Nucleic acid - Guided biosensing to trace endosulfan via graphene oxide-assisted SELEX

Aptamer-based biosensors (aptasensors) offer high specificity and sensitivity for detecting small molecules, but their broader use is limited by the lack of suitable aptamers. Endosulfan (ES), a toxic organochlorine pesticide, currently lacks an aptamer for selective detection. In this study, we employed graphene oxide (GO)-assisted SELEX to isolate a high-affinity aptamer for ES, leveraging GO's ability to enhance aptamer-target interactions. The selection process was optimized to minimize cross-reactivity with structurally related pesticides, including isodrin, aldrin, chlorpyrifos, malathion, methidathion, monocrotophos and deltamethrin. The identified aptamer, ESGO-251, showed a dissociation constant (K_d) of 23.14 μM, indicating affinity toward ES. This aptamer was integrated into a screen-printed carbon electrode (SPCE) to develop an electrochemical biosensor. Target binding triggered conformational changes in the aptamer, enabling sensitive ES detection. The biosensor achieved a limit of detection (LOD) of 0.60 ng/mL and a limit of quantification (LOQ) of 1.82 ng/mL. This portable, sensitive platform holds promise for on-site monitoring of ES in environmental and agricultural settings. Overall, the study demonstrates the effectiveness of GO-assisted SELEX in developing aptamers for small-molecule biosensing applications.