Toward a rapid and convenient nanoplastic quantification method in laboratory-scale study based on fluorescence intensity

The thorough investigation of nanoplastics (NPs) in aqueous environments requires efficient and expeditious quantitative analytical methods that are sensitive to environmentally relevant NP concentrations and convenient to employ. Optical analysis-based quantitative methods have been acknowledged as effective and rapid approaches for quantifying NP concentrations in laboratory-scale studies. Herein, we compared three commonly used optical response indicators, namely fluorescence intensity (FI), ultraviolet absorbance, and turbidity, to assess their performance in quantifying NPs. Furthermore, orthogonal experiments were conducted to evaluate the influence of various water quality parameters on the preferred indicator-based quantification method. The results revealed that FI exhibits the highest correlation coefficient (> 0.99) with NP concentration. Notably, the limit of quantification (LOQ) for various types of NPs is exceptionally low, ranging from 0.0089 to 0.0584 mg/L in ultrapure water, well below environmentally relevant concentrations. Despite variations in water quality parameters such as pH, salinity, suspended solids (SS), and humic acid, a robust relationship between detectable FI and NP concentration was identified. However, an increased matrix, especially SS in water samples, results in an enhanced LOQ for NPs. Nevertheless, the quantitative method remains applicable in real water bodies, especially in drinking water, with NP LOQ as low as 0.0157-0.0711 mg/L. This exceeds the previously reported detectable concentration for 100 nm NPs at 40 mu g/mL using surface-enhanced Raman spectroscopy. This study confirms the potential of FI as a reliable indicator for the rapid quantification of NPs in aqueous environments, offering substantial advantages in terms of both convenience and cost-effectiveness.