Acid-Triggered Degradation of Three-In-One Ag₂S Quantum Dots for In Situ Ratiometric NIR-II Fluorescence Imaging-Guided Ion/Gas Combination Therapy

Smart theranostic nanoprobes with the integration of multiple therapeutic modalities are preferred for precise diagnosis and efficient therapy of tumors. However, it remains a big challenge to arrange the imaging and two or more kinds of therapeutic agents without weakening the intended performances. In addition, most existing fluorescence (FL) imaging agents suffer from low spatiotemporal resolution due to the short emission wavelength (<900 nm). Here, novel three-in-one Ag₂S quantum dot (QD)-based smart theranostic nanoprobes were proposed for in situ ratiometric NIR-II FL imaging-guided ion/gas combination therapy of tumors. Under the acidic tumor microenvironment, three-in-one Ag₂S QDs underwent destructive degradation, generating toxic Ag⁺ and H₂S. Meanwhile, their FL emission at 1270 nm was weakened. Upon introduction of a downconversion nanoparticle (DCNP) as the delivery carrier and NIR-II FL reference signal unit, the formed Ag₂S QD-based theranostic nanoprobes could achieve precise diagnosis of tumors through ratiometric NIR-II FL signals. Also, the generated Ag⁺ and H₂S enabled specific ion/gas combination therapy toward tumors. By combining the imaging and therapeutic functions, three-in-one Ag₂S QDs may open a simple yet reliable avenue to design theranostic nanoprobes.