In vitro selection of a single-stranded DNA molecular recognition element for the pesticide malathion

Many large-scale applications of the organophosphate pesticide malathion have led to widespread environmental contamination. Concentrations are found in the environment well above those which are harmful to humans and environmental organisms. No current method of detection for this pesticide is rapid, cost-effective, and specific for malathion. Therefore, we utilized a stringent Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process to identify a Molecular Recognition Element (MRE) for malathion. This MRE was identified from a large ssDNA library and has an equilibrium dissociation constant (K_d) in the low-nanomolar range. Additionally, it has significant selectivity for malathion in comparison to various other pesticides and metabolites of malathion, which were used as negative targets of selection. The high affinity and selectivity of the ssDNA MRE for malathion is a product of the stringent SELEX selection scheme and will be useful for rapid, inexpensive, and specific detection of malathion in the environment.