Selective and Sensitive Detection of Intracellular O2•- Using Au NPs/Cytochrome c as SERS Nanosensors

A novel surface-enhanced Raman scattering (SERS) nanosensor was developed by modifying oxidized cytochrome c (Cyt c) on gold nanoparticles (Au NPs) for the sensitive and selective determination of intracellular superoxide anion radical (O-2(center dot-)). On the basis of the differences in the SERS spectra between the oxidized and reduced form of Cyt c, this nanosensor could be employed to investigate O-2(center dot-) concentration by measuring the SERS spectra of the reduced Cyt c. Using this SERS nanosensor, a detection limit of 1.0 X 10(-8) M for O-2(center dot-) could be attained. Additionally, the selectivity of the SERS nanosensor for O-2(center dot-) was examined, showing that other reactive oxygen species (ROS) and biologically relevant species did not influence the detection of O-2(center dot-). More importantly, the nanosensor could be delivered to the living HeLa and normal human liver cells and permitted the concentration of O-2(center dot-) to be monitored in real time and in a noninvasive manner, which indicates that this nanosensor will be suitable for the qualitative and quantitative analysis of O-2(center dot-) in biosystems, thus leading to a greater understanding of oxidative-stress-related diseases at a cellular level.