Visual detection of lead(II) using a simple device based on P(NIPAM-co-B18C6Am) hydrogel
A simple and portable device equipped with poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-B18C6Am)) hydrogel is developed for visual detection of Pb2+ ions. The device consisted of a compartment for incorporating the hydrogel, a flow channel and an indicating liquid chamber with colored solution, and a dense and elastic polyethylene (PE) membrane to separate the hydrogel and the colored solution. The device works like a mercury thermometer, in which the P(NIPAM-co-B18C6Am) hydrogel and the PE membrane act as the Pb2+ sensor and actuator and the colored liquid column in the flow channel acts as the indicator. The volume of P(NIPAM-co-B18C6Am) hydrogel changes in response to Pb2+ concentration at a certain temperature due to the formation of B18C6Am/Pb2+ host–guest complexes, and the volume change of the hydrogel causes elastic deformation of the PE diaphragm, which pushes out the colored solution from the liquid chamber into the flow channel to form a liquid column. Therefore, the Pb2+ concentration can be detected quantitatively by simply and easily measuring of the liquid column length. The device shows excellent sensitivity towards Pb2+ ions. The detection performances of the proposed devices are satisfactorily stable and repeatable. This simple and portable device enables visual detection of Pb2+ concentration without the help of electrical amplification or spectroscopic measurements.