Selective inclusion of polycyclic aromatic hydrocarbons (PAHs) on calixarene coated silica nanospheres englobed with CdTe nanocrystals

Highly luminescent and stable calixarene (CA[n], n = 4, 7) coated silica nanospheres englobed with CdTe nanocrystals were prepared via a sol-gel technique in aqueous media, and were characterized by luminescence spectroscopy, ultraviolet-visible spectroscopy (UV-vis), FT-IR spectroscopy, transmission electron microscopy (TEM), etc. The nanocomposites (CA[n]@ SiO2@CdTe) showed higher fluorescence intensity and were more stable in comparison with the previous SiO2@ CdTe nanoparticles (NPs). The CA[n]@ SiO2@ CdTe NPs allowed highly sensitive determinations of PAHs by changing the calixarene coating via enhancement of the response of the fluorescence intensity of the CA[n]@ SiO2@ CdTe NPs. The CA[4]@ SiO2@ CdTe and CA[7]@ SiO2@ CdTe NPs turned out to be sensitive to the presence of anthracene and pyrene, respectively. Under optimal conditions, the relative fluorescence intensities of CA[4]@SiO2@ CdTe and CA[7]@ SiO2@ CdTe NPs both increased linearly with increasing anthracene and pyrene concentration in the range 0.1-50 mu M, with the corresponding detection limits (3 alpha) of 2.45 x 6 10(-8) M and 2.94 x 6 10(-8) M, respectively, while the fluorescence of CA[n]@ SiO2@ CdTe NPs in response to other PAHs (including acenaphthene, anthracene, 9,9-diflurofluorene, carbazole, fluoranthene, phenanthrene, biphenyl, fluorene, pyrene) were negligible. It was found that anthracene enhanced the luminescence of the CA[4]@ SiO2@ CdTe and pyrene enhanced that of CA[7]@ SiO2@ CdTe nanocomposites in a concentration dependence that is best described by a Langmuir binding isotherm equation. The possible mechanism is discussed.