Switchable Photoacoustic Imaging of Glutathione Using MnO2 Nanotubes for Cancer Diagnosis.

Glutathione is overexpressed in tumor cells and regulates cancer growth, metastasis and drug resistance. Therefore, detecting glutathione levels may greatly facilitate cancer diagnosis and treatment response monitoring. Photoacoustic (PA) imaging is a noninvasive modality for high-sensitivity, high-resolution, deep-tissue optical imaging. Switchable PA probes that offer signal on/off responses to tumor targets would further improve the detection sensitivity and signal-to-noise ratio of PA imaging. Here we explore the use of MnO2 nanotubes as a switchable and biodegradable PA probe for dynamic imaging of glutathione in cancer. Glutathione reduces black MnO2 nanotubes into colorless Mn2+ ions, leading to decreased and "signal off" PA amplitude. In phantoms, we observed a linear response of reduced PA signals of MnO2 nanotubes to increased glutathione concentrations. Using melanoma as the disease model, we demonstrated that MnO2 nanotubes-based PA imaging of glutathione successfully distinguished B16F10 melanoma cells from BEAS-2b normal cells and discriminated B16F10 tumors from healthy skin tissues. Our results showed that MnO2 nanotubes are a potent switchable and biodegradable PA probe for glutathione imaging in cancer diagnosis.