Acid-Resistant bioorthogonal quantum nanoprobes for noninvasive NIR-II imaging of simulated microgravity-induced gastric bacterial alterations in rats

Extensive research has demonstrated that the microgravity condition during spaceflight can alter the gastrointestinal homeostasis. However, the microgravity-induced gastric bacterial change and its related pathological effects have not been well investigated. Herein, we present the development of second near-infrared (NIR-II) fluorescence imaging nanoprobes for noninvasively monitoring gastric bacterial alterations in rats under simulated microgravity (SMG) through a hindlimb unloading (HU) model. By rational functionalization and screening of different types of bacteria-targeting quantum nanoprobes, it was showed that DBCO-group-modified Ag₂S (Ag₂S@DBCO) with ultra-stable NIR-II emission can withstand the strong acidic and harsh digestive environment in the stomach, together with the bioorthogonally metabolic labeling capability towards gastric bacteria via click chemistry. Such acid-resistant quantum nanoprobes were successfully applied to in vivo stomach bacteria imaging in SMG rats. The NIR-II imaging results revealed that the gastric bacterial level in SMG rats is significantly higher than that of normal rats, indicating a closed relevance with the microgravity-induced stomach inflammatory responses and injuries. This study provides experimental evidence for understanding the biological implications of gastric bacterial imbalance against aerospace special environment stimulation. We envision that integrating the NIR-II quantum nanoprobes with noninvasive imaging modality will bring new opportunities for space biomedical research.