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The sulfur-containing reagents dithizone, 2,3-dimercapto-1-propanol, 2-thenoyltrifluoroacetone, 1,3,4-thiadiazole-2,5-dithiol, and 1-(2-thiazolylazo)-2-naphthol (TAN) were first examined with respect to their stabilizing effect on CdTe nanocrystals. The indicator TAN was found to best passivate the surface of CdTe NCs if added during synthesis of the NCs at 100 °C. These NCs (referred to as NC-1) have an emission that peaks at 430 nm, and a quantum yield (QY) of 25 %. If, however, TAN-capped particles are prepared in presence of an ionic liquid at room temperature, the QY of such nanocrystals (referred to as NC-2) is increased by 80 % and the emission peak is shifted to 460 nm. The NC-1 particles bind Ag(I), Pb(II), Hg(II), Fe(III), Cr(III), and Cu(II) in phosphate buffer of pH 6.5 while NC-2 particles bind Cu(II) only. Binding of metal ions is associated with a drop in fluorescence intensity. In case of NC-1, quenching is observed in the 23.3 nM to 23.3 μM Cu(II) concentration range with detection limit of 0.5 nM. In case of NC-2, quenching occurs in the 233 nM to 233 μM Cu(II) concentration range with detection limit of 5.0 nM. The method was applied to the determination of Cu(II) in spiked biosamples, and recoveries of Cu(II) (at a 233 nM level) in BSA and fetal bovine serum using NC-2 are 95 % and 92 %. This is better than the recoveries from the same media with NC-1 (70 % and 32 %). These findings demonstrate that the NC-2 material is superior in terms of selectivity and stability but inferior in terms of detection limit. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

CdTe quantum dots capped with thioglycolic acid (TGA) display a strong turn-on fluorescence response if exposed to solutions of cysteine (Cys). In order to exploit this effect, a molecularly imprinted polymer (MIP) for Cys was covalently linked to the QDs via allyl mercaptan. The resulting nanomaterials (QDs, MIP-coated QDs, and nonimprint-coated QDs) were characterized by FTIR and scanning electron microscopy. The adsorption of Cys was studied in phosphate buffer (pH 7.4) with respect to equilibration times (5, 15, and 40 min, respectively), binding constants [2.98, 2.42, and 0.96 (×10 M)], and Langmuir isotherms (R = 0.9995, 0.9999, and 0.9983) in the Cys concentration range between 3.33 μM to 500 μM. The method has a detection limit of 0.85 μM (3σ, blank, for n = 10). The selectivity of the MIP-coated QDs for Cys over 19 other amino acids is similar to that of bare QDs, but MIP-QDs afford better recoveries of Cys from solutions also containing bovine serum albumin (90 %) and fetal bovine serum (97 %), respectively, when compared to the recoveries that are obtained with bare (non-imprinted) QDs (135 % and 120 %). This is probably due to the fact that the outer MIP shell largely reduces protein wrapping, dot aggregation, and matrix inclusion. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]