A smart-phone based ratiometric nanoprobe for label-free detection of methyl parathion

The widespread use of pesticides in pest management has boosted the demands for developing highly sensitive probes for on-site monitoring. Herein we presented a sensitive enzyme-free ratiometric probe for determination of methyl parathion (MP), as an organophosphate pesticide using TGA-capped CdTe QDs and carbon dots (CDs). Unlike previous methods in which hydrolysis product of MP is instrumental in the response of the sensors, here, self-assembly of cetyltrimethylammonium bromide (CTAB) on the surface of non-modified yellow-emissive CdTe QDs facilitates the quenching of CTAB-QDs upon addition of MP while the fluorescence intensity of CDs remains constant. Using a smartphone, the ratiometric probe shows visual emission color changes from orange-peach into pink, purple, weak blue, and dark blue, which is highly appropriate for quantitative detection of MP based on the hue-saturation-lightness color model. A wide linear range from 0.001 μg.mL−1 to 10 μg. mL−1 MP with a low limit of detection of 1.2 ng. mL−1 (S/N = 3) were obtained under optimized condition. Furthermore, with high sensitivity and selectivity, this platform has the capability to detect MP in rice and tap water samples with desired results.