Ultrasensitive aptamer biosensor for malathion detection based on cationic polymer and gold nanoparticles

In this work, we have demonstrated a novel sensing strategy for an organophosphorus pesticide namely, malathion, employing unmodified gold nanoparticles, aptamer and a positively charged, water-soluble polyelectrolyte Polydiallyldimethylammonium chloride (PDDA). The PDDA when associated with the aptamer prevents the aggregation of the gold-nanoparticles while no such inhibition is observed when the aptamer specific pesticide is added to the solution, thereby changing the color of the solution from red to blue. This type of biosensor is quite simple and straightforward and can be completed in a few minutes without the need of any expensive equipment or trained personnel. The proposed method was linear in the concentration range of 0.5-1000 pM with 0.06 pM as the limit of detection. Moreover, the proposed assay selectively recognized malathion in the presence of other interfering substances and thus, can be applied to real samples for the rapid screening of malathion.