In vivo real-time and in situ sensing of nitric oxide in virus-infected mouse lungs using organic near-infrared-to-visible triplet–triplet annihilation upconversion nanoprobes

Nitric oxide (NO) is a crucial gaseous signaling molecule, and its local concentration fluctuations in vivo can reflect the onset and progression of various pulmonary diseases, such as idiopathic pulmonary fibrosis and viral lung infections. Previous studies have demonstrated a positive correlation between in vivo NO concentration and disease progression, highlighting the urgent need to develop a class of bioprobes capable of highly sensitive and specific real-time NO sensing within living organisms. Herein, we report a “turn-on” near-infrared fluorescence sensing nanoprobe for nitric oxide (NO), which integrates a near-infrared-to-visible triplet–triplet annihilation upconversion (TTA-UC) system with an NO-responsive Bodipy dye. By co-encapsulating both components into the amphiphilic polymer F127, we constructed TTA micelles with excellent photostability and biocompatibility. In vitro studies demonstrated that the TTA nanomicelles can sensitively and specifically respond to exogenous NO. In a pseudotyped mouse model of pulmonary viral infection induced by SARS-CoV-2 spike protein (SP), the upconversion fluorescence of the TTA nmicelles was gradually activated over time, indicating that the developed nanoprobe can dynamically reflect the real-time progression of lung infection in mice. Therefore, the TTA micelles can rapidly diagnose the onset of lung infection at early stages, thereby potentially improving the efficiency of subsequent treatments.