Measurements of nanoparticle number concentrations and size distributions in contrasting aquatic environments using nanoparticle tracking analysis

Environmental context. Manufactured and unintentionally produced nanoparticles have been of environmental concern owing to potential harm to humans and ecosystems, but very little is known of the actual concentrations of these owing to limitations of available methods. In order to understand both the potential adverse effects and the underlying natural processes, improved measurement techniques are needed. Here, we explore the feasibility of a novel minimum perturbation method that relates the diffusive movement of nanoparticles in a light field to their size distributions. Abstract. A feasibility study of nanoparticle tracking analysis (NTA) for aquatic environmental samples is presented here. The method has certain virtues such as minimum perturbation of the samples, high sensitivity in terms of particle concentration, and provision of number-based size distributions for aquatic samples. NTA gave linear calibration curves in terms of number concentration and accurately reproduced size measurements of certified reference material nanoparticles. However, the accuracy of the size distributions obtained with this method exhibited a high dependence on set-up parameters and the concentrations were shown to be strongly correlated with the refractive index of the material under examination. Different detection cameras and different data acquisition modes were compared and evaluated. Also, the effect of filtration of the samples was assessed. The size distributions for the contrasting environmental samples were fairly reasonable compared with other studies but an underestimation of small sizes was observed, which can be explained by a material-dependent lower detection limit in terms of size. The number concentrations obtained for the natural nanoparticles ranged from 0.5 to 20 × 108 particles mL–1 and correlated well with conventional turbidity measurements.