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eous solution of Rh(III) nitrate. The desired amount of the rhodium solution was added dropwise into the titanium dioxide suspension, and heated under slightly basic conditions for three hours. The solids were then filtered and the slurry was exposed to UV radiation. “During the irradiation process, Rh cations are anchored on certain surface sites of the titanium dioxide,” and excess rhodium particles can be later washed off, FlytzaniStephanopoulos says.

a Fluorophores a

“Perhaps the most exciting aspect of this work is the discovery that the catalytically active sites are dispersed rhodium complexes, rather than rhodium nanoparticles, as many chemists might have expected,” Hermans writes. The study “therefore links homogeneous organometallic chemistry— which typically involves the reactivity of individual metal complexes—with solidphase (heterogeneous) catalysis, and illustrates the importance of understanding catalysts at the atomic scale.” Doug Main

b PNS Imaging c

b

c PNS Sensing

Fluorescent nanodiamonds detect H2O2

T

he detection and imaging of hydrogen peroxide (H2O2) in complex biological environments is very important because of the involvement of this destructive oxidant in signaling and cellular development. Cellular imbalance of H2O2 has been connected to aging and various severe diseases, including cancer, cardiovascular disorders, and Alzheimer’s. A nanosensor for the detection of H2O2 in intracellular environments has been developed by researchers at The University of Adelaide, Australia, by combining fluorescent nanodiamonds and organic fluorescent probes. The hybrid peroxynanosensor exhibits unprecedented photostability and is capable of ratiometric detection of H2O2. Carboxy peroxyfluor-1 (PF1) is an organic fluorescent probe designed to track H2O2, and is one of the two fluorescent components of the newly synthesized hybrid material, as reported in a recent issue of Scientific Reports (doi:10.1038/ s41598-017-15772-0). The probes are attached on the surface of nitrogen-vacancy (NV) nanodiamonds, which are nontoxic nanoparticles that have been engineered to contain high concentrations of NV centers. These NV centers are fluorescent point defects consisting of a nitrogen atom (which substitutes a carbon in the lattice) and an adjacent lattice vacancy. Upon binding to H2O2, carboxyPF1 increases the intensity of its green

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(a) Structures of organic fluorophores PF1 and carboxy-PF1. (b) Scheme of peroxynanosensor (PNS) imaging. The nanodiamond is excited at 550 nm and emits stable fluorescence around 700 nm enabling long-term imaging. (c) Scheme of H2O2 sensing by PNS. The surface bound fluorophores (carboxyPF1) are excited at 490 nm. In the absence of H2O2 it is mostly nonfluorescent and becomes highly fluorescent (520 nm) upon exposure to H2O2. Credit: Malcolm Purdey.

fluorescence emission. But like other organic fluorescent probes that are often used to identify biomolecules and indicate their position under the light of a fluorescence microscope, carboxy-PF1 suffers from