Two-Channel Graphene pH Sensor Using Semi-Ionic Fluorinated Graphene Reference Electrode

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Ion-sensitive field-effect transistor (ISFET) sensors require a reference electrode, typically Ag/AgCl, for operation in electrolyte solutions.
• The limitations of Ag/AgCl reference electrodes hinder the full potential of ISFET sensors.
• A need exists for integrated reference systems within ISFET devices.

Purpose of the Study:

• To fabricate and characterize a two-channel graphene solution gate field-effect transistor (G-SGFET) capable of pH detection without an external Ag/AgCl reference electrode.
• To demonstrate the feasibility of using one channel as a sensing element and the other as an integrated reference electrode.
• To evaluate the performance and stability of the developed G-SGFET for real-time pH monitoring.

Main Methods:

• Fabrication of a two-channel G-SGFET with an oxygenated sensing channel and a partially fluorinated reference channel.
• Direct exposure of both channels to the electrolyte solution, bypassing traditional sensing membranes and passivation layers.
• Analysis of transfer characteristics to observe ambipolar FET behavior and determine pH sensitivity.
• Measurement of reference channel leakage current and real-time pH detection stability.

Main Results:

• The two-channel G-SGFET exhibited ambipolar FET behavior (p-channel and n-channel).
• A pH sensitivity of 18.2 mV/pH was achieved in the range of pH 4 to 10.
• The integrated reference channel demonstrated a low leakage current of 16.48 nA.
• Stable real-time pH detection was maintained for 60 minutes in a buffer solution.

Conclusions:

• The developed two-channel G-SGFET successfully functions as a pH sensor without an external Ag/AgCl reference electrode.
• The integrated reference channel design offers a promising alternative for simplified ISFET sensor systems.
• This approach enhances the advantages of graphene-based ISFETs for electrolyte sensing applications.