Selective determination of caffeic acid in wines with electrochemical sensor based on molecularly imprinted siloxanes

Caffeic acid (CA) is one of the phenolic compounds widely found in wines and it is associated to the quality of this beverage and also to various beneficial effects on health. Thus, a novel electrochemical sensor based on molecularly imprinted siloxanes (MIS) film was developed for the highly selective determination of CA. The MIS film was prepared by sol–gel process, using the acid catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS), phenyltriethoxysilane (PTEOS) and 3-aminopropyltrimethoxysilane (3-APTMS) in presence of CA as template molecule. The MIS film was immobilized onto Au electrode surface pre-modified with 3-mercaptopropyltrimethoxysilane (3-MPTS) and then characterized by Differential Pulse Voltammetry (DPV), Field Emission Scanning Electron Micrographs (FESEM) and Cross Polarization-Magic Angle Spinning Nuclear Magnetic Resonance of 29Si (29Si CP-MAS NMR). Under the optimized conditions, the sensor showed a linear current response to the target CA concentration in the range from 0.500 to 60.0 μmol/L, with a detection limit of 0.15 μmol/L. The film exhibited high selectivity toward the template CA, as well as good stability and repeatability for CA determinations as well as for sensor preparation. Furthermore, the proposed sensor was applied to determine CA in wines samples and the results were in agreement with those obtained by a chromatographic method. The acceptable values of recovery implied its feasibility for practical application.