In this contribution, bovine serum albumin stabilized gold nanoclusters as novel fluorescent probes were successfully utilized for the detection of methotrexate for the first time. Our prepared gold nanoclusters exhibited strong emission with peak maximum at 633.5 nm. However, the addition of methotrexate induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by methotrexate allowed the sensitive detection of methotrexate in the range of 0.0016 μg mL(-1) to 24 μg mL(-1). The detection limit for methotrexate is 0.9 ng mL(-1) at a signal-to-noise ratio of 3. The present sensor for methotrexate detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.

In this contribution, novel chitosan-stabilized gold nanoparticles (AuNPs) were prepared by mixing chitosan with citrate-reductive AuNPs under appropriate conditions. The as-prepared chitosan-stabilized AuNPs were positively charged and highly stably dispersed in aqueous solution. They exhibited weak resonance light scattering (RLS) intensity and a wine red color. In addition, the chitosan-stabilized AuNPs were successfully utilized as novel sensitive probes for the detection of heparin for the first time. It was found that the addition of heparin induced a strong increase of RLS intensity for AuNPs and the color change from red to blue. The increase in RLS intensity and the color change of chitosan-stabilized AuNPs caused by heparin allowed the sensitive detection of heparin in the range of 0.2–60 μM (~6.7 U/mL). The detection limit for heparin is 0.8 μM at a signal-to-noise ratio of 3. The present sensor for heparin detection possessed a low detection limit and wide linear range. Additionally, the proposed method was also applied to the detection of heparin in biological media with satisfactory results.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-013-1930-9) contains supplementary material, which is available to authorized users.

In this paper, we reported the development of a highly sensitive and selective resonance light scattering (RLS) technique for glutathione using gold nanoparticle probes. The assay relies upon the distance-dependent optical properties of gold nanoparticles, the self-assembly of glutathione on gold nanoparticles, and the interaction of a 2 : 1 glutathione-Cu(2+) complex. In the presence of Cu(2+), glutathione could rapidly induce the aggregation of gold nanoparticles, thereby resulting in greatly enhanced RLS intensity and red-to-blue (or purple) color change. The concentration of glutathione can be determined by the naked eye or a fluorescence spectrometer. Under the optical conditions, the detection of glutathione can be finished within 20 min, and the detection limit of 10 nM can be reached. The concentration range of the probe is 40-280 nM. The proposed method holds a specific selectivity toward glutathione and it is applied to the detection of glutathione in human serum with satisfactory results. In addition, the assay shows great potential application for disease-associated biomarkers, and it will meet the great demand for amino acid determination in fields such as food processing, biochemistry, pharmaceutical, and clinical analysis.

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