After adding 2 mL of PHSA liquid and 10 μL of DDT to the reaction flask, the reaction was stirred for 15 min at 25°C. Subsequently, 30 μL of ICG fluorescent dye was added, and the reaction was stirred for 12 h in the dark at 25°C. After the reaction, the pH of the purified water was adjusted to 7.0–7.5 to be used as dialysis solution with PBS, and the solution in the reaction bottle was dialyzed against the light for 24 h in the adjusted pH aqueous solution. The dialysis-purified PHSA-ICG was placed in a refrigerator at 4°C for subsequent use.