Biomimetic Single‐Domain Magnetic Nanochains Surpassing Magnetotactic Bacteria in Hyperthermia Efficiency

Magnetosome chains biosynthesized by magnetotactic bacteria combine high magnetic responsivity with efficient magnetothermal conversion but face limitations due to fragile assembly and potential biosafety risks. Here, we report a biomimetic Stöber-based encapsulation strategy that preserves the native chain architecture while imparting structural robustness and enhanced safety. The resulting B-MNC exhibit a coercivity (33.6 mT), approximately 5× higher than magnetosomes, 1.4× higher than intact magnetotactic bacteria, and 2.2× higher than chemically synthesized analogs (C-MNC22). Magnetic characterization reveals ideally uniaxial single-domain behavior with a remanence ratio (M_rs/M_s) of 0.5, outperforming magnetosomes (0.35), bacteria (0.46), and C-MNC22 (0.27). Under an alternating magnetic field (144.1 kHz, 34.7 kA m^-1), aligned B-MNC achieve a specific absorption rate (SAR) of 1749.7 W g^-1, which is approximately 4.72× greater than purified magnetosomes, enabling rapid and efficient heating. In vitro, silica encapsulation markedly improves colloidal stability and cytocompatibility. Upon magnetic hyperthermia (42°C, 20 min), B-MNC induce 71.4% death of MB49 bladder cancer cells versus only 12.4% for bare magnetosomes. This biomimetic assembly preserves the superior magnetic properties of native magnetosome chains while enhancing magnetic hyperthermia efficacy and biostability, establishing B-MNC as a promising platform for safe and effective magnetic cancer therapy.