green synthesis of gold nanoparticles with pectinase: a highly selective and ultra-sensitive colorimetric assay for mg2+

A highly selective and ultra-sensitive colorimetric assay has been developed for detecting the magnesium ion (mg2+) based on pectinase (pe)-protected au nanoparticles (pe-aunps). this is the first study reporting the use of pectinase for green synthesizing gold nanoparticles. aggregation of pe-aunps was induced immediately following the addition of mg2+ ion under tris-hcl buffer at ph 4.0, yielding a color change from red to blue, and the characteristic surface plasmon resonance (spr) peak of pe-aunps was red-shifted to 665 nm. the effects of parameters such as ph, the amount of pe-aunps, and incubation time on the sensitivity of colorimetric assay were investigated in detail. the mg2+-induced aggregation of pe-aunps could be monitored by both the naked eye and uv–vis spectrophotometry. the lowest detection concentration with the naked eye is 0.52 μm. a linear relationship between the absorbance ratio (a 665/a 523) and mg2+ concentration was observed in two ranges of mg2+ concentration by uv–vis spectrophotometry, including 5.34 × 10−7 μm to 51.4 μm and 5.12 × 102 μm to 3.19 × 103 μm. the mg2+ detection limit was determined to be 4.0 × 10−9 μm with uv–vis spectrophotometer. the proposed colorimetric assay possesses a highly selective response for mg2+ over other metal ions. this method has been successfully applied to determine the mg2+ ion in some water samples.