Colorimetric Gold-Nanoparticle Aptasensor

Aptamer-coated gold nanoparticles are one of the simplest biosensors ever built: no reader is required, because target binding triggers salt-induced aggregation that shifts the plasmon absorption band and changes the solution's color from red to purple to blue in front of your eyes. This simulator renders a cuvette of nanoparticles in 3D and drives real Langmuir binding kinetics and the plasmon-ruler coupling equation from four controls — target concentration, ionic strength, particle diameter and aptamer affinity — with live readouts for the plasmon peak wavelength, the A650/A520 colorimetric ratio, the binding fraction and the aggregation level, plus a swatch showing the resulting perceived solution color.