In situ SERS monitoring of intracellular H 2 O 2 in single living cells based on label-free bifunctional Fe 3 O 4 @Ag nanoparticles.

Visualization of signaling molecules in single living cells is crucial for understanding cellular metabolism and physiology, which can provide valuable insights into early diagnoses and treatments of diseases. Highly sensitive in situ monitoring of intracellular analytes released from single living cells by virtue of label-free nanosensors is urgently needed, which can avoid interferences from molecular labeling. Here, we proposed an ultrasensitive strategy for in situ imaging of intracellular H 2 O 2 in single living cancer cells by surface-enhanced Raman scattering (SERS) spectroscopy with the utilization of label-free Fe 3 O 4 @Ag core-satellite nanoparticles (NPs). The Fe 3 O 4 @Ag NPs can efficiently and selectively catalyze the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . Additionally, they exhibit excellent SERS activity that allows for in situ monitoring of intracellular H 2 O 2 in living cells through establishing the correlation between the H 2 O 2 level and the SERS intensity of the catalytic oxidation product of TMB. The H 2 O 2 concentration is revealed through the SERS intensity of oxidized TMB with a good linear response in a wide range from 1 fM to 1 mM. Moreover, the intracellular H 2 O 2 level in live cancer cells and imaging of the distribution of H 2 O 2 inside single cells can be achieved by using such a label-free nanosensor based strategy. Our work demonstrates that the label-free Fe 3 O 4 @Ag NP-based SERS imaging and quantification strategy is a promising and powerful approach to assess intracellular H 2 O 2 in living cells and allows us to monitor single-cell signaling molecules with nanoscale resolution.