Aluminum is a hazardous element, found abundantly in the environment. Although many methods have been reported for the efficient detection of aluminum, an easy and accessible sensor for fast detection of aqueous aluminum has not been devised to date. In this approach, we have synthesized indole-2-carboxylic acid capped silver nanoparticles (I2CA-AgNPs) using a one-pot method and used them as label-free nanosensors for the detection of Al3+ in the presence of interfering metal ions. I2CA-AgNPs were synthesized by two methods at different temperatures. AgNPs synthesized by the heating method were further used as detection probes as they showed a strong and narrow surface plasmon resonance (SPR) peak in the visible region. The sensitivity of the detection probe has been optimized by variations in size and distribution of nanoparticles. Synthesized AgNPs were characterized by UV–vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR), zeta potential, and dynamic light scattering (DLS) analysis. Based on these results, I2CA-AgNPs could be used as colorimetric sensors to selectively detect the presence of Al3+. Further, results are confirmed by theoretical calculations of binding energy by density functional theory (DFT). Moreover, the nanosensor can also be applied to trace aluminum contamination in different types of water samples. The lower detection limit of the proposed method is 0.01 ppm (S/N = 3) which falls in the permissible limit set by the United States Environmental Protection Agency (USEPA), i.e. 50 ppm.

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In this paper, we report a simple, novel, and highly selective plasmonic nanoparticles (NPs)-based colorimetric nanoprobe for the detection of Al(III) ions in aqueous solution. 5-Hydroxy indole-2-carboxylic acid (5H-I2CA) was utilized as a reducing as well as capping agent for the preparation of silver nanoparticles (5H-I2CA@AgNPs). The interaction between Al(III) and AgNPs was determined by UV–vis absorption spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, and dynamic light scattering techniques. The absorption values ( A 452–410 ) of the 5H-I2CA@AgNPs solution exhibited a linear correlation with Al(III) ion concentrations within the linear range of 0.1–50 nM. An outstanding selectivity toward Al(III) was demonstrated by the proposed nanoprobe in the presence of interfering cations. Kinetics was used to study the selectivity of nanoprobe, which indicated second-order kinetics, and the rate constant was very high. The activation energies of Al(III) were found to be the lowest compared to those of other interfering ions. The results of kinetics and thermodynamic study of Al(III) were compared to those of four other competing ions. The thermodynamic data reveal that the interaction best suited for Al(III) ion compared to other metal ions (Al(III) > Co(II) > Hg(II) > Cr(III) ≅ Cr(VI)). The lower detection limit of the proposed nanoprobe for Al(III) is 1 nM. The present method also holds practical applicability for real water samples.