Principles of Electronic Nanobiosensors
Unit 3: Sensitivity
Lecture 3.6: Potentiometric Sensors:
How to Beat Screening
By Muhammad A. Alam
Professor of Electrical and Computer Engineering Purdue University
alam@purdue.edu
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Outline
•Challenges of charge screening
•Techniques to overcome screening
–De-screening of DNA at high frequencies
–Device Approach: Giant Nernst Sensor
–Tag-based approach
•Conclusions
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Alam, Principles of Nanobiosensors, 2013 |
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DNA binding and Salt screening
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De-screening at High Frequencies
At 1 MHz, molecules |
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are frozen, but the |
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dipoles are not |
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φ =φ0 1+r L |
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D |
100 mM gives ~ 1nm. |
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L = kW ε0kBT |
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D |
q2 I0 |
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φ =φ0e |
−x LD |
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G. Kulkarni and Z. Zhong, Nano letters, 2011. |
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Alam, Principles of Nanobiosensors, 2013 |
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Screening is frequency dependent
Small signal
Capacitance (F)
2x 10-13
1.5
1
0.5
0 |
0 |
1 |
10 |
2 |
10 |
3 |
10 |
5 |
10 |
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10 |
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10 |
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Frequency (Hz) |
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Distance
Potential
~ LD
Potential |
Potential |
Distance |
Distance |