Detection of heavy metal ion using photonic crystals of polymer brushes with reflective laser beam system

Polyacrylonitrile (PAN) brushes were grafted from the line array of halogen group-modified layer as photonic crystals (PCs). The tethered PAN PCs were further converted to tethered polyvinyltetrazole (PVT) PCs by a cyano-to-tetrazole reaction, employed to adsorb metal ions with the tetrazolyl groups. Geometrical structure of the PVT PCs was changed after metal ions adsorption due to the electrostatic force. A laser beam system was employed to analyze the optical feature with a characteristic diffraction effect of the PVT PCs at a 45° incident angle with respect to the surface of the line array, oriented such that its lines were parallel (LII) or perpendicular (LT) to the beam's projection onto the PC, was employed to analyze the two- and three-dimensional reflective diffraction signals of the PC. Change in diffraction intensity of the PVT PCs was correlated with the metal ion adsorption to obtain limit of detection (LOD) as low as 10 μg·L⁻¹ of Cr(III) with linear range from 10 to 170 μg·L⁻¹ and selectivity. Traces of the metal ions can be determined with less milliliter sample using the reflective diffraction intensity with PVT PC, which can provide a simple method to monitor the heavy ions in environment in-field.