Gradient-Oxidized Bacterial Cellulose for Self-Sustained Soil Moisture Sensing

Soil moisture monitoring is pivotal to precision agricultural irrigation. Conventional soil moisture sensors rely on external power supplies and suffer from poor environmental compatibility. The facile fabrication of hydrovoltaic devices with asymmetric film structures remains challenging, and related designs tailored for soil scenarios are still insufficient. Here, we report an in situ-grown planar asymmetric encapsulated bacterial cellulose (AEBC) device for self-powered soil moisture sensing. Graphene oxide (GO) and carbon nanotubes (CNT) are sequentially embedded on opposite sides of the growing cellulose network via gravity-assisted in situ assembly, forming an oxygen-functional gradient. A LiCl-doped Ecoflex hygroscopic layer is further integrated to continuously provide mobile ions and stabilize moisture uptake. The 35 µm-thick device delivers a volumetric power density of 211.37 µW·cm^-3 and maintains stable operation for over 20 days across wide temperature and pH ranges. A wireless monitoring system integrating the AEBC with deep learning-based signal recognition achieves accurate soil moisture detection. The bacterial cellulose matrix can be biodegraded in soil, and degradation residues exert no adverse effects on plant growth. This work provides an in situ fabrication strategy for asymmetric hydrovoltaic films, offering a promising sustainable platform for self-powered agricultural monitoring.