Competitive displacement: a sensitive and selective method for the detection of unlabeled molecules.

We propose a new method for molecular detection that retains the sensitivity of fluorescence, but without requiring fluorescence labeling of the sample. The method works by spiking the sample solution with one or more labeled molecular species of known concentration. With proper choice of these "competitor" species, their binding kinetics can be used to quantitatively determine the concentration of unlabeled target species. This method can be applied to any fluorescence transduction mechanism that allows real-time signal acquisition, and represents an advance in mitigating certain sample processing steps. We demonstrate the method for the detection of a DNA sequence containing a single-nucleotide polymorphism (SNP).