Enhanced Sensor Capability of Juxtaposed β-Cyclodextrin Rings in TiO2 Ultrathin Matrix as Determined by Cyclic Surface-Polarization Impedance Measurement

Abstract

The present study was focused on the sensitive detection of organic substances by electrochemical impedance spectroscopy (EIS), i.e., cyclic surface-polarization impedance (cSPI) measurement that detects the difference in interactions between the electrode and chemicals in aqueous phase. For cSPI measurement, Pt electrodes were modified with three different types of self-assembled monolayer (SAM) of-OH,-COOH, and-pyridine (Py) terminal groups. Among them, the Pt/SAM-OH electrode was additionally modified with an ultrathin TiO 2 gel layer and a 2:1 complex of β-cyclodextrin (β-CD) and bisphenol A (BPA), and then the BPA moiety was removed by washing in methanol. A highly sensitive and selective detection of BPA was achieved by the synergic effect of molecular imprinting and host-guest interaction in the ultrathin TiO 2 layer. The resulting BPA-imprinted TiO 2 /β-CD film showed a linear increase in ∆R p at-0.1 V for BPA of 2×10-8 to 2×10-6 M. However, BPA was barely detected on the SAM-modified electrodes at low concentrations, although their sensor responses were markedly enhanced at a concentration of 2×10-6 M, compared with that of the bare Pt electrode. The current approach suggests the simple concept and use of sensor films for the sensitive detection of various organic molecules including environmental pollutants.