An efficacious fabrication of Tara gum reduced/stabilized gold nanoparticles and its post functionalization with quercetin for sensitive and selective optical detection of iodide ion

Herein, we reported Tara gum (TG), mediated synthesis of stable and dispersed gold nanoparticles (AuNPs). TG was applied for the first time as the reducing/capping agent for AuNPs synthesis, through heating with gold salt, stirring at 80 °C for 1 h under NaOH support. Reddish color AuNPs solution, exhibiting absorption maximum at 521 nm, with an average particle size of 10.5 ± 1.8 nm, was obtained. The synthesized TG-AuNPs was characterized using various equipment, including TEM, FESEM, ATR-FTIR, Raman spectroscopy, XRD, TGA/DTG, DLS/zeta potential and XPS, which confirmed the dispersal of small-sized AuNPs in TG polymeric structure. TG-AuNPs was further modified with Quercetin (QT), a notable polyphenolic compound, to realize TG-AuNPs-QT nanoparticles which was applied as optical nanoprobe for Iodide ion (I^-) detection. The addition of silver ion [Ag⁺], to the TG-AuNPs-QT probe results in color change, from red to yellow, followed with an absorption spectra blue shift from 521 nm to 420 nm, owing to QT mediated in-situ reduction of Ag⁺ to its nanoparticles, which was deposited on pre-formed AuNPs, yielding Au@Ag nanostructure. However, when I^- (various concentrations), were pre-mixed with an optimized Ag⁺ concentration, reverse color and absorption spectra perturbations were observed, which is attributed to the high binding interaction between Ag⁺ and I^-, forming AgI complex in solution. At the optimal I^- detection conditions, the analytical response applied, (A_o-A_i)@405 nm, was linear with I- concentrations from 1.0 to 65.0 μM, with a limit of detection/quantification (LOD/LOQ) of 250 nM and 0.82 μM, respectively. Practical applications of the probe was demonstrated on water and diverse food samples, with satisfactory accuracy.