Feasibility study on the differentiation between engineered and natural nanoparticles based on the elemental ratios

To understand the fate and exposure of engineered nanoparticles (ENPs) to environmental media, it is important to identify ENPs in the natural occurring nanoparticles (NNPs). Although nanomaterials have unique physical properties such as uniform particle size, hierarchical nanostructure, well-defined crystalline structure, and high surface area, compared to bulk materials, these properties are not suitable references to differentiate between ENPs and NNPs. Therefore, the identification and quantification of ENPs pose a big challenge to analysis. Herein, we did a feasibility study to distinguish between ENPs and NNPs based on the elemental ratio of target elements (Ti and Zn) to background elements (Fe and Al). Morphologies, particle size, and elemental analysis for 12 NNPs, 4 ENPs, and 3 NPs contained in consumer products were conducted. NPs were extracted from raw materials via density gradient ultracentrifugation and alkaline digestion. In a logarithm plot for the elemental ratio of {Ti+Zn} to {Ti/Zn}/{Fe+Al} and ternary plot of {Ti+Zn}, Fe, and Al ions for all samples, ENPs have a distinct contrast with NNPs. Therefore, it is expected that the suggested analysis for elemental ratio could be a preliminary screening tool to differentiate between ENPs and NNPs.