Selection and Application of DNA Aptamers Against Sulfaquinoxaline Assisted by Graphene Oxide–Based SELEX

Single-stranded DNA aptamers that specifically bind to sulfaquinoxaline (SQX) were selected by a graphene oxide–based SEL EX (GO-SELEX) technique assisted by a non-immobilizing TAMRA-labeled oligonucleotide library. After 8 rounds of selection against SQX, two aptamer candidates (i.e., SBA 1 and SBA 2) were obtained. Furthermore, the two full-length aptamers were truncated to obtain the aptamers (i.e. SBA 1-1, SBA 2-1, and SBA 2-2). These candidate aptamers were subjected to binding assays to evaluate their binding affinities and specificities to SQX. Our results show that the dissociation constants Kd of the aptamers ranged from 82.54 to 630.41 nM. Using truncated aptamer SBA 2-1 with the highest affinity as the recognition element, a GO-based fluorescent aptasensor was developed for SQX detection with a linear range from 0.05 to 50 ng mL−1 and a limit of detection of 0.11 ng mL−1 with excellent selectivity. Furthermore, the new aptasensor was used to detect SQX in milk samples. Our results showed that the aptasensor demonstrated recoveries ranging from 96.6 to 106.7%, suggesting that the proposed GO-based fluorescent aptasensor holds great potential as promising tool for sensitive detection of SQX in food safety inspection.