Multifunctional nanosheets based on folic acid modified manganese oxide for tumor-targeting theranostic application.

It is highly desirable to develop smart nanocarriers with stimuli-responsive drug-releasing and diagnostic-imaging functions for cancer theranostics. Herein, we develop a reduction and pH dual-responsive tumor theranostic platform based on degradable manganese dioxide (MnO2) nanosheets. The MnO2 nanosheets with a size of 20-60 nm were first synthesized and modified with (3-Aminopropyl) trimethoxysilane (APTMS) to get amine-functionalized MnO2, and then functionalized by NH2-PEG2000-COOH (PEG). The tumor-targeting group, folic acid (FA), was finally conjugated with the PEGylated MnO2 nanosheets. Then, doxorubicin (DOX), a chemotherapeutic agent, was loaded onto the modified nanosheets through a physical adsorption, which was designated as MnO2-PEG-FA/DOX. The prepared MnO2-PEG-FA/DOX nanosheets with good biocompatibility can not only efficiently deliver DOX to tumor cells in vitro and in vivo, leading to enhanced anti-tumor efficiency, but can also respond to a slightly acidic environment and high concentration of reduced glutathione (GSH), which caused degradation of MnO2 into manganese ions enabling magnetic resonance imaging (MRI). The longitudinal relaxation rate r1 was 2.26 mM(-1) s(-1) at pH 5.0 containing 2 mM GSH. These reduction and pH dual-responsive biodegradable nanosheets combining efficient MRI and chemotherapy provide a novel and promising platform for tumor-targeting theranostic application.