Cytochrome c (Cyt c) release and cellular pH change are two important mediators of apoptosis. Effective methods to regulate or monitor such two events are therefore highly desired for apoptosis research and cancer cell therapy. Herein, we exploited electrostimulation to regulate cellular Cyt c release and apoptosis process, and by designing and preparing a smart and efficient plasmonic nanorobot (with surface-modified Cyt c-specific aptamer and 4mercaptobenzoic acid) that is capable of Cyt c capture and self-sensing, we achieved real-time SERS monitoring of dynamic Cyt c release and simultaneous cell acidification in apoptosis during electrostimulation. Distinctly different molecular stress responses in the two events for cancerous MCF-7 and HeLa cells and normal L929 cells were identified and revealed. The method and results are valuable and promising for apoptosis and Cyt c-mediated biology studies.

Metallic plasmonic nanoparticles have been intensively exploited as theranostic nanoprobes for plasmonic photothermal therapy (PPT) and surface-enhanced Raman spectroscopy (SERS) applications. But the underlying molecular mechanisms associated with PPT-induced apoptosis between cancerous and normal cells have remained largely unknown or disputed. In this study, we designed an organelle-targeting theranostic plasmonic SERS nanoprobe (CDs−Ag/Au NS) composed of porous Ag/Au nanoshell (p-Ag/Au NSs) and carbon dots (CDs) for nucleus and mitochondria targeted PPT of cells. The differences in molecular stress response in the PPT-induced hyperthermia cell death between cancerous HeLa and normal L929 and H8 cells have been revealed by site-specific single-cell SERS detection. The contents of tryptophan (Trp), phenylalanine (Phe), and tyrosine (Tyr) in HeLa cells were found more evidently increased than L929 and H8 cells during the PPT-induced celldeath process. And from the mitochondria point of view, we found that the PPT-induced cell apoptosis for HeLa cells mainly stems from (or is regulated through) cellular thermal stress-responsive proteins, while for L929 and H8 cells it seems more related to DNA. Understanding molecular stress response difference of the PPT-induced cell apoptosis between cancerous and normal cells is helpful for diagnosis and treatment of cancer, and the method will open an avenue for single-cell studies.