Principles of Electronic Nanobiosensors
Unit 3: Sensitivity
Lecture 3.2: Potentiometric Sensors:
Charge Screening for a Planar Sensor
By Muhammad A. Alam
Professor of Electrical and Computer Engineering Purdue University
alam@purdue.edu
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Outline
•Background: From a MOSFET to a biosensor
•Biocharges, salt and screening
•Debye theory response of a planar sensor
•Response of planar sensors at high salt concentration: Gouy-Chapman theory
•Conclusions
•Appendix: Derivation of Gouy-Chapman theory
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Alam, Principles of Nanobiosensors, 2013 |
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Sensitivity of a MOSFET-based
potentiometric sensor
analyte
ID,before |
S ≡ |
ID,after −ID,before |
≡ |
∆I |
D ρ0 |
ID,before |
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ID |
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analyte
ID,after
Alam, Principles of Nanobiosensors, 2013 |
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DNA binding and Salt screening
Salt
DNA
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Salt and screeningInt rpreting Leiber’s Results
Salt is ionized in water.
Cl Na
Na Na Cl
Cl
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ID |
U = − |
q2 |
× |
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Bjerrum length |
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4πε0r |
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Q |
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n |
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I0 Nave |
+qψ kBTL |
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n+ ~ I0 Nave−qψ 
kBTL
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