Nanoplastics pollution has led to a severe environmental crisis because of a large accumulation of these smaller nanoplastic particles in the aquatic environment and atmospheric conditions. Detection of these nanoplastics is crucial for food safety monitoring and human health. In this work, we report a simple and eco-friendly method to prepare a SERS-substrate-based nanoporous Ag nanoparticle (NP) film through vacuum thermal evaporation onto a vacuum-compatible deep eutectic solvent (DES) coated growth substrate for quantitative detection of nanoplastics in environmental samples. The nanoporous Ag NP films with controlled pores were achieved by the soft-templating role of DESs over the growth substrate, which enabled the self-assembly of deposited Ag NPs over the surface of DES. The optimized nanoporous Ag substrate provides high sensitivity in the detection of analyte molecules, crystal violet (CV), and rhodamine 6G (R6G) with a limit of detection (LOD) up to 1.5 × 10-13 M, excellent signal reproducibility, and storage stability. Moreover, we analyzed quantitative SERS detection of polyethene terephthalate (PET, size of 200 nm) and polystyrene (PS, size of 100 nm) nanoplastics with an LOD of 0.38 and 0.98 μg/mL, respectively. In addition, the SERS substrate efficiently detects PET and PS nanoplastics in real environmental samples, such as tap water, lake water, and diluted milk. The enhanced SERS sensing ability of the proposed nanoporous Ag NP film substrate holds immense potential for the sensitive detection of various nanoplastic contaminants present in environmental water.