Quantification of nanoparticles in aqueous food matrices using Particle-Induced X-ray Emission

Nanoparticles (NPs) of SiO2 (15 nm) or Ag (20 - 40 nm) were dispersed in water, coffee and milk at several aqueous dilutions. The NPs dispersions concentrations were quantified with an ion beam technique: Particle-Induced X-ray Emission. Additional measurements in relation to the state of the NPs dispersions were done: particle size distribution by centrifuge liquid sedimentation and the extreme surface composition by X-ray photoelectron spectroscopy. The particle size distribution of SiO2 and Ag NPs dispersions in water and Ag NPs in coffee remained mostly as primary particles with hydrodynamic diameters close to the reported pristine NPs diameter. SiO2 NPs agglomerated in coffee. In milk, both NPs presented an adsorption with milk lipids. Extreme surface composition corroborated adsorption in milk and showed that SiO2 agglomerates adsorb some coffee components. A linear tendency in the measurement of the concentration dilutions of all dispersions was measured, and a lack of media influence in the slope of each curve was found. Limits of detection with the current setup were estimated at 0.5 and 0.3 mg/ml for SiO2 and Ag NPs, respectively.