Plasmonic Nanosensor: LSPR Refractive-Index Shift

Gold and silver nanoparticles just tens of nanometers across support a collective oscillation of their free electrons called a localized surface plasmon resonance — the same effect behind stained-glass colors and, in engineered form, behind real label-free biosensors. This simulation renders the electron cloud sloshing under an oscillating incident field in 3D and computes the particle's extinction spectrum from a Drude free-electron model of the metal. Because the plasmon resonance frequency depends on the refractive index of the surrounding medium, raising that index — as happens when a protein or other analyte binds to the particle's surface — measurably redshifts the resonance peak. Switch between gold and silver, resize the nanoparticle, and either drag the refractive-index slider or click "Bind analyte layer" to watch the live extinction spectrum and the reported sensitivity (nm shift per refractive-index unit) update in real time, exactly the quantity real LSPR sensor designs are judged on.