Background: It has been known for quite some time now that silver nanoparticles (AgNP) can inhibit microbial growth and even kill microbes. Our investigation reports the antimicrobial activity of AgNP against a model bacterium, Escherichia coli.

Here, we are reporting two methods for detection of Cu ?2 ion and Hg ?2 ions using biosynthesized silver nanoparticles. The detection of Cu ?2 ion was based on changes in absorbance resulting from complex formation of the metal ion. Various concentrations of Cu ?2 ion were used to test the linearity and sensitivity of the method. A new peak at around 770 nm, in addition to the peak of the AgNP at 406 nm, was observed in each case (above 20 lM). With the increase of concentration of Cu ?2 ion solution, the absorbance at 406 nm peak decreased and that of 770 nm increased gradually. The calibration curve obtained from the ratio of the absorption coefficients of these two peaks (Ex 770/406 ) versus concentration of Cu ?2 ions enables one to estimate quantitatively the amount of Cu ?2 ions present in water in lM levels. This AgNP was further functionalized with 3-mercapto-1, 2-propanediol (MPD) for detection of Hg ?2 present in water by colorimetric method. As soon as Hg ?2 solution was added in MPDfunctionalized AgNP (MPD-AgNP), a new peak at around 606 nm appeared along with the peak at 404 nm. The new peak might be due to the aggregations occurred by the recognition of heavy metal ion Hg ?2 by MPD-AgNP through dipropionate ion. A calibration curve between the ratios of the absorption coefficients of these two peaks (Ex 404/606 ) and concentration of Hg ?2 was drawn for quantitative estimation of Hg ?2 present in water at lM level.

In this work, we report a green method for the synthesis of gold nanoparticles (GNP) using the aqueous extract of red tomato (Lycopersicon esculentum). We believe that citric acid and ascorbic acid present in tomato juice are responsible for the reduction of gold ions. This biosynthesized GNP in the presence of sodium dodecyl sulfate has been used as a colorimetric sensor to detect and estimate the pesticide, methyl parathion. The GNP in the presence of methyl parathion shows a new peak at 400 nm due to the formation of 4-nitrophenolate ion by catalytic hydrolysis of methyl parathion in alkaline medium. A calibration curve between the absorption coefficients of the 400-nm peak versus the concentration of the pesticide allows the quantitative estimation of the 4-nitrophenolate ion, thereby enabling indirect estimation of methyl parathion present in the system.

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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.