The use of a colour camera for quantitative detection of protein-binding nanoparticles

Metal nanoparticles posses the property of changing their optical properties as a function of both internal characteristics (size, shape, dielectric function) and refractive index of the local environment. A special class of applications in the field of biosensing uses the dependency of the nanoparticle's plasmonic peak localization on the local refractive index change. The response of this type of sensors is usually monitored by the change of the extinction spectrum of an ensemble of nanoparticles where analytes interact with functionalized nanoparticles in solution or immobilized at an interface; detection is done with a spectrophotometer. This type of sensors has a limited sensitivity. This can be overcome by using single nanoparticle based biosensors. This type of sensors measures the changes of the scatter spectrum of a collection of individually addressable functionalized nanoparticles in the presence of analytes. Here we report on a new detection method of binding events of analytes to functionalized gold nanoparticle using a standard colour camera attached to a darkfield microscopy setup. This setup is capable of parallel detection of the spectral shifts of thousands of 60 nm antibody-functionalized gold spheres as a result of binding events of protein analyte molecules. This setup can be the basis for multiplexing and quantification