Folic acid-conjugated gold nanorod@polypyrrole@Fe3O4 nanocomposites for targeted MR/CT/PA multimodal imaging and chemo-photothermal therapy

Abstract

Integrating multimodal bioimaging and different therapies into one nanoplatform is a promising strategy for biomedical applications, but remains a great challenge. Herein, we have synthesized a biocompatible folic acid (FA) functionalized gold nanorod@polypyrrole@Fe₃O₄ (GNR@PPy@Fe₃O₄-FA) nanocomposite through a facile method. The conjugated FA has endowed the nanocomposite with the ability to recognize targeted cancer cells. Importantly, the nanocomposite has been successfully utilized for magnetic resonance (MR), computed tomography (CT) and photoacoustic (PA) multimodal imaging. Moreover, the GNR@PPy@Fe₃O₄-DOX nanocomposite shows pH-responsive chemotherapy and enables the integration of photothermal therapy and chemotherapy to achieve superior antitumor efficacy. The GNR@PPy@Fe₃O₄-DOX nanocomposites have a drug release of 23.64%, and the photothermal efficiency of the GNR@PPy@Fe₃O₄ nanocomposites reaches 51.46%. Cell viability decreases to 15.83% and 16.47% because of the combination of chemo-photothermal therapy effects. Moreover, the GNR@PPy@Fe₃O₄-DOX-FA nanocomposite could target cancer cells via folic acid and under a magnetic field. The in vivo multimodal imaging and chemo-photothermal therapy effects showed that the GNR@PPy@Fe₃O₄-DOX-FA nanocomposites are a good contrast and theranostic agent. Thus, this multifunctional nanocomposite could be a promising theranostic platform for cancer diagnosis and therapy.

Fig. 1. Schematic illustration of synthetic route and chemo-photothermal therapy for GNR@PPy@Fe₃O₄-DOX-FA nanocomposites.

Fig. 2. TEM images of (A) GNRs, (B) GNR@PPy nanoparticles, and (C) GNR@PPy@Fe₃O₄ nanocomposites.

Fig. 3. (A) UV-Vis-NIR absorption spectra of GNRs (a), GNR@PPy (b), GNR@PPy@Fe₃O₄ (c), GNR@PPy@Fe₃O₄-DOX (d), GNR@PPy@Fe₃O₄-DOX-FA (e), DOX (f) and FA (g) nanocomposites, where the concentrations of these nanocomposites were about 40 μg mL⁻¹; (B) the FTIR spectra of the prepared GNR@PPy (a), GNR@PPy@Fe₃O₄ (b), GNR@PPy@Fe₃O₄-DOX (c) and GNR@PPy@Fe₃O₄-DOX-FA (d) nanocomposites. The inset shows the characteristic peaks of GNR@PPy@Fe₃O₄-DOX-FA nanocomposites at 1646 cm⁻¹, 1606 cm⁻¹ and 1574 cm⁻¹. Inset is the spectrum in the wavenumber range of 1550–1660 cm⁻¹.

Fig. 4. DOX release profile of GNR@PPy@Fe₃O₄-DOX nanocomposites at different pH values.

Fig. 5. Photothermal effect of GNR@PPy@Fe₃O₄ nanocomposites. (A) Photothermal heating curves of GNR@PPy@Fe₃O₄ nanocomposites with different concentrations exposed to 808 nm laser irradiation for 10 min at a power of 2 W; (B) photothermal characteristics of 25 μg mL⁻¹ GNR@PPy@Fe₃O₄ nanocomposites under 808 nm laser irradiation at various powers for 10 min.

Fig. 6. (A) The temperature change curve of GNR@PPy@Fe₃O₄ aqueous solutions under 808 nm laser irradiation for 10 min; (B) the corresponding linear fitting of the irradiation time obtained from the cooling phase and −ln (θ); (C) evaluation of photothermal stability of GNR@PPy@Fe₃O₄ nanocomposites at a concentration of 25 μg mL⁻¹ through five cycles of an on-and-off laser.

Fig. 7. CLSM images of HepG2 cells incubated with 200 μg mL⁻¹ GNR@PPy@Fe₃O₄-DOX and GNR@PPy@Fe₃O₄-DOX-FA nanocomposites for 4 h with or without an external magnetic field. Scale bar: 20 μm.

Fig. 8. CLSM images of HepG2 cells incubated with 300 μg mL⁻¹ GNR@PPy@Fe₃O₄-DOX-FA nanocomposites for 1, 4, 6 and 8 h. Scale bar: 50 μm.

Fig. 9. Cell viabilities of HepG2 (A) and SMMC-7721 (C) cells treated with different concentrations of GNR@PPy@Fe₃O₄ and GNR@PPy@Fe₃O₄-FA nanocomposites. Viabilities of HepG2 (B) and SMMC-7721 (D) cells after incubation with different concentrations of GNR@PPy@Fe₃O₄-FA and GNR@PPy@Fe₃O₄-DOX-FA nanocomposites with or without 808 nm laser irradiation. The p values were calculated using multiple t tests (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).

Fig. 10. (A) CT images of GNR@PPy@Fe₃O₄-FA nanocomposites with different Au concentrations and their CT values (HU) as a function of Au concentration. (B) T₂-weighted MRI photographs of GNR@PPy@Fe₃O₄-FA nanocomposites dispersed in water with different Fe concentrations and the transverse relaxation rate (1/T₂) as a function of Fe concentration (C) PA images and corresponding PA intensity of GNR@PPy@Fe₃O₄-FA nanocomposites of different concentrations. The PA signal values at different concentrations were obtained by using an 808 nm laser.

Fig. 11. In vivo CT images (A), MR images (B) and PA images (C) of GNR@PPy@Fe₃O₄-FA nanocomposites before and 24 h after injection.

Fig. 12. (A) Tumor growth curves of different groups after various treatments. The p values were calculated using multiple t tests (*p < 0.05, **p < 0.01). (B) Body weights of mice in different treatment groups; (C) representative photographs of different groups of mice on days 0 and 13 after various treatments.