Abstract
Polyacrylonitrile (PAN) was grafted on silica (Si) surfaces in the form of one-dimensional (1D) gratings to form well-defined line patterns. The tethered PAN 1D gratings were then subjected to a cyano-to-tetrazole conversion reaction to generate a tethered polyvinyltetrazole (PVT) 1D grating. This results in different properties for the transverse magnetic (TM) and transverse electric (TE) polarizations, i.e. perpendicular and parallel to the line patterns, respectively. After adsorption of Cr(III), the negative charges of PVT chains were neutralized, and this results in a collapse of the polymer brushes. As a result, the effective refractive indices vary with the concentration of Cr(III). This causes a gradual color change from yellow via green to blue at incident angles of 30–40°. The adsorption of the ions Na+, Ag+, Ca2+, Cd2+, Fe3+, Zn2+ and Cr6+ ions, in contrast, does not cause significant changes in the effective refractive index. The Cr(III)-induced deswelling transitions can be reversed by treatment with acid. The assay has a limit of detection (LOD) as low as 20 μg·L−1 of Cr(III). The ions Pb(II), Cu(II) and Cr(VI) are also adsorbed by the PVT grating, but the respective LODs are higher (80, 100 and 40 μg·L−1).
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