Provided herein are targetable constructs that are multivalent carriers of bi-specific antibodies, i.e., each molecule of a targetable construct can serve as a carrier of two or more bi-specific antibodies. Also provided are targetable complexes formed by the association of a targetable construct with two or more bi-specific antibodies. The targetable constructs and targetable complexes of the invention are incorporated into biosensors, kits and pharmaceutical compositions, and are used in a variety of therapeutic and other methods.