Colorimetric Readout for Potentiometric Sensors with Closed Bipolar Electrodes

Area of Science:

• Electrochemistry
• Analytical Chemistry
• Materials Science

Background:

• Potentiometric probes measure ion concentrations via electrical potential changes.
• Optical detection methods offer advantages in certain applications but require different transduction mechanisms.
• Integrating potentiometric sensing with optical readout can broaden sensor applicability.

Purpose of the Study:

• To develop a general strategy for translating potentiometric signals into tunable color readouts.
• To demonstrate a novel sensor design that physically separates the sample from the detection zone.
• To showcase the versatility of the approach with different ion-selective materials and a common redox indicator.

Main Methods:

• Utilizing a closed bipolar electrode configuration.
• Confining ion-selective components to one electrode end and color generation to the other.
• Imposing an electrical potential across the electrode, modulated by sample-side potentiometric changes.
• Employing a redox indicator (ferroin) in the detection layer to generate a color change.

Main Results:

• Successfully demonstrated the principle with chloride- and calcium-selective electrodes.
• Achieved a tunable color readout directly correlated with ion concentration changes.
• Validated the physical separation of the sample and detection compartments.
• Showcased the redox indicator's response to modulated electrical potentials.

Conclusions:

• The presented strategy offers a robust method for potentiometric-to-optical signal transduction.
• The closed bipolar electrode design enables remote and separated sensing.
• The approach is adaptable to various ion detection materials and optical readout principles, paving the way for new sensor development.