《电分析化学》（英文版）Lecture 7 UMES

Ultramicroelectrodes Electroanalytical Chemistr Lecture #7 22-Feb-211

22-Feb-21 1 Ultramicroelectrodes Electroanalytical Chemistry Lecture #7

UMES Geometries ◆Disk ◆ Recessed disk C.S. Henry: I Fritsch Anal. Chem 199971.550-6. ◆Band Cylinder ◆ Materials Carbon fiber

UME’s  Geometries  Disk  Recessed disk C.S. Henry; I. Fritsch Anal. Chem. 1999, 71, 550-6.  Band  Cylinder  Materials  Carbon fiber

UME's- Advantages ◆ Reduced capacitance ◆ Low iR drop

UME’s - Advantages  Reduced capacitance  Low iR drop

UMES- Disadvantages ◆ Noise Electrochemical Fouling ◆ Analyte Method of electrode prep'n(epoxy) Stray capacitance ◆ Impurities ◆ Maintenance ◆Cost ◆ fragile construction

UME’s - Disadvantages  Noise  Electrochemical Fouling  Analyte  Method of electrode prep’n (epoxy)  Stray capacitance  Impurities  Maintenance  Cost  Fragile construction

UME's- Applications ◆ Determine[ analyte ◆ Study reactions at low temperatures frozen glasses o in solvents of moderate to high permittivity W/o electrolyte in solvents of high resistance ◆ in solid state ◆ in gas phase

UME’s - Applications  Determine [analyte]  Study reactions  at low temperatures = frozen glasses  in solvents of moderate to high permittivity w/o electrolyte  in solvents of high resistance  in solid state  in gas phase

UMES-Applications (contd) ◆ Biological systems ◆ Single cells ◆ organelles ◆ Fast kinetics 4 development of analytical tools for electrode/solution interface ◆SECM(Bard) ◆EQCM ◆SERS( Van Duyne)

UME’s - Applications (cont’d)  Biological systems  Single cells  organelles  Fast kinetics  Development of analytical tools for electrode/solution interface  SECM (Bard)  EQCM  SERS (Van Duyne)

Scanning electrochemical Microscopy(seCM) R Diffusion is hemispherical =nfC D where a= diam of UME Acquire I vs tip position (x, y) Plot of d vs tip position piezoelectric positioning d ◆ Bipotentiostat Sample Ref Bard et al. Science 1991.254.68-74

Scanning Electrochemical Microscopy (SECM)  Diffusion is hemispherical  i ss = 4 n F Co * Do a where a = diam. of UME  Acquire I vs. tip position (x,y)  Plot of d vs. tip position  piezoelectric positioning  Bipotentiostat Sample C W R Ref.: Bard et al. Science 1991, 254, 68-74. d

SECM(cont'd CwR◆W-100n( diam) Determines resolution ◆2 nm best at present Sample ◆ Conducting ◆ Insulator Mineral ◆ Biological Sample ◆ Semiconductor

SECM (cont’d)  W - 100 nm (diam.)  Determines resolution  2 nm best at present  Sample  Conducting  Insulator  Mineral  Biological  Semiconductor Sample C W R

Common modes of Operation Feedback ◆ Positive or negative ◆ Collection flux of species generated/consumed probed

Common Modes of Operation  Feedback  Positive or negative  Collection  flux of species generated/consumed probed

SECM- Positive W F eeabac k R t If sample conductive we get positive feedback 1>1 SS R O Conductive Samp

SECM- Positive Feedback  If sample conductive, we get positive feedback i > iss Conductive Sample C W R R O