This paper reports the use of fluorescent gold nanoclusters synthesized using bovine serum albumin (Au-BSA) for the sensing of copper ions in live cells. The fluorescence of the clusters was found to be quenched by Cu(2+) enabling its detection in cells. The selectivity of the nanosensor was demonstrated in the presence of several cations excluding Hg(2+). We did not study the effect of Hg(2+) since it was reported earlier. The present study suggests that Cu(2+) induced fluorescence quenching is due to its binding to BSA rather than the fluorescence quenching by metal-metal interaction as in the case of Hg(2+). The Au-BSA showed excellent selectivity to Cu(2+) at various pH conditions. The 'turn off' of fluorescence can be retrieved by a Cu(2+) chelator glycine. Our results showed that gold clusters can be used as a 'turn off' sensor for copper and a 'turn on' sensor for glycine. Under the experimental conditions, the probe showed a response for Cu(2+) over a range of 100 μM to 5 mM with a detection limit of 50 μM. The role of Cu(2+) in the misfolding and disassembly of Prion Protein (PrP) leading to various maladies is well ascertained. The methodology we reported here seems to be useful in supplementing other techniques in predicting disease conditions involving Cu(2+).

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Colloidal gold is extensively used for molecular sensing because of the flexibilities it offers in terms of modification of the gold nanoparticle surface with a variety of functional groups using thiol chemistry. We describe a simple assay that allows the visual detection of glucose in aqueous samples and demonstrates its applicability by estimating glucose in urine. To enable the glucose detection, we functionalized the thiol capped gold nanoparticles with glucose oxidase, the enzyme specific to β-D glucose, using carbodiimide chemistry. The visible color change of the GOD-functionalized gold nanoparticles from red to blue on interaction with glucose is the principle applied here for the sensing of urine glucose level. The solution turns blue when the glucose concentration exceeds 100 μg/mL. The approach depicted here seems to be important, particularly in third world countries where high tech diagnostics aids are inaccessible to the bulk of the population.

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