Colorimetric Gold-Nanoparticle Spoilage Sensor (2D)

This 2D counterpart models the same real point-of-care food-safety chemistry as the 3D version: a colloid of citrate-capped gold nanoparticles that visibly changes color when it meets the biogenic amines released by spoiling fish or meat. Each nanoparticle in this flat field diffuses by Brownian motion, drawn each frame from the Stokes–Einstein diffusion coefficient for its size. Every close pass between two free particles is tested, from scratch, against a per-collision sticking probability set by the amine and salt sliders; as biogenic-amine concentration and ionic strength rise, that probability climbs and the electrostatic barrier that normally keeps particles apart (DLVO theory) collapses faster. Bonded clusters couple their plasmon resonances, red-shifting the sensor's absorption peak from red toward blue — tracked live in a color-vs-time strip chart alongside the SPR peak wavelength, redshift, weight-average aggregation number and a rendered solution-color swatch with a fresh/spoiled verdict.