In Vitro Evaluation of Silica-Coated Bi₂Se₃ Nanoplatelets as Photothermal Nanomaterials

Silica-coated Bi₂Se₃ nanoplatelets were evaluated in vitro for their photothermal properties and biological response as a more biocompatible alternative to previously reported glycol-coated Bi₂Se₃ systems. The assessment was performed using HeLa cells under 808 nm laser irradiation. The silica shell retains the characteristic optical absorption response of Bi₂Se₃ and even increases absorption across the UV-vis-NIR spectral range. However, this enhancement is thickness-dependent, as silica layers thicker than ≈50 nm can diminish the optical response of Bi₂Se₃. Both thin- and thick-silica-coated nanoplatelets (BiSe@Si-thin and BiSe@Si-thick samples) exhibit pronounced photothermal heating under 808 nm irradiation, reaching 45-52 °C at 0.3 g/L under 1 W/cm² irradiation, corresponding to the subcoagulative hyperthermia regime. This was associated with a significant reduction in cell viability and activation of apoptosis and autophagy pathways. The effect is more pronounced in the BiSe@Si-thin sample, consistent with its higher temperature increase and enhanced cellular association and internalization. No cytotoxicity is observed in the absence of irradiation, confirming that cell death is governed by the photothermal effect.