Investigation of the Adsorption of Gaseous Aromatic Compounds at Surfaces Coated with Heptakis(6-thio-6-deoxy)-β-cyclodextrin by Surface-Enhanced Raman Scattering

Heptakis(6-thio-6-deoxy)-β-cyclodextrin (TCD) was prepared and chemisorbed at the surface of rough silver substrates for surface-enhanced Raman scattering (SERS). The enhanced adsorption of methyl orange and the stability of its azo form at the TCD-coated substrates proved the capability of the immobilized TCD to form inclusion complexes with organic guest molecules. This complexation was used for the detection of aromatics in the gas phase. Toluene, ethylbenzene, m-xylene, chlorobenzene, and m-dichlorobenzene were strongly adsorbed at the TCD-coated substrates, thus making possible the detection of low concentrations, as for example 15 ppm of m-dichlorobenzene. Benzene was weakly adsorbed and detectable in high concentrations only. Since the strongly adsorbed aromatics desorb very slowly, TCD-coated substrates may be applicable for the detection of slowly changing concentrations or as integrating sensors in the surveillance of chemical exposures. The capability of immobilized TCD to adsorb also polycyclic aromatic hydrocarbons was demonstrated using naphthalene.