Disclosed are compositions and methods for detecting small quantities of analytes such as proteins and peptides. The method involves associating a primer with an
analyte and subsequently using the primer to mediate
rolling circle replication of a
circular DNA molecule. Amplification of the
DNA circle is dependent on the presence of the primer. Thus, the disclosed method produces an amplified
signal, via rolling circle amplification, from any
analyte of interest. The amplified
DNA remains associated with the
analyte, via the primer, and so allows spatial detection of the analyte. The disclosed method can be used to detect and analyze proteins and peptides. Multiple proteins can be analyzed using microarrays to which the various proteins are immobilized. A
rolling circle replication primer is then associated with the various proteins using a conjugate of the primer and a molecule that specifically binds the proteins to be detectable.
Rolling circle replication from the primers results in production of a large amount of
DNA at the sites in the array where the proteins are immobilized. The DNA produced by
rolling circle replication can be further amplified in secondary and higher order amplification processes using second-stage or higher order primers in conjunction with second-stage or higher order amplification target circles. The amplified DNA serves as a readily detectable
signal for the proteins. The disclosed method can also be used to compare the proteins expressed in two or more different samples. The information generated is analogous to the type of information gathered in
nucleic acid expression profiles. The disclosed method allows sensitive and accurate detection and quantitation of proteins expressed in any
cell or tissue.