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

Low concentrations of reactive oxygen species, notably hydrogen peroxide (H2O2), mediate various signalling processes in the cell(1,2). Production of these signals is highly regulated(3) 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 H2O2 generation in living cells. The Y0.6Eu0.4VO4 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 H2O2 with a 30-s temporal resolution and a dynamic range of 1-45 mu M. The differences in the timing of intracellular H2O2 production triggered by different signals were also measured using these nanoparticles. Although the probe is not selective towards H2O2, in many signalling processes H2O2 is, however, the dominant oxidant(3-6). In conjunction with appropriate controls, this probe is a powerful tool for unravelling pathways that involve reactive oxygen species.