<p>Aqueous concentrations of nanoplastics are critical for their risk assessment. Here we developed an optical manipulation and surface-enhanced Raman scattering set-up to capture, enrich and detect nanoplastics in aquatic environments. A small-sized (20 µm) gold nanoparticle stack was used to design a gold nanoparticle stack/polylactic acid optical tweezer, and individual nanoplastics were precisely manipulated. A large-sized (80 µm) gold nanoparticle stack enabled massive enrichment of nanoplastics, and high enrichment recoveries (for example, 89.3–94.3% for polystyrene) and low limits of detection (for example, 150 ng l⁻¹ for polystyrene) of nanoplastics were achieved. Moreover, interference from natural organic matter was eliminated by adding a cleaning step before detection. The nanoplastics in natural waters (required volume, ≤7.2 ml) were thus successfully enriched and analysed, with determined concentrations of polystyrene nanoplastics of 6.5–8.5, 1.4–1.8 and 0.7–1.0 μg l⁻¹ for water samples from a river, a mariculture farm and a beach, respectively. This newly developed optical manipulation–surface-enhanced Raman scattering approach is able to simultaneously enrich and detect nanoplastics in natural waters.</p>