Enzymatic SPR Approach for the Detection of Nano and Microplastic Particles Using Rainwater as Matrices

The increasing presence of microplastics (MPs) and nanoplastics (NPs) in environmental matrices presents substantial analytical challenges due to their small size and chemical diversity. This study introduces a novel enzymatic biosensor based on the Surface Plasmon Resonance (SPR) platform for the sensitive detection of MPs and NPs, utilizing laccase as the recognition element. Standard plastic particles, including polystyrene (PS, 0.1 µm), polymethyl methacrylate (PMMA, 1.0 µm and 100 µm), and polyethylene (PE, 34–50 µm), were analyzed using SPR angular interrogation along with a fixed-angle scheme. The angular approach revealed a clear relationship between the resonance angle, particle size, and refractive index, while the fixed-angle method, combined with immobilized laccase, facilitated specific detection through enzyme/substrate interactions. The analytical parameters showed detection limits ranging from 7.5 × 10−4 µg/mL (PE, 34–50 µm) to 253.2 µg/mL (PMMA, 1 µm), with significant differences based on polymer type and enzymatic affinity. Application of the biosensor to real rainwater samples collected from two regions in Mexico (Tula and Molango) confirmed its functionality, although performance varied depending on matrix composition, exhibiting inhibition in samples with high manganese (Mn2+), chromium (Cr2+), and zinc (Zn2+) content. Despite these limitations, the sensor achieved a 113% recovery rate in Tula rainwater, demonstrating its potential for straightforward in situ environmental monitoring. This study highlights the capabilities of laccase-based SPR biosensors in enhancing microplastic detection and underscores the necessity of considering matrix effects for real-world applications.