Electrochemistry in Nanoelectronics & NanosensorsSlide 2Slide 3Slide 4Quantum Confinement & Standing WavesConductance Quantization Metal NanowiresElectrochemical FabricationSlide 8From Conductance Quantization to Quantum TunnelingSlide 10Slide 11Slide 12Electrochemical Molecular FETElectrochemical Gate“p-type”: FerrocenesFerrocenes: Gate EffectMechanism“n-type”: PTCDISlide 19Slide 20Slide 21Optical Detection - Nanoparticles Metal Ion Colorimetric SensorOptical Detection- Nanoparticles Metal Ion Colorimetric SensorSlide 24Some Mechanical SensorsTuning Fork SensorTuning Fork ArraysFrom Micro- to Nano-Slide 29Nanotubes/wires/belts SensorsThe Basic PrinciplePd Nanowire Hydrogen SensorSlide 33Slide 34Electrochemical DetectionCombine Electrical & EC DetectionHybrid Electrical-Electrochemical DetectionSlide 38Single Molecule Sensors?PeptidespH SensorSlide 42How about DNA?DNA DuplexesSlide 45Detection of Base Pair MismatchesSlide 47Slide 48Slide 49Slide 50Slide 51Nano-Sensors?Slide 53NANO-Nano Asian Dining 189 Main Street, Annapolis, MDSlide 56Looking into the FutureWho is Allan Kay?Slide 59Questions?Electrochemistry in Nanoelectronics & NanosensorsN.J. TaoN.J. TaoArizona State UniversityArizona State UniversityConductance QuantizationL >> electron mean free pathD>> F, electron wavelengthL  2/2DLR2~1DRG G changes continuously as D.DConductanceDG (G0)Classical conductance:L < electron mean free path ballistic transport (no collisions).D~ F, electron wavelength wave nature of electron important.D=FD=F/2MotionFreeQuantizedN=1MotionFreeQuantizedN=2010NGTGGNnnwhere, N=0, 1, 2, 3, …and G0 = 2e2/h=77SG (G0)D12345F ~ 1-3 ÅConductance QuantizationR0=13 kQuantum Confinement & Standing WavesConductance Quantization Metal NanowiresF ~ 1-3 Å – must be atomically thin! l e ~ nm. Room temperature.How to fabricate such wires?How to fabricate such wires?substrateRECEBipotentiostatElectrolyteMetal wireSubstrateinsulationEtching Depositiontip+++++---------++++++++++Electrochemical FabricationLi & TaoAppl. Phys. Lett.0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0T i m e ( m s )Conductance (2e2/h)Etching (dissolution)246810Etching0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0T i m e ( m s )Conductance (2e2/h)Deposition246810DepositionFrom Conductance Quantization to Quantum TunnelingorLarge gapDepositionDepositionEtchingEtchingLi & Tao, Nanotechnology, 10, 221(1999).Morpurgo et al., Appl. Phys. Lett., 13, 2082(1999).Large gapEtchingEtchingDepositionDeposition 9.58.57.56.55.54.5T i m e ( s e c . / d i v i s i o n )0123- 1- 2Gap Width (A)ln (I/nA)TunnelingcurrentLn(I) ~ widthTunneling!From Conductance Quantization to From Conductance Quantization to Quantum TunnelingQuantum Tunneling-10123 -2-1012 Gap Width (A)7.58.59.58.56.55.57.56.55.54.5ln (I/nA)10msabI ~ exp(-bL) ln(I) ~ - LI ~ exp(-bL) ln(I) ~ - L• StepwiseStepwise ln(I) ln(I) leads to leads to discrete change of discrete change of ss!!Stepwise Tunneling Current – Log scales• Discrete Nature of AtomDiscrete Nature of AtomCharge Transport in Single MoleculesElectrochemical Molecular FETElectrochemical Molecular FETGateSourceDrainKDrainSourceGateFeNSHONOHSRedox moleculeCEREWE1WE2GateSource DrainHOMOLUMOEFEFHOMOLUMOEFEFVgG=G0=2e2/h?Electrochemical GateElectrochemical Gate“p-type”: FerrocenesFeNSHONOHSCysteamine-Fc-cysteamine (Fc-1)Xu et al., JACS, 2005Ferrocenes: Gate Effect• Reversible gate effect with hysteresis• Current increases with gate voltage with large “noise”• On-off ratio is < 10.HOMOLUMOEFEFHOMOLUMOEFEFoxidationreductionLess conductiveMore conductiveOxidized stateReduced stateMechanism• Conductance increases• Reversible with large hysteresis• Large stochastic switchingoxidizedreduced“n-type”: PTCDI Synthesized by Prof. Ling Zhang - 1 . 1- 0 . 9- 0 . 7 - 0 . 5 - 0 . 3 - 0 . 10 . 1- 1 0- 5051 0P o t e n t i a l ( V v s . A g / A g C l )I (A)HOMOLUMO2.5 eVEFEFGate-Vg SourceDrainSHNNSHOOOOHNNHVs dreduction(Perylene tetracarboxylic diimide)PTCDI: Gate EffectCurrent (nA)Isd(on)Isd(off)~ 1000• • “n-type”ElectrochemistryNanoelectronicsNanosensorsSignal Transduction - Convert a Chemical Binding Event into a Readable Signal- Convert a Chemical Binding Event into a Readable Signal• Optical • Electrical•Mechanical• Electrochemical• ……..Optical Detection - Nanoparticles Metal Ion Colorimetric SensorBlueRedYi Lu, JACS, 2003The color of the sensor with different metal ions and Pb(II) concentrations.You just look at it !Optical Detection- Nanoparticles Metal Ion Colorimetric SensorSignal Transduction - Convert a Chemical Binding Event into a Readable Signal- Convert a Chemical Binding Event into a Readable Signal• Optical • Electrical•Mechanical• Electrochemical• ……..Some Mechanical Sensors• Quartz Microbalance: Detect mass changes• Microcantilevers: Detect mass changes Surface stress changesmkf21Tuning Fork SensorTao et al., NanoLett., mkf21• Conventional Quartz Microbalance: detects changes in m• Our approach: detects changes in k (or Force).Why? Better sensitivity and specificitym or k?01/13/19Tuning Fork ArraysSame circuitSeparate them in frequency spaceFrom Micro- to Nano-Micro-Nano-Signal Transduction - Convert a Chemical Binding Event into a Readable Signal- Convert a Chemical Binding Event into a Readable Signal• Optical • Electrical•Mechanical• Electrochemical• …….. Easy to amplify, processing, display and transmissionNanotubes/wires/belts SensorsNanotubes/wires/belts SensorsCarbon NanotubesNanowiresNanobeltsThe Basic PrincipleThe Basic PrincipleNanotube/naowires/nanobeltreceptorsanalytesKong, J.; et al. Science 2000, 287, 622; Collins, P. G. et al. Science 2000, 287, 1801; Cui, Y. et al., Science, 291, 630(2001)Pd Nanowire Hydrogen SensorPd Nanowire Hydrogen SensorWalter, E. C.; Favier, F.; Penner, R. M. Anal. Chem. 2002, 74, 1546. Favier, F.; Walter, E. C.; Zach, M. P.; Benter, T.; Penner, R. M. Science 2001, 293, 2227Pd Nanowire Hydrogen SensorPd Nanowire Hydrogen SensorResponse to four gases Response to hydrogen only! The conductance increases from zero in the presence of hydrogen The detection limit of the sensor is ~ 0.5% H2. Response time ~ ms. Different wires for different gas moleculesSignal Transduction - Convert a Chemical Binding Event into a Readable Signal- Convert a Chemical Binding Event into a