Naked-Eye Detection of Copper(II) Ions Using Ion-Imprinted Polymer Deposited on Nanosilica

In this study, nanosilica was utilized as a substrate for the deposition of polymeric layers imprinted with copper(II) ions, which were used for the colorimetric detection of Cu(II). The nanosilica was first prepared using the Stober method and then used in an in situ polymerization of aminopropyltriethoxysilane and tetraethyl orthosilicate in the presence of the template copper ions. Following the elution process, the polymer was washed with a proper solution to obtain the Cu(II)-imprinted polymers on nanosilica (SiO2@MIP), which were characterized by transmission electron microscopy to reveal the diameter of the silica core to be approximately 350 nm, and the polymeric layers were about 40 nm in thickness. The SiO2@MIP was successfully employed in the colorimetric detection of Cu(II) in aqueous solutions with concentrations ranging from 0.001 to 0.1 M, using xylenol orange as the colorimetric indicator. The color change could be easily observed by the naked eye, with colors shifting from yellowish-orange to dark purple. The sensing signal was quantitatively assessed using UV–vis absorbance, and the limit of detection for Cu(II) was determined to be 0.064 mg/mL. Additionally, SiO2@MIP was demonstrated to be highly specific for the adsorption of Cu(II) with the imprinted cavities. The proposed Cu(II) imprinted polymers show promise in real-world detection of Cu(II) with advantages of low cost, user-friendliness, and high selectivity.