Silicon to be Replaced by Proteins?

I’m revamping my Molecular Biology course and have stumbled upon a few interesting nanotechnology topics that might be of interest to some people…

A few years ago, I attended a very interesting lecture about the use of biological molecules in building computers. Why, you might ask, would you want to use biological molecules to build computers? The answer is that biological molecules are small – typically on the order of nanoscale (one millionth of a millimeter), whereas most silicon-based chips are at the microscale (one thousands of a millimeter). Thus, if we could use proteins and DNA to build the logic gates and memory circuitry, we could miniaturize computers by at least 1,000 fold. This could have many applications, not the least of which are medical applications. Think of injecting small robots into your bloodstream that are autonomous and can direct themselves to the appropriate location, execute repairs, and leave your body without the intervention of surgeons. It gives a whole new meaning to “take two pills and call me in the morning”.

DNA seems a very likely candidate for building logic gates, and perhaps I’ll discuss them here soon. In the meantime, I just wanted to mention the potential of proteins in serving in memory chips. Proteins are the workhorses in your body. They do everything from digesting bread, to synthesizing fats from ingested sugars, to pigmenting your skin, to making up the bulk of your hair.

One protein in particular, rhodopsin, has attracted a lot of attention for its nanotechnology potential. Rhodopsin is a protein found in your eyes. It is found at the back of the eye and serves as a sensor for light of a specific wavelength (i.e. colour). When light of a specific colour strikes rhodopsin, it causes the protein to change its shape. This change generates a signal that your nervous system interprets as the perception of light or colour. The critical property of this protein is that it can exist in one of two forms, one when it has been hit by light of a certain colour, and another in the absence of light.

Now think of a small cube, maybe 1cm by 1 cm by 1cm that you fill with an ordered array of rhodopsin. You know where each molecule of rhodopsin is in this cube. Each molecule of rhodopsin is tiny – so tiny in fact that we know its atomic composition in great detail. Each molecule lives at a particular place in the cube, and it exists in one of two shapes. Since each rhodopsin lives at a certain fixed physical address, you can shine a laser (i.e. light of a specific wavelength) at that spot and change the shape of one specific rhodopsin molecule in the cube.

Does this start to sound a little bit like the memory of a computer? A memory chip (or a CD or DVD for that matter) is simply a material on which there are several “cells” that live at specific addresses and that exist in one of two states: ON or OFF, or another way of thinking about it is 1 and 0 (the famous binary code). Typically, each of these cells is microscopic.

Hopefully, you see the parallel with the cube of rhodopsin. It’s the same thing, except that the rhodopsin cube encodes the information at a 1,000 fold smaller scale. So for a similar sized disk, you could encode 1 meg of information with silicon technology, or 1 gig of information with biological nanotechnology.

A few issues remain to be worked out. How to “reset” the protein once you have changed its shape, for example. However, this technology is very promising…