Recombinant Anti-FN1 x Anti-HSG Bispecific Antibody (Tandem scFv) is designed to be expressed as a scFv from an anti-FN1 antibody variable domains fused with a scFv from an anti-HSG antibody variable domains. It contains a His-tag at the C/N terminus for affinity purification. The BsAb exits as monomer in reducing and non-reducing conditions. This BsAb can be used in pretargeting system of PET, radioimaging or radiotherapy. It can mediate targeting of radioactivity to tumor cells. It is designed for the research of Solid tumors imaging and therapy.