A conjugated oligoelectrolyte for the recognition of uranyl ion in aqueous and soil samples via RGB method

The development of selective and practically applicable sensors for monitoring trace uranyl ions (UO₂²⁺) in an aqueous medium is the biggest challenge. This study presents the development of a conjugated oligoelectrolyte-based probe (COE) for the selective detection of UO₂²⁺ ions in water bodies. The COE is a water-soluble probe having an organic backbone with two ionic pendants at the terminal points. It changes its color to a dark yellow selectively in the presence of UO₂²⁺ ions. This visible change was integrated with a smartphone RGB color quantification method. The COE displayed an RGB chemo-dosimeter to selectively monitor UO₂²⁺ ions without interference from other metal ions. In the parallel experiment, COE displays a spectrofluorimetric emission signal at λ_ems. = 525 nm (with λ_exc. = 420 nm), which exhibits quenching of signal when interacted with UO₂²⁺ ions. The limit of detection (LOD) is found to be 3.07 × 10^-2 µM and 4.50 µM by spectrofluorimetric and RGB color value methods, respectively. ¹H NMR and XPS analysis investigated the mode of interaction, and it suggested that the quenching of the emission signal was due to the interaction between the electron-rich azomethine site of COE and UO₂²⁺ ion. The smartphone-based RGB color analysis makes COE a potential probe with reduced operation time and offers a fresh approach for the immediate, real-time detection of UO₂²⁺ ions in aqueous and soil samples.