Tuning photothermal properties of gold nanodendrites for in vivo cancer therapy within a wide near infrared range by simply controlling their degree of branching

Abstract

Although dendritic nanoparticles have been prepared by many different methods, control over their degree of branching (DB) is still impossible, preventing us from understanding the effect of the DB on the properties of the nanodendrites as cancer therapeutics. Herein, we developed a novel seed-mediated method to prepare gold nanodendrites (AuNDs) in an organic solvent using long chain amines as a structural directing agent. We discovered that the DB could be tuned facilely by simply adjusting synthetic parameters, such as the solvent type, the type and concentration of the long chain amines. We found that DB tuning resulted in dramatic tunability in the optical properties in the near infrared (NIR) range, which led to significantly different performance in the photothermal cancer therapy. Our in vitro and in vivo studies revealed that AuNDs with a higher DB were more efficient in photothermal tumor destruction under a lower wavelength NIR irradiation. In contrast, those with a lower DB performed better in tumor destruction under a higher wavelength NIR irradiation, indicating that AuNDs of even lower DB should have even better photothermal cancer therapy efficiency within the second NIR window. Thus, the tunable optical properties of AuNDs in the NIR range allow us to selectively determine a suitable laser wavelength for the best cancer therapeutic performance.

Keywords: Cancer therapy; Degree of branching; Gold; Nanodendrites.

Fig. 1

TEM images of AuNPs synthesized in the ethanolic solution of amines of different carbon chain lengths: (a) butylamine, (b) octylamine, (c) dodecylamine, (d) hexadecylamine, (e) octadecylamine and (f) oleylamine. Dendritic structures can be seen unambiguously in amines with longer chains (c–f). Scale bar: 50 nm, which is applied to all images.

Fig. 2

Control over the AuND size can be realized by adjusting the stoichiometry of the seeds and HAuCl₄. In the figure, the concentration of HAuCl₄ was kept constant. The amount of seeds used was 16 × 10¹¹, 4 × 10¹¹, 2 × 10¹¹, and 0.5 × 10¹¹ particles per ml (a–d), respectively. Scale bar: 40 nm, which is applied to all images.

Fig. 3

TEM images of the AuNDs of high (a), medium (b) and low (c) degree of branching for the photothermal studies. The AuNDs were synthesized in (a) 0.1 M of hexadecylamine in ethanol, (b) 0.4 M of oleylamine in chloroform and (c) 1.0 M of oleylamine in chloroform, under the same amount of seeds and HAuCl₄. The average diameter of branches is 7.0 ± 0.5 nm, 6.7 ± 0.2 nm, and 6.7 ± 0.4 nm in a, b and c, respectively. Scale bar: 100 nm, which is applied to all images.

Fig. 4

Dependence of optical and photothermal properties of AuNDs on DB. (a) Extinction spectra; (b) Molar extinction coefficient of AuNDs at 808, 980 and 1064 nm; (c) Temperature profiles of aqueous AuNDs solutions irradiated by 808 and 980 nm laser, both with a power density of 1.0 W/cm², for 5 min; (d) In vitro study of cell viability after irradiation of 808 and 980 nm laser of different power densities. H, M, and L are corresponding to AuNDs of high, medium and low DB respectively. H-100, H-50 and H-25 in c mean 100, 50 and 25 µg/ml AuNDs of high DB, respectively, and so as other symbols with the prefix M and L.

Fig. 5

In vivo photothermal treatment of MCF-7 tumors by using AuNDs of different DB. (a, b), Posttreatment tracking of tumor volume in groups treated by 808 nm and 980 nm laser, respectively; (c) Photographs of a typical mouse in each group on day 1 and day 12 posttreatment; (d) Real-time tracking of temperature increase inside tumors during the photothermal treatment by an infrared camera.