Facile Labeling of Gram-Negative Bacteria with NIR-II Fluorescent Nanoprobes for Intestinal Bacteria Imaging

The gut bacteria not only play a crucial role in maintaining human health but also exhibit close associations with the occurrence of numerous diseases. Understanding the physiological and pathological functions of gut bacteria and enabling early diagnosis of gut diseases heavily relies on accurate knowledge about their in vivo distribution. Consequently, there is a significant demand for noninvasive imaging techniques capable of providing real-time localization information regarding gut bacteria. In this work, we developed a second near-infrared (NIR-II) fluorescent nanoprobe labeling-based visualization strategy for real-time tracking of the biodistribution of Gram-negative bacteria in the gastrointestinal tract of mice. By utilizing positively charged silver sulfide quantum dots (Ag₂S QDs) as NIR-II nanoprobes and exploiting electrostatic interactions to efficiently label the Gram-negative probiotic Escherichia coli Nissle 1917 with negative surface charges, we have achieved rapid and effective labeling. Leveraging the exceptional NIR-II fluorescent performance of Ag₂S QDs, our approach enables high spatiotemporal resolution visualization via NIR-II imaging in mouse gastrointestinal areas where Ag₂S QD-labeled probiotics are present, facilitating real-time in vivo tracking capabilities for these labeled probiotics. This work not only establishes a powerful intestinal bacterial imaging strategy but also introduces novel concepts for constructing nanomaterial-bacteria hybrid systems.