As marine resource exploration and underwater environmental monitoring expand rapidly, conventional underwater sensors face a critical bottleneck: they typically rely on combinations of multiple functional materials to detect temperature and pressure simultaneously, requiring additional waterproof encapsulation that complicates system integration and compromises reliability. Now, researchers from Nanjing Tech University, Tsinghua University, and Tohoku University, led by Professor Peng-an Zong and Professor Heng Liu, have presented a breakthrough single-material dual-mode sensor that operates natively in both air and underwater environments.

The Pyramid Interface Advantage

Traditional dual-mode sensors often employ heterogeneous composites—such as PDMS/carbon nanotube sponges or laser-induced porous carbon films—that suffer from interfacial delamination and baseline drift upon water infiltration. Hydrophobic coatings (e.g., PDMS, polyimide) are commonly applied, but these organic layers involve complex processing, exhibit poor corrosion resistance, and attenuate signal transmission. The novel pyramid-interface-structured Bi₂Se₃ layer overcomes these limitations by combining intrinsic hydrophobicity, high thermoelectric performance, and piezoresistive sensitivity within a single electrochemically deposited architecture—eliminating the need for external waterproof encapsulation.

Innovative Design and Mechanism

The material is synthesized through pulsed electrochemical deposition of Bi₂Se₃ onto flexible carbon paper (CP), followed by thermal annealing at 300°C. DFT calculations and finite-element modeling reveal that the pyramid microstructure originates from optimized ion aggregation and nucleation kinetics at −0.02 V deposition potential. The pyramid geometry achieves a stable Cassie–Baxter state with a water contact angle of 143.7°, minimizing solid–liquid contact and promoting droplet roll-off. Simultaneously, the sloped facets induce a stress-concentration effect, causing the interlayer contact area to vary nonlinearly with pressure—enabling high sensitivity across a broad detection range. The stacked Bi₂Se₃/CP/Bi₂Se₃ multilayer assembly leverages the Seebeck effect for temperature detection (voltage signal) and piezoresistive interlayer contact modulation for pressure detection (resistance signal), with fully decoupled signal origins.

Outstanding Performance

The optimized Bi₂Se₃/CP film delivers a power factor of 106.0 μW m^-1 K^-2—nine times that of bare carbon paper—with an electrical conductivity of 779.3 S cm^-1 and a Seebeck coefficient of −36.9 μV K^-1. The stacked sensor achieves a rapid temperature response time of 0.9 s and a pressure sensitivity of 0.94% kPa^-1, with a minimum detectable pressure of 0.1 kPa and an upper limit of 100 kPa. Notably, the sensor maintains complete signal decoupling: pressure variations show no effect on temperature sensitivity, and temperature changes do not alter pressure response—verified in both air and underwater environments. The device also exhibits exceptional environmental resilience: >62 dB electromagnetic interference shielding effectiveness across the X-band (>99.9% attenuation), stable operation after 1000 bending cycles, 100 immersion cycles, direct flame exposure for 200 s without ignition, and sustained performance in 5 wt% NaCl solution at 60°C for 100 h.

Applications and Future Outlook

When integrated into a smart mask, the sensor tracks respiratory rate in real time, distinguishing between sitting (17.09 bpm), standing (18.75 bpm), and squatting (26.67 bpm) states. A 3×3 underwater sensor array enables touch-encoded word recognition ("age," "bed," "hic") and simultaneous spatiotemporal mapping of thermal and mechanical stimuli—demonstrating potential for underwater human–machine interaction. The sensor precisely monitors human joint motions (finger bending, wrist rotation, elbow flexion) and captures subtle facial expressions on moist skin, supporting underwater communication and emotion-aware diving assistants. Mounted on a robotic fish, it tracks tail-flapping propulsion for 200 s with stable periodic signal output. This work establishes a new paradigm for amphibious wearable sensing, opening promising avenues for marine exploration, environmental monitoring, and next-generation underwater robotics.

Stay tuned for more groundbreaking research from this collaborative team at Nanjing Tech University, Tsinghua University, and Tohoku University!