Labeling of estradiol and testosterone alkyloxime derivatives with a europium chelate for time-resolved fluoroimmunoassays

O-Carboxymethyl-, O-(4-aminobutyl)-, and O-(6-aminohexyl)-oximes of 6-oxoestradiol and testosterone were labeled using a described general labeling method with a europium chelate. A stable amide or thiourea bond was formed between the europium label and carboxyl or amino derivative of the steroid, respectively. These labeled “tracers” were purified and briefly tested in a competitive time-resolved fluoroimmunoassay using monoclonal antibodies raised against O-(carboxymethyloxime)-bovine serum albumin derivatives of estradiol and testosterone. Only buffer-based standards were used in a model system for the testing. These studies indicate only minor functional differences while using these antibodies due to the length of the spacer arm, and a higher sensitivity in the clinically relevant standard range was reached with the longer spacers.