In situ aqueous synthesis of genetically engineered polypeptide-capped AgS quantum dots for second near-infrared fluorescence/photoacoustic imaging and photothermal therapy.

AgS quantum dots have received extensive attention as theranostic agents for second near-infrared (NIR-II) fluorescence and photoacoustic dual-mode imaging, and photothermal therapy. However, it is still greatly challenging to synthesize AgS quantum dots using aqueous synthesis. In this study, genetically engineered polypeptide-capped AgS quantum dots were successfully synthesized. Three cysteines were integrated to the C-terminal and N-terminal of RGDPCA to enhance the stability and brightness of the synthesized AgS quantum dots. The RGDPCA-capped AgS quantum dots exhibited excellent stability, outstanding resistance to photobleaching, and a superior quantum yield of up to 3.78% in the NIR-II biological window. The in vitro and in vivo results showed that the RGDPCA-capped AgS quantum dots possessed typical NIR-II fluorescence, photoacoustic imaging, and photothermal therapeutic effectiveness against tumors. Moreover, the results of toxicity assays suggested that the RGDPCA-capped AgS quantum dots have negligible long-term toxicity. These findings open up the possibility for synthesizing theranostic agents by using this aqueous method.