Figure 17. Optimization of graphene-based photothermal agents. (a) AFM images of different graphene derivatives: while nGO-PEG and nRGO-PEG showed similar ultrasmall sizes at about 20−30 nm, the size of RGO-PEG was about 60−70 nm. Insets are photos of the respective solutions. RGO-PEG and nRGO-PEG showed much enhanced optical absorbance as compared to nGO-PEG. (b) The blood circulation of GO derivatives measured by collecting blood from mice iv injected with 125 I labeled nGO-PEG, nRGO-PEG, and RGO-PEG at various time points (n = 3). (c) The biodistribution of GO derivatives in 4T1 tumor-bearing mice 2 days after injection. The radioactivities in tissue and blood samples were determined by a gamma counter. (d) The 4T1 tumor growth curves of mice after various treatments indicated. The laser irradiation was conducted at the power density of 0.15 W/cm 2 for 5 min. (e) Survival of tumor-bearing mice after various treatments indicated. Reprinted with permission from ref 169.

Owing to their unique physical and chemical properties, graphene and its derivatives such as graphene oxide (GO), reduced graphene oxide (RGO) and GO-nanocomposites have attracted tremendous interest in many different fields including biomedicine in recent years. With every atom exposed on its surface, single-layered graphene shows ultra-high surface area available for efficient molecular loading and bioconjugation, and has been widely explored as novel nano-carriers for drug and gene delivery. Utilizing the intrinsic near-infrared (NIR) optical absorbance, in vivo graphene-based photothermal therapy has been realized, achieving excellent anti-tumor therapeutic efficacy in animal experiments. A variety of inorganic nanoparticles can be grown on the surface of nano-graphene, obtaining functional graphene-based nanocomposites with interesting optical and magnetic properties useful for multi-modal imaging and imaging-guided cancer therapy. Moreover, significant efforts have also been devoted to study the behaviors and toxicology of functionalized nano-graphene in animals. It has been uncovered that both surface chemistry and sizes play key roles in controlling the biodistribution, excretion, and toxicity of nano-graphene. Biocompatibly coated nano-graphene with ultra-small sizes can be cleared out from body after systemic administration, without rendering noticeable toxicity to the treated mice. In this review article, we will summarize the latest progress in this rapidly growing field, and discuss future prospects and challenges of using graphene-based materials for theranostic applications.

MoS2 nanosheets functionalized with poly-ethylene glycol are for the first time used as a multifunctional drug delivery system with high drug loading capacities. Using doxorubicin as the model drug and taking advantages of the strong near-infrared absorbance of MoS2, combined photothermal and chemotherapy of cancer is realized in animal experiments, achieving excellent synergistic anti-tumor effect upon systemic administration.

Graphene with unique physical and chemical properties has shown various potential applications in biomedicine. In this work, a photosensitizer molecule, Chlorin e6 (Ce6), is loaded on polyethylene glycol (PEG)-functionalized graphene oxide (GO) via supramolecular π-π stacking. The obtained GO-PEG-Ce6 complex shows excellent water solubility and is able to generate cytotoxic singlet oxygen under light excitation for photodynamic therapy (PDT). Owing to the significantly enhanced intracellular trafficking of photosensitizers, our GO-PEG-Ce6 complex offers a remarkably improved cancer cell photodynamic destruction effect compared to free Ce6. More importantly, we show that the photothermal effect of graphene can be utilized to promote the delivery of Ce6 molecules by mild local heating when exposed to a near-infrared laser at a low power density, further enhancing the PDT efficacy against cancer cells. Our work highlights the promise of using graphene for potential multifunctional cancer therapies.

In the original manuscript, the concentration reported in the caption of Figure 1h was incorrect. Rather than the concentration of 100 µM quoted, the concentration of H 2 O 2 used was 1 mM. The analysis and conclusions of the article are not affected. The caption should thus read: "h) Oxygen generation in H 2 O 2 solutions (1 × 10 −3 M) with HMCP added under different pH values (7.4 and 6.5). The decrease of oxygen concentration in the system for the sample under pH 7.4 (after ≈150 s) was due to rapid consumption of H 2 O 2 .