Synthesis of Ultrathin Biotite Nanosheets as an Intelligent Theranostic Platform for Combination Cancer Therapy

Biotite, also called black mica (BM), is a group of sheet silicate minerals with great potential in various fields. However, synthesis of high‐quality BM nanosheets (NSs) remains a huge challenge. Here, an exfoliation approach is provided that combines calcination, n ‐butyllithium exchange and intercalation, and liquid exfoliating processes for the high‐yield synthesis of ultrathin BM NSs. Due to the presence of MgO, Fe 2 O 3 , and FeO in these NSs, PEGylated BM can be engineered as an intelligent theranostic platform with the following unique features: i) Fe 3+ can damage the tumor microenvironment (TME) through glutathione consumption and O 2 production; ii) Generated O 2 can be further catalyzed by MgO with oxygen vacancy to generate ·O 2 − ; iii) The Fe 2+ ‐catalyzed Fenton reaction can produce ·OH by disproportionation reactions of H 2 O 2 in the TME; iv) Reactions in (i) and (iii) circularly regenerate Fe 2+ and Fe 3+ for continuous consumption of glutathione and H 2 O 2 and constant production of ·OH and O 2 ; v) The NSs can be triggered by a 650 nm laser to generate ·O 2 − from O 2 as well as by an 808 nm laser to generate local hyperthermia; and vi) The fluorescent, photoacoustic, and photothermal imaging capabilities of the engineered NSs allow for multimodal imaging‐guided breast cancer treatment.