Ionic Transport Through Nanopores: From Living Cells to Ionic Diodes and Transistors Zuzanna S.
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Ionic Transport Through Nanopores: From Living Cells to Ionic Diodes and Transistors Zuzanna S. Siwy Department of Physics and Astronomy University of California, Irvine Main Object of Our Studies Our main object of studies is a single nanopore in a polymer film - + 12 mm Several nanometers, typically 2-6 nm ~ 1 mm We study ionic transport through single conical nanopores Outline 1. Motivation for studies of single nanopores 2. Fabrication of single nanopores by the track-etching technique. polymer foil heavy ion 3. Motivation for studying conically shaped nanopores. 4. Preparation of ionic devices controlling transport of ions in water solutions: Preparation of ionic unipolar rectifiers. Preparation of an ionic bipolar diode and transistor (BJT); similarities and differences to semiconductor devices. On the way to make a field effect transistor for ions. Ionic diodes as biosensors. 5. Nanoprecipitation in nanopores and electrochemical oscillations. 6. Conclusions. Lessons from Nature Transport Proteins are Nature’s Nanotubes Impermeable lipid bilayer membrane Membrane-Bound Transport Proteins Allow for highly selective transport of ions, sugars, amino acids, etc. across the lipid bilayer membrane Biological Pores are Smart “Holes” – Very Selective Transport of Millions of Ions per 1 s A potassium selective channel is a very important player in the nerve signaling. < 1 nm Potassium selective channel with four K+ in the selectivity filter (right panel). R. MacKinnon, P. Agre 2003 E. Gouaux, R. MacKinnon, Science 310, 1461 (2005). S. Berneche, B.Roux, Nature 414, 73 (2001). Selectivity of L-Type Calcium Channels (Heart Muscle Regulation) Negative groups COOE.W. McCleskey, J. Gen. Physiol. 113, 765 (1999) [Ca2+] << [Na+] W. Nonner, D. Gillespie, D. Henderson, B. Eisenberg, J. Phys. Chem. 105, 6427 (2001); Ca2+ and Na+ have basically the same diameter. PHYSICS approach Preparation of the Simplest Calcium Channel/Pore Theoretical predictions: highly charged lining of the pore and small pore volume lead to Ca2+ selectivity. ~1 e/nm2 COO- COO- COO- COO- ~1 COO- COO- e = electron charge COO- COO- COO- e/nm2 COO- = carboxyl group with charge -e Our synthetic analogue (a synthetic hole) is indeed Ca2+ selective! Gillespie, D., Boda, D., He Y. Apel, P., Siwy, Z.S. (2008) Synthetic Nanopores as a Test Case for Ion Channel Theories: The Anomalous Mole Fraction Effect. Biophysical Journal 95, 609-619. Diode - Like Characteristics of Biological Channels A diode perfectly rectifies currents so that it flows in one direction rectifier I [pA] V [mV] diode Y. Jiang et al. Nature 417, 515 (2002) PHYSICS approach T. Baukrowitz et al. EMBO 18, 847 (1999) Many biological channels are switches for ions What are the Physical Requirements for Making Ionic Diodes and Transistors? Perhaps a Basis for Ionic Electronics? Nanopores – Studying Interactions at the Nanoscale Nanopores have very large surface! + + + + + + + + + + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Nanopores give a unique possibility to control transport of ions and charged molecules in water-based solutions. Nanopores as Basis for Biosensors Sub-femtoliter volume! Very few molecules actually fit there! Basis for single molecule detection! I Will Talk About.. • Preparation of various components of IONIC CIRCUITS for ions and molecules in a water solution: urgent need for systems that operate in water. • For that we need: TEMPLATE - robust single nanopores with tunable geometry and surface chemistry i.e. tunable electrochemical potential. Outline 1. Motivation for studies of single nanopores. 2. Fabrication of single nanopores by the track-etching technique.polymer foil 3. Motivation for studying conically shaped nanopores. heavy ion 4. Preparation of ionic devices controlling transport of ions in water solutions: Preparation of ionic unipolar rectifiers. Preparation of an ionic bipolar diode and transistor (BJT); similarities and differences to semiconductor devices. On the way to make a field effect transistor for ions. Ionic diodes as biosensors. 5. Nanoprecipitation in nanopores and electrochemical oscillations. 6. Conclusions. Heavy Ions as a Working Tool 1. Irradiation with e.g. Xe, Au, U (~2.2 GeV i.e. ~ 15% c) Latent tracks E. Loriot Linear accelerator UNILAC, GSI Darmstadt, Germany 2. Chemical etching 1 ion 1 latent track 1 pore ! R.L. Fleischer, P.B. Price, R.M. Walker (1975) Heavy Ions as a Working Tool 1. Irradiation with e.g. Xe, Au, U (~2.2 GeV i.e. ~ 15% c) E. Loriot Linear accelerator UNILAC, GSI Darmstadt, Germany 2. Chemical etching 1 ion 1 latent track 1 pore ! R.L. Fleischer, P.B. Price, R.M. Walker (1975) Tuning the Pore Shape during Etching Vb Vt Vb – Rate of non-specific etching the so-called bulk etching Vt - Rate of etching along the latent track Recipes for cylindrical and conical nanopores: Cylindrical pores: high Vt and low Vb; for PET 0.5 M NaOH in 70 ºC Conical pores: low Vt and high Vb; for PET 9 M NaOH, RT Why Do We Want to Work with Asymmetric Pores? Tapered cone Cylindrical pore L D d d 4L R1 2 d >> 4L R2 dD Example for 0.5 V, 1 M KCl, L = 10mm d=1 nm results in current of 3.9 pA. d=1 nm, D=2 mm, results in current of ~740 pA. Conical Pores are Obtained by Putting Etch Solution on One Side of Membrane and Stop Solution of the Other Single ion irradiation 200 U NaOH acidic solution current(pA) (pA) Current I 150 100 50 0 242 244 246 248 250 252 time (min) time (min) Z. Siwy et al. Nucl. Instr. Meth. B 208, 143-148 (2003); Applied Physics A 76, 781-785; Surface Science 532-535, 1061-1066 (2003). Gold Replica of a Single Conical Pore ~ 2 – 10 nm P. Scopece et al. Nanotechnology 17, 3951 (2006) Electro-Stopping Technique to Prepare Double-Conical Pores For polyethylene terephthalate Anode Etch solution Etch solution 9 M NaOH 9 M NaOH Cathode Cross – Section of Membranes with Double-Conical Nanopores P. Apel, Dubna Hydrolysis of Ester Bonds with NaOH in PET Causes Formation of COOH Groups OHThe surface density of COOH groups was estimated to be ~ 1.0 per nm2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Outline 1. Motivation for studies of single nanopores 2. Fabrication of single nanopores by the track-etching technique. 3. Motivation for studying conically shaped nanopores. polymer foil heavy ion 4. Preparation of ionic devices controlling transport of ions in water solutions: Preparation of ionic unipolar rectifiers. Preparation of an ionic bipolar diode and transistor (BJT); similarities and differences to semiconductor devices. On the way to make a field effect transistor for ions. Ionic diodes as biosensors. 5. Nanoprecipitation in nanopores and electrochemical oscillations. 6. Conclusions. Transport Properties of Conical Nanopores I U 0.1 M KCl 0.1 M KCl Single Conical Nanopores Rectify Ion Current Current (nA) 0.6 COOH 0.3 0.1 M KCl, pH 3 -1000 -500 500 1000 Voltage (mV) -0.3 Vb - Vt 0.1 M KCl, pH 8 - COO -0.6 Vt ~ 3 nm ~ 600 nm Vb _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Z. Siwy et al. Europhys. Lett. 60, 349 (2002); Z. Siwy et al. Surface Science 532-535, 1061 (2003) Which Ions Are Transported? PET and Kapton pores are selective for positive ions (cations) I t+ ~ 0.80 __ _ _ _ _ _ _ _ U _ _ _ _ _ _ _ _ Z. Siwy, A Fulinski, Phys. Rev. Lett. 89, 198103 (2002); Am. J. Phys. 72, 567 (2004). Siwy Z., Adv. Funct. Mat.16, 735 (2006). UNIPOLAR DEVICE – mainly pass through Why do Asymmetric and Charged Pores Rectify The profile of electric potential V(z) of a cation in an asymmetric nanopore z Siwy Z., Fulinski A. Phys. Rev. Lett. 89, 198103 (2002); Siwy Z., Fulinski A. The American Journal of Physics 74 (2004) 567; Siwy Z., Adv. Funct. Mat.16, 735 (2006). Cervera, J., Schiedt, B., Ramirez, P. Europhys. Lett. 71, 35-41 (2005). PROBLEM: Degree of Rectification of Conical Nanopores I (nA) 1 -3 U (V) -2 f rec -4 3 I U I U f rec 10 Ideally, from application stand point one wants a SWITCH i.e. basically zero leakage current. How to Make an Ionic Switch? + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ + + + + + + + + + _ _ _ _ _ _ _ _ Depletion zone H. Daiguji, P. Yang, A. Majumdar, NanoLett., 4, 137 (2005). I. Vlassiouk, Z.S. Siwy, Nano Lett. 7, 553 (2007) HIGH Conductance State of Nanopore Eric Kalman + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ + + + + + + + + + _ _ _ _ _ _ _ _ BIPOLAR DEVICE – current carried by both Targeted Modification of the Tip GOAL! , The negative groups (COO-) at the narrow opening have to be changed into groups with positive charges, e.g. NH3+ Ethylenediamine + EDC Steady-State Solution of Diffusion Problem C0 x 1.0 Targeted modification of the tip c (x) 0.8 CL=0 Distribution of concentration of a reagent introduced only on the tip side of the membrane 0.6 aL c( x ) c0 1 A x 0.4 0.2 0.0 100 200 300 400 500 x [nm] Only the region of the pore close to the tip with high enough EDC and amines concentration will be modified! Modification Chemistry Ethylenediamine + EDC Succinide anhydride + EDC Ethylene diamine + EDC, 0.1 M KCl, pH 5.5 _ _ _ _ _ _ _ _ _ _ _ 0.1 M KCl, pH 5.5 _ _ _ _ _ _ _ An Ionic Diode Made From a Nanopore with a Positive Tip I ( 5V ) 217 I ( 5V ) 12 0.1 M KCl, pH 5.5 Current (nA) 10 8 6 4 2 0 -5 -4 -3 -2 -1 0 1 Voltage (V) I. Vlassiouk, Z.S. Siwy, Nano Lett. 7, 553 (2007) 2 3 4 5 Positively Charged Nanopore + + + + + + + + + + + + + + + + + + 12 Current (nA) 10 0.1 M KCl, pH 5.5 8 6 4 2 I ( 5V ) 7 I ( 5V ) 0 -2 -5 -4 -3 -2 -1 0 1 Voltage (V) 2 3 4 5 An Ionic Diode Made From a Nanopore with a Negative Tip 0.1 M KCl, pH 5.5 I ( 5V ) 61 I ( 5V ) 0 Current (nA) -2 -4 -6 -8 -10 -12 -5 -4 -3 -2 -1 0 1 2 3 Voltage (V) I. Vlassiouk, Z.S. Siwy, Nano Lett. 7, 553 (2007) 4 5 Tuning Rectification We can measure ion rectification degree in situ during the modification! I. Vlassiouk, Z.S. Siwy, Nano Lett. 7, 553 (2007) Diode Pattern Realized in a Bacterial Biopore WITHOUT charges WITH charges Miedema, H.; Vrouenraets, M.; Wierenga, J.; Meijberg, W.; Robillard, G.; Eisenberg, B. A Biological Porin Engineered into a Molecular, Nanofluidic Diode. Nano Letters 7 (2007) 2886-2891. Unipolar Diodes Were Also Prepared 10 mM KCl Voltage (V) R. Karnik, C. Duan, K. Castelino, H. Daiguji, A. Majumdar Nano Letters 7, 547-551 (2007). I. Vlassiouk, S. Smirnov, Z. Siwy, ACS Nano 2, 1589 (2008) Poisson-Nernst-Planck Modeling of Ionic Diodes _ _ _+++ _ _ _ +++ o e(C C ) zi eCi J D ( C ) i i i k BT Ci – concentration of positive and negative ions - electric potential - dielectric constant Ji – flux of an ion i with charge zi Density of charge carriers is described by the Boltzmann statistics A Semiconductor Diode Vs an Ionic Diode p-doped electrons (-) n-doped Concentration, M holes (+) 1 mm long, 0.5 e/nm2, 0.1 M KCl 0.5 0.4 0.3 K+ Cl- 0.2 0.1 0.0 480 500 520 x, nm 0.04 Voltage, V Carrier concentration _ _ _+++ _ _ _ +++ Voltage 0.02 0.00 Voltage -0.02 480 500 x, nm Numerical solutions of PNP 520 1-D Analytical Approximations for Diodes Depletion zone 1 ln , p _ _ _+++ _ _ _ +++ Na 0 V N d N d N a 2e ldep Va 0 a – pore radius - surface charge density doping I open I hgen I egen keVT e B 1 2 ea eDC BP V Vo 2 I open L 2k B T Current Current Voltage I closed I gen h I gen e N.W. Ashcroft, N.D. Mermin, Solid State Physics, Thomas Learning, 1976 Voltage BP I closed 3 2 a Cbulk 2e 2D L I. Vlassiouk, S. Smirnov, Z. Siwy, ACS Nano 2, 1589 (2008) Depletion Zone in LONG Pores + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ + + + + + + + + + _ _ _ _ _ _ _ _ Depletion zone I. Vlassiouk, S. Smirnov, ACS Nano 2, 1589 (2008) Depletion Zone in SHORT Pores + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ + + + + + + + + + _ _ _ _ _ _ _ _ The depletion zone fills the whole pore, which can be treated as a neutral pore I. Vlassiouk, S. Smirnov, ACS Nano 2, 1589 (2008) Opening of Short Diodes I (nA) -40 BP diode charged reservoirs BP diode neutral reservoirs L=2nm L=4nm L=8nm L=10nm L=12nm L=16nm L=2nm L=4nm L= 8nm L=10nm L=12nm L=16nm -20 0 A (V) I (nA) -40 B UP diode neutral reservoirs UP diode charged reservoirs L=2nm L=4nm L=6nm L=10nm L=25nm L=2nm L=4nm L=6nm L=10nm L=25nm -20 0 D C 20 4 2 0 -2 -4 4 Bias (V) Cbulk = 0.1 M KCl, charge density 0.5 e/nm2, radius 4 nm 2 0 Bias (V) -2 -4 Preparation of Ionic Bipolar Junction: Transistor I V diode P-N junctions + + + + + + + + + + + + Cl- + + + + + + K+ Cl- + + + + + + P. Apel, Dubna Step-by-Step Modifications _ _ _ _ _ __ _ _ 0.1 M KCl 0.1 M KCl _ _ _ _ _ _ _ _ _ Current (pA) (a) 400 200 0 -200 -400 -4 -2 0 2 4 Voltage (V) (b) + + _ _ _ _ _ + _ 0.1 M KCl 0.1 M KCl _ _ _ _ _ _ + + + Current (pA) 0 -400 -800 -1200 -4 -2 0 2 4 Voltage (V) + + _ _ +++ + _ 0.1 M KCl 0.1 M KCl _ _ _ _ + + + + + Current (pA) (c) 20 10 0 -10 -20 -4 E. Kalman, I. Vlassiouk, Z. Siwy, Advanced Materials 20, 293 (2008). -2 0 2 Voltage (V) 4 Performance of Ionic BJT Current (pA) 200 100 0 0.5 M 0.25 M 0.1 M -100 -200 -4 -2 0 2 + + _ _ +++ + _ 0.5 M KCl 0.5 M KCl _ _ _ _ + + + + + 4 Voltage (V) Salt concentration determines the potential in the pore and thus the leakage current level in BJT Performance of Ionic BJT – pH response + + + + + + + + + + + + p n + + + + + + p + + + + + + 60 + ++ + + + +++ +++ + + + + + + + + + + + + “+ 0 +” junction 200 “+ - +” junction 20 0 -20 pH 8.0 pH 7.0 -40 -60 -4 -2 0 2 Voltage (V) E. Kalman, I. Vlassiouk, Z. Siwy, Advanced Materials 20, 293 (2008). 4 Current (pA) Current (pA) 40 100 0 pH 5.4 pH 6.0 pH 7.0 pH 8.0 pH 9.0 -100 -200 -4 -2 “0 - 0” “0 - 0” junction 0 Voltage (V) 2 4 Ionic Gated Channel with Electrically Addressable Gate – On the Way to Make FET Tektronix AFG320 Function Generator Ti Adhesion Layers _ Voltage + Keithley 6487 Picoammeter Voltage _ + Current Out SiO2 Insulating Layer Au Gate Electrode Ground Positive Bias Current Input 12 mm PET Gate Electrode Membrane Faraday Cage Not to scale 0.1 M KCl 0.1 M KCl In Gated Conical Nanopore Current (nA) 16 Air 0V - 0.2V -0.4V -0.6V -0.8V -1.0V -1.0 0V 12 8 4 -1.0 V -0.5 0.5 -4 1.0 Voltage Um (V) Applying negative gate voltage to the gate causes suppression of ion currents Gated Conical Nanopore Concentration depletion induced by a gate electrode - + - - - - + Active exclusion zone - + - - - + Bias voltage E. Kalman, O. Sudre, I. Vlassiouk, Z. Siwy, Analytical and Bioanalytical Chemistry 394, 413 (2009) - + - + - +- - - + + - - - - + - - - - + + + - Silica layer Gold - + - + - + - - - - + + + + + + layer + -- + - + + - + 10nm + + + - + + + + - + + 50nm 50nm + + + - Outline 1. Motivation for studies of single nanopores 2. Fabrication of single nanopores by the track-etching technique. 3. Motivation for studying conically shaped nanopores. 4. Preparation of ionic devices controlling transport of ions in water solutions: Preparation of ionic unipolar rectifiers. Preparation of an ionic bipolar diode and transistor (BJT); similarities and differences to semiconductor devices. On the way to make a field effect transistor for ions. Ionic Diodes as Biosensors 5. Nanoprecipitation in nanopores and electrochemical oscillations. 6. Conclusions. Summary: Tuning Current-Voltage Curves Of Nanopores by the Surface Charge Surface charge patterns AND Corresponding current-voltage curves I U I I U Changes of the surface pattern are induced upon binding of an analyte I Vlassiouk, T, Kozel, Z.S. Siwy, JACS 131, 8211-8220. U Prototype of the Sensor for Avidin and Streptavidin _ _ _ _ _ _ _ _ + _ _ _ Current + + Avidin (+) _ _ biotin _ _ _ _ _ KCl as the background electrolyte Current Voltage Voltage + Prototype of the Sensor for Avidin I I U U 10 mM KCl 10 mM KCl avidin 10 mM KCl Current (nA) 8 6 With avidin 0.5 mM, 2 h 4 Nanopore with the tip modified with biotin; 10 mM KCl, pH 7.0 2 -6 -4 -2 -2 -4 With biotin -6 2 4 6 Voltage (V) Tip modified with biotin Avidin on top 10 mM KCl avidin Prototype of the Sensor for Streptavidin _ _ biotin _ _ + _ _ _ _ Streptavidin, pI ~ 6 _ + _ pH < 6 pH > 6 Current (nA) pH 4.2 0.4 -2 -1 1 -0.4 pH 5.8 pH 8.0 -0.8 -1.2 2 Voltage (V) 10 mM KCl Rectification degree I(+2V)/I(-2) 0.8 4 3 2 pI 1 4 5 6 pH 7 8 GOAL Label-free sensor for antigens that are bioterrorism agents Prototype: Monitoring infection with Bacillus anthracis www.wikipedia.org Bacillus anthracis Capsule of poly-g-glutamic acid (gDPGA) thus it is heavily negatively charged Infection with Bacillus anthracis results in gDFGA in the blood at the levels that are higher than 20 ng/ml (~10 pM gDFGA). Sensor for a Real “Stuff” – pI of the mAb for gDPGA _ _ _ _ _ _ _ + _ + + _ pH < pI Monoclonal antibody for polyglutamic acid Prof. T. Kozel, University of Nevada (F2G26) _ _ _ _ 0 0 _ pH 4.8 8 4 pH 6.0 -2 _ _ pH > pI Current (nA) 16 -4 _ 0 pH ~ pI 12 _ 2 4 Voltage (V) pH 8.0 -4 I Vlassiouk, T, Kozel, Z.S. Siwy, JACS 131, 8211-8220. _ _ _ Sensing Signal Current (nA) _ _ 16 pH 4.8 Current (nA) 12 _ 8 _ _ -4 4 -2 pH 8.0 2 -4 Monoclonal antibody for polyglutamic acid -2 2 -10 -20 pH 6.0 pH 6.0 4 pH 8.0 100 10 Before adding gDPGA 1 0.1 After adding gDPGA 0.01 4 5 6 pH 7 4 Voltage (V) _ _ _ -30 Voltage (V) Rectification degree I(+5V)/I(-5) _ -4 + polyglutamic acid pH 4.8 8 _ -40 _ _ Outline 1. Motivation for studies of single nanopores 2. Fabrication of single nanopores by the track-etching technique. 3. Motivation for studying conically shaped nanopores. 4. Preparation of ionic devices controlling transport of ions in water solutions: Preparation of ionic unipolar rectifiers. Preparation of an ionic bipolar diode and transistor (BJT); similarities and differences to semiconductor devices. On the way to make a field effect transistor for ions. Ionic Diodes as Biosensors. 5. Nanoprecipitation in nanopores and electrochemical oscillations. 6. Conclusions. Conductivity Cell Used for Recording Current-Voltage Curves I U 0.1 M KCl + Ca2+ 0.1 M KCl + Ca2+ [Ca2+] << [K+] or [Mg2+] << [K+] or [Co2+] << [K+] Precipitation in a Nanopore _ [Mg2+] [OH-]2 >> Ksp Mg(OH)2 A ‘plug’ can be created inside a nanopore!! [Mg2+] [OH-]2 <Ksp=5.6 10-12 0.1 M KCl – background electrolyte • Ionic concentrations inside a nanopore depend on the surface charge and applied voltage •Concentration of cations in a negatively charged pore can be much higher than in the bulk. Evidence for the Precipitation, Mg(OH)2 B -500 KCl 50 mM -1000 -1500 -2000 5.0 mM Mg2+ -1000 -500 0 500 A -1000 -2000 20 s 0.5 mM Mg2+ A 0 Mg2+ 1000 B 0 Current (pA) Current (pA) 0 Current (pA) 500 -100 -200 40 s Voltage (mV) Mg(OH)2 Ksp = 5.61·10-12 M. Powell et al. Nature Nanotechn. 3, 51 (2008) Modeling by the Poisson-Nernst-Planck Equations Products of ionic activities at -1 V are above the solubility product for Mg(OH)2 Products of ionic activities at +1 V are below the solubility product Modeling by the Poisson-Nernst-Planck Equations Products of ionic activities are very strongly voltage-dependent! Evidence for the Precipitation (I) CaHPO4 CaHPO4 Ksp 2 ·10-7 Current (nA) 2 1 0 0.1 M KCl -1 0.1 M KCl + 0.1 mM CaCl2 -2 0.1 M KCl + 0.4 mM CaCl2 -3 0.1 M KCl + 0.7 mM CaCl2 -4 -2 -1 0 1 2 pH 8, 2 mM PBS Voltage (V) Z. Siwy et al. Nano Lett. 6 (2006) 473-477. Pore opening 5 nm Evidence for the Precipitation 600 -600 0.1 mM Ca2+ 0.5 mM Ca2+ 1.0 mM Ca2+ A -1000 -500 0 500 Current (pA) -400 KCl C B 0 -200 F E 0.1 mM PBS 0.2 mM PBS -400 -600 1000 1.0 mM PBS D -1000 Voltage (mV) Current (pA) 0.2 mM Ca2+ 200 Current (pA) 0 5.0 mM PBS -500 0 500 1000 Voltage (mV) 0 0 -400 -200 -400 10 s A D -800 -600 0 -200 B -400 Current (pA) Current (pA) 20 s 0 -400 2s C -400 400 ms Current (pA) 0 -200 E -200 400 ms Current (pA) Current (pA) 200 -200 400 2 mM PBS 400 0 -200 F -400 1s Current (pA) Evidence for the Precipitation (II), CoHPO4 -600 A KCl 0.01 mM Co2+ 0.10 mM Co2+ -800 -1200 20 s 1 0 -200 -400 20 -1.0 -0.5 0.0 Voltage (V) 0.5 40 Time (s) 1.0 1 0 IN 0 (pA) -1600 -400 20 s IN 0 (pA) -400 -200 B Current (pA) 0 Current (pA) Current (pA) 400 0 -200 -400 4s 32 36 Time (s) CoHPO4 Ksp 1 ·10-7 M. Powell et al. Nature Nanotechn. 3, 51 (2008) Singing of Divalent Cations 4 pA 2 0 1 2 3 0.1 M KCl + 0.1 mM Co2+ 4 0 IN 0 (pA) IN 0 (pA) pA 0.1 M KCl + 0.1 mM Ca2+ -200 -400 20 s -400 1s 0 48 50 Time (s) Ca2+ 52 20 Time (s) Co2+ 40 Application of the System with Calcium/Cobalt to Build Stochastic Sensors? Detecting Neomycin Detecting Spermine Conclusions We have a lot of fun doing research with nanopores! 1. Unipolar and Bipolar ionic diodes were prepared on the basis of conical nanopores with tailored surface chemistry. 2. The principle of operation of the bipolar diode is analogous to that of a bipolar semiconductor diode. SIWY GROUP Dr. Dragos Constantin Alumni Eric Kalman Graduate students Dr. Ivan Vlassiouk Matt Powell Matt Davenport Laura Inees – IM-SURE and UROP Fellow Mike Chiang, MCSB student Catherine Smith Gael Nguyen Acknowledgments UC Irvine • Prof. Clare Yu • Prof. Craig Martens • Prof. Reg Penner • Prof. Thorsten Ritz • Prof. Ken Shea • TEMPO group (Prof. Steve White, Prof. Doug Tobias • Prof. Thomas Kozel, University of Nevada • Prof. Vicente Aguillella • Prof. Robert S. Eisenberg, Rush Medical College, Chicago • Gesellschaft fuer Schwerionenforschung (GSI), Darmstadt, Germany • Dr. Christina Trautmann, GSI, Germany • Dr. Olivier Sudre, Teledyne & Imaging, Thousand Oaks • Prof. S. Smirnov, New Mexico State University A.P. Sloan Foundation RCE Pacific Southwest ACS Petroleum Research Fund Institute for Complex Adaptive Matter Institute for Surface and Interface Science