Specificity of [99mTc(CO)
]+to His-tagged protein was demonstrated via (a) SDS-PAGE followed by (b) phosphor imaging. Non-His-tagged protein (C2Ac, 15 kDa) was co-incubated with His-tagged protein (α-CD33 scFv, 29 kDa) and [99mTc(CO)3]+. The proteins were then separated using SDS-PAGE, and radiolabelling was visualised using phosphor imaging. Lanes M, molecular weight marker; lanes 1, C2Ac + α-CD33 scFv; lanes 2, C2Ac; lanes 3, α-CD33 scFv. Radioactive markers, indicated by black arrows, were placed at 2.5, 15, 30 and 110 kDa.