Characterization of volatile, hydrophobic cyclodextrin derivatives as thin films for sensor applications

Successful development of chemical sensors and multi-sensor arrays critically depends on the availability of appropriate coatings. In the present studies, we synthesized hydrophobic and thermally stable cyclodextrin (CD) derivatives and, using a physical vapor deposition method, successfully deposited them on surfaces as thin films. ¹³C NMR and FT-IR spectroscopy verified that while heptakis(6-O-tert-butyldimethylsilyl-2,3-di-O-methyl)cyclomaltoheptaose (DMe-CD) remained chemically intact after the deposition, heptakis(6-O-tert-butyldimethylsilyl-2,3-di-O-acetyl)cyclomaltoheptaose (DAc-CD) showed some variations. The hydrophobicity and refractive indices of the prepared thin films were determined using, respectively, contact angle measurements and ellipsometry. Selectivity patterns of the prepared CD films with respect to a series of analytes were defined using surface plasmon resonance. Because the chemical structure of the DAc-CD derivatives is compromised during the PVD process and any structural change may affect the selectivity of these thin films, additional attention should be given to the PVD process. In addition, thin films of the DMe-CD derivative were tested as protective coatings on silver island films for sensors based on surface enhanced Raman spectroscopy (SERS). The observed kinetics of SERS signals indicates that medium molecular weight analytes are able to rapidly diffuse through the CD films and reach the underlying silver islands.