Outer physical world exists in the form of electromagnetic field and matter. The field quanta and molecules of the matter influence the receptor layers of human sensor systems; and this influence transforms into electric signals which are transmitted to the central nervous system for processing. It is possible to say that the receiving layers of sensor receptors are the “windows” through which the external signals (photons, molecules, etc.) enter our consciousness. The structure and chemical composition of the receiving layers of human sensor receptors determine the capabilities to perceive the physical world.
Based on our perceptions, we constantly create the picture of the surrounding world in our brain.
It is known today that the physical world surrounding us has electromagnetic fields of a broad energy spectrum but our receptors are able to respond only to a very narrow range of electromagnetic field wavelengths — 400–750 nanometer — termed ‘visible light.’ Visual receptors can form a response to a single absorbed quantum of light. That means that the receiving layer of the human visual receptor — retina — has the maximum possible photosensitivity. In order to achieve this high efficiency level, the evolution process created a nanostructured biomaterial of an hierarchical structure containing cones and rods that use nano-sized protein complexes (rhodopsin) as the absorbing centres for light quanta.
The characteristics of these complexes determine the fact that we “see” the world around us in such a narrow spectral range but with the one-light-quantum sensitivity.
The sensor system of the living organisms that allows to “feel” the molecules of the matter in the environment is the sense of smell. Membrane proteins (nanostructures) of the olfactory receptor cells are able to bind the molecules of various chemical substances. The receiving layers based on such proteins can create the response to extremely low molecule concentrations (up to several molecules per cubic meter) to distinguish molecules differing from each other with a single atom — for example, oxygen and ozone.
Interestingly, the receptor centres of the olfactory and the visual systems are based on the proteins belonging to the same class of proteins containing seven membrane domains. Given the fact that visual receptors were created on a later stage of evolution, it is possible to say that nature used the “ready models” to address visual reception issue after supplementing them with new features.
The photosensitive and chemosensitive nano-structured materials and devices based on them that exist today are close to natural sensor systems concerning their characteristics.
M. V. ALFIMOV, editor-in-chief, academician
The Russian Nanotechnologies magazine, #7-8, 2011