SPR responsive xylenol orange functionalized gold nanoparticles- optical sensor for estimation of Al³⁺ in water

Xylenol orange functionalized gold nanoparticles (XO-AuNPs), prepared by reducing HAuCl₄ in presence of xylenol orange were found to be selective and sensitive for optical sensing of Al³⁺ in water. XO-AuNPs nanoparticles were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS); the nanoparticles formed were of spherical shape and of uniform size of 3-12 nm. The interaction between Al³⁺ and XO-AuNPs at pH ~3 was studied by XPS analysis. XPS and TEM studies revealed that aggregation of XO-AuNPs in the presence of Al³⁺ takes place through analyte induced cross-linkage mechanism. Al³⁺ induced selective aggregation of the XO-AuNPs lead to a visual change in color of the colloidal solution from deep red to blue. The changes in characteristic absorption peak of XO-AuNPs were monitored; the ratio of A_550nm/A_515nm was used to quantify the concentration of Al³⁺ in water samples. The method gave a linear response from 50-300 ppb (R² = 0.985) of Al³⁺ in drinking water with a detection limit of 12 ppb. The proposed method did not suffer any major interference from concomitant transition metal ions and anions. The developed method was simple, rapid and useful for determination of Al³⁺ in drinking water samples.