Trivalent lanthanide ions are known for their ability to interact with calcium-binding sites in various proteins. There is a need to assess the bioavailability of lanthanides and other heavy metals introduced into the body as components of implants or as contrast agents. This study aimed to develop a method to address bioavailability and/or presence of trivalent lanthanide ions by examining electrophoretic mobility in an agarose gel of a plasmid harboring the human metallothionein-II gene (). Mobility of the plasmid was specifically altered by a monoclonal antibody raised against the zinc-binding transcription factor that controls the activity of the gene. This study showed that the plasmid acquired a lanthanide-specific mobility pattern that allowed the presence of lanthanide ions to be readily determined in a 0.8% agarose gel. These findings suggest that this plasmid/monoclonal antibody combination under selected conditions may be useful in industrial, environmental, and biomedical settings to identify, separate, or capture lanthanide ions in complex mixtures that contain an array of metal ions.