A method of manufacturing a plurality of pairs of proximity probes, wherein each pair of proximity probes comprises a first and a second proximity probe and each pair is capable of binding to a different target analyte, wherein each proximity probe comprises an analyte binding domain and a partially double-stranded nucleic acid domain and each proximity probe of a pair can simultaneously bind to a target analyte, and wherein the nucleic acid domains of a pair of proximity probes are able to interact directly upon binding of the pair of proximity probes to their target analyte, said method comprising: a. conjugating a first universal oligonucleotide to each of a plurality of first analyte binding moieties, to form a set of first universal conjugates; b. conjugating a second universal oligonucleotide to each of a plurality of second analyte binding moieties, to form a set of second universal conjugates; c. hybridising to each first universal oligonucleotide of the set of first universal conjugates one of a plurality of different first tag oligonucleotides, each different first tag oligonucleotide comprising a first universal complement domain which is common to all first tag oligonucleotides and which is complementary to the first universal oligonucleotide, and a first unique domain which is unique to each different first tag oligonucleotide and which is not capable of hybridising to a first or second universal oligonucleotide, thereby to form a plurality of first proximity probes; d. hybridising to each second universal oligonucleotide of the set of second universal conjugates one of a plurality of different second cognate tag oligonucleotides, each different second tag oligonucleotide comprising a second universal complement domain which is common to all second tag oligonucleotides and which is complementary to the second universal oligonucleotide and a second unique domain which is unique to each different second tag oligonucleotide, and which is not capable of hybridising to a first or second universal oligonucleotide, thereby to form a plurality of second proximity probes; e. selecting multiple first proximity probes from said plurality of first proximity probes and multiple cognate second proximity probes from said plurality of second proximity probes, thereby to provide a plurality of pairs of proximity probes; wherein the first tag oligonucleotide of at least one first proximity probe is capable of interacting with the second tag oligonucleotide of more than one second proximity probe, wherein said first and second tag oligonucleotides are capable of interacting by hybridisation. a. conjugating a first universal oligonucleotide to each of a plurality of first analyte binding moieties, to form a set of first universal conjugates; b. conjugating a second universal oligonucleotide to each of a plurality of second analyte binding moieties, to form a set of second universal conjugates; c. hybridising to each first universal oligonucleotide of the set of first universal conjugates one of a plurality of different first tag oligonucleotides, each different first tag oligonucleotide comprising a first universal complement domain which is common to all first tag oligonucleotides and which is complementary to the first universal oligonucleotide, and a first unique domain which is unique to each different first tag oligonucleotide and which is not capable of hybridising to a first or second universal oligonucleotide, thereby to form a plurality of first proximity probes; d. hybridising to each second universal oligonucleotide of the set of second universal conjugates one of a plurality of different second cognate tag oligonucleotides, each different second tag oligonucleotide comprising a second universal complement domain which is common to all second tag oligonucleotides and which is complementary to the second universal oligonucleotide and a second unique domain which is unique to each different second tag oligonucleotide, and which is not capable of hybridising to a first or second universal oligonucleotide, thereby to form a plurality of second proximity probes; e. selecting multiple first proximity probes from said plurality of first proximity probes and multiple cognate second proximity probes from said plurality of second proximity probes, thereby to provide a plurality of pairs of proximity probes;