A rapid and sensitive non-competitive avidin-biotin assay for lactoferrin

We have developed an avidin-biotin assay for the detection of lactoferrin in human seminal plasma. We compared 5 modifications of this assay, and found the non-competitive avidin-biotin assay (NABA) to be the most sensitive. The detection limit of 3-step NABA was 0.2 or 0.1 ng lactoferrin/ml, depending whether avidin-biotin-peroxidase complex (ABC) or avidin-peroxidase was used. The intra-assay and inter-assay coefficients of variation for 3-step NABA were 6.2 and 8.5%, respectively. The lactoferrin levels of human seminal plasma samples measured by 3-step NABA and radioimmunoassay (RIA) showed good correlation (r = 0.96). The total performance time of 3-step NABA is flexible and the method can be modified for rapid (less than 1 h) or overnight assay according to need.