Аннотация
Atomic force microscopy (AFM) was used to image and quantify natural nanoparticles (prefiltered < 25Â nm) from three different freshwater sites (Vale Lake, Bailey Brook and Tern Rivers). Four fractions were analysed by AFM; the prefiltered fraction (< 25Â nm) and three fractions collected after separation of this prefiltered sample by flow field-flow fractionation (FlFFF) which corresponds to material which has size ranges of < 4.2Â nm, 4.2â15.8Â nm and 15.8â32.4Â nm, as determined by FlFFF theory. The large majority of materials in all samples appeared as < 3Â nm nanoparticles, nearly spherical and rich in chromophores active at 254Â nm UV, which thus correspond to natural organic matter. However, nanoparticles were also imaged up to slightly more than 25Â nm in size, indicating a slight disagreement in sizing between filtration and FlFFF. In addition, some particles in certain fractions were found to be covered with a thin film of less than 0.5â1.0Â nm. Substantial differences between sites were observed.
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