Memory Using Bacteriorhodopsin

While magnetic and semiconductor based information storage devices have been in use since the middle 1950's, today's computers and volumes of information require increasingly more efficient and faster methods of storing data. While the speed of integrated circuit random access memory (RAM) has increased steadily over the past ten to fifteen years, the limits of these systems are rapidly approaching. In response to the rapidly changing face of computing and demand for physically smaller, greater capacity, bandwidth, a number of alternative methods to integrated circuit information storage have surfaced recently. Bacteriorhodopsin, a light harvesting bacterial protein, is the basic unit of protein memory and is the key protein in halo bacterial photosynthesis. It functions like a light-driven photo pump. Under exposure to light it transports photons from the hollow bacterial cell to another medium, changes its mode of operation from photosynthesis to respiration, and converts light energy to chemical energy thus can be utilized to frame protein memories.

The initial resting state of the molecule is known as ‘bR’. Green light transforms the initial ‘bR’ state to the intermediate state ‘K’. Next ‘K’ relaxes, forms another intermediate state ‘M’ and then ‘O’ converts to another intermediate state ’P’, which then relaxes to a more stable state ‘Q’. Blue light converts ‘Q’ black to the initial state ‘bR’. Here the idea is to assign any two long-lasting states to the binary values of ‘0’ and ‘1’, to store the  required  information. Many of the memory devices based on Bacteriorhodopsin could operate only at extreme cold temperatures of liquid nitrogen, where light-induced switching between ‘bR’ and the intermediate state ‘K’ could be controlled. These devices were much faster than conventional semiconductor-based devices, as these exhibited the speed of a few trillionths of a second. Today, most Bacteriorhodopsin based devices function even at room temperature, switching between ‘bR’ and another intermediate stable state ‘M’. If a number of Bacteriorhodopsin molecules are arranged in a 3-dimensional fashion, high-speed, high-density, low-cost memories with vast capacities that can handle large volumes of data can be realized. Such memories offer over 300-fold improvement in storage capacity over their two-dimensional counterparts. Read/Write operations on these can be performed with the help of colored lasers that are fixed at such points as to direct the beams through the required points in the plane of the cube.

Retrieval of stored data is carried out in a manner similar to storing the information, except that a detector images the light passing through the memory cube and senses 1’s and 0’s. Here the property of selective absorption of red light by the intermediate state ‘O’ is relied upon. The detector senses the luminescent power falling upon it and converts the variations of optical power into a correspondingly varying electric current.