Surface-Enhanced Raman Scattering-Fluorescence Dual-Mode Nanosensors for Quantitative Detection of Cytochrome c in Living Cells

During apoptosis process, the release of cytochrome c (Cyt c) is considered to be a key factor in the intrinsic pathway and is often defined as no regression point. Quantitative detection of intracellular Cyt c remains a challenge. Herein, we have developed surface-enhanced Raman scattering (SERS)-fluorescence dual-mode nanosensors for the quantitative assay of Cyt c in living cells. Dual signal detection was achieved by constructing gold nanotriangles (AuNTs) nanosensors capable of specifically recognizing Cyt c. The nanosensors were prepared by modifying the aptamer of Cyt c on AuNTs and connecting the complementary strands modified with Cy5. The AuNTs provided both enhanced SERS signals and fluorescence quenching effects. Once cells were induced by external stimulus (such as toxins) to release Cyt c, Cyt c would specifically bind to its aptamer, and the complementary strands modified with Cy5 would detach which would result in weakened SERS signal and recovery of fluorescence signal. The experimental results showed that the nanosensors not only had excellent selectivity and sensitivity but also realized real-time monitoring of Cyt c translocation event from mitochondria to cytoplasm. The SERS and fluorescence intensity showed good linear relationship with Cyt c concentration ranging from 0.044 to 9.95 μM and achieved a minimum limit of detection (LOD) of 0.02 μM in living cells. The accuracy of intracellular Cyt c quantitative results was more than 90% compared with the ELISA results.