Label-Free Colorimetric Nanosensor for the Selective On-Site Detection of Aqueous Al3+

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.