The real-time polymerase chain reaction (PCR) is the most commonly used method for quantitative gene expression profiling; it allows extremely sensitive measurement of hundreds of mRNA transcripts in parallel. We propose a method by which protein abundances can be quantitated using the same technology. This is achieved by implementing a sandwich immuno-assay format in which the detection antibodies are labeled with different DNA sequences. Real-time PCR is then used to quantify all of the DNA labels in parallel, thus revealing the quantities of the cognate proteins in the biological samples. Preliminary experiments show that real-time PCR using such antibody-DNA conjugates gives over two orders of magnitude more sensitive detection and almost three orders of magnitude increased dynamic range in comparison to standard ELISA, and standard deviations are very low (CV approximately 5%). Initial evidence supporting the ability to multiplex this method has also been obtained.
