Efficient Screening of Pesticide Diazinon-Binding Aptamers Using the Sol-Gel-Coated Nanoporous Membrane-Assisted SELEX Process and Next-Generation Sequencing.

Aptamer-based methods for detecting pesticides are more efficient than antibody-based methods by high thermal stability, low molecular weight, easy modification, and low cost. In this study, the systematic evolution of ligands by exponential enrichment (SELEX) process, combined with next-generation sequencing (NGS), was performed to select aptamers specific to the pesticide, diazinon, which was fixed on a sol-gel-coated nanoporous-anodized aluminum oxide membrane to overcome the immobilization effect of general method and simplify the elution step. The frequency of specific nucleotide sequences obtained after SELEX rounds was directly analyzed using NGS to eliminate the time-consuming cloning process used in the general SELEX methods. Nine sequences with the highest frequency after SELEX round 10 followed by NGS were selected and tested to derive their binding affinity with the target, diazinon, through circular dichroism (CD) spectrophotometry. The CD signal difference of the aptamer candidates ranged from 0.13 to 2.242 mdeg between diazinon-only treated and diazinon-aptamer-treated samples at a wavelength near 270 nm. Aptamer D-4, which had the highest binding affinity from CD spectrophotometry analysis, showed no cross-reactivity with non-target pesticides, such as baycarb, bifenthrin, and pyridaben, but interacted with the other pesticides, fipronil and 2-phenylphenol. Therefore, an aptamer was effectively screened by selection of high-frequency candidates after SELEX-NGS followed by CD analysis with the highest difference signal. A follow-up study is needed to confirm whether the proposed SELEX process combined with NGS for the discovery of aptamers for new targets can further shorten the SELEX cycle by reducing the number of SELEX rounds to 10 or less.