Fabrication of a flexible, printable, and recyclable dual-mode sensor for highly sensitive capacitive and triboelectric sensing.

A printable and recyclable dual-mode sensor (DMS) has been developed by screen-printing interdigital silver electrodes onto a sustainable bio-based polyurethane (bio-PU) substrate, and using Ecoflex-30 as a dielectric encapsulation layer. This unique structural design enables the DMS to be operated under two modes: a capacitive sensing mode and a free-standing triboelectric nanogenerator (FS-TENG) type triboelectric sensing mode. Notably, given the high dielectric constant of bio-PU substrate (5.32), the DMS exhibited improved triboelectric and capacitive sensing performance with high sensitivity (29.34%/kPa), fast response time (30 ms), and low detection limit (6 Pa), showing versatile applications, including micro-object detection, human pulse and motion monitoring, Morse-code-based information transmission, non-contact object recognition, and real-time liquid-level detection. Benefiting from the excellent mechanical robustness and durability of the bio-PU substrate, the bio-PU substrate can be recycled by selectively dissolving the silver electrode with acetone, enabling its reuse to fabricate new dual-mode sensors. The recycled dual-mode sensor still retains reliable sensing performance, and the retention rate of peak relative capacitance changes and output voltage is above 80% after the first recycling cycle. This work presents a sustainable strategy for developing an eco-friendly dual-mode sensor to reduce the generation of E-waste.