Ratiometric fluorescence detection of O₂^•- based on dual-emission schiff base polymer/rhodamine-B nanocomposites

A novel ratiometric fluorescent sensor for superoxide radical (O₂^•-) detection was developed based on Schiff base polymer (SBP)/rhodamine-B (SBP/RDB) nanocomposites. The SBP/RDB was investigated by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, N₂ adsorption/desorption isotherms and fluorescence spectroscopy, etc. The results showed the SBP was two-dimensional (2D) crystalline nanosheet with the thickness of 0.5 nm. RDB could be self-assembled on each of 2D SBP surface to form SBP/RDB due to the hydrogen bond between N atoms of SBP and -COOH of RDB as well as π-π interaction. The SBP/RDB exhibited the characteristic fluorescence emission of both SBP at 485 nm and RDB at 585 nm under an excitation of 270 nm. The 2D SBP was not only acted as template to assemble RDB, but also used as reference fluorescence for O₂^•- detection. The SBP/RDB fluorescence probe for O₂^•- detection demonstrated high sensitivity and selectivity with good linear range (11.1 ± 0.76 nM-8.0 ± 0.36 μM) and low detection limit (3.7 ± 0.42 nM). Because of the low cost and simple operation, the work sheds some new light to construct ratiometric fluorescent sensors based on SBP to detect O₂^•- in drinking water and human blood serum for commercial applications.