Measurement of engineered nanoparticles in foods - electron microscopy method development and validation

The increasing interest in use of nanotechnology by the food industry brought concerns over safety of engineered nanoparticle application in the foods and food contact materials. To aid the risk assessment in 2010 a project NanoLyse was funded by the European Union under Framework Programme 7. The project was focused on the development and validation of methods for analysing engineered nanoparticles in food matrices. The research presented in this thesis was a part of NanoLyse and was concerned with electron microscopy methods. The aim of this research was optimization of sample preparation procedures and validation of electron microscopy as an analytical technique for engineered nanoparticle measurement in foods. Thus the comparison of different sample preparation techniques was carried out for engineered nanoparticles in food matrices. Best procedures were chosen: blotting for liquid and sedimentation of the sample onto electron microscopy grid for solid food samples. These sample preparation techniques were then included in validation of electron microscopy. In view of unavailability of the reference materials electron microscopy results were compared against other analytical methods selected based on the literature review. These techniques were: nanoparticle tracking analysis, gas-phase electrophoretic mobility molecular analyser, centrifugal liquid sedimentation and asymmetric flow field flow fractionation. To render the comparison possible also for studied aggregated, non-spherical particles of synthetic amorphous silica, the concept of data transformation into mass equivalent diameter was developed. Thanks to this it was possible to note that electron microscopy tended to overestimate small particle number in size distribution due to the sample preparation. Subsequently sample preparation for electron microscopy was calibrated for the measurement of engineered nanoparticles of silica. Lastly remaining challenges and knowledge gaps in regards to the measurement of engineered nanoparticles in food were highlighted and discussed against NanoLyse project achievements.