What is Protein Memory?<br />Protein memory is based on bacteriorhodopsin that is extracted from bacteria. <br />Bacteriorhodopsin is an organic molecule that can exist in a variety of chemical states. It is relatively easy to detect which state the molecules are in, because each state has different absorptions to light. <br />By choosing two of these states, one for binary zero and the other as binary one, it is possible to use this as a memory device.<br />
Source of BR<br />ArchaebacteriaHalobacteriaSalinariumare the source of bacteriorhodopsin<br />They are halophilic bacteria (found in very salty water e.g. Great Salt Lake)<br />This particular bacteria live in salt marshes.<br />Salt marshes have very high salinity and temperatures can reach 140 degrees Fahrenheit. <br /> Unlike most proteins, bacteriorhodopsin does not break down at these high temperatures.<br />
What is the Purple Membrane?<br />The purple membrane patches are areas on the membrane where BR is concentrated<br />BR absorbs light @ 570 nm (visible green light)<br />Red and Blue light is reflected, giving membrane its purple colour<br />
Why Bacteriorhodopsin?<br />The protein is extremely stable to degradation, both thermally and photochemically. <br />It uses light energy to transport charges thereby converting energy from light to chemical forms. <br />It self assembles into thin films. <br /> Additionally, current advances in molecular biology imply that these proteins can be easily mass produced<br />
Making of Protein Cube<br />First the bacterial DNA is splice and mutated to make the protein more efficient for use as a volumetric memory. <br />The bacteria must be grown in large batches and the protein extracted.<br />Bacteriorhodopsin is then combined with inert transparent gel and stored in a cube.<br />
PHOTOCYCLE OF BACTERIORHODOPSIN <br />Bacteriorhodopsin comprises a light absorbing component known as CHROMOPHORE , that absorbs light energy and triggers a series of complex internal structural changes to alter the protein’s optical and electrical characteristics. This phenomenon is known as photocycle.<br /> Green light Changes the initial resting state known as Br to the intermediate K.<br />Next K relaxes, forming M and then O.<br />The O state is the red absorbing intermediate state.<br />O converts to the P state and quickly relaxes to the Q state-a form that remains stable indefinitely. Blue light will however convert Q back to bR<br />
Principle of Storage<br />Two lasers are positioned next to the cube, one looking vertically through the cube (red laser), and the other looking horizontally down (green laser). Each laser has an LCD display between the laser and the cube. <br />The green laser (paging LCD) illuminates a vertical slice of matter called ‘page memory’<br />The red laser (write laser) illuminates the pattern displayed on the LCD (which is a binary representation of the data) onto the matter on the cube as in fig. <br />Contd.<br />
The matter that is illuminated by the green laser and also hit by the red laser shifts state. It requires both lasers to shift state, so the rest of the matter that is illuminated by the green laser or the red laser only is not affected. <br />The pattern that was displayed on the LCD in front of the red laser has thus been transferred onto the illuminated page of memory<br />On the opposite side of the cube, in front of the red laser there is a CCD (charge-coupled device) detector that is used to read the data from the memory.<br />
Data Operation<br />Data Writing Technique<br />Data Reading Technique<br />Data Erasing<br />Refreshing the memory<br />
Data Writing Technique<br /><ul><li>The green or paging beams activates the photocycle of the protein in any selected square plane, or page, within the cube.
After a few milliseconds, the number of intermediate O stages of bacteriorhodopsin reaches near maximum.
Now red beams is fired which is programmed to strike only the region of the activated square where the data bits are to be written, switching molecules there to the P structure.
The P intermediate then quickly relaxes to the highly stable Q state.
We then assign the initially-excited state, the O state, to a binary value of 0, and the P and Q states are assigned a binary value of 1. </li></li></ul><li>Data Reading Technique<br /> First, the green paging beam is fired at the square of protein to be read. <br />After two milliseconds the entire red laser array is turned on at a very low intensity of red light. <br />The molecules that are in the binary state 1 (P or Q intermediate states) do not absorb the red light, or change their states, as they have already been excited by the intense red light during the data writing stage.<br />However, the molecules which started out in the binary state 0 (the O intermediate state), do absorb the low-intensity red beams. <br />A detector then images (reads) the light passing through the cube of memory and records the location of the O and P or Q structures; or in terms of binary code, the detector reads 0's and 1's.<br /> The process is complete in approximately 10 milliseconds, a rate of 10 megabytes per second for each page of memory.<br />
Data Erasing<br />To erase data, a brief pulse from a blue laser returns molecules in the Q state back to the rest state. <br />The blue light doesn't necessarily have to be a laser.<br />We can bulk-erase the cuvette by exposing it to an incandescent light with ultraviolet output.<br />
Refreshing the memory<br />To ensure data integrity during selective page-erase operations<br />A page of data can be read nondestructively about 5000 times. <br />Each page is monitored by a counter, and after 1024 reads, the page is refreshed via a new write operation.<br />
Issues Left to be resolved: <br />The polymer gel that the protein is put in breaks down faster than the protein itself. The protein can withstand the laser light, but the gel breaks down after a while. This is a major obstacle for protein memory<br />Mutations could affect the photochemical properties of the protein <br />
Advantages of using protein memory: <br />Because it is protein based it is inexpensive to produce in quantity <br />Can operate over a wider range of temperatures much larger than semiconductor memory <br />Non-volatile, can be used for storage and memory <br />