The disclosure provides methods for detecting the concurrent presence of at least two targets within a biological sample. The method includes contacting said biological sample with a first binding agent, said first binding agent operably linked to a first sortase molecule, wherein said first binding agent specifically binds to a first target; contacting said biological sample with a second binding agent, said second binding agent operably linked to a first sortase recognition sequence peptide, wherein said second binding agent specifically binds to a second target; adding a sortase substrate under conditions where a first sortase-mediated ligation of the sortase substrate to the first sortase recognition sequence will produce a ligation product, and detecting the ligation product, wherein detection of said ligation product indicates the concurrent presence of the first target and the second target in the biological sample. Also disclosed are kits comprising reagents for performing the methods as claimed.