Colorimetric detection of glutathione based on phthalic acid assisted synthesis of silver nanoparticles

A new rapid, sensitive and selective colorimetric sensing platform for the detection of glutathione (GSH) in dietary supplements was developed by phthalic acid (PTA) assisted synthesis of silver nanoparticles (AgNPs). The di-carboxylic functional groups of PTA were used to modify the surface of AgNPs. The resulting AgNPs product was characterized by surface plasmon resonance (SPR) Ultraviolet-visible spectroscopy (UV-vis), Zeta potential analyzer, Fourietransform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD) techniques, demonstrated that PTA is an effective capping agent to stabilize AgNPs. AgNPs stabilized with PTA could cause the strong affinity to GSH. As the GSH concentration increased, the color of AgNPs solutions was gradually changed from yellow to orange and light purple as well as the SPR shifted from 400 nm to 556 nm upon an aggregation of AgNPs due to electrostatic interaction. The proposed colorimetric sensor was exhibited a linear response in the range of 0.1-100 nM (R-2=0.9992), with low detection limit (LOD) of 0.16 +/- 0.01 nM. The sensor showed better precision with relative standard deviation (RSD) of 2.10% and 1.13% for ten repetitive measurements of 25 nM and 75 nM GSH solution, respectively. The sensitivity of AgNPs for GSH detection can be clearly differentiated towards other coexisting substances (Fe3+, Zn2+, Cu2+, K+, Ca2+, Mg2+, glucose, sucrose, cysteine, ascorbic acid and citric acid). The AgNPs colorimetric sensor could discriminatively detect GSH in dietary supplement samples with the recoveries values in the range of 98.5%-103.0%.