Gamma radiolytically synthesized phosphate decorated gold nanoparticles for ultra-trace level detection of U(VI) in water

We describe the ⁶⁰Co-Gamma radiolytic synthesis of stable poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MEP) -decorated gold nanoparticles (PB2MEP-Au) for spectrophotometric detection of uranium (U(VI)) in the ppb level. The developed technique is based on the Localize Surface Plasmon Resonance (LSPR) band intensity quenching, accompanied by a red shift in the wavelength range 523-545 nm at higher concentrations, due to interaction between U(VI) ion and phosphate group bearing PB2MEP-Au. The response was linear in the 5-80 ppb U(VI) concentration range, with LOD of 8.6 ppb. Samples were characterized by transmission electron microscopy, Particle Size Analysis and Zeta Potential measurements to determine morphological transitions upon analyte interaction. Density Functional Theory (DFT) calculations were invoked to study the Au nanoparticle stabilization mechanism, and revealed the interaction of U(VI) with PB2MEP-Au to be thermodynamically spontaneous for the formation of [UO₂(B2MEP)₂(H₂O)]²⁺ complex, the stability primarily driven by entropy. Interference by other coexisting metal ions was negligible up to interferent:target ratios of 10:1. The method was validated through quantification of U(VI) in water samples spiked with known U(VI) concentrations, the results being in corroboration with those reported using laser fluorimetric method. A T-test confirmed the results derived from the proposed method were not significantly different from those obtained using the standard estimation protocol at a 95% confidence level.