Chitosan-enhanced photothermal efficiency and rapid bacterial eradication using MgFe₂O₄ nanocomposites under NIR light

Photothermal nanomaterials that enable light-triggered bacterial eradication at low dose are emerging as promising alternatives to conventional antibiotics. In this work, nanocrystalline MgFe₂O₄ was synthesized via a citrate–nitrate combustion route and integrated with chitosan to form MgFe₂O₄–chitosan nanocomposites with varying polymer content. X-ray diffraction confirmed phase-pure cubic spinel MgFe₂O₄ with an average crystallite size of ~ 40 nm, while FTIR and SEM–EDS verified successful incorporation of chitosan without altering the ferrite crystal structure. Optical studies revealed strong visible–NIR absorption with a gradual reduction in band gap from ~ 1.99 eV (pure MgFe₂O₄) to ~ 1.89 eV for high chitosan loading. Under 808 nm near-infrared irradiation, the composites exhibited enhanced photothermal performance, with the 80% chitosan composite reaching ~ 63.5 °C and achieving photothermal conversion efficiency exceeding 80% at a low material concentration (1 mg mL⁻¹). This efficient heat generation translated into potent light-activated antibacterial activity, resulting in near-complete eradication of both Gram-positive Streptococcus pyogenes and Gram-negative Acinetobacter baumannii within 5 min of NIR exposure. The study demonstrates that chitosan not only improves biocompatibility but also synergistically enhances the photothermal efficiency and antibacterial performance of MgFe₂O₄, highlighting the potential of ferrite–polymer hybrids as low-cost, magnetically responsive photothermal antibacterial platforms.