Multipurpose Paper-Based Sensors by Hydrogel-Assisted Metal Deposition

With the rapid development of wearable devices, paper-based sensors have attracted considerable attention due to their ubiquitous availability, light weight, and sustainability. In this study, we present a kind of multifunctional paper-based copper sensor fabricated by hydrogel-assisted electroless metal deposition. A uniform and highly conductive copper layer was successfully deposited on paper by in situ reduction of cupric ions through a catalyst-loaded UV-cured hydrogel layer. The as-prepared copper paper exhibits superior electrical conductivity of up to (5.356 ± 0.231) × 10 7 S/m and remarkable long-term stability under ambient conditions and can be folded into 3D origami structures for dynamic deformation detection based on its inherent foldability. More importantly, the piezoresistive sensor made of multilayer copper paper exhibited a fast response time (760 ms), quick recovery (20 ms), and good durability over 1000 loading–unloading cycles, which enabled successful Morse code sensing. Furthermore, hydrophilic poly(acrylic acid) endows copper paper with humidity-responsiveness and ammonia detection capability, as evidenced by reversible resistance changes in correlation with NH 3 concentration. In addition, copper paper showed a high electric heating effect and heated up rapidly to ∼90 °C at low voltage due to its electroconductive property. This work provides a strategy for developing easy-fabricated, multipurpose, and sensitive paper-based copper platforms for flexible sensing.