Biosynthesis of NIR‐II Ag2Se Quantum Dots with Bacterial Catalase for Photoacoustic Imaging and Alleviating‐Hypoxia Photothermal Therapy

Developing the second near‐infrared (NIR‐II) photoacoustic (PA) agent is of great interest in bioimaging. Ag2Se quantum dots (QDs) are one kind of potential probe for applications in NIR‐II photoacoustic imaging (PAI). However, the surfaces with excess anions of Ag2Se QDs, which increase the probability of nonradiative transitions of excitons benefiting PA imaging, are not conducive to binding electron donor ligands for potential biolabeling and imaging. In this study, Staphylococcus aureus (S. aureus) cells are driven for the biosynthesis of Ag2Se QDs with catalase (CAT). Biosynthesized Ag2Se (bio‐Ag2Se‐CAT) QDs are produced in Se‐enriched environment of S. aureus and have a high Se‐rich surface. The photothermal conversion efficiency of bio‐Ag2Se‐CAT QDs at 808 and 1064 nm is calculated as 75.3% and 51.7%, respectively. Additionally, the PA signal responsiveness of bio‐Ag2Se‐CAT QDs is ≈10 times that of the commercial PA contrast agent indocyanine green. In particular, the bacterial CAT is naturally attached to bio‐Ag2Se‐CAT QDs surface, which can effectively relieve tumor hypoxia. The bio‐Ag2Se‐CAT QDs can relieve heat‐initiated oxidative stress while undergoing effective photothermal therapy (PTT). Such biosynthesis method of NIR‐II bio‐Ag2Se‐CAT QDs opens a new avenue for developing multifunctional nanomaterials, showing great promise for PAI, hypoxia alleviation, and PTT. The Staphylococcus aureus cells provide selenium‐rich environments for the biosynthesis of Ag2Se quantum dots (QDs) with selenium‐rich surfaces and equip QDs with catalase (CAT). The biosynthesized Ag2Se QDs with CAT (Bio‐Ag2Se‐CAT) provide high‐contrast photoacoustic imaging (PAI), alleviate tumor hypoxia, and perform tumor photothermal therapy (PTT) while relieving heat‐initiated oxidative stress.