Seed-Mediated Synthesis of Polypeptide-Engineered Stabilized Fluorescence-Enhanced Core/Shell Ag2S Quantum Dots and Their Application in pH Sensing and Bacterial Imaging in Extreme Acidity

The value of pH plays an important role in biological systems, and fluorescence pH probes enable noninvasive monitoring of the change and distribution of pH. Here, we introduce a new class of pH probe based on the genetically engineered polypeptide stabilized second near-infrared fluorescence-enhanced core/shell Ag2S quantum dots. The core/shell Ag2S quantum dots synthesized by seed-mediated growth methods showed a good linear relationship between fluorescence intensity and pH value in the range 2.1–7.2. In addition, the core/shell Ag2S quantum dots exhibited excellent reversibility and good biocompatibility, which can serve as multifunctional probes for the imaging and detecting of Gram-negative bacteria without the influence of autofluorescence in the extremely acidic environment.