The polyanion polystyrene sulfonate (PSS), the polycation poly (allylamine hydrochloride) (PAH), and the anionic poly (N-isopropylacrylamide-co-acrylic acid) [P(NIPAM-co-AA)] microgels were self-assembled onto the polyethylene imine (PEI) adsorbed gold surfaces of quartz crystal microbalance (QCM) because of the electrostatic attractions. The interactions of various metal particles including Ca2+, Bi3+, Cu2+, Zn2+, Ni2+, Sn2+, Co2+, and Cd2+ with the obtained PEI/PSS/PAH/microgel layer in aqueous solutions were evaluated by QCM. The PEI/PSS/PAH/Microgel covered QCM sensor demonstrates the lowest detection limit of 0.1 ppm in aqueous solutions and the obviously linear connection between the frequency response and Ni2+ concentration from 0.1 to 20 ppm, which is due to the complexation of Ni2+ with the carboxyl groups of microgels. Atomic force microscopy (AFM) was used to reveal the morphology and stability of the self-assembled polyelectrolyte/microgel layer before and after adsorbing heavy metal ions. These self-assembled materials of polyelectrolyte/microgel layer will be helpful for manufacturing ion-selective materials for separation and identification purposes.

Preparation and ion sensing property of the self-assembled microgels by QCM