Single europium-doped nanoparticles measure temporal pattern of reactive oxygen species production inside cells

Low concentrations of reactive oxygen species, notably hydrogen peroxide (H 2 O 2), mediate various signalling processes in the cell. Production of these signals is highly regulated and a suitable probe is needed to measure these events. Here, we show that a probe based on a single nanoparticle can quantitatively measure transient H 2 O 2 generation in living cells. The Y 0.6 Eu 0.4 VO 4 nanoparticles undergo photoreduction under laser irradiation but re-oxidize in the presence of oxidants, leading to a recovery in luminescence. Our probe can be regenerated and reliably detects intracellular H 2 O 2 with a 30-s temporal resolution and a dynamic range of 1-45νM. The differences in the timing of intracellular H 2 O 2 production triggered by different signals were also measured using these nanoparticles. Although the probe is not selective towards H 2 O 2, in many signalling processes H 2 O 2 is, however, the dominant oxidant. In conjunction with appropriate controls, this probe is a powerful tool for unravelling pathways that involve reactive oxygen species.