Mercaptoacetic acid capped CdS quantum dots as fluorescence single shot probe for mercury(II)

Water soluble CdS quantum dots (QDs) have been synthesised using mercaptoacetic acid (MAA) as surface modifying agent through a one step process by using safe and low cost materials. These MAA capped CdS QDs are highly stable in aqueous solution and have strong affinity for mercury ion as a result of interaction with the functional group present in the capping agent. This probe is based on the characteristic of fluorescence quenching of functionalised CdS QDs. Under the optimum conditions, the fluorescence intensity of CdS QDs is linearly proportional to the mercury ion concentration in the range 0.05 × 10−7 to 4.0 × 10−7 M with a detection limit of 4.2 × 10−9 M. There is no significant wavelength shift on the fluorescence-quenched signals in the presence of mercury ion at the pH 7.4. Compare to the organic dyes, these nanoparticles are brighter and more stable against photobleaching. The effect of common foreign cations on the fluorescence of the QDs was examined to evaluate the selectivity and the results showed a high selectivity of the MAA capped CdS QDs towards Hg(II) ions. The method presented here is simple, rapid, inexpensive, sensitive and suitable for practical application.