Selective on-site detection and quantification of polystyrene microplastics in water using fluorescence-tagged peptides and electrochemical impedance spectroscopy

In this study, we developed a method for the on-site selective detection and quantification of microplastics in various water matrices using fluorescence-tagged peptides combined with electrochemical impedance spectroscopy (EIS). Among the types of plastics found in seawater, polystyrene (PS) microplastics were selected. Fluorometry, scanning electron microscopy (SEM), and Raman spectroscopy were used to verify the specific interaction of these peptides with PS spherical particles of different sizes (ranging from 0.1 to 250 µm). Principal component analysis (PCA) was employed to determine the effects of temperature (25-65 °C), incubation time (5 and 10 min), and particle size on plastic-peptide bonding efficiency, based on fluorescence intensity. For each water type (pure, tap, NaCl (0.5 M), and seawater), EIS plots (Nyquist and Bode) were generated. Significant factors affecting the EIS response, including particle size, shape, and material, were analyzed by measuring electrical parameters for different microplastic concentrations (50 ppb to 20 ppm). The EIS parameters changed with increasing plastic concentration, determining a limit of detection (LOD) of 50 ppb (ng/mL) for pure and tap water and 400 ppb for saline water, as the lowest concentration producing a significant change in EIS parameters compared to the baseline. The sensor proved highly effective for detecting microplastics in low ionic strength environments such as pure and tap water. However, in high ionic strength environments like saline and seawater, the detection capability diminished, likely due to the masking effect of ions on the EIS response.