A Label-Free Colorimetric Biosensor for 17β-Estradiol Detection Using Nanoparticles Assembled by Aptamer and Cationic Polymer

Concern is mounting regarding the human health and environment effects of 17 beta-estradiol (E2), a natural oestrogen excreted by human beings and animals. In this paper, a sensitive and selective biosensor for the detection of E2 using gold nanoparticles (AuNPs), label-free E2-specific aptamer, and poly(diallyldimethylammonium chloride) (PDDA) was developed. In the absence of E2, PDDA can electrostatically interact with E2-specific aptamer, and the charge responsible for inducing AuNPs aggregation was destroyed. However, the introduction of E2 can specifically interact with the aptamer to form E2-aptamer complex so that PDDA can aggregate AuNPs and cause a remarkable change in colour from wine red to blue, which enables colorimetric detection of E2 with selectivity and a detection limit of 1.57 nM.