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]/SiO 2 /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 SiO 2 /CdTe nanoparticles (NPs). The C[4]/SiO 2 /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 μM with a detection limit of 0.08 μM of methomyl, while the FL intensity of C[4]/SiO 2 /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]/SiO 2 /CdTe NPs in a concentration of methomyl dependence is best described by a Langmuir binding isotherm equation. The possible mechanism is discussed.