Peroxidase activity of biogenic platinum nanoparticles: A colorimetric probe towards selective detection of mercuric ions in water samples

- Green platinum nanoparticles of 4.4 nm size were produced with gum olibanum.
- Produced nanoparticles shown excellent peroxidase activity.
- Peroxidase activity of nanoparticles was selectively inhibited by mercuric ions.
- Detection was linear in the range of 50-500 nM of mercuric ion concentration.
- Pt NP based colorimetric probe can be used for screening and Hg2+ field detection.

A biogenic green method for the synthesis of platinum nanoparticles (Pt NP) was developed using non-toxic, renewable, biodegradable plant exudate gum, gum olibanum (Boswellia serrata). The effect of parameters such as concentrations of gum (0.1-0.5%) and chloroplatinic acid (0.125-1.0 mM) on nanoparticle synthesis was studied. Techniques such as UV-vis spectroscopy (UV-vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential measurements were used to characterize the generated nanoparticles. The Pt NP formation was evidenced from the broad continuous absorption in the UV-vis spectra and appearance of black colour. The XRD pattern established the face centered cubic crystal structure of the fabricated nanoparticles. The produced NP were quasi-spherical in shape with a particle size of 4.4 ± 0.5 nm. The resulting nanoparticles exhibited excellent peroxidase activity which catalyzes the oxidation of the chromogen 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to a blue colour product, in the presence of hydrogen peroxide. The peroxidase activity of the nanoparticles was selectively inhibited by mercuric ions (Hg2+) due to the formation of amalgam by Hg-Pt specific interaction. Notably, the inhibition was not affected by other metal ions even at a concentration of 5 μM. The decrease in oxidized TMB intensity at 652 nm (blue colour), upon addition of mercuric ions was linear in the range of 50-500 nM for MilliQ, tap and ground waters and the respective limit of quantification values for Hg2+ using the developed method were 16.9, 26 and 47.3 nM. The proposed method was effectively applied for the determination of Hg2+ in various ground water samples and verified with CVAAS. We envisage that the biogenic Pt NP based colorimetric probe can have promising applications in the screening and field detection of mercuric ions in various water bodies and public drinking water distribution systems.