In-situ heterojunction on high-aspect-ratio cellulose nanocrystals for long-range charge transport in e-skin

Long-range piezoelectric transduction in flexible hydrogels is limited by the "trade-off" of conductive pathways between accelerating charge dissipation and suppressing dipole formation. Here, we introduce a surface-heterojunction strategy converting cellulose nanocrystals (CNCs) into conductive dipolar nanorods by deprotonation of poly(aminophenylboronic acid) (PABA) coating. Boronated ester bonding and hydrogen-bonds at CNCs/PABA interface collectively strengthen dipole moments while inducing n-type doping in PABA and thus enabling charge transport for 18.9-fold conductivity. Integrating molecular-level interfacial alignment of conjugated moieties, CNCs with higher aspect-ratio further promote percolation and reduce threshold by ∼14%. The charge transport range in hydrogel is then elongated, which improves its conductivity by 7.0 times and yields robust piezo-electric/resistive dual-mode responsiveness. The hydrogen-bond network also improves adhesion, and imparts intrinsic sensitivity to temperature, salinity, and pH, for distinguishing complex motions and physiological events. This heterojunction-driven co-engineering of dipoles and conductivity offers a generalizable materials concept for advancing high-fidelity soft bioelectronic sensing.