Monolithic Photoacoustic Trace-Gas Sensors Enabled by Interface-Engineered Reconfigurable Piezocomposites

Compact photoacoustic trace-gas sensors require acoustic detectors that combine high sensitivity with mechanical integrability, but conventional high-performance detectors are typically rigid, discrete components that are difficult to merge with shape-adaptive acoustic architectures. Here, we report a monolithic photoacoustic CO2 sensor enabled by an interface-engineered reconfigurable piezocomposite, in which the sensing film itself can serve as both the acoustic cavity wall and the piezoelectric detector. The water-processed composite combines Cu@PZT metal-ferroelectric heterointerfaces, sparse MWCNT electrical bridges and a glucose-urea-reconstructed cellulose matrix. Surface-anchored Cu domains on PZT act as localized charge-regulation sites that mitigate polymer dielectric shielding and depolarization effects, yielding a piezoelectric coefficient of 83.2 pC N-1, while the dynamic hydrogen-bonded cellulose network provides the deformability required for conformal and tubular architectures. In a planar PAS configuration, the piezocomposite functions as a flexible acoustic detector attached to a discrete resonant cavity, giving a CO2 sensitivity of 2.92 mV ppm-1 and a detection limit of 148 ppb. When rolled into a monolithic tubular sensor, the same film forms the resonant cavity wall and performs wall-active acoustic-to-electrical transduction, increasing the sensitivity to 7.11 mV ppm-1 and lowering the detection limit to 13 ppb at a 10 s integration time, with a normalized noise equivalent absorption of 2.03 × 10-8 cm-1 W Hz-1/2. This work establishes a material-to-sensor-architecture route for wall-active photoacoustic trace-gas detection, showing how reconfigurable piezocomposites can integrate acoustic resonance and electrical detection within a single deformable sensing structure.