Boron nitride nanotubes (BNNTs) combine a wide electronic bandgap, high thermal conductivity, and chemical stability, characteristics that make them attractive candidates for photothermal and photodynamic therapeutic platforms. However, translation into biomedical applications has been constrained by two main limitations: poor aqueous dispersibility and a weak optical response under excitation conditions compatible with biological systems. This study addresses those barriers by applying noncovalent surface functionalization to create a BNNT formulation that is both water-dispersible and optically responsive at low irradiation intensities.
The authors prepared highly water-dispersible BNNTs by adsorbing sodium dodecyl sulfate (SDS) on the nanotube surface. Comprehensive analyses confirmed uniform surfactant adsorption, yielding stable aqueous suspensions suitable for biological testing. The work focuses on noncovalent surfactant modification rather than chemical grafting, preserving the core BNNT structure while improving colloidal stability.
Characterization of the SDS-functionalized BNNTs revealed the emergence of defect-mediated surface states. These new surface states broadened the optical absorption profile of BNNTs into the visible range, which is not typical for pristine BNNTs with their wide bandgap. The presence of these states was linked to the altered optical response and underpins the ability of the functionalized material to respond to lower-energy visible light as well as to ultraviolet (UV) irradiation.
Using mild 520 nm excitation, the SDS-functionalized BNNTs produced measurable photothermal heating. The study emphasizes that this heating occurred under low-intensity visible irradiation, indicating that the surfactant-induced surface states enable thermal actuation without requiring high-power lasers. The observed photothermal effect suggests potential for localized hyperthermia-based therapies that can be actuated with relatively low-energy visible light sources.
Separate from the visible-light heating, UV irradiation of the functionalized BNNTs generated potent reactive oxygen species (ROS). The ROS generation was sufficient to induce cytotoxic effects in cell culture experiments even when cells were exposed only to BNNT-containing supernatants that had been irradiated with UV light—i.e., cytotoxicity occurred without direct nanotube–cell contact. The UV-triggered photochemical pathway therefore provides an orthogonal activation mode compared with the photothermal response to visible light.
Biocompatibility assays using PC12 neural cells indicated low intrinsic toxicity of SDS-functionalized BNNTs at concentrations up to 25 µg ml-1 in the absence of irradiation. When BNNT suspensions or supernatants were irradiated with UV, however, treated samples induced marked reductions in cell viability. Irradiated supernatants produced pronounced nuclear abnormalities consistent with apoptosis, supporting a mechanism in which photochemically generated oxidative species damage cellular structures and trigger programmed cell death. The report documents these in vitro outcomes but does not provide in vivo toxicity or pharmacokinetic data.
The key mechanistic insight is that SDS adsorption produces uniform surfactant coverage and defect-mediated surface electronic states that extend optical absorption into the visible region. These surface states enable two orthogonal optical activation pathways at low energy thresholds: (1) visible-light-driven photothermal heating and (2) UV-driven photodynamic generation of ROS. The photothermal and photodynamic effects are therefore functionally separable and can be engaged independently depending on the irradiation wavelength.
These results establish SDS-functionalized BNNTs as a multifunctional nanoplatform capable of dual-mode optical activation under low-intensity irradiation. The combination of measurable photothermal response at 520 nm and strong UV-induced ROS production may enable synergistic or sequential therapeutic approaches that exploit both hyperthermia and oxidative damage. The authors note that this platform circumvents some limitations associated with carbon-based nanostructures and avoids reliance on high-power actuation methods.
Crucially, the study identifies several areas requiring further investigation: in vivo efficacy testing, biodistribution studies, long-term biocompatibility and clearance, and detailed dose–response characterization across cell types and irradiation regimens. The source article does not report any in vivo data or long-term safety results.
SDS-functionalized BNNTs demonstrate a broadened optical response and dual-mode activation under low-intensity irradiation: photothermal heating with visible light (520 nm) and photodynamic ROS-mediated cytotoxicity under UV light. In vitro assays using PC12 cells show low baseline toxicity up to 25 µg ml-1 but significant UV-activated cytotoxic effects consistent with apoptosis. The work presents a novel, water-dispersible BNNT formulation that may support minimally invasive, synergistic photothermal–photodynamic therapies, while underscoring the need for comprehensive in vivo and safety studies before therapeutic application.