The PNIPAM low critical solution temperature (LCST) was approximately 32 ℃ but could be modified and that of GPPD was approximately 42 ℃ (
Fig. 2A). GNP- and DOX-loaded polymers thus had temperature-controlled release. GNP and GPPD size distributions were evaluated by dynamic light scattering (DLS). The particle size increased after GNPs embedding on the liposome membrane with a size of 400–500 nm. The particle size of GPPD was also increased after irradiation by NIR light (Table S1). GPPD doped with PNIPAM showed an increase in particle size after NIR irradiation and became spherical due to self-polymerization (
Fig. 2B). Good photothermal conversion
in vitro was shown (
Figs. 2A and
B). The photothermal conversion efficiency (
η) of GPPD was 16.3% (Fig. S1 in Supporting information). GPPD had a volume phase transition temperature of approximately 42 ℃. POPC delivery of DOX and NIR irradiation of GNP, which led to the breakage of hydrogen bonds as the temperature increased, gave the system reduced toxicity. PNIPAM underwent a chain to globular shape transition, enlarging the liposome void and releasing the drug. The photothermal PNIPAM contraction, which allowed controlled drug release, indicated successful system construction and precipitated tumor cell death. PNIPAM contraction produced thermosensitive changes which mediated passive targeting [
27]. Therapeutic nanomedicine applications of the photothermal properties of gold have previously been demonstrated by Zhang
et al. [
28]. The combination of GNP and PNIPAM has great potential to improve past research results. Transmission electron microscopy (TEM) was used to examine the GNPs (
Fig. 2C) and the size of the GPPD was found to be approximately 400–500 nm (
Fig. 2D). A similar value was derived by DLS. The DLS (Table S1) and TEM (
Figs. 2C and
D) data demonstrated the successful synthesis of the system. The photothermal conduction efficiency of 100 µg/mL GNPs and GPPD with continuous NIR light (808 nm, 1 W/cm
2, 6 min) at different time points allowed the temperature to increase with illumination duration (
Fig. 2E). The favorable photothermal conversion efficiency would facilitate the PNIPAM structural transformation which enables drug release. The photothermal effect of 100 µg/mL GNP was greater than that of 100 µg/mL GPPD and both were good relative to ddH
2O (
Fig. 2F). Small GNPs were readily embedded into the liposome membrane for tissue permeability and retention. The GPPD encapsulation efficiency was 48.21% and drug loading was 17.84% (Table S1). The percentage of GNPs and PNIPAM in GPPD nanoparticles analyzed by thermal gravimetric analyzer (TGA) was 9.37% and 26.58% (Fig. S2 in Supporting information). Ultraviolet–visible spectroscopy (UV–vis) measured GNP absorbance at 400–600 nm and GPPD at 800–1000 nm (
Fig. 2G). The 808 nm laser was chosen for subsequent experiments. Drug release was stimulated by laser irradiation for 5 min at 37 ℃ and also by increased temperature so that the drug could be measured in the solution (
Fig. 2H). However, liposomes failed to reach a stable drug release plateau quickly at 37 ℃
in vitro. Laser irradiation caused the tumor microenvironment to achieve a temperature that exceeded the GPPD LCST of 42 ℃ with the result that PNIPAM released the chemotherapeutic drugs. In summary, GPPD with temperature-controlled release and photothermal synergy was successfully constructed.