Towards a low-cost, rapid microplastic optical detection system using fluorescent staining through Nile Red for in situ ocean deployment

Millions of tons of plastics are released into the ocean each year. Environmental forces break down these plastics into micro and nano-sized fragments, referred to respectively as microplastics (MPs) and nanoplastics (NPs). Their small size allows these plastic fragments to propagate across the planet’s ecosystems. The grave health consequences of plastic proliferation within the marine environment have increasingly garnered public concern. Given that current methodologies of analyzing MPs in environmental samples are expensive and time-intensive, there exists an urgent need for inexpensive, real-time microplastic detection systems. This research presents a proof-of-concept rapid microplastic detection system designed to be portable and low-cost. The system relies on a fluorescence-based optical-detection approach utilizing the staining of plastics with the fluorescent dye, Nile Red (NR). In this study, known quantities of polypropylene MPs were added to solutions of Nile Red. Resulting emissions were detected using a optical lens to focus fluorescent light on a silicon photodiode. Preliminary results showed that the system output signal is linear with the MP concentration of the measurement sample. This proof-of-concept serves as the basis for a low-cost, field-deployable instrument capable of rapid in situ MP detection. Future work will improve the sensitivity and resolution of the system, and work towards incorporating field tests.