Bioelectricity and Biophotonics Engineering WSC331 Loughborough University PDF

WSC331 Bioelectricity and Biophotonics Engineering Felipe Iza P 3G Plasma and Pulsed Power Group Loughborough University, U.K....

WSC331 Bioelectricity and Biophotonics Engineering Felipe Iza P 3G Plasma and Pulsed Power Group Loughborough University, U.K. Slide Set Bioelec 4 [email protected] http://www.lboro.ac.uk/departments/meme/staff/felipe-iza 1 Recap from previous lecture 2 Today’s lecture  Transport phenomena  Transport Mechanisms  Diffusion  Conduction  Nernst-Plank Equation (drift-diffusion equation) 3  Transport mechanisms  Advection (“convection”): transport of a substance with a moving fluid (drag force). E.g. transport of oxygen in the blood stream  Diffusion: transport from a high concentration region to a low concentration region as a result of the random motion of particles. E.g. Osmosis, i.e. diffusion of a solvent (frequently water) through a semi- permeable membrane  Electric field mediated:  Electrophoresis: Transport of electrically charged particles.  Dielectrophoresis: Transport of non-charged dielectric particles in an inhomogeneous field.  Electrorotation, Pearl chain formation, Levitation, Electro-osmosis… 4  Surface Area and Diffusion  As organisms get bigger their surface area/volume ratio gets smaller.  Bacteria are all surface with not much Length scale inside, while whales are all insides (m) without much surface. Proteins and 10-8  So as organisms become bigger it is nucleic acids more difficult for them to exchange materials with their surroundings. Organelles 10-7 Cells 10-5 – 10-6 Capillary 10-4 spacing Organs 10-1 Whole body 1 5  Main transport mechanism? Transport by convection  L2   v  vL Peclet number       Transport by diffusion  D  L  D Truskey, G. A., F. Yuan, and D. F. Katz. Transport Phenomena in Biological Systems. East Rutherford, NJ: Prentice Hall, 2003 6  Diffusion vs convection Diffusion time: td=L2/D Time for convection: tc=L/v 105 104 Convection 10-4 cm/s Diffusion plays a Diffusion 10-6 cm2/s 103 Diffusion 10-7 cm2/s critical role in short 102 distances transport 101 but it is inefficient in Time (s) 10-0 10-1 transporting to large 10-2 distances. 10-3 (Note: diffusion time 10-4 scales with L2) 10-7 10-6 10-5 10-4 10-3 Distance (m) 7  A few definitions… Solution = Solvent + Solute  Solution: homogeneous mixture composed of two or more substances.  Solute: Substance that is dissolved.  Solvent: liquid that dissolves a solid, liquid, or gaseous solute. The most common solvent in a biological sample is water.  Electrolyte: ionic solution, i.e. a solution with ions as solutes (e.g. Na+,K+,Ca2+,Cl−) electrically conductive  Anion: Negatively charged ion. (goes to the anode)  Cation: Positively charged ion. (goes to the cathode) 8  Ionic vs Electronic conduction Current in Current in solutions metals Charge Ions Electrons carriers Mass transfer Yes No Electron flow + On the electrode-electrolyte interface: Electric field Anion(-) flow ionic current  electronic current Cation(+) flow “Redox chemical reaction” 9  Electronic/ionic conductivity Material Type of conductivity Conductivity (S/m) Superconductor Electronic  Silver Electronic 63x106 Copper Electronic 58x106 Gold Electronic 45x106 Aluminium Electronic 35x106 Graphite Electronic 17x103 NaCl in water 0.9% 37C Ionic 2 Blood Ionic 0.7 Muscle Ionic 0.4 Undoped Silicon Electronic 300x10-6 Living bone Ionic 10x10-3 De-ionised water Ionic 4x10-6 Dry bone Ionic? 100x10-12 Transformer oil Ionic? 10x10-12 PTFE(Teflon) Electronic 10x10-15 10  Moles/sec vs amperes  Chemists:  Mole: Unit to measure the amount of a substance. One mole contains Avogadro's number (6.022x1023) entities Note: one mole of iron contains the same number of atoms as one mole of gold (although they have different weight!!)  Current = Ion flow  Moles/sec  Electrical Engineers:  Coulomb: amount of electric charge transported by a current of 1 ampere in 1 second. Unitary charge: q=1.6x10-19C  Current = Ion flow  C/sec = A 11  Faraday’s constant F=… Chemist  X moles/sec Y=FX Engineer  Y Coulombs/sec (A) Keep in mind that Faraday’s constant normally comes into equations from the need to convert current flows from moles per second to electrical current (A), or vice versa: Current in Amps = F x Flow in mol/second 12  Electrolyte composition  The most important ions are sodium (Na+) and potassium (K+), which play a critical role in excitable cells. Other important ions include chloride (Cl -) and calcium (Ca++).  Concentrations of these ions varies from extracellular to intracellular regions: Muscle (Frog) Nerve (Squid axon) Intracellular Extracellular Intracellular Extracellular mM mM mM mM K+ 124 2.2 397 20 Na+ 4 109 50 437 Cl- 1.5 77 40 556 A- 126.5 A-: large impermeable ion, e.g. DNA mM: 10-3 moles/liter 13  Molarity  Molarity or molar concentration C is defined as moles of solute per unit volume of solution  Molarity is measured traditionally in mol/litre although the SI units are mol/m3.  The unit mol/litre is often denoted by a capital letter M (pronounced "molar"). This way, "millimolar" (mM) and "micromolar" (μM) refer to 10-3 mol/L and 10-6 mol/L respectively. 14  Exercise  Consider 2 grams of NaCl dissolved in 15 mL of water. What is the molarity of the solution?  Most proteins present in a bacteria are replicated 60 times (or fewer). What is the molar concentration of a typical protein? Atomic mass in Da = amu = gr/mol 15  Solution  Exercise 1:  Exercise 2: 16  Diffusion jd  ???  Diffusion: transport from a high concentration region to a low concentration region as a result of the random motion of particles. 17  Diffusion  Fick’s first law The flux is proportional to  jd  DC the density gradient and tends to remove spatial inhomogeneities. where: jd is the diffusion flux (moles/m2-sec) D is the diffusion coefficient or diffusivity (m2/sec) C is the concentration (mol/m3) X is the position (m) Typical value of D for Na+, K+, Cl-: ~1.5x10-5cm2/sec 18 Diffusion: Temperature dependence Diffusion is a thermally activated process and the diffusion coefficient depends on the temperature of the solution:  ΔE  D D oexp     RT Hot Cold D = Diffusion coefficient D0 = Pre-factor E = Activation energy Rg = Universal gas constant T = Temperature 19  Osmosis C1 < C2 C1 = C2 Selectively permeable membrane Osmosis: Process in which a solvent diffuses across a semi permeable membrane (permeable to the solvent, but not the solute) from the region of low concentration to the region of large concentration. 20  Tonicity  Hypotonic Solution: One solution has a lower concentration of solute than another.  Hypertonic Solution: One solution has a higher concentration of solute than another.  Isotonic Solution: Both solutions have same concentrations of solute. 21  Question  Why do creases appear at the tip of the fingers after a long exposure to water? 22  Mobility  In the presence of an electric field, charged particles are subject to an electrical force. E=0 =0 = sign(Z) E E0 : Mobility (m2/V-sec) Z: valence: -1 for electrons 0 for neutrals >0 for cations