Abstract
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.
Highlights
Investigations of the fate of nanoparticles in biological systems and environmental matrices frequently encounter the challenge to detect the applied nanoparticles on a chemically identical natural background (Gibson et al 2011) and in very low concentrations in experimental settings mimicking realistically low exposure scenarios
Radiolabelled nanoparticles have been applied in in vitro (e.g. Marmorato et al 2011; Simonelli et al 2011; Ponti et al 2009) and in in vivo toxicological (e.g. Schleh et al 2013; Kreyling et al 2017a, b, c; Xie et al 2010; Zhang et al 2009) and environmental studies (e.g. Kleiven et al 2018; Chekli et al 2016; Vitorge et al 2014; Coutris et al 2012; Oughton et al 2008) where they demonstrated the advantage of very high detection sensitivity and easy quantification, usually without special specimen preparation procedures (Bello and Warheit 2017; Llop et al 2013; Weiss and Diabate 2011)
The washing was carried on until the 44Ti activity determined in the filtrate was well below 1 Bq, in order to start the leaching experiments on a lower background of free 44Ti in the stock suspension
Summary
Investigations of the fate of nanoparticles in biological systems and environmental matrices frequently encounter the challenge to detect the applied nanoparticles on a chemically identical natural background (Gibson et al 2011) and in very low concentrations in experimental settings mimicking realistically low exposure scenarios. It is a drawback of many investigations that they compensate for insufficient detection sensitivity by unrealistically high dosage or exposure The effects of the radiolabelling technique on the properties of the industrial manufactured nanoparticles have to be addressed appropriately In such tracer experiments, the distribution and quantification of the radiolabelled nanoparticles is determined on the basis of the radiation emitted by the radiolabel. This implies that the integrity of the radiolabel-nanoparticle construct has to be ensured at least over the envisaged duration of the experiments
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