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

[Display omitted] •A red-shift in fluorescence spectra of CdTe QDs due to self-assembly of CTAB on the surface of CdTe QDs.•Double-emitter fluorescence ratiometric nanoprobe using Carbon dots (CDs) and orange-emissive CTAB-CdTe QDs.•CTAB-mediated quenching of CdTe and no change in fluorescence intensity of CDs in presence of methyl parathion pesticide.•Wide emission color change of the probe in presence of different concentrations of MP using smartphone.•Visual tracking of methyl parathion in rice samples at low concentrations. 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.