Highly Stretchable Potentiometric pH Sensor Fabricated via Laser Carbonization and Machining of Carbon−Polyaniline Composite

TLDR

Stretchable sensors are increasingly used in wearable and robotics applications for health monitoring, motion detection, and human‑machine interfaces. The study presents a highly stretchable electrochemical pH sensor for wearable point‑of‑care use, featuring a pH‑sensitive working electrode and a liquid‑junction‑free reference electrode with laser‑carbonized, micromachined conductive interconnections on a polyimide/Ecoflex substrate. The sensor’s interconnections are fabricated by laser‑carbonizing 2D serpentine traces on polyimide, then permeating them with polyaniline to serve as conductive filler, binder, and pH‑sensitive membrane. Experimental and simulation results show that the serpentine PANI/C‑PI interconnections can endure up to 135 % elongation and 12 000 stretch‑release cycles at 20 % strain without resistance change, while the pH sensor exhibits a linear sensitivity of –53 mV/pH (R² = 0.976) across pH 4–10, maintains stable performance under up to 100 % strain with <±4 mV deviation, and demonstrates biocompatibility with NIH 3T3 fibroblasts.

Abstract

The development of stretchable sensors has recently attracted considerable attention. These sensors have been used in wearable and robotics applications, such as personalized health-monitoring, motion detection, and human-machine interfaces. Herein, we report on a highly stretchable electrochemical pH sensor for wearable point-of-care applications that consists of a pH-sensitive working electrode and a liquid-junction-free reference electrode, in which the stretchable conductive interconnections are fabricated by laser carbonizing and micromachining of a polyimide sheet bonded to an Ecoflex substrate. This method produces highly porous carbonized 2D serpentine traces that are subsequently permeated with polyaniline (PANI) as the conductive filler, binding material, and pH-sensitive membrane. The experimental and simulation results demonstrate that the stretchable serpentine PANI/C-PI interconnections with an optimal trace width of 0.3 mm can withstand elongations of up to 135% and are robust to more than 12 000 stretch-and-release cycles at 20% strain without noticeable change in the resistance. The pH sensor displays a linear sensitivity of -53 mV/pH (r2 = 0.976) with stable performance in the physiological range of pH 4-10. The sensor shows excellent stability to applied longitudinal and transverse strains up to 100% in different pH buffer solutions with a minimal deviation of less than ±4 mV. The material biocompatibility is confirmed with NIH 3T3 fibroblast cells via PrestoBlue assays.