Detection of Phaeocystis globosa by aptamer-based and Exo III-assisted dot lateral flow assay

As one of the most typical harmful algal blooms (HABs)-forming species, Phaeocystis globosa not only poses a serious threat to the operation safety of nuclear power plants, but also negatively affects coastal ecosystems, fisheries, and human health. Accordingly, the development of rapid detection method for P. globosa is essential to control and prevent the harmful effects caused by this alga. Here, we established a novel method referred to as aptamer-based and exonuclease III (Exo III)-assisted dot lateral flow assay (ABEA-DLFA) by using aptamer as recognition element of target cell and amplifying detection signal with Exo III, aimed at accomplishing the rapid detection of P. globosa. The aptamer against P. globosa was screened by cell systematic evolution of ligands by exponential enrichment. After 16 cycles of selection, an aptamer library was obtained and introduced into molecular cloning, sequencing, and bioinformatics analysis, from which four candidate aptamers (Pg-Apt1, Pg-Apt2, Pg-Apt3, and Pg-Apt4) were finally identified. Comparative tests of these candidate aptamers showed that Pg-Apt2 was the most excellent one with the best specificity and the strongest affinity (K_D = 94.8 nM ± 22.3 nM) with P. globosa. By employing manually-prepared dot lateral flow test strip as analytical platform, Pg-Apt2 as a probe targeting P. globosa cells, and Exo III-assisted amplification to amplify detection signal, an integrated novel method, i.e., ABEA-DLFA, was established and optimized for rapid and convenient detection of P. globosa. ABEA-DLFA displayed a high specificity for P. globosa with a detection limit of 1.8 × 10¹ cells mL^-1. The practicability of ABEA-DLFA was verified by the test with simulated natural water samples, exhibiting a detection limit of 1.8 × 10² cells mL^-1. In conclusion, the developed ABEA-DLFA that is characterized by high sensitivity, accuracy, and simplicity may be promising for the early warning of P. globosa-forming HABs.