Silver nanoparticles prepared from <i>Schinus therebinthifolius</i> extract as new colorimetric sensor for Hg²⁺ determination

A colorimetric sensor based on silver nanoparticles for mercury (Hg²⁺) determination in environmental samples, including stream water, treated water, and drilling fluid has been developed. The silver nanoparticles were synthesised via a biological method using aqueous extract of <i>S. terebinthifolius</i> leaves and characterised by visible spectrophotometry, transition electronic microscopy, dynamic light scattering, and Zeta potential analyses. In addition, the antibacterial activity of the obtained silver nanoparticles and the extract of <i>S. terebinthifolius</i> were also evaluated. The green synthetised silver nanoparticles showed a spherical morphology, high stability, and sensitivity to the presence of Hg²⁺ and Fe²⁺, being useful for quantification of both analytes. The obtained calibration curves for Hg²⁺ showed a R² of 0.9982 and LOD of 0.10 mg L⁻¹ and for Fe²⁺, with R² of 0.9938 and LOD of 0.20 mg L⁻¹. However, reflecting the high environmental concern of Hg²⁺, it was selected for the sensor´s application. This way, a simple masking alternative using H₂ O₂ and 1,10- phenanthroline was proposed to minimise potential interferences of Fe²⁺ on Hg²⁺ determination. The accuracy and the precision of the proposed sensor, evaluated by recovery tests (80–118%) and relative standard deviation (2–23%), were suitable for Hg²⁺ determination. The silver nanoparticles also showed promising antibacterial activity, especially against the gram- negative bacterium <i>Escherichia coli</i>. Thus, the colorimetric sensor based on silver nanoparticles presents a viable alternative for determination of Hg²⁺ with a suitable LOD for environmental samples.