Provided herein are affinity reagents having affinity for particular target, each reagent having a unique DNA barcode, and methods for using the same to measure the abundance of targets in a sample. In particular, methods are provided in which unique barcodes linked to affinity reagents are contacted to a sample to bind antigens if present in said sample. In cases in which the affinity reagents are antibodies and the targets are antigens, antibodies that are bound to their target antigens can be separated from unbound antibodies and the DNA barcode associated with the affinity reagent is amplified, such as with a PCR reaction. In some cases, amplified barcode DNA is subjected to DNA sequencing as a measure of the levels of the target protein in the sample.