Gold core-labeled TiO2 nanoparticles for tracking behavior in complex matrices: synthesis, characterization, and demonstration

Titanium dioxide nanoparticles (TiO2 NPs) are increasingly entering natural systems due to their widespread production and use. It is critical that TiO2 NP behavior is studied in real-world systems, but experimental work is complicated by the high levels of background titanium present in every environmental compartment. To assist in distinguishing between engineered NPs and background titanium, labeled particles with gold nanoparticle cores and TiO2 shells (Au@TiO2 NPs) were developed and the properties and behavior compared to unlabeled TiO2 NPs. Both particle types had primary particle diameters of approximately 200 nm and were stable in solutions at ionic strengths up to 500 mM due to a polyvinylpyrrolidone surface coating. To demonstrate utility, the Au@TiO2 NPs were used in several spike-and-recovery experiments in complex matrices such as activated sludge and a river water-sunscreen mixture. Au@TiO2 NPs were accurately quantified at using instrumental neutron activation analysis and inductively coupled plasma optical emission spectrometry.