Optical activation of surface-functionalized BNNTs for dual-mode photothermal and photodynamic effects under low-intensity irradiation

Abstract

Boron nitride nanotubes (BNNTs) offer a unique combination of wide bandgap, high thermal conductivity, and chemical stability that positions them as promising candidates for emerging photothermal and photodynamic cancer therapies; however, their biomedical use has been limited by poor aqueous dispersibility and weak optical response under physiologically compatible excitation. In this work, highly water-dispersible BNNTs were synthesized through sodium dodecyl sulfate (SDS) surface functionalization, enabling, for the first time, a dual-mode optical response under low-intensity visible and ultraviolet (UV) irradiation. Comprehensive structural and compositional analyses confirmed uniform surfactant adsorption and the emergence of defect-mediated surface states that broaden optical absorption into the visible range. These modified BNNTs exhibited measurable photothermal heating under mild 520 nm excitation and, uniquely, generated potent ROS under UV exposure, leading to strong cytotoxicity even without direct nanotube–cell contact. Biocompatibility assays with PC12 neural cells demonstrated low intrinsic toxicity up to 25 µg ml−1, while UV -irradiated BNNT supernatants induced marked reductions in viability and pronounced nuclear abnormalities, consistent with apoptosis driven by photochemically generated oxidative species. The discovery that SDS-functionalized BNNTs can be activated through two orthogonal optical pathways at low energy thresholds establishes a novel multifunctional nanoplatform that circumvents limitations of traditional carbon-based nanostructures and high-power actuation methods. These findings highlight the potential of BNNT systems for minimally invasive, synergistic photothermal–photodynamic therapy and underscore the need for future in vivo studies to evaluate therapeutic efficacy, biodistribution, and long-term biocompatibility.