RESUMO
Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.
Assuntos
Raios gama , Grafite/química , Luminescência , Fotoquimioterapia/métodos , Pontos Quânticos/química , Espectroscopia de Ressonância de Spin Eletrônica , Microscopia de Força Atômica , Tamanho da Partícula , Fármacos Fotossensibilizantes/farmacologia , Oxigênio Singlete/química , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
The excellent photoluminescent properties of graphene quantum dots (GQD) makes them suitable candidates for biomedical applications, but their cytotoxicity has not been extensively studied. Here we show that electrochemically produced GQD irradiated with blue light (470 nm, 1W) generate reactive oxygen species, including singlet oxygen, and kill U251 human glioma cells by causing oxidative stress. The cell death induced by photoexcited GQD displayed morphological and/or biochemical characteristics of both apoptosis (phosphatidylserine externalization, caspase activation, DNA fragmentation) and autophagy (formation of autophagic vesicles, LC3-I/LC3-II conversion, degradation of autophagic target p62). Moreover, a genetic inactivation of autophagy-essential LC3B protein partly abrogated the photodynamic cytotoxicity of GQD. These data indicate potential usefulness of GQD in photodynamic therapy, but also raise concerns about their possible toxicity.
Assuntos
Grafite/química , Fármacos Fotossensibilizantes/farmacologia , Pontos Quânticos , Apoptose , Autofagia , Caspases/metabolismo , Linhagem Celular Tumoral , Sobrevivência Celular , Fragmentação do DNA , Relação Dose-Resposta a Droga , Eletroquímica/métodos , Ativação Enzimática , Citometria de Fluxo/métodos , Humanos , Luminescência , Microscopia Eletrônica de Transmissão/métodos , Estresse Oxidativo , Oxigênio/química , Interferência de RNA , Fatores de TempoRESUMO
The present study compared the photothermal anticancer activity of near-infrared (NIR)-excited graphene nanoparticles and carbon nanotubes (CNT). Despite lower NIR-absorbing capacity, suspension of polyvinylpyrrolidone-coated graphene sheets exposed to NIR radiation (808 nm, 2 W/cm(2)) generated more heat than DNA or sodium dodecylbenzenesulfonate-solubilized single-wall CNT under the same conditions. Accordingly, graphene nanoparticles performed significantly better than CNT in inducing photothermal death of U251 human glioma cells in vitro. The superior photothermal sensitivity of graphene sheets could be largely explained by their better dispersivity, which has been supported by a simple calculation taking into account thermodynamic, optical and geometrical properties of the two type of carbon nanoparticles. The mechanisms of graphene-mediated photothermal killing of cancer cells apparently involved oxidative stress and mitochondrial membrane depolarization resulting in mixed apoptotic and necrotic cell death characterized by caspase activation/DNA fragmentation and cell membrane damage, respectively.