Patent ID: 8137920

Claim:
A method for determining the presence or absence of a complex of a first reagent and a second reagent in a mixture comprising determining a first absorbance value at a first wavelength and a second absorbance value at a second wavelength upon mixing the first reagent with the second reagent, wherein the first reagent or the second reagent is conjugated to a metal nanoparticle or nanoshell, and wherein the first wavelength is within the absorbance wavelength region of the absorption spectrum for the metal nanoparticle or nanoshell and the second wavelength is within a scattering wavelength region of the absorption spectrum for the metal nanoparticle or nanoshell; determining the ratio of the first absorbance value to the second absorbance value; and comparing the ratio of the absorbance values to a pre-determined value, wherein the comparison is indicative of the presence of the complex of the first reagent and the second reagent.