Rapid detection of unconjugated estriol in the serum via superparamagnetic lateral flow immunochromatographic assay

Unconjugated estriol (uE(3)) is one of the main naturally occurring estrogens that plays an important role in growth and development of the fetus. Usually, the level of uE(3) is very low in men and non-pregnant women, but in pregnant women, the level of estriol has been found to be quite high. Therefore, the combination of uE(3), AFP, and hCG is now widely used for Down Syndrome screening as a triple marker. Here, we developed a superparamagnetic lateral flow immunochromatographic assay to quantitatively detect uE(3). The detection limit of this assay was 0.86 nmol/L and the linear range for the determination of uE(3) was from 1 to 100 nmol/L. The detection time was 15 min and the assay had very low cross-reactivity with estrone (E-1), estradiol (E-2), and progesterone. The coefficient of variation (CV) of intra- and inter-assay ranged from 5% to 13%. The magnetic signals were stable under 37 A degrees C within 7 d. Moreover, the concentrations of uE(3) measured by lateral flow immunochromatographic assay in 230 serum samples collected from pregnant women at the Chinese People's Liberation Army General Hospital had a good correlation with those measured by time-resolved fluorescence immunoassay (R = 0.946).