A Novel Indolino-Spironaphthooxazine As the Highly Sensitive and Selective Probe for Colorimetric Detection of Au3+

A novel colorimetric probe in a spironaphthooxazine class, SPNO, was successfully synthesized. The single crystal and spectroscopic analyses were utilized to confirm its molecular structure and photo properties. The results showed that SPNO in a 1,4-dioxane-H2O solution displayed remarkable selectivity and sensitivity for colorimetric detection of Au3+ over other competing cations. Based on the UV-vis absorption study, the mixtures of SPNO and Au3+ exhibited a new absorption band at 580 nm due to the structural isomerization of SPNO into its merocyanine form which acts as a ligand to form an SPNO-Au3+ complex. The stoichiometric ratio of SPNO to gold(III) cations in the complexes was determined using Job's plot and the results indicated that the complexes were formed at a 1:2 mol ratio. The detection limit of Au3+ in 1,4-dioxane-H2O was investigated to be 335 nM. Moreover, the SPNO-coated test strips were also prepared to demonstrate that this probe can be used practically as a tool for highly sensitive detection of Au3+ in mixed 1,4-dioxane:water solutions. Finally, the sensitivity of SPNO toward Au3+ in drinking water was determined to verify its applicability in real samples.