Synthesis of CdTe quantum dots in sol-gel-derived composite silica spheres coated with calix[4]arene as luminescent probes for pesticides

Highly luminescent and stable CdTe quantum dots (QDs) in sol-gel-derived composite silica spheres coated with 5,11,17,23-tetra-tert-butyl-25,27-diethoxy-26,28-dihydroxycalix[4]arene (C[4]/SiO2/CdTe) are prepared via the sol-gel technique in aqueous media, which are characterized by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), fluorescence spectroscopy, UV-vis spectroscopy, and FT-IR spectroscopy. The synthesized nanocomposites show higher fluorescence (FL) intensity and are more stable in comparison with the SiO2/CdTe nanoparticles (NPs). The C[4]/SiO2/CdTe NPs allow a highly sensitive determination of methomyl via significant FL intensity enhancement. Under optimal conditions, the relative FL intensity is increased linearly with increasing methomyl concentration in the range of 0.1-50 mu M with a detection limit of 0.08 mu M of methomyl, while the FL intensity of C[4]/SiO2/CdTe NPs to other pesticides including parathion-methyl, fenamithion, optunal, and acetamiprid is negligible. It is found that the enhanced luminescence intensity of the C[4]/SiO2/CdTe NPs in a concentration of methomyl dependence is best described by a Langmuir binding isotherm equation. The possible mechanism is discussed.