Dynamic interactions between peroxidase-mimic silver NanoZymes and chlorpyrifos-specific aptamers enable highly-specific pesticide sensing in river water.

With growing environmental and health concerns over persistent organic compounds such as organophosphates, regulatory bodies have imposed strict regulations for their use and monitoring in water bodies. Although conventional analytical tools exist for the detection of organophosphorus pesticides, new strategies need to be developed to fulfil the ASSURED (affordable, sensitive, specific, user-friendly, rapid, equipment-free and deliverable to end users) criteria of the World Health Organisation. One such strategy is to employ the ability of certain nanoparticles to mimic the enzymatic activity of natural enzymes to develop optical sensors. We show that the intrinsic peroxidase-mimic NanoZyme activity of tyrosine-capped silver nanoparticles (Ag-NanoZyme) can be exploited for highly specific and rapid detection of chlorpyrifos, an organophosphorus pesticide. The underlying working principle of the proposed aptasensor is based on the dynamic non-covalent interaction of the chlorpyrifos specific aptamer (Chl) with the NanoZyme (sensor probe) vs. the pesticide target (analyte). The incorporation of the Chl aptamer ensures high specificity leading to a colorimetric response specifically in the presence of chlorpyrifos, while the sensor remains unresponsive to other pesticides from organophosphate and non-organophosphate groups. The robustness of the sensor to work directly in environmental samples was established by evaluating its ability to detect chlorpyrifos in river water samples. The excellent recovery rates demonstrate the sensor robustness, while the simplicity, and rapid sensor response (2 min) to detect the presence of chlorpyrifos highlights the capabilities of the proposed colorimetric sensing system.