Tannic acid-coated gold nanorod as a spectrometric probe for sensitive and selective detection of Al³⁺ in aqueous system

This work introduces an efficient probe for sensitive and selective detection of Al³⁺ based on gold nanorods (AuNRs) with tannic acid (TA) surface modification. TA, which contains five digalloyl ester groups covalently attached to a glucose core, exhibits preferential complexation and binding to Al³⁺, leading to the formation of side-by-side assembly of AuNRs and consequently inducing a change in the UV–vis absorbance spectra of their aqueous suspension. By increasing the Al³⁺ concentration to 7.4 μM, a rapid, linear blue-shift in the longitudinal LSPR band and a decrease in its intensity are exhibited, with a 0.09 μM limit of detection (LOD). Furthermore, the probe shows good selectivity to Al³⁺, along with the capability of detecting this cation in real water samples.