Methods are provided for detecting, separating, isolating and quantifying
contaminants in starting materials by separating the contaminant from the
starting material using a bead coupled to an affinity moiety and quantum
dot-labeling the contaminant. The contaminant is detected by the
characteristic emission spectrum of the quantum dot. Also, competitive
binding methods are provided wherein the starting material and a control
material are contacted with a quantum dot coupled to an affinity moiety
capable of binding the contaminant and a competitor complex. A decrease
in the intensity of the characteristic emission spectrum of the quantum
dot associated with the competitor complex from the starting material as
compared to that of the control material is indicative of the presence of
the contaminant in the starting material.