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 (O2•–). 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 O2•– concentration by measuring the SERS spectra of the reduced Cyt c. Using this SERS nanosensor, a detection limit of 1.0 × 10–8 M for O2•– could be attained. Additionally, the selectivity of the SERS nanosensor for O2•– was examined, showing that other reactive oxygen species (ROS) and biologically relevant species did not influence the detection of O2•–. More importantly, the nanosensor could be delivered to the living HeLa and normal human liver cells and permitted the concentration of O2•– 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 O2•– in biosystems, thus leading to a greater understanding of oxidative-stress-related diseases at a cellular level.