Highly Sensitive Detection of Bisphenol A by NanoAptamer Assay with Truncated Aptamer

For the sensitive quantification of bisphenol A (BPA), we have developed NanoAptamer assay, which employs aptamer and complementary signaling DNA, a set of quantum dots (QD), and magnetic beads (MBs). Signaling DNA–QD 655 was tethered to MB–QD 565 via the aptamer. The affinity of the aptamer to BPA resulted in the release of the signaling DNA–QD 655 from the complex and hence the corresponding decrease in the QD 655 fluorescence measurement signal. Three new aptamers (23, 58, and 24-mer) were designed via truncation of the reference aptamer (73-mer). The sensitivity and selectivity of each aptamer for BPA detection via NanoAptamer assay were investigated. One of the truncated aptamers (24-mer) has shown a significantly better performance (limit of detection, LOD, 0.17 pg/mL) than the reference 73-mer aptamer (LOD, 570 pg/mL). It has also shown the best selectivity for BPA detection over BPA analogues (i.e., bisphenol B, bisphenol C, and diethylstilbestrol). It corresponded to a normalized fluorescence change of 33.7% at the environmentally relevant concentration of 1 ng/mL (1 ppb) BPA; however, the analogues remained unchanged (2.3–3.9%).