Colorimetric Assays for the Detection of Hg(II) Ions Using Functionalized Gold and Silver Nanoparticles

Abstract

In this work, we are reporting a simpler alternative method for field-portable, rapid, inexpensive and accurate optical detection of mercury in water. The sensing properties of the functionalized gold and silver nanoparticles have been utilised in this contribution. Functionalization of nanoparticles has been carried out by betacyanins molecules present in the aqueous extract of beet root (Beta vulgaris). The stability of the sol may be due to the formation of coating of betacyanins on the surface, which might have occurred through metal-N bonding. Betacyanins possess an indole-2-carboxylic acid moiety, which is N-linked to a pyridine dicarboxylic acid group, through an acetyl group, which helps it to act as a chelating ligand. The strong binding of the Hg(II) metal ion with the chelating ligand facilitates the aggregation of nanoparticles. The luminescence quenching occurs through aggregation induced by Hg(II)-carboxylate bonding and strong Hg-Au metallophilic interaction. In an attempt to detect and estimate the concentration of Hg(II) ions present in tap water various solutions having different concentrations were prepared and the fluorescence and UV-Visible studies were performed. It is observed that this probe can detect Hg(II) ions present at concentrations as low as 25 M by fluorescence upon excitation at 380 nm.

An Update on the Use of Natural Pigments and Pigment Nanoparticle Adducts for Metal Detection Based on Colour Response

“…The lowest concentration of mercury ions (Hg 2+ ) in water samples was detectable in the most recent study using anthocyanin hydrogel (LOD 0.2 µM by linear-graph estimation) [110], followed by curcumin-gold nanoparticles, with a visual LOD of 2 µM [86], compared to betalain (LOD 25 µM) and chlorophyll (LOD 2.7 µM with UV-Vis spectrophotometry, 60 µM visually) [71,117]. Mohan and Prakash also reported that a colour change at 10 µM can be visually observable, but the lowest concentration for naked eye observation was not reported [110].…”

“…Recent studies have reported that different types of metal detectors have been developed using red beet pigment (Table 1), namely a functionalised nanoparticles [71] and a smartphone-based analyser [58]. Formerly in 2013, Gonçalves et al used betanin (additive E-162) pigment as a colorimetric sensor for the detection of calcium dipicolinate (CaDPA) in bacterial spores [73].…”

“…In the following year, Barman et al developed a colorimetric assay specifically purposed for mercury (Hg 2+ ) detection using synthesised betacyanin-gold and betacyaninsilver nanoparticles [71]. Betacyanin was formerly extracted from Beta vulgaris through aqueous thermal extraction and filtration.…”

“…The strong metalophilic interaction of Hg-Au and Hg 2+ -carboacylate induced luminescence quenching in the spectrofluorometer. The sensor was highly sensitive and generated fluorescence intensity for quantitative Hg 2+ determination, resulting in a minimum detection of Hg 2+ at 25 µM and a maximum detection at 50 µM [71]. The instrumental uses in this development made it less practical for rapid and portable detection, since UV-Vis spectrophotometers and spectrofluorometers are only used in laboratories.…”

Biosynthesized silver nanoparticles from shoot and seed extracts of Asphodelus tenufolius for heavy metal sensing

“…It is to mention here that the concentration of Cu, Ni, Co and Zn solution below 200 µl/ml of AgNPs did not affect the absorbance SPR of AgNPs. Due to strong electron donating ability which is responsible for the complex formation of Cu, Cd, and other metals with silver, the instability in silver nanoparticles was profoundly noted as compared to Zn and Ni [28][29][30].…”