Fine-Tuning an ISFET-Based Dual pH-Total Alkalinity Sensor for Operation in Seawater Using an Adjustable, Suspended...

Area of Science:

• Analytical Chemistry
• Environmental Science
• Materials Science

Background:

• Traditional ion-sensitive field-effect transistor (ISFET) sensors for seawater analysis require complex nanofabrication.
• Existing designs often involve custom fabrication or back-end processing, limiting accessibility and adaptability.
• A need exists for simplified, robust ISFET sensor designs for environmental monitoring.

Purpose of the Study:

• To present a re-envisioned, simplified design of an ISFET-based solid-state sensor for seawater pH and total alkalinity measurement.
• To demonstrate a novel sensor configuration using off-the-shelf components and a suspended titrant-generating electrode.
• To analyze the impact of electrode spacing and current on sensor performance and resolution.

Main Methods:

• Developed a novel ISFET sensor configuration with a suspended titrant-generating electrode, avoiding direct deposition on the ISFET chip.
• Investigated the sensitivity of total alkalinity measurements to anode-gate distance and applied electric current.
• Tested the sensor across three different seawater total alkalinity compositions.

Main Results:

• The suspended anode configuration achieved the greatest sensor resolution in seawater at low anode current (5 μA) and anode-gate distances of approximately 150-200 μm.
• The new design demonstrated sharper inflections for equivalence point determination compared to on-chip anode configurations.
• An average sensor error of 2.85 μmol kg⁻¹ was achieved over 131 measurements with averaging (N=5).

Conclusions:

• The off-the-shelf, suspended anode ISFET sensor offers a simplified and effective approach for measuring seawater pH and total alkalinity.
• This design avoids disrupting ISFET functionality and allows for easier exploration of electrode parameters.
• The enhanced equivalence point determination and achieved sensor error highlight the potential of this re-envisioned sensor for marine chemistry applications.