Fluorescence imaging of Cys in keratinocytes upon UVB exposure using phenyl doped graphitic carbon nitride Nanosheets-Au nanoparticles nanocomposite.

Ultraviolet B (UVB) irradiation induces the generation of reactive oxygen species (ROS) and causes damages to human skin. The depletion of glutathione (GSH) to scavenge ROS can protect skin cells from oxidative damage. However, little is known about the concentration level changes of cysteine (Cys), a precursor of GSH in skin cells after exposure to UVB irradiation. Herein, phenyl doped graphitic carbon nitride nanosheets-Au nanoparticles nanocomposite was prepared by in situ deposition of Au nanoparticles on the surface of phenyl doped graphitic carbon nitride nanosheets and showed a turn-on fluorescence response toward Cys over homocysteine, glutathione under physiological conditions. In the presence of Cys, remarkable enhancement of green fluorescence was observed. This nanocomposite was successfully applied for fluorescence imaging of Cys in human skin epidermal cells and monitoring the changes of Cys concentration level under the oxidative stress upon exposure to UVB irradiation in keratinocytes. It was found that the concentration of Cys was increased in the initial period after exposure to UVB irradiation and then gradually decreased to the normal level for the synthesis of GSH to defense the oxidative stress. Our result helps to understand the physiological function of Cys in human skin cells under UVB exposure.