An antigen complex, comprising: a nanoparticle sorting agent comprising: a nanoparticle; a polynucleotide detection tag having at least one coding region forming a barcode, the polynucleotide detection tag being conjugated to the nanoparticle; and a first polynucleotide hybridization domain conjugated to the polynucleotide detection tag; and a peptide-loaded streptavidin major histocompatability complex (MHC) tetramer, comprising: a modified streptavidin protein; four biotin-modified MHC proteins each independently conjugated to the modified streptavidin protein; an antigen peptide bound to the biotin-modified MHC proteins; and a second polynucleotide hybridization domain different from the first polynucleotide hybridization domain and conjugated to the modified streptavidin protein, the nanoparticle sorting agent being linked to the peptide-loaded streptavidin MHC tetramer by hybridization of the first polynucleotide hybridization domain to the second polynucleotide hybridization domain, wherein the at least one coding region: is a set of nucleotides with a unique and specific sequence that is separate from another polynucleotide, and provides a unique antigen-specific sequence for identification of the barcoded nanoparticle-antigen-MHC complex. a nanoparticle sorting agent comprising: a nanoparticle; a polynucleotide detection tag having at least one coding region forming a barcode, the polynucleotide detection tag being conjugated to the nanoparticle; and a first polynucleotide hybridization domain conjugated to the polynucleotide detection tag; and a nanoparticle; a polynucleotide detection tag having at least one coding region forming a barcode, the polynucleotide detection tag being conjugated to the nanoparticle; and a first polynucleotide hybridization domain conjugated to the polynucleotide detection tag; and a peptide-loaded streptavidin major histocompatability complex (MHC) tetramer, comprising: a modified streptavidin protein; four biotin-modified MHC proteins each independently conjugated to the modified streptavidin protein; an antigen peptide bound to the biotin-modified MHC proteins; and a second polynucleotide hybridization domain different from the first polynucleotide hybridization domain and conjugated to the modified streptavidin protein, the nanoparticle sorting agent being linked to the peptide-loaded streptavidin MHC tetramer by hybridization of the first polynucleotide hybridization domain to the second polynucleotide hybridization domain, wherein the at least one coding region: is a set of nucleotides with a unique and specific sequence that is separate from another polynucleotide, and provides a unique antigen-specific sequence for identification of the barcoded nanoparticle-antigen-MHC complex. a modified streptavidin protein; four biotin-modified MHC proteins each independently conjugated to the modified streptavidin protein; an antigen peptide bound to the biotin-modified MHC proteins; and a second polynucleotide hybridization domain different from the first polynucleotide hybridization domain and conjugated to the modified streptavidin protein, the nanoparticle sorting agent being linked to the peptide-loaded streptavidin MHC tetramer by hybridization of the first polynucleotide hybridization domain to the second polynucleotide hybridization domain, wherein the at least one coding region: is a set of nucleotides with a unique and specific sequence that is separate from another polynucleotide, and provides a unique antigen-specific sequence for identification of the barcoded nanoparticle-antigen-MHC complex. is a set of nucleotides with a unique and specific sequence that is separate from another polynucleotide, and provides a unique antigen-specific sequence for identification of the barcoded nanoparticle-antigen-MHC complex. <EOS>