time and with dramatically low power.
2. HYBRID PERIPHERALS:
Hybrid peripherals will perform limited signal processing, e.g. through gene regulatory networks, under the direction of high performance electronic systems. Responses may address the development of biological computer peripheral components such as: sensors or actuators; mechanisms for performing in situ signal processing; communication and interfaces to electronic computers. These integrated peripherals should demonstrate how a modicum of bioengineered preprocessing can vastly reduce the need for electronic post processing or otherwise enable new application capabilities or venues.
3. HYBRID STORAGE:
Hybrid storage will develop mechanisms for data storage and retrieval from organic, cellular, or tissue-based memory subsystems. Symbolic constructs for tissue-based abstractions and models of data storage will be developed. A demonstration of technology that enables greater than one bit per cubic nanometer data storage capability is of particular interest.
4. ULTRASCALE PROTOTYPES:
DARPA also solicits proposals for application specific prototypes of other ultrascale technology that demonstrate dramatically enhanced performance over conventional processing. The living cell contains incredible molecule machines that manipulate information encoding molecules in ways that are fundamentally very similar to computation.
Conclusion:
Biological Computation is still in its infancy stage. There have been stray advances from different quarters in different aspects of Biological computing. We are still far from the final goal of a biological computer. A lot of things still need major improvements, but all the same this is one areas to be followed closely, as it has the potential of simply redefining or replacing the entire silicon technology used today in computer manufacturing.
This achievement is significant step towards building a new generation of chips, computers and smart gadgets thousands of times more powerful that those used today, but which use far less electricity. Their potential remains in realms of the imagination for now, developers say, with a commercial application not expected a decade or more. The technology could be used some day to deliver the processing power of desktop computers wrist watches, mobile phones or ultra-thin wearable computing systems.
Glossary
DNA- It is the gene that decides the animals’ features and its structure.
Molecule- Smallest elements in living organisms.
Bio-electronic circuits- Circuits those use biological elements in place of
electrical elements for power transfer.
Toggle switch- Switch that shifts between two phases-on and off.
Photo bleaching-emission of light.
Laser irradiation- Application of laser beam.
Silicon computer- Computers that use silicon chips for memory.
Membrane- a thin flexible skin like tissue.
Polynucleotide- A chain that contains more than two molecules.
Nanowire- Wire having its diameter nanometer-sized.
Hybrid – Made artificially of more than one type of different elements.
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