44 Ti diffusion labelling of commercially available, engineered TiO2 and SiO2 nanoparticles

In realistic exposure scenarios, the detection and quantification of engineered nanoparticles in complex environmental or biological matrixes is a challenge since nanoparticle concentrations are frequently low and have to be discerned from a background that may contain the same elements in various chemical forms in much higher concentrations. The use of radiolabelled nanoparticles may overcome these difficulties offering high detection sensitivity without the necessity of complex sample preparation procedures. However, the labelling procedure must not alter the physicochemical and biological properties of the nanoparticles. In the present work, the radiolabelling of three different types of TiO2 nanoparticles with primary particle sizes between 5 nm and 26 nm with commercially available 44Ti has been investigated applying a simple diffusion heat treatment at 180 °C for 2.5 h on nanoparticles impregnated with a solution containing the 44Ti radiolabel. The same treatment has been investigated to radiolabel amorphous SiO2 nanoparticles with 44Ti. The radiolabels are stably integrated in the nanoparticle matrix, and the release is less than 0.1% in aqueous suspension at neutral pH for at least 4 weeks. The method appears to be fast and reliable. By transmission electron microscopy, dynamic light scattering and ζ-potential measurements, only minor alterations of the nanoparticle size could be detected in the range of 1 to 2 nm.