Dual-enhanced photothermal conversion properties of reduced graphene oxide-coated gold superparticles for light-triggered acoustic and thermal theranostics

Abstract

A rational design of highly efficient photothermal agents that possess excellent light-to-heat conversion properties is a fascinating topic in nanotheranostics. Herein, we present a facile route to fabricate size-tunable reduced graphene oxide (rGO)-coated gold superparticles (rGO-GSPs) and demonstrate their dual-enhanced photothermal conversion properties for photoacoustic imaging and photothermal therapy. For the first time, graphene oxide (GO) was directly used as an emulsifying agent for the preparation of gold superparticles (GSPs) with near-infrared absorption by the emulsion method. Moreover, GO spontaneously deposited on the surface of GSPs could also act as the precursor of the rGO shell. Importantly, both the plasmonic coupling of the self-assembled gold nanoparticles and the interaction between GSPs and rGO endow rGO-GSPs with enhanced photothermal conversion properties, allowing rGO-GSPs to be used for sensitive photoacoustic detection and efficient photothermal ablation of tumours in vivo. This study provides a facile approach to prepare colloidal superparticles-graphene hybrid nanostructures and will pave the way toward the design and optimization of photothermal nanomaterials with improved properties for theranostic applications.

Fig. 1

(a) TEM image of oleylamine/oleic acid-capped GNPs. (b) Atomic force microscopy (AFM) image (b₁) and the corresponding height image of GO (b₂). (c) TEM images of 60 nm (c₁, c₂), 90 nm (c₃, c₄), and 130 nm (c₅, c₆) GO-GSPs at low (c₁, c₃, c₅) and high (c₂, c₄, c₆) magnifications. The red arrows point to the GO shell. (d) UV-vis spectra of hydrophobic GNPs in chloroform and differently sized GO-GSPs in water. (e) TEM image of 90 nm rGO-GSPs. The red arrows point to the rGO shell.

Fig. 2

(a) Temperature elevation of aqueous dispersions of different gold-based nanomaterials (OD₈₀₈ = 1.0) exposed to an 808 nm laser (1 W cm⁻²) as a function of irradiation time. The samples were irradiated for 5 min, and then the laser was turned off. (b) Infrared thermal images and (c) corresponding photothermal heating curves of the aqueous rGO-GSP solution (OD₈₀₈ = 1.0) under 808 nm laser irradiation at different power densities. (d) PA signals of rGO-GSPs, mixture of GSPs and rGO, GSPs, and GNRs as a function of OD₈₀₈. (e) PA images of rGO-GSPs and the mixture of GSPs and rGO at different OD₈₀₈ values.

Fig. 3

(a) Fluorescence images of calcein AM (green, live cells) and PI (red, dead cells) co-stained U87MG cells after 4 h of incubation with 100 μg mL⁻¹ PEG-rGO-GSPs and 5 min of exposure to an 808 nm laser at different power densities. (b) Cell viability of U87MG cells treated with 100 μg mL⁻¹ PEG-rGO-GSPs and laser irradiation at different power densities. (c) Cell viability of U87MG, MDA-MB-435, and PC-3 cells after incubation with increased concentrations of PEG-rGO-GSPs for 24 h.

Fig. 4

(a) In vivo PA images: (a₁) 2D ultrasonic (US) and PA images of tumour at pre-injection and 24 h post-injection of PEG-rGO-GSPs, and (a₂) 3D images of tumour at 0, 4 or 24 h post-injection of PEG-rGO-GSPs. (b) PA intensities of tumour tissue at different time points after intravenous injection of PEG-rGO-GSPs or PBS as control.

Fig. 5

In vivo PTT. (a) Infrared thermal images of U87MG tumour-bearing mice exposed to an 808 nm laser for 5 min at 24 h post-injection of PBS or PEG-rGO-GSPs. (b) Tumour growth curves, (c) survival curves, and (d) representative photos of different groups of mice after various treatments. (e) Images of H&E-stained tumour sections collected from different groups of mice immediately after laser irradiation.

Scheme 1

(a) Schematic illustration of the formation of PEG-rGO-GSPs through an emulsion-based self-assembly method that exploits GO as the emulsifying agent and the precursor of rGO. (b) NIR light-triggered acoustic and thermal theranostics based on PEG-rGO-GSPs with dual-enhanced photothermal conversion properties arising from the plasmonic coupling of adjacent GNPs and the interaction of GSPs with rGO.