Titan g2 f20

PST NPs were prepared via self-polymerization of serotonin (5-HT). Briefly, 5-HT·HCl (10 mg, 0.047 mmol) was dissolved in 5 mL ultrapure water and then added to 10 μL NaOH (10 μM) to adjust the pH to 7.0 for 48 h oxidative polymerization. Then, PST NPs were collected via centrifugation (4°C, 16000 rpm, 15 min). To prepare PDM NPs, 200 μL PST NPs (1 mg mL⁻¹), 100 μL NaCl (1.5 M), and 20 μL DZ (100 μM) were mixed and incubated for 30 min to adsorb DZ on the surface of PST NPs. Then, 10 μL TA (40 mg mL⁻¹) and 10 μL MnCl₂ (10 mg mL⁻¹) were quickly mixed with the above solution. After 5 min stir, 100 μL HEPES (100 mM, pH 7.6) was added and further sonicated for 5 min, and then vigorously stirred at 30°C for 4 h. Finally, the PDM NPs were collected by centrifugation (16000 rpm, 15 min, 4°C) and dispersed in ultrapure water for further use. The ultraviolet-visible (UV-vis) spectra were obtained by using a UV-2600 spectrophotometer (UV-2600, Shimadzu). The size distribution and zeta potential were determined by the Malvern Zeta Sizer Nano series (Nano ZS, Malvern Instruments, UK). The morphology was observed using transmission electron microscopy (TEM) (Titan G2-F20, FEI, USA). The stability in PBS and serum were assessed by measuring particle size over 72 h incubation.