Interdigitated Electrodes Based Affinity sensing by Cyclic Voltammetry by broverya75

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									                Presented at the COMSOL Users Conference 2006 Boston




Interdigitated Electrodes Based
Affinity Sensing by Cyclic
Voltammetry
 Xiaoling Yang1 and Guigen Zhang1,2,3

 1 Micro/Nano  Bioengineering Laboratory
 2 Nanoscale Science and Engineering Center
 3 Faculty of Engineering

 The University of Georgia
 Athens, GA 30602, USA
Introduction
 Affinity sensing
   Probe target binding (Complimentary binding)

   Probe: Antibody                    Oligonucleotide

   Target: Antigen                    DNA

   Subsequent surface blockage
   Reduced effective electron transfer rate (ETR) of redox probe

   e- e-   e- e-   e- e-   e- e-   e- e-                          Antigen
                                                                  Antibody
                                            e-   e-     e-   e-     e-
             electrode


                                                 electrode
Introduction
 Issues with affinity sensing measurement

  Electrochemcial Impedance Spectroscopy (EIS):
  high sensitivity, long experiment time
    Electrodes used currently:
    Single electrode, Nano particles modified electrode,
    Interdigitated electrodes (IDEs)

  Cyclic Voltalmmetry (CV): low sensitivity, short
  experiment time
    Electrode used currently:
    Single electrode
Question and Objectives
Research question
 Can we take advantages of modified electrodes to
 improve the CV performance?
 -- Short experiment time, high sensitivity, low
 detection limit
Research objectives
 Investigate the CV performance of IDEs at various
 ETR, and compare it with single electrode
 Explore a way to further improve the CV based
 affinity sensing by changing the IDEs configuration
Methods

 Develop 2D and 3D model for IDEs to
 simulate the redox activity at various ETRs by
 considering the followings
  Butler-Volmer kinetics
  Voltammetry of a redox couple with IDEs
  Mass transport by diffusion
  Varying dimensions for IDEs
Geometric Consideration (2D)
• Coplana inlaid IDEs and single flat electrode




                                      Working         Counter



                Repeating                Repeating              IDEs
 Single flat
                 unit cell                unit cell
 electrode Symm            Symm   Symm                Symm      w=10 μm
                                                                w=1 μm
                                             w
                w=20 μm              w/2          w/2           w=100nm
                   W                     W        C
Geometric Consideration (3D)
•    Nanorod modified, elevated, and coplanar IDEs
                            A                                B




    Nanorod (264.9nm) modified IDEs       Elevated (100nm) IDEs

                                                C

                                                          w =100nm



                         Coplanar inlaid IDEs
Electrochemical Processes

  +E                                                           EC=0 (V)                               0.8




                               3−
                                       Diffusion                   3−
                                                                                                      0.6

                     [Fe(CN)6 ]                           [Fe(CN)6 ]
  Generator
  Working




              e-
                                                                                                      0.4




                                                                                 Collector
                                                                                 Counter
                      +E




                                                                                             Et (V)
                                                                                                      0.2

                                      kf
                   [Fe(CN)6-E3− + e − ← kb [Fe(CN)6 ]4−
                                       ⎯→
                                                                                                      0.0
                            ]
                               4−
                                       Diffusion                       4−
                                                                            e-                        -0.2



                     [Fe(CN)6 ]                           [Fe(CN)6 ]                                  -0.4
                                                                                                             0   20     40       60   80    100

              e-                                                                                                      Time (s)


  -E



Butler-Volmer kinetics:

  − j g = −k0 ⋅ exp[−αF ( Et − Estd ) / RT ] ⋅ cO + k0 ⋅ exp[(1 − α ) F ( Et − Estd ) / RT ] ⋅ cR
                                                                                                                                           K0 : ETR
  − jc = −k0 ⋅ exp[−αF (0 − Estd ) / RT ] ⋅ cO + k0 ⋅ exp[(1 − α ) F (0 − Estd ) / RT ] ⋅ cR
Mass Transport

 Nernst-Plank equation

              ∂ci
                  = D i ∇ 2 c i + z i u i Fc i ∇ φ − ν ⋅ ∇ c i
              ∂t

 Unstirred electrochemical solution with a supporting electrolyte
   Neglect convection and electromigration

 Diffusion-controlled mass transport

                         ∂ci
                             = Di ∇ 2 ci
                         ∂t
Parameters
    Electrokinetic flow:      C R : [Fe(CN)6 ]4−     CO : [Fe(CN)6 ]3−
    Boundary conditions:
        Flux at electrodes;
        Symmetric elsewhere


   DO            7.8×10-10 (m2/s)        Estd          0.265 (V)
   DR            7.8×10-10 (m2/s)         α              0.5
   CO              5 (mol/m3)             F        9.65 ×104 (C/mol)
   CR              5 (mol/m3)             R         8.31 (J/K/mol)
 K0(ETR) 1.5 ×10-3 ~1.5 ×10-9 (m/s)       T            298 (K)
Results and Discussion
CV at Coplanar IDEs with various electrode
width (2D)
                                                          B
                      A




         10 μm IDEs                          1 μm IDEs

                      C                                   D




         100nm IDEs                    Single flat electrode
              CV behaviour at various ETR
CV peak current as a funtion of ETR (2D)




Peak-current of IDEs and single flat electrode varies as a function of ETR.
CV peak current density as a function of ETR (2D)



                                             25
                                                        10 micron
                                             20         1 micron


                    Current Density (A/m )
                                                        100 nm
                    2                                   Flat electrode
                                             15


                                             10


                                             5


                                             0



                                              1e-9      1e-8             1e-7       1e-6
                                                     Electron Transfer Rate (m/s)




 The peak-current density of IDEs varies as a function of ETR.
 Inset: Zoom-in view of the peak-current density of IDEs at ETR <=1.5×10-7.
CV at Coplanar IDEs with various electrode
width (2D)
 The CV peak-current at IDEs and flat single
 electrode decreased with decreasing ETR.

 The IDEs were more sensitive to the change of ETR
 than the flat single electrode.

 With IDEs, sensitive detection range is different
 when electrode width is different.

 A higher sensitivity and lower detection limit was
 found at IDE with smaller electrode width.
Nanorod modified, elevated and coplanar inlaid
IDEs (3D)




    Nano rod modified IDEs                Elevated IDEs




                          Coplanar IDEs
              CV behaviour at various ETR ( w= 100nm)
 CV peak current as a function of ETR (3D)
                        0.35
                                  Nano rod modified IDEs
                        0.30      Elevated IDEs
                                  Flat IDEs
                        0.25
         Current (nA)




                        0.20

                        0.15

                        0.10

                        0.05

                        0.00


                           1e-8   1e-7      1e-6     1e-5    1e-4       1e-3   1e-2
                                         Electron Transfer Rate (m/s)



CV Peak-current of IDEs in 3D unit cell varies as a function of log ETR
CV of nanorod modified, elevated and coplanar
IDEs (3D)

  The nanorod modified IDE and elevated IDE are more sensitive
  to ETR change than the flat inlaid IDEs.

  The nanorod modified IDE have higher sensitivity than the
  elevated IDE when the amount of electrode material are the
  same.
Conclusions

The IDEs were more sensitive to the change of ETR than
the flat single electrode

With IDEs, sensitive detection range is different when
electrode width is different

A higher sensitivity and lower detection limit was found at
smaller electrode width.

The sensing performance (sensitivity and detection limit)
of an affinity-based biosensor was improved by using
nanorod modified IDEs along with the CV method when
the width of the electrode fingers is small.
                 Thank you !

Acknowledgement
  The National Science Foundation
  The Institute of Faculty of Engineering at The University of
  Georgia
  The College of Agricultural & Environmental Science at The
  University of Georgia

								
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