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Electrochemical piezoelectric-excited millimeter-sized cantilever (ePEMC) for
simultaneous dual transduction biosensing
[SUPPLEMENTARY MATERIALS]
Blake N. Johnson and Raj Mutharasan∗
Department of Chemical and Biological Engineering,
Drexel University, Philadelphia, PA 19104
Submitted to:
Editor, Analyst
*Corresponding author, Tel.: (215) 895-2236. Fax: (215) 895-5837
Email: [email protected]
Electronic Supplementary Material (ESI) for AnalystThis journal is © The Royal Society of Chemistry 2013
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These supplementary materials show photographs comparing the ePEMC sensor and flow
cell with an EQCM. We also provide comparison of equivalent circuit models useful for
examining ePEMC EIS response. Figures S.1 and S.2 compare the sensors, and Figure S.3
compares the flow cells. Figure S.4 shows the EIS spectrum of a representative ePEMC prior to
biosensing with the fits of three equivalent circuit models that facilitate calculation of the charge
transfer resistance parameter (RCT) used to transduce molecular binding in the electrochemical
sensing modality of ePEMC.
Electronic Supplementary Material (ESI) for AnalystThis journal is © The Royal Society of Chemistry 2013
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Figure S.1– Comparison of ePEMC with a commercially available electrochemical-quartz crystal
microbalance (EQCM) (Stanford Research Systems, SRS, Sunnyvale, CA).
ePEMCEQCM
Piezo-driving electrodes
Surface electrodes
Sensing electrode
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Figure S-2 – Close-up view of sensor working electrodes. EQCM sensor has working electrode
area ~ cm2; ePEMC sensor has working electrode ~ mm2.
Sensing electrode
Electronic Supplementary Material (ESI) for AnalystThis journal is © The Royal Society of Chemistry 2013
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Figure S.3 – (A) Flow cells used for EQCM sensing and ePEMC sensing. Reactor hold-up
volumes were 150 μL and ~300 μL, respectively. Finite element modeling software (COMSOL
Multiphysics, Vers. 3.5a) was used to calculate flow cell velocity profiles in both the
commercially available EQCM (B) and the ePEMC (C) device. Solution was examined in 2-
dimensions (2D) using Lagrange-P2P1 type elements.
EQCMFlow cell
Inlet Outlet
Inlet
OutletePEMCFlow cell
ePEMC
EQCM
B C
A
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Figure S.4 – (A) Schematics of equivalent circuit models for ePEMC. (B) Fit of above
equivalent circuit models via the Simplex Method (Gamry Analyst Software) to ePEMC EIS
data. All models accurately capture the biosensing parameter RCT (34, 29, and 35 Ω, respective
to the order shown above). These values compared well with the semicircle distance of 34 Ω.
Best fit was obtained using the modified Randles circuit (right panel of part (A)) which contains
a constant phase element (CPE) in place of the double layer capacitance (CDL). Note both
circuits contain an infinite Warburg element (ZW) in series with the charge transfer resistance
(RCT).
0
10
20
30
40
0 50 100 150
-Im(Z
)
Re(Z)
Mod. Randles(CDL replaced with CPE)
Mod. Randles(ZW added)
Randles
RS
ZW
CDL
RCT
RS
ZW
CPE
RCT
RS
CDL
RCT
Randles Mod. Randles(ZW added)
Mod. Randles (CDLreplaced with CPE)
A
B
Electronic Supplementary Material (ESI) for AnalystThis journal is © The Royal Society of Chemistry 2013