Download Prof. Jeffery Lang (EECS) - MIT Sea Grant

Sensors for Measuring Carbon Dioxide,
Bicarbonate, and pH in the Ocean
Prof. Timothy M. Swager (Chemistry)
Prof. Jeffery Lang (EECS)
Dr. Suchol Savagatrup
Ms. Vera Schröder
Massachusetts Institute of Technology
MIT Sea Grant
November 29, 2016
Comprehensive Solutions Require Big Data
http://www.argo.ucsd.edu/
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Spatial and temporal variability in concentrations of chemical

Under-sampling due to limitation of sensors is problematic
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Low Power Sensors with Minimal Complexity
Honeywell Durafet®
Satlantic SeaFETTM
Argo, UCSD

High operational complexity or cost of maintenance

“Simple sensor systems that are capable of operating without
drift for long periods of time and that are sufficiently selective
and sensitive are not yet available…”
Johnson et al. Chem. Rev. 2007, 107, 623.
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Ion-Selective Field-Effect Transistors (i-FETs)

Chemiresistors afford the simplicity

i-FET Sensors offer additional dimensions of sensing

Highly specific molecular recognition (significant
departure from Ion Sensitive FETS) and simplicity in
operation
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Differential Amplifier for Stability/Sensitivity
Current Mirror

Chemically-active (Sense) and ocean reference (Ref) electrodes

Minimal electronics, current-based transduction to reduce noise
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Change in the Fermi Level due to Ion Binding

Changes in Redox potential, not just electrostatic

Anion binding (e.g., HCO3–) raises the Fermi level

Protonation lowers the Fermi level
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Receptor Design to Bind Carbonate

Transduction materials composed of two elements:

Redox active scaffold:

Recognition domain with high degree of
preorganization designed to bind the ion of interest:
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Receptor Designed to Bind Carbonate
Redox active scaffold
Cl- receptor
Recognition domain
HCO3- receptor

Challenge: differentiation between ions in sea water

Dual-binding site leads to selective binding of
bicarbonate (HCO3-)
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Receptor Designed to Bind Carbonate
O
O
Cl
NH 2
NH 2
O
R
N
S
or
NH 2
-2
Cl
S
S
Cl
CO3H-H+
NH 2

Organized geometry arranged to bind carbonate ions

Binding of carbonate (CO32-) will favor oxidation of
thianthrene unit; differentiation over nitrate (NO3-)

R-group offers opportunity for immobilization of receptor
through polymerization
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Measuring pH – functionalized Graphene
Prospective pH active units
Resonance structure of ionized unit

Two examples of phenol groups that are expected to
ionize around pH ≈ 7

Ionization of the OH-group attached to the aromatic ring
leads to donation of electron density into graphene/CNT
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Measuring pH – Conducting Polymer
Canopied polypyrrole

Highly reversible pH response in conductivity and
electroactivity. Can be used as chemiresistor or pH
responsive coating

Insoluble and stable under harsh conditions resulting in
highly robust thin films
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Challenges and Possible solutions

Harsh conditions and drift (immobilization of receptor on
electrode through polymerization)

Drifts and fouling of the sensors (Each i-FET has a
internal reference, with the current mirror in the circuit)

Selectivity towards specific ions in the complex electrolyte
system (receptor with high degree of pre-organization)
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Thank you!
Questions?
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