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Measurement of the Effective Refractive Index of Suspensions Containing 5 µm Diameter Spherical Polystyrene Microparticles by Surface Plasmon Resonance and Scattering
Summary
Researchers developed a surface plasmon resonance method combined with Mie scattering theory to measure concentrations of 5-micrometer polystyrene microparticles in water. The system achieved good sensitivity with a detection limit of 0.001% concentration and strong linearity, demonstrating a promising optical approach for microplastic detection in aqueous samples.
Microplastics (MP) have been found not only in the environment but also in living beings, including humans. As an initial step in MP detection, a method is proposed to measure the effective refractive index of a solution containing 5 µm diameter spherical polystyrene particles (SPSP) in distilled water, based on surface plasmon resonance (SPR) technique and Mie scattering theory. The reflectances of the samples are obtained with their resonance angles and depths that must be normalized and adjusted according to the reference of the air and the distilled water, to subsequently find its effective refraction index corresponding to the Mie scattering theory. The system has an optical sensor with a Kretschmann-Raether configuration, consisting of a semicircular prism, a thin gold film, and a cell for solutions samples with different concentrations (0.00, 0.20, 0.05, 0.50 and 1.00 %). The experimental result provided a good linear fit with an R2=0.986, a sensitivity of 7.4526 ×10-5 RIU/%, LOD=0.001% and LOQ=0.0035%. The optomechatronic system and the applications developed for the SPR-Scattering theory allowed us to measure the effective refractive index and concentration for solutions with 5 µm diameter SPSP in distilled water.