New sampling technique for collection of nanoparticles from liquids

Transmission electron microscopy (TEM) is the only technique which can give accurate information on the individual size, shape and composition of NPs. However, in dilute forms it is difficult to collect a sufficient number of NPs on an electron microscope grid for TEM analysis without some means of concentrating the dispersion of NPs. This study introduces a novel TEM sampling technique which overcomes this shortcoming and allows for both the natural and engineered NPs in dilute dispersions as found in waste and contaminated waters to be selectively sampled, based on their electrical charge. The technique is based on the use of carefully functionalized collector surfaces built by using the layer-by-layer assembly of polyelectrolytes on TEM grids. The layers are electrically charged and the top layer will attract and retain oppositely charged sampled NPs from aqueous solutions. The ability of the collector to attract both single particles and particle aggregates on the top polyelectrolyte layer collected from dilute aqueous dispersions after a short sampling time is demonstrated from the TEM images. The nature of the particles attracted to the collector can be identified from the TEM images, their diffraction pattern and the EDX spectrum. A large variety of equipment is nowadays being used worldwide for the detection and characterization of nanoparticles (NPs) dispersed in aqueous environmental liquids. To take advantage of these advanced analytical tools there is an increased need for the development of sampling technologies capable of collecting nanoparticle samples directly on suitable substrates (TEM grids or filters).