Nanoporous Carbon Materials as Solid Contacts for Microneedle Ion-Selective Sensors

Area of Science:

• Materials Science
• Electrochemistry
• Biomedical Engineering

Background:

• Continuous monitoring of biomarkers like potassium (K+) and pH in wearable sensors requires miniaturized ion-selective electrodes.
• Nanostructured carbon materials offer potential as solid contacts for these miniaturized electrodes.

Purpose of the Study:

• To compare three different nanostructured carbon materials (colloid-imprinted mesoporous carbon, mesoporous carbon nanospheres, and Super P carbon black) as solid contacts in microneedle-based ion-selective and reference electrodes.
• To evaluate the impact of carbon material architecture and composition on specific capacitance, ion-selective membrane integration, and sensor performance for K+ and H+ detection.

Main Methods:

• Fabrication of microneedle-based ion-selective and reference electrodes using gold-coated stainless-steel microneedles with three distinct carbon materials as solid contacts.
• Characterization of carbon materials' pore structure, specific capacitance, and their ability to incorporate ion-selective membrane components.
• Performance evaluation of fabricated sensors, including response linearity (near-Nernstian), stability (potential drift), and selectivity (no O2 response).

Main Results:

• All three carbon materials enabled the fabrication of functional K+ and H+ ion-selective and reference electrodes with near-Nernstian responses in clinically relevant ranges.
• Sensors demonstrated stability, were free from detrimental water layers, showed no O2 interference, and allowed for nearly 1 day of calibration-free continuous operation due to low potential drift.
• While K+ sensor stability was similar across all carbon types, pH sensors utilizing colloid-imprinted mesoporous carbon (CIM) exhibited superior long-term stability, attributed to its higher specific capacitance and pore accessibility.

Conclusions:

• Nanostructured carbon materials are viable solid contacts for miniaturized microneedle-based ion-selective electrodes in wearable sensors.
• The choice of carbon material can influence sensor performance, particularly for pH sensing, where CIM demonstrated enhanced stability.
• These findings support the development of advanced wearable devices for continuous, calibration-free biomarker monitoring.