Bioelectronics is a new, rapidly developing applied area connecting condensed matter physics, organic chemistry, biophysics, and medical engineering. Its main task is to create methods and devices that effectively exchange information between tissues and cells of living organisms and electronic circuits. Since such an exchange almost always involves the use of electrical or optical signals, the basis of our course is to get acquainted with the advanced concepts of the mechanisms of charge and energy transfer in bioorganic systems and with experimental methods for their determination using specific examples from the course authors' work and scientific articles of other teams.
The main drivers of applied bioelectronics are medical companies that develop so-called electroceuticals - drugs and devices that replace classical organic drugs with artificial stimulators of nervous activity, which leads to a long-term therapeutic effect. Also of great importance for bioelectronics is the request to create neural interfaces aimed at prosthetics for patients’ lost senses and motor skills and the creation of exoskeletons. In this regard, the focus of the course is on the problems of fabricating reliable non-damaging contacts between organic and inorganic materials. The latter leads to the need to touch upon the topic of the so-called green lithography within the course, the purpose of which is to maximize the introduction into practice of low-energy consumer electronics, which accounts for the lion's share of electronic waste on the planet, methods that allow the use of biodegradable and biocompatible materials. In the same context, we consider the principles of operation of (bio)organic transistors and ways to improve their efficiency.
An area relatively close to bioelectronics is industrial bioelectrosynthesis, the purpose of which is the design of microorganisms and biocenoses capable of synthesizing the chemical compounds required by the economy from simple low-molecular precursors and electricity “from the socket.” The success of both directions fundamentally depends on our ability to control the processes of charge and energy transfer both within living systems and during their interaction with an inorganic substrate.
The second part of the course is devoted to the mechanisms of biological sensory systems. Particular attention is paid to the physical principles of their functioning, implementing practical solutions for processing the raw signal and isolating its significant part directly in the sense organ. Within the course framework, questions about the post-processing of signals from sensory systems in the brain are practically not discussed. However, within the framework of two lectures, on organic neuromorphic systems and excitable environments, the topics of alternative computing environments are discussed.
Since the course is read for senior physics students, it is assumed that the mathematical apparatus is used relatively actively as well as essential information from the general physics course.
Lecture I
Course Introduction
The main problems and definitions. Wearable and implantable electronics, green electronics, electroceuticals, electrosynthesis of useful substances and materials by industrial microorganisms. Simple bioelectronic devices. Neurointerfaces and the evolution of prosthetic systems. USA FDA website with information on certification of new electroceuticals for the last month – a brief review of actual cases.
The universal concept of an excitable medium. Autowave processes in chemistry (Belousov-Zhabotinsky reaction) and biology. Biological excitable media: cardiac and neural tussiues. Transmembrane ion potentials in biology. Ion channels and ion pumps. Refractory period. The patch clamp technique. Artificial control of ionic transmembrane currents: optogenetics, magnetothermal effect, ultrasound, etc.
References and links:
Lecture III
Electron Conductivity in Condensed Matter Physics
Review of the mechanisms of electron conductivity in condensed matter physics: Drude model, Drude-Sommerfeld model, nearly free electron model, Bloch’s theorem, tight binding model, LCAO model, various options for hopping and tunneling. Phenomenological equation of Jonscher. Percolation theory. Examples.
Using electronic conductivity models to describe ionic conductivity. Examples.
M. Pollak, B.I. Shklovskii, Hopping transport in solids, Elsevier Science Pub. Co., 1991
Lecture IV
Types of Charge Carriers and the Effects of Water
Types of charge carriers. The problem of determining the nature of a charge carrier in a condensed state and methods for its solution. Importance of the large temperature range measurements. Effect of water on conductivity in bioorganics. Review of the main methods: Hall effect; impedance spectroscopy; PdH – based proton-conductive contacts; assistance from proton NMR and neutron scattering techniques; thermal electromotive force; electrochemical transistors.
Special case of protons. Why the problem of proton conductivity for bioelectronics is no less topical than the problem of electronic conductivity: the future belongs to proton energy, the largest electrical potentials in biology are produced by protons, the highest speed transistors operate on proton gates. Importance of proton transmembrane potentials for cellular energetics – a brief review of ATP synthase structure. How are proton and electron similar to each other. States of proton in aqueous medium and in bioorganics. Proton delocalization. Anomalous proton mobility. Proton “superconductivity” and “superconductors”. Activation of proton transport on phase borders. Water floating bridges and the possibility of electrohydrodynamic phenomena in biological systems. Isotopic effects and proton/deuteron mobility. Proton wires in proteins.
Electron Conductivity in Bioorganics. Marcus Theory
Electron conductivity in biological systems. Chemical viewpoint on hopping: Marcus theory, electron transfer in proteins as a chain of redox-reactions. Long-range electron transfer in biology. Electrogenic bacteria (Shewanella, Geobacter, Desulfobulbus). Why band electronic conduction for aerobic life forms is unlikely. Reactive oxygen species. Efficiency management of ATP synthesis in mitochondria.
References and links:
Lecture VII
Molecular Electronics
“There is plenty of room in the bottom” and Moore’s empirical rule. 1D and 2D molecular electronics. Revolution of conductive polymers. Single-molecule electronics, examples. How to work with single-molecule: the brief review of methods. Conductivity and conductance. Methods of single-molecule electronics as a proxy to the understanding of biomolecules properties. Conjugation with optical methods.
Motivation. The need for consumer low-energy green electronics. Creation of reliable contacts between metals, silicon, and bioorganic matter. Stability of bioorganics under different external conditions. A brief review of bioorganic materials utilized as lithography resists. Perspective methods: ice lithography, photoswitches, magnetic and nanoparticle-based control of resists development.
Neuromorphic system: what is it? Formal functions of nervous systems. Development of memristors. An energy-efficient neuron that acts as an adder and a threshold function. More complex neural network architectures (reservoirs, short-term memory memristors, self-coupled memristors, etc.). Mimicking of natural nervous systems to solve applied problems. Oxide memristors, phase change memristors (PCM), neuromorphic spintronic devices, organic neuromorphic systems and other approaches. Perspectives.
General features of biological sensory systems. Classification of the senses. Modality. Intensity. Adaptation. Receptive Fields. Examples of cerebral analysis of different senses.
Chemistry and Physics Behind Biological Senses: Limits and Opportunities
Isomerization of retinal and photochamical aspects of vision. Young's modulus of various different biological structures. Piezo effect in proteins. Decomposition of the sound spectrum. Physical limits to magnetosensitivity. Detection of polarized light.