Bio Molecular Computers

About

Molecular computing is an emerging field to which chemistry, biophysics, molecular biology, electronic engineering, solid state physics and computer science contribute to a large extent. It involves the encoding, manipulation and retrieval of information at a macromolecular level in contrast to the current techniques, which accomplish the above functions via 1C miniaturization of bulk devices. The biological systems have unique abilities such as pattern recognition, learning, self-assembly and self-reproduction as well as high speed and parallel information processing.

Protein Based Optical Computing Memories

Much research has gone in developing high-speed optics random access memory based on bacteriorhodopsin. Bacteriorhodopsin is a purple coloured pigment occurring in the cell membrane of Halobacterium halobium. It utilizes solar energy to move protons across the membrane, resulting in difference in the proton levels. Now it is known that under a high proton concentration, the formation of ATP takes place and this ATP is used to catalyse a reaction. By measuring the rate of reaction, one can create a logic gate. On being cooled to sufficiently low temperatures, a nanometer-sized section of the bR molecule will kink out of shape when struck by a green laser. But, most importantly, the altered bR molecules can be made to snap back to their original form, if hit by a red laser. Hence, bR can act as the basis for a molecular binary switch. This can be used to make large optical memories with access time below two nano seconds. Currently, access times of 20ns have been achieved, the major limitation being the speed at which optical beams can be positioned to read or write single bits.

What About Efficiency?

In both the solid-surface glass-plate approach and the test tube approach, each DNA strand represents one possible answer to the problem that the computer is trying to solve. The strands have been synthesized by combining the building blocks of DNA, called nucleotides, with one another, using techniques developed for biotechnology. The set of DNA strands is manufactured so that all conceivable answers are included. Because a set of strands is tailored to a specific problem, a new set would have to be made for each new problem.

Design And Fabrication

The costs to design and build a 64 mega-bit memory chip run into billions of dollars and these costs would raise higher for larger memory-sized chips. In contrast, some bio molecular systems like bR offer the promise of being economically grown in a vat and can quickly be harvested in a normal environment which is controlled via ordinary chemistry or use of shelf laser diodes.

Quantum Effects

They are introduced due to very small size of solid-state devices. This is important when the feature size reduces to a point where one is dealing with individual atoms. The quantum effects like unwanted tunneling of electrons pose a great difficulty. These effects can be nullified using an average output through redundant circuits making the fabrication costlier.

Thermal Build Up

Semiconductor designers are always trying to shrink circuit line widths in order to increase overall processor speed. But this causes massive thermal dissipation problems. The tightly spaced electronic switches generate huge amounts of heat, which has to be dissipated at a high speed. Such problems will not arise in bio molecular devices.

New Devolopments

The first applications were "brute force" solutions in which random DNA molecules were generated, and then the correct sequence was identified. The first problems solved by DNA computations involved finding the optimal path by which a travelling salesman could visit a fixed number of cities once each. Recent work showed how DNA can be employed to carry out a fundamental computer operation, addition of two numbers expressed in binary."

Conclusion

Biomolecular computers have the real potential for solving problems of high computational complexities and therefore, many problems are still associated with this field. The difficulty of devising an interface is therefore the sensitive dependence on a biological environment, susceptibility to degradation, senescence and infection, etc. Nevertheless, it offers the best approach to human cognitive equivalence.