Enhancement of the Sensitivity of a Lateral Flow Immunoassay by Using the Biotin–Streptavidin System

A new approach based on the use of a complex conjugate is proposed for improving the sensitivity of a lateral flow immunoassay. The complex conjugate is an agglomerate of gold nanoparticles formed by binding biotinylated antibodies labeled with gold nanoparticles to streptavidin. The amplification of the analytical signal is due to the accumulation of the agglomerates of gold nanoparticles in the test zone of the strip. The proposed test system is implemented in the lateral flow immunoassay of a model protein, procalcitonin. This system makes it possible to perform the analysis in a single step without resorting to additional reagents or manipulations. The procalcitonin detection range was 0.5–100 ng/mL and the limit of detection was 0.25 ng/mL; i.e., the sensitivity of the method is four times better than that of the conventional lateral flow immunoassay, in which spherical gold nanoparticles are used as a label.