Two-photon excited fluorescent silica nanoparticles loaded with iron(II) as a probe for determination and imaging of hydrogen peroxide in living cells.

A method is described for determination and optical imaging of hydrogen peroxide (H2O2) by using the two-photon (TP) excited fluorescence of silica (SiO2) nanoparticles containing Fe(II) ions. In the presence of H2O2, hydroxyl radicals (•OH) are produced via the Fenton reaction. This leads to quenching of the green fluorescence of a TP-excitable organic dye loaded into the SiO2NPs. Fluorescence is excited at 370 nm and has an emission peaking at 447 nm. The degree of quenching increases linearly in the 2.5 to 100 μM H2O2 concentration range. The nanoprobe is highly selective and sensitive, with a detection limit of 336 nM. The nanoprobe is biocompatible and was successfully used to image changes in the H2O2 concentration in HeLa cells via TP fluorescence imaging. Graphical abstractSchematic rpresentation of the detection of H2O2 by using the two-photon excited fluorescence of silica nanoparticles (TP-SiO2NPs) containing Fe2+. H2O2 triggers the Fenton reaction to produce hydroxyl radicals (•OH), which quench the green fluorescence of the SiO2NPs.