Poly(2‐n‐propyl‐2‐oxazoline) Surface Modified Quartz Crystal Microbalance Sensor for Highly Sensitive Detection of Alkali Cyanides, Alkali Chlorides, and Other Ionic Species in Water

Abstract Poly(2‐oxazoline)s are a class of organic polymers having tertiary amide groups in their chemical structure. They are currently under intense study for potential applications in many different fields due to the tunability of their physical and chemical properties. In this work, poly(2‐oxazoline)s are demonstrated for the first time as the sensing elements for chemical sensors. More specifically, a poly(2‐n‐propyl‐2‐oxazoline) (PnPropOx) with a xanthate end‐group is synthesized and used to modify a quartz crystal microbalance (QCM) transducer. The general liquid sensing properties and sensor responses of the resulting PnPropOx‐QCM sensor to a variety of ionic compounds in aqueous solutions have been evaluated revealing excellent liquid sensing properties showing a strong response to alkali chlorides and cyanides, especially. The sensor response is fast and fully reversible and the selectivity for alkali chlorides and cyanides is remarkably high. The observed sensitivity using 5 MHz PnPropOx‐QCMs reaches ≈8 Hz µM⁻¹ at 30 °C, enabling analyte detection down to a limit of detection of 0.2 µM concentration. According to these results, it can be concluded that PnPropOx, and possibly poly(2‐oxazoline)s in general, is very promising as a sensing material for chemical sensors in liquids to selectively detect a variety of ionic species.