An innovative synthesis of (Ag0-pullulan-Ag+) as an optical nanoprobe for sensitive and selective detection of Fe2+ ion based on redox reaction

Herein, we Synthesized an efficacious optical nanoprobe (Ag0-pullulan-Ag+) for sensitive and discriminative detection of ferrous ions (Fe2+) over ferric ions (Fe3+) in solution. Pullulan (PUL) biopolymer was used as the reductant of excess AgNO3, at moderate heating, so that stable and dispersed silver nanoparticles (AgNPs or Ag0) were formed, which also contained an unreduced silver ion (Ag+), all intertwined in the pullulan polymeric matrix. Extensive characterization confirmed the role of PUL as a capping agent, while sharp Ag0 and Ag+ peaks were validated using X-ray photoelectron spectroscopy (XPS). The Ag0-PUL-Ag+ probe showed a sharp absorption maximum at 415 nm, having a majority size distribution around 20–30 nm, from TEM. The addition of Ag0-PUL-Ag+, acetate buffer pH 5.0, and Fe2+ under room temperature incubation led to Fe2+ reduction of available Ag+ to more AgNPs, based on redox reaction, with color progression from light yellow to yellow, orange, and brownish yellow. The ΔA@411 plotted against Fe2+ concentration was linear within 1.0–20.0 and 20.0–125.0 μM, with a limit of detection (LOD) of 0.15 μM. The assay was selective to only Fe2+ over other metal ions and was applied to Fe2+ detection in tap water and in ferrous fumarate tablets with satisfactory accuracy/precision. Our work showed that with careful control of nanomaterial synthesis conditions, a sensitive detection probe could be obtained for impressive analyte sensing/detection.