Polypyrrole Nanosheets Prepared By In-Situ Polymerization For NIR-Ⅱ Region Photoacoustic Imaging Guided Photothermal Therapy Of Cancer

Photothermal therapy(PTT),which uses light absorbers to generate heat at the tumor site under near-infrared(NIR)laser irradiation,is a very promising method for thermal ablation of cancer cells.Different from traditional cancer treatment,PTT is a minimally invasive or non-invasive treatment with unique advantages,such as simple surgery and rapid recovery after cancer treatment,and has always been widely concerned and researched.To achieve effective PTT,it is necessary to find nanostructured materials with prominent photothermal conversion efficiency.Nowadays,the development of practical photothermal agents(PTA)for clinical applications still remains a major challenge.Polypyrrole(PPy)nanomaterials has been widely studied for photothermal treatment of cancer due to their excellent biological safety and photothermal properties.However,most of the current studies on PPy nanomaterials in photothermal therapy are concentrated on the first near-infrared region(NIR-Ⅰ),and there are relatively few studies on the second nearinfrared region(NIR-Ⅱ),In this study,a new method was used to synthesize PPy with a two-dimensional(2D)structure,which showed excellent photothermal ablation ability in the NIR-Ⅱ region.In view of the fact that pyrrole was easily oxidized to form PPy in the presence of an oxidant,this study used manganese dioxide(MnO2)nanosheets as a 2D template and oxidant to form PPy nanosheets by in-situ oxidation of pyrrole under acidic conditions.The synthesis method was simple in operation and extremely fast,and the polymerization could be completed in a few seconds without adding additional oxidants.The surface of the synthesized PPy nanosheets could be easily modified by mPEG-DSPE to improve the dispersion and stability of the solution.The PPy nanosheets exhibited strong and broad absorption in the NIR region,and the absorption value at 1064 nm was higher than 808 nm.Through the related research on photothermal performance,it was found that compared with the NIR-Ⅰ region,PPy nanosheets could achieve a faster photothermal heating effect in the NIR-Ⅱ region.In addition,the photothermal conversion efficiency(PTCE)of the nanosheets was 58.27%in the the NIR-Ⅰ region,and as high as 66.01%in the NIR-Ⅱ region.Both in vitro and in vivo experiments had proved that PPy nanosheets have excellent biological safety and low cytotoxicity,and can achieve more efficient photothermal cancer treatment effects under the NIR-Ⅱ region laser irradiation.When the 1064 nm laser was used for photothermal treatment,the mice tumors were even completely ablated.In addition,the PPy nanosheets exhibited a stronger photoacoustic imaging signal in the NIR-Ⅱ region than the NIR-Ⅰ region,which can effectively reflect the accumulation of materials at the tumor site.Therefore,PPy nanosheets could use photoacoustic imaging-guided to achieve a more efficient photothermal treatment effect in the NIR-Ⅱ region,thereby realizing the integration of diagnosis and treatment.