| Copper nanoclusters(CuNCs) as a new nanomaterial have showed a tremendous application potential in chemical detection, industrial catalysis, molecular devices, cell imaging and biomarker owing to their excellent optical properties, catalytic activity and biocompatibility. However, the synthesis of CuNCs is more difficult than noble metal nanoclusters. There are many shortcomings exist in reported method for synthesis of CuNCs, such as long reaction time, which resulted in low quantum yield, poor stability, single function. The above weaknesses presents considerable challenges when it was applied in ultra-low analyte detection and complex system. Therefore, it is greatly important to develop a fast and simple synthesis method and exploit its application of CuNCs.For the first time, we found that hydrogen peroxide could significantly accelerate the formation of copper nanoclusters. Based on this principle, a fast synthesis method for water-soluble CuNCs was developed. In an alkaline environment, bovine serum albumin(BSA) reacted with copper ions(Cu2+) to form stable BSA-Cu complex. Then, Cu2+ was rapidly reduced into Cu0 in the presence of H2O2 and bovine serum albumin(BSA), further leading to the production of CuNCs. Under optimized conditions, the synthesis only needed 1 h to achieve a high conversion rate of Cu2+. The reaction rate was 8-fold of traditional preparation methods. More importantly than all of that, the as-prepared BSA-CuNCs displayed better optical performance when compared with the CuNCs prepared by the conventional method. Upon excitation at 345 nm, the BSA-CuNCs exhibited excitation emission at 420 nm, the total QY of BSA-CuNCs in aqueous solution at room temperature was determined to be 17.81%. Under a xenon lamp irradiation(350 W), the fluorescence intensity of remained almost unchanged within the irradiation time of 60 min, indicating an excellent photostability. Research on resonance light scattering, synchronous fluorescence and circular dichroism spectroscopy revealed the addition of H2O2 in the BSA solution brought an obvious reduction of a-helix, and increased the degree of exposure of free thiol and amino groups. These changes played an important role in the process of copper nanoclusters formation. This results enhanced reduction ability of BSA towards Cu2+. Cu2+ could be reduced into Cu0 by more thiol. Otherwise, H2O2 as a ligand was to combine with BSA-Cu complex to form BSA-Cu-H2O2 complex, which decrease the reduction potential of Cu2+/Cu and leaded to the fast reduction from Cu2+ to Cu0.A nanosensor based on the fluorescence quenching of BSA-CuNCs was described for the high sensitive sensing of Hg2+. The experiment showed that after the addition of Hg2+ into the system, it rapidly combined with the sulfhydryl group attached on the surface of BSA-CuNCs to form an Hg-S covalent bond. Simultaneously, a part of Cu-S bonds was destroyed by Hg2+ due to stronger interaction between Hg2+ and sulfhydryl group. This leaded to the agglomeration of BSA-CuNCs and decreased fluorescence intensity with a detection limit of 4.7×10-12 mol/L(S/N = 3) and a dynamic range of 1.0×10-5~1.0×10-11 mol/L. It had been successfully used for the detection of Hg2+ in water samples. Besides that, the result was consistent with AAS methods, which demonstrated that the proposed method was satisfactory for the analysis of Hg2+ with good repeatability, stability and anti-interference.An ultra-sensitive and wide-range pH sensor based on the BSA-capped BSA-CuNCs was developed using a fast synthesis method through the use of hydrogen peroxide as an additive. Owing to its strong oxidation capacity, hydrogen peroxide partially destroyed the peptide and disulfide bonds in the BSA molecule and resulted in an increased exposure of hydrophilic groups capable of protonation, which greatly accelerated the formation of BSA-CuNCs and improved the response of the BSA-CuNCs towards pH fluctuation in the surrounding environment. The results demonstrated that the decrease in repulsion and conformational change of BSA with decreasing pH values induced the aggregation of BSA-CuNCs, leading to a color change and fluorescence quenching of the BSA-CuNCs at low pH values. The fluorescence intensity exhibited a linear relationship over the pH range of 2.0~14.0 and increased by around 20-fold with greater fluorescence at higher pH values. Surprisingly, the sensitivity and pH range were much better than those of other metal nanocluster pH sensors reported in the literature. The pH probe was also sensitive to different buffer solutions. Moreover, the ionic strength of the buffers had little influence on the pH responsive behaviour. Finally, the proposed pH sensor had been successfully applied for measuring the pH value of natural water and the intracellular pH of RBL-2H3 cells.CuNCs stabilized by the amino acid have received attention due to their special performance, but the poor stability has restricted its widespread use. D-penicillamine(DPA) and BSA co-stabilized copper nanoclusters(DS-CuNCs) solved these problems. Firstly, Cu2+ was reduced into Cu0 by DPA, further leading to form DPA-capped DPA-CuNCs. Then, BSA was introduced into DPA-CuNCs to obtain DS-CuNCs by their electrostatic attraction. The as-prepared DS-CuNCs exhibit prominently enhanced fluorescence intensity and photostability. The fluorescence intensity was more than 2-fold that of DPA-CuNCs. More importantly, due to the synergistic effect between DPA and BSA, the mimic enzyme based on DS-CuNCs gave catalytic ability and ultrasensitive fluorescence response towards H2O2. DS-CuNCs and glucose oxidase were combined to produce a dual function complex enzyme with catalytic ability and fluorescence response, which showed a high sensitive fluorescence response to glucose. The fluorescence intensity linearly reduced with the increase of glucose concentration in the range of 2.0×10-5~1.0×10-2 mol/L with the detection limit of 7.56×10-6 mol/L(S/N = 3). It had been successfully applied in the detection of glucose in water samples. The proposed method had higher long-term stability, sensitivity, repeatability and stability when compared with present glucose sensors.The catalytic mechanism of H2O2 convertting BSA-Cu2+ into BSA-CuNCs was discussed in this study. Based on that mechanism a fast synthetic method for water-soluble CuNCs and its application were developed, which provided important theoretical guidance for a new high-quality metal nanocluster. In addition, multi-functional copper nanoclusters were fabricated by using multiple stabilizers in this work, which not only solved the problem of poor stability of amino-capped CuNCs, but also improved the fluorescence intensity. More importantly, the study opened a new avenue for the fabrication of functional metal nanoclusters that held great promise in potential applications such as biocatalysts, nanosensors and molecular carriers. |
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