1. Simulation of biofilm and biological interface
This paper mainly studies the electrochemical thermodynamic properties of membranes, the transport of substances across membranes and the transfer of bioelectricity.
Electrochemical study on (1)SAM membrane simulated biofilm
SAM is a thermodynamically stable ordered thin film with the lowest energy, which is based on the strong chemical bonding of long-chain organic molecules on the substrate surface and the spontaneous adsorption on the solid/liquid or gas/solid interface due to the interaction between organic molecular chains. In the monolayer, the molecules are aligned, orderly and closely. By changing the types and lengths of the head group, tail group and chain of the molecules, the structure and properties of the membrane can be adjusted. Therefore, SAM has become an ideal model system to study various complex interface phenomena, such as membrane permeability, friction, wear, wetting, adhesion, corrosion, biological fermentation, surface charge distribution and electron transfer theory. The electrochemistry of self-assembled films mainly studies the absolute coverage, defect distribution, thickness, ion permeability, surface potential distribution and electron transfer of self-assembled films by electrochemical methods. SAM can be used to study the trans-SAM electron transfer between redox species in solution and electrode, and the electron transfer between electroactive SAM itself and electrode. The self-assembled film formed by thiol compounds on the surface of gold electrode is the most typical and studied system in membrane electrochemistry. Because long-chain thiol compounds are very similar to natural biological bilayer membranes in terms of molecular size, tissue model and natural formation of membranes, they also have molecular recognition function, selective response and high stability. Therefore, the self-assembled film formed by thiol compounds on gold electrode is of great significance to bionic research. For example, the selectivity of SAM surface molecules can be used to study the adsorption of protein; Based on the self-assembled film of alkyl mercaptan compounds on gold, the long-range and interface transfer mechanism of electrons in redox proteins was studied. By depositing phospholipids on thiol SAM, it is easy to construct a double-layer phospholipid membrane. In the research of biosensor, it is used to simulate the quasi-biological environment of double-layer phospholipid membrane and the immobilization of enzyme, so that the enzyme can be directly transferred. For example, cystine or cysteine is used as SAM, and mediators (such as TCNQ, ferrocene, quinones, etc. ) and enzyme are combined by condensation reaction to form various biosensors for measuring glucose, glutathione, bilirubin, malic acid and the like.
(2) Electrochemical study of liquid/liquid interface simulated biofilm.
The so-called liquid/liquid (L/L) interface refers to the interface formed between two immiscible electrolyte solutions, also known as the oil/water (O/W) interface. The research scope of liquid/liquid interface electrochemistry is very wide, including liquid/liquid interface electric double layer, liquid/liquid interface charge transfer mechanism and kinetics, biofilm simulation and electrochemical analysis application. L/L interface can be regarded as a semi-biofilm model in contact with surrounding electrolytes. Biofilm is a self-assembled structure of phospholipids with polar ends facing intracellular and extracellular aqueous solutions respectively, and lipophilic chains of phospholipids form an oil-like inner layer. Therefore, in a sense, the L/L interface of phospholipid-adsorbed monolayer is very close to the biofilm/aqueous solution interface. Phospholipid is an ideal experimental material, which can be well adsorbed on the L/L interface. The coupling between charge or potential and the surface tension of phospholipid monolayer is considered as the basic driving force of lipid-like movement in cells and cells. It can be seen that L/L interface bioelectrochemistry is a very vital research field and will continue to be widely valued by people.
Biological cell membrane is a special type of semi-permeable membrane.
The permeability of cell membrane to K+Cl-Na+ plasma is also different.
The plasma concentration of K+Cl-Na+ is different inside and outside the cell membrane, so the generated membrane potential is called (cell) biomembrane potential.
Different currents pass through animal cell membranes, and the behaviors of dead cells and living cells are also different.
2. Bioelectrochemical application technology
Because life phenomena are closely related to electrochemical processes, electrochemical methods are widely used in life sciences, mainly including: direct introduction of electric pulse genes, electric field accelerating crop growth, electrochemical treatment of cancer, electrochemical control of drug release, electrochemical methods in vivo research, electrochemical behavior of biomolecules, electrochemical research of thrombosis and cardiovascular diseases, electro-growth of bones, research of electrocardiogram and electroencephalogram, and biological batteries.
The direct introduction of electric pulse gene is based on the fact that negatively charged plasmid DNA or gene fragment is "shot" to the recipient cell under the action of high-voltage pulsed electric field, and at the same time, the permeability of cell membrane is increased under the action of electric field (dielectric breakdown effect), so that the gene is successfully introduced into the recipient cell. Due to the reversibility of electric breakdown of cell membrane, when the electric field is removed, the cell membrane and all its functions can be restored. This method has been applied in molecular biology. The cell transformation efficiency is high, reaching1010 transformants per microgram of DNA, which is 20 times higher than that of competent cells prepared by chemical methods.
Promoting crop growth by electric field is a new research topic. Matsuzaki et al reported that maize and soybean seedlings were cultured in a medium containing 0.5mmol/l K2SO4, and electric pulses of 20Hz, 3V or 4V (peak-to-peak) were added. After 6 days, compared with the control group, the root system of the seedlings was developed and the growth was obviously accelerated. The reason may be that the electric field stimulates the ion pumping of growth and metabolism.
Electrochemical therapy of cancer is a new method to treat cancer proposed by Swedish radiologist Nordenstrom. Its principle is that under the action of DC electric field, it causes a series of biochemical changes in cancer focus, leading to tissue metabolism disorder, protein degeneration, precipitation and necrosis, leading to the disintegration of cancer cells. Generally, the positive electrode of platinum electrode is placed in the center of cancer focus, and 1 ~ 5 platinum electrodes are tied around it as negative electrodes, and a voltage of 6 ~ 10V is applied. The current is controlled at 30 ~ 100 Ma, and the treatment time is 2 ~ 6 hours. The power consumption per cm diameter cancer focus is100 ~/kloc-. This therapy has been popularized for the treatment of liver cancer and skin cancer. The treatment of body surface tumors is particularly simple and effective.
Drug controlled release technology refers to the control of drug release speed and release site in a certain period of time to obtain the best curative effect, and at the same time, slow release is conducive to reducing drug toxicity. Electrochemical control of drug release is a new drug release method. In this method, drug molecules or ions are combined with a polymer carrier, so that the polymer carrier is fixed on the surface of the electrode to form a chemically modified electrode, and then the drug molecules or ions are released into the solution by controlling the redox process of the electrode. The loading modes of drugs on carrier polymers can be divided into * * * valence bond type and ionic bond type. Valence bond loading is to bond the drug molecules to the polymer skeleton through chemical synthesis, and then fix the polymer on the surface of the solid electrode by coating to form a polymer film modified electrode. In the process of oxidation or reduction, the valence bond between drug molecules and polymers is broken, so that drug molecules are released from the membrane. Ionic bond loading is the use of electroactive conductive polymers, such as polypyrrole and polyaniline, to load drug ions into polymer films. Accompanied by the intercalation of ions as counter ions during oxidation or reduction, and then drug ions are released from the membrane through reduction or oxidation.
In vivo study is an important method of physiological research, which aims to understand the mechanism of action and physiological activities of cells, tissues and organs from the overall level. Because some neuroactive substances (neurotransmitters) have electrochemical activity, electrochemical methods are first used to study the brain nervous system in vivo. When microelectrodes were inserted into animal brains for in vivo voltammetric determination, people immediately attracted great interest. After continuous improvement, this technology is recognized as the most effective way to track and monitor the neural activity of animals' brains under normal physiological conditions. The neurotransmitters that can usually be detected are dopamine, norepinephrine, serotonin and their metabolites. Microelectrode voltammetry has become a powerful tool for continuous monitoring of primary neurotransmitters entering intercellular fluid. In vivo research generally adopts fast cyclic voltammetry (thousands of volts per second) and fast chronoamperometry. Rapid cyclic voltammetry has also been used to study the release of neurotransmitters by a single nerve cell, which has developed into so-called "cell electrochemistry".
The study of electrochemical behavior of biomolecules is a basic research field of bioelectrochemistry, and its purpose is to obtain the mechanism of redox electron transfer reaction and electrocatalytic reaction of biomolecules, thus providing basic data for correctly understanding the biological functions of bioactive molecules. The biomolecules studied include small molecules such as amino acids, alkaloids, coenzymes and sugars, as well as biomacromolecules such as redox proteins, RNA, DNA and polysaccharides.
3. Electrochemical biosensor and biomolecule device sensor, communication system and computer constitute a modern information processing system. Sensors are equivalent to human senses, interfaces between computers and nature and society, and tools to provide information for computers.
Sensors are usually composed of sensitive (identification) elements, conversion elements, electronic circuits and corresponding structural accessories. Biosensor refers to a sensor that uses fixed biological components (enzymes, antigens, antibodies, hormones, etc.). ) or the organism itself (cells, organelles, tissues, etc. ) as a sensing element. Electrochemical biosensor refers to a sensor with biomaterials as sensing elements and electrodes (solid electrodes, ion-selective electrodes, gas-sensitive electrodes, etc.). ) as a conversion element, and detects a signal characterized by a potential or a current. Because biomaterials are used as sensitive elements of sensors, electrochemical biosensors are highly selective, and they are ideal analytical tools for quickly and directly obtaining information of complex systems. Some research results have been applied to biotechnology, food industry, clinical laboratory, pharmaceutical industry, biomedicine, environmental analysis and other fields.
According to the different biomaterials used in sensing elements, electrochemical biosensors can be divided into enzyme electrode sensor, microbial electrode sensor, electrochemical immunosensor, tissue electrode and organelle electrode sensor, electrochemical DNA sensor and so on.
(1) enzyme electrode sensor
The working principle of glucose oxidase electrode is briefly described. Under the catalysis of GOD, glucose (C6H 12O6) is oxidized by oxygen to produce gluconic acid (C6H 12O6) and hydrogen peroxide. According to the above reaction, it is obvious that the glucose content can be indirectly determined by oxygen electrode (measuring the consumption of oxygen), hydrogen peroxide electrode (measuring the production of H2O2) and PH electrode (measuring the change of acidity). Therefore, as long as GOD is fixed on the electrode surface, a GOD sensor for measuring glucose can be formed. This is the so-called first-generation enzyme electrode sensor. Because this sensor is an indirect measurement method, there are many interference factors. The second generation enzyme electrode sensor uses redox electron mediator to transfer electrons between the redox active center of enzyme and the electrode. The second-generation enzyme electrode sensor is not limited by the measuring system, and has a wide linear range of measuring concentration and less interference. Now many researchers are trying to develop the third-generation enzyme electrode sensor, that is, the redox active center of the enzyme directly exchanges electrons with the electrode surface.
At present, commercial enzyme electrode sensors include: GOD electrode sensor, L- lactic acid monooxygenase electrode sensor, uricase electrode sensor and so on. (2) Microbial electrode sensor
The electrochemical biosensor composed of microorganisms (commonly used bacteria and yeasts) fixed on the electrode surface is called microbial electrode sensor. Its working principle can be roughly divided into three types: first, it uses the enzyme system (single enzyme or compound enzyme) contained in microorganisms to recognize molecules, similar to enzyme electrodes; Secondly, the concentration of organic matter is indirectly determined by detecting the increase of respiration activity (oxygen uptake) by using the assimilation of microorganisms to organic matter, that is, the decrease of oxygen in the system is measured by oxygen electrode; Thirdly, by measuring the sensitive metabolites of the electrode, some organic substances that can be assimilated by anaerobic microorganisms are indirectly determined.
Microbial electrode sensors have applications in fermentation industry, food inspection, medical care and other fields. For example; Pseudomonas electrode for glucose determination in food fermentation process: methanogen electrode for methane determination: Citrobacter freundii bacterial electrode for antibiotic cephalosporin determination. Microbial electrode sensor has low price and long service life, and has a good application prospect, but its selectivity and long-term stability need to be further improved.
(3) Electrochemical immunosensor
Antibodies have unique recognition and binding functions to corresponding antigens. Electrochemical immunosensor is a detection device that combines antibodies or antigens with electrodes by using this recognition and binding function. Electrochemical immunosensor can be divided into two types: direct type and indirect type. The characteristic of direct type is that the information of antibody immune reaction is directly converted into electrical signals while recognizing and binding its corresponding antigen. This kind of sensor can be further divided into two types in structure: combined type and separated type. The former is that the antibody or antigen is directly fixed on the surface of the electrode, and the sensor is combined with the corresponding antibody or antigen, and the potential changes at the same time; The latter is an antibody membrane or an antigen membrane made of antibodies or antigens. When it reacts with the corresponding ligand, the membrane potential changes, and the electrode for measuring the membrane potential is separated from the membrane. The indirect type is characterized by converting the information combined with antigen and antibody into another intermediate information, and then converting this intermediate information into an electrical signal. This kind of sensor can be further divided into two types in structure: combined type and separated type. The former is to immobilize antibodies or antigens on electrodes; The latter antibody or antigen is completely separated from the electrode. Indirect electrochemical immunosensor usually uses enzymes or other electroactive compounds to label and chemically amplify the concentration information of antibodies or antigens to achieve high sensitivity.
Examples of electrochemical immunosensor are: HCG immunosensor for diagnosing early pregnancy; Alpha-fetoprotein immunosensor for diagnosis of primary liver cancer: immunosensor for determination of human serum protein (HSA); There are IgG immunosensor, insulin immunosensor and so on.
(4) tissue electrode and organelle electrode sensor
An electrochemical sensor that directly uses animal and plant tissue slices as sensitive elements is called a tissue electrode sensor. Its principle is to use enzymes in animal and plant tissues. Its advantages are higher enzyme activity and stability than isolated enzyme, easily available raw materials, simple preparation and long service life. However, there are still some shortcomings in selectivity, sensitivity and response time.
Animal tissue electrodes mainly include: kidney tissue electrode, liver tissue electrode, intestinal tissue electrode, muscle tissue electrode, thymus tissue electrode and so on. The material selection range of plant tissue electrode sensitive elements is very wide, including roots, stems, leaves, flowers and fruits of different plants. Compared with animal tissue electrode, plant tissue electrode is simpler, cheaper and easier to store. Cell organelle electrode sensor is a sensor that uses animal and plant organelles as sensitive elements. Cell organelles refer to tiny "organs" existing in cells surrounded by membranes, such as mitochondria, microsomes, lysosomes, hydrogen peroxide bodies, chloroplasts, hydrogenase particles, magnetic particles and so on. Its principle is to use enzymes contained in organelles (often multi-enzyme systems).
(5) electrochemical DNA sensor
Electrochemical DNA sensor is a new type of biosensor developed rapidly in recent years. Its purpose is to detect genes and some substances that can specifically interact with DNA. Electrochemical DNA sensor is a device that uses single-stranded DNA(ssDNA) or gene probe as a sensitive element and fixes it on the surface of solid electrode, and adds electroactive indicator (called hybridization indicator) to identify hybridization information. Its working principle is that double-stranded DNA(dsDNA) is formed by specific recognition (molecular hybridization) between the specific sequence of ssDNA fixed on the electrode surface and the homologous sequence in solution (the properties of the electrode surface change), and at the same time, the purpose of gene detection is achieved by the change of the current response signal of the hybridization indicator that can recognize ssDNA and dsDNA.
4. Bioenergetics and metabolic processes
Including enzyme-catalyzed redox reaction mechanics, mitochondrial respiratory chain, photoredox reaction and photosynthesis. As a whole process, photosynthesis includes the process of electron excitation after photon absorption, the generation of membrane potential, the transfer of electrons and protons, and a series of subsequent metabolic reactions.
At present, in addition to the traditional electrochemical methods, electrochemical ultraviolet-visible spectroscopy, electrochemical in-situ infrared spectroscopy, electrochemical in-situ Raman spectroscopy, X-ray diffraction, scanning probe technology, electrochemical time-sensitive crystal microbalance and other methods are widely used.
Biomaterial sensing element+electrode conversion element
For example: enzyme electrode sensor
Take the glucose oxidase (GOD) electrode as an example.
Its working principle is that glucose (C6H 12O6) is catalyzed by God.
Oxidized by oxygen to produce gluconic acid (C6H 12O7) and hydrogen peroxide.
equation
According to the above reaction, the content of glucose can be indirectly measured by measuring the consumption of oxygen (oxygen electrode) or the production of hydrogen peroxide (hydrogen peroxide electrode).
This is the so-called first-generation enzyme electrode sensor. At present, there are many kinds, including those used to detect whether drivers drink alcohol. Alcohol oxidase electrode sensor.
Patented technology: connect the ethanol oxidase electrode sensor with the automobile ignition device.
Structure and Mechanism of Cell Membrane Water Channels and Ion Channels: A Brief Introduction to the 2003 Nobel Prize in Chemistry
Peter Agre: American scientist. 1949 was born in Northfield, Minnesota, USA. 1974 received his doctor's degree in medicine from Johns Hopkins University School of Medicine in Baltimore, and now he is a professor of biochemistry and medicine. Roderick mackinnon: American scientist. Born in 1956, grew up in Burlington, a small town near Boston, USA. 1982 received a doctorate in medicine from Tufts Medical College, and is now a professor of molecular neurobiology and biophysics at Rockefeller University.
bioelectrochemistry
Scientific contribution
They discovered the membrane water channel and made a pioneering contribution to the study of the structure and mechanism of ion channels. This is an important discovery, which opens the door to biochemical, physiological and genetic research on water channels of bacteria, plants and mammals.
Influence on life
Aqueous solution accounts for 70% of human body weight. The aqueous solution in organisms is mainly composed of water molecules and various ions. Their entry and exit in cell membrane channels can realize many functions of cells. How do water molecules get in and out of human cells? Understanding this mechanism will greatly help people better understand many diseases, such as heart disease and nervous system diseases. Their findings show how salt and water enter and leave the cells that make up life. For example, how the kidney reabsorbs water from the original urine and how electrical signals are generated and transmitted in cells are of great significance for human beings to explore many diseases such as kidney, heart, muscle and nervous system.
In fact, as early as the middle of19th century, people suspected that human cells must have special channels for transporting water. However, it was not until 1988 that Agrell successfully isolated a membrane protein. About a year later, he understood that this protein must be the water passage he had been looking for for for a long time. This decisive discovery opened the door to a series of complete biochemical, physiological and genetic studies, which led to water channels in bacteria, plants and mammals. Nowadays, scholars have learned in detail how water molecules pass through the cell membrane, and also understand why only water molecules can pass through, while other smaller molecules or ions can't.
Modern biochemistry has reached the atomic level in solving the basic principles of life processes. Another type of membrane channel is ion channel. Ion channels are of great significance in nervous and muscular stress systems. When the ion channels on the surface of nerve cells are opened by the chemical signals of neighboring nerve cells, an effect called nerve cell voltage will be produced, so the electric pulse signal will be transmitted along the surface of nerve cells through the ion channels that are opened and closed in a few milliseconds. Mckinnon confirmed the spatial structure of potassium ion channel (high resolution electron microscope) in 1998, which shocked the whole academic community. This contribution makes us know now that ions can flow through channels, and the opening and closing of these channels are controlled by different cell signals.