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Biological Spintronic Semiconductors: Frontiers

Spintronics

Spintronics is an emerging field of basic and applied research in physics and engineering.  Spintronics, meaning “spin transport electronics”, exploits the intrinsic spin of electrons, in addition to their electronic charge, in solid-state devices like sensors.

Spintronic devices make use of spin properties instead of, or in addition to electron charge to carry information, thereby offering opportunities for novel micro‐ and nano‐electronic devices. These devices are expected to become the ideal memory media for computing and main operating media for future quantum computing..  In spintronics the spin of an electron is controlled by an external magnetic field and polarize the electrons. These polarized electrons are used to control the electric current. The goal of spintronics is to develop a semiconductor that can manipulate the magnetism of an electron…  External magnetic fields can be applied so that the spins are aligned (all up or all down), allowing a new way to store binary data in the form of one’s (all spins up) and zeroes (all spins down).

Biological materials are being investigated in spintronics as in the face of continued miniaturization of components and circuitry in microelectronics, conventional semiconductor microelectronics is rapidly approaching its useful miniaturization limits… For an alternative approach…. biological molecules are known to self‐assemble with nanometer scale resolution and possess some unique qualities that might be crucial for nanoscale fabrication.  A Fakhar 2008.

Biological Semiconductors

The concept of biological semiconductors has been around for some years (e.g A V Vannikov 1970. Bioelectrical signals play critical roles in many biological processes such as energy harvesting, rapid communications and inter/intra cellular synchronisation.  Specific examples include photosynthesis, vision, carbohydrate metabolism, neurophysiology, wound healing, tissue regeneration and embryonic development.

Biological semiconductors already identified include melanin and peptides. Charge transport has also been found in a variety of naturally-derived small molecule, semiconducting biological compounds including carotenoids (produced by plants and bacteria), which offer protection against oxidative species, pigmentation, and light harvesting for photosynthesis. M Mukovich 2012.  

The Giese Group, examined electron transfer along a series of polypeptides and demonstrated that the existence of central aromatic acids can serve as stepping stones to support the electron hopping mechanism. W Sun 2016.  It has been noted that ‘assuming an electron or hole in a polypeptide is located on any peptide group, then if the life of this state is comparable with the period of interpeptide vibrations, the distances between all the bonds in the peptide group are changed and stabilised in this state.  Furthermore, in the neighbourhood of this peptide group, the distances between neighbouring peptitdes also becomes different, which changes the probability of transfer from group to group.  It is observed that the proposed mechanism for this is extremely similar to the mechanism of the motion of a polaron in an oxide semiconductor’. L I. Boguslavskii – 2013.

Spintronics, Spin Chemistry and Quantum Biology 

Spin chemistry is an older field of science than spintronics.  It has been drawn upon by those attempting to explain room temperature quantum mechanical effects in photosynthesis and (possibly) magnetoreception (N Lambert 2013).

Very recently it has been recognised that the fields of spin chemistry and spintronics  are working on very similar areas of science and there is a strong argument for drawing the two fields together.

 J Matysik (2017)  has provided an initial ontology that describes the similarities and differences  between the findings of each field.  It might also be useful to turn this into a semantic web ontology to assist in research, and also connect in other fields including quantum biology, and broader biology.  It is important that there is more communication between chemistry, physics and biology around spin in biological materials.

There are various theories relating to quantum biology, but it is hoped that with the drawing together of scientific disciplines, the exact mechanisms will become clearer.

Quantum Biology as Biological Spintronic Semiconductors.

There are several evidenced examples in biology of processes which involve ultra-fast electron transfer, singlet and triplet spin mechanisms and quantum coherence (taking place at room temperature).

  1. Evidence of the solid state photo-CIDNP effect, singlet and triplet states, ultra-fast electron transfer, and quantum coherence in photosynthesis.
  2. Evidence of the solid state photo-CIDNP effect, singlet and triplet states and ultra-fast electron transfer in some flavoproteins.  In addition there are widely explored scientific theories of cryptochrome (a flavoprotein) and/or magnetite triggering a quantum mechanical effect during ‘magnetoreception’.

Manifestations of quantum coherence in different solid state systems include semiconductor confined systems, magnetic systems, crystals and superconductors. Ultrafast electron transfer and charge separation is possible in semiconductors A Ayzner 2015, S Gélinas 2014.

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