A composition comprising a prostate specific membrane antigen inhibitor (PSMAi)/chelator construct covalently attached to a macromolecule, wherein the macromolecule is a nanoparticle comprising silica, wherein the nanoparticle has a diameter no greater than 20 nm, and wherein the construct has the structure: wherein: L 1 is a peptidic fragment comprising from 1 to about 10 natural or unnatural amino acid residues, or an optionally substituted, bivalent, C 1-20 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -CHOH-, -NR-, - N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, -C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 2 is an optionally substituted, bivalent, C 1-10 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -Cy-, -CHOH-, - NR-, -N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, - C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 3 is a covalent bond or a crosslinker derived from a bifunctional crosslinking reagent capable of conjugating a reactive moiety of the (PSMAi)/chelator construct with a reactive moiety of the macromolecule, each -Cy- is independently an optionally substituted 5-8 membered bivalent, saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an optionally substituted 8-10 membered bivalent saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur; Y is a chelator moiety; and R is hydrogen, C 1-6 alkyl, or a nitrogen protecting group; wherein each amino acid residue, unless otherwise indicated, may be protected or unprotected on its terminus and/or side chain group. wherein the macromolecule is a nanoparticle comprising silica, wherein the nanoparticle has a diameter no greater than 20 nm, and wherein the construct has the structure: wherein: L 1 is a peptidic fragment comprising from 1 to about 10 natural or unnatural amino acid residues, or an optionally substituted, bivalent, C 1-20 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -CHOH-, -NR-, - N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, -C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 2 is an optionally substituted, bivalent, C 1-10 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -Cy-, -CHOH-, - NR-, -N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, - C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 3 is a covalent bond or a crosslinker derived from a bifunctional crosslinking reagent capable of conjugating a reactive moiety of the (PSMAi)/chelator construct with a reactive moiety of the macromolecule, each -Cy- is independently an optionally substituted 5-8 membered bivalent, saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an optionally substituted 8-10 membered bivalent saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur; Y is a chelator moiety; and R is hydrogen, C 1-6 alkyl, or a nitrogen protecting group; wherein each amino acid residue, unless otherwise indicated, may be protected or unprotected on its terminus and/or side chain group. L 1 is a peptidic fragment comprising from 1 to about 10 natural or unnatural amino acid residues, or an optionally substituted, bivalent, C 1-20 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -CHOH-, -NR-, - N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, -C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 2 is an optionally substituted, bivalent, C 1-10 saturated or unsaturated, straight or branched, hydrocarbon chain, wherein one or more methylene units of the hydrocarbon chain are optionally and independently replaced by -Cy-, -CHOH-, - NR-, -N C -, -C N -, -N SO 2 -, -SO 2 N -, -O-, -C -, -OC -, - C O-, -S-, -SO-, -SO 2 -, -C(=S)-, or -C(=NR)-; L 3 is a covalent bond or a crosslinker derived from a bifunctional crosslinking reagent capable of conjugating a reactive moiety of the (PSMAi)/chelator construct with a reactive moiety of the macromolecule, each -Cy- is independently an optionally substituted 5-8 membered bivalent, saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an optionally substituted 8-10 membered bivalent saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur; Y is a chelator moiety; and R is hydrogen, C 1-6 alkyl, or a nitrogen protecting group; wherein each amino acid residue, unless otherwise indicated, may be protected or unprotected on its terminus and/or side chain group.