Quantum dots QDs which exhibit excellent

Quantum dots (QDs), which exhibit excellent fluorescence quantum yields (QYs), high extinction coefficients and size-tunable narrow emission have highly attracted great interest in various applications such as in solar cells, sensors, and bioimaging [16], [17], [18], [19], [20]. However, QDs suffered from poor chemical/photo-stability toward extreme pH or high ionic strength, which restricts their actual application [21], [22]. Several strategies for improving the stability of QDs have been developed, such as modification of a shell with a large band gap semiconductor [23], [24], encapsulation in amphiphilic copolymers [25], [26] or silica shells [27], [28] and the other surface modification [29], [30]. Methods mentioned above mostly need multi-step operation, which were sophisticated. QDs’ behavior is often affected by the outermost ligands of QDs [31]. Good stability of QDs requires the ligands which have a high affinity with core from the nanocrystal aggregating and passivate the surface defect sites. A number of studies were focused on monothiol stabilized QDs, however, monothiols have a significant limitation clearly that the monothiols have a lower affinity with metal ion of the outermost shell layer of the QDs [32], [33]. Mattoussi et al. adopted dihydrolipoic Flubendazole kinase (DHLA) as a convenient ligand, which demonstrated to be a good ligand for long-term stability [34], [35], [36], [37], [38]. However, the dithiol passivated QDs were mainly prepared by ligand-exchanged with hydrophobic QDs, which could adversely affect the optical properties of QDs. There are little reports about dithiol stabilized QDs directly in aqueous solution. Ju and his coworkers controlled the rate of generation of Te2- by electrochemical reduction to prepare DMSA-CdTe QDs. The Te2- is slowly generated in this system, however, the surface of DMSA-CdTe QDs is hardly passivated [39], [40], [41]. Acar and his coworker prepared CdS QDs and AgS QDs using the DMSA as the S source and surface ligand, and the S2- is gradually released from DMSA [42], [43]. The DMSA-CdS QDs and DMSA-AgS QDs have many shortages, such as time-consuming, low quantum yields, broad FWHM (full width at half maximum) and poor stability. Adegoke prepared L-cysteine capped gradient and homogenous alloyed CdZnTeS QDs respectively, then they found that fixed composition alloying produces QDs with higher PL QYs and smaller diameter, comparing to composition-dependent alloying [44]. However, the synthetic process is complicated, which need perform in an ice bath for over 5 h only without the dissolved oxygen, so we prepared homogenous alloyed CdZnTeS QDs under the air condition by fixed-composition via a one-pot hydrothermal route using Na2TeO3 as the Te source. The QDs prepared by this novel one-step method have a lot of advantages, such as high quantum yield, good stability and low toxicity. A simple method for rapid and sensitive detection of H2O2 and glucose was developed by Rox-DNA functionalized CdZnTeS QDs as a ratiometric fluorescent probe previously by our group [45]. In this study, we prepared homogenous alloyed CdZnTeS QDs for rapid, sensitive and accurate determination of Cu2+ and galactose oxidase. The NAC and DMSA were the surface ligands of the QDs, containing abundant -SH and -COOH. The Ksp value of Cu-S and Cu-OH is perfectly low, therefore, the Cu2+ would show strong binding activity with the surface ligands, thus decreased the fluorescence of QDs by photoinduced electron transfer, as shown in Scheme 1. On the basis of the varies in fluorescence intensities of QDs with different amounts of Cu2+ and galactose oxidase, a simple and effective fluorescent method for detecting Cu2+ and galactose oxidase was proposed. This fluorescent sensor based on QDs for detecting Cu2+ and galactose oxidase displays attractive selectivity and sensitivity, which was further used in practical samples analysis with the satisfactory results.
Materials and methods
Results and discussion