科研之友
微信
新浪微博
Facebook
分享链接
摘要
Singlet oxygen (O-1(2)) plays an important role in various applications, such as in the photodynamic therapy (PDT) of cancers, photodynamic inactivation of microorganisms, photo-degradation of toxic compounds, and photo-oxidation in synthetic chemistry. Recently, water-soluble metal nanoclusters (NCs) have been utilized as photosensitizers for the generation of highly reactive O-1(2) because of their high water solubility, low toxicity, and surface functionalizability for targeted substances. In the case of metal NC-based photosensitizers, the photo-physical properties depend on the core size of the NCs and the core/ligand interfacial structures. A wide range of atomically precise gold NCs have been reported; however, reports on the synthesis of atomically precise silver NCs are limited due to the high reactivity and low photostability (i.e., easy oxidation) of Ag NCs. In addition, there have been few reports on what kinds of metal NCs can generate large amounts of O-1(2). In this study, we developed a new one-pot synthesis method of water-soluble Ag-7(MBISA)(6) (MBISA = 2-mercapto-5-benzimidazolesulfonic acid sodium salt) NCs with highly efficient O-1(2) generation ability under the irradiation of white light emitting diodes (LEDs). The molecular formula and purity were determined by electrospray ionization mass spectrometry and gel electrophoresis. To the best of our knowledge, this is the first report on atomically precise thiolate silver clusters (Ag-n(SR)(m)) for efficient (1O)(2) generation under visible light irradiation. The O-1(2) generation efficiency of Ag-7(MBISA)(6) NCs was higher than those of the following known water-soluble metal NCs: bovine serum albumin (BSA)-Au-25 NCs, BSA-Ag-8 NCs, BSA-Ag-14 NCs, Ag-25(dihydrolipoic acid)(14) NCs, Ag-35(glutathione)(18) NCs, and Ag-75(glutathione)(40) NCs. The metal NCs examined in this study showed the following order of O-1(2) generation efficiency under white light irradiation: Ag-7(MBISA)(6) > BSA-Ag-14 > Ag-75(SG)(40) > Ag-35(SG)(18) > BSA-Au-25 >> BSA-Ag-8 (not detected) and Ag-25(DHLA)(14) (not detected). For further improving the (1O)(2) generation of Ag-7(MBISA)(6) NCs, we developed a novel fluorescence resonance energy transfer (FRET) system by conjugating Ag-7(MBISA)(6) NCs with quinacrine (QC) (molar ratio of Ag NCs to QC is 1:0.5). We observed the FRET process, from QC to Ag-7(MBISA)(6) NCs, occurring in the conjugate. That is, the QC works as a donor chromophore, while the Ag NCs work as an acceptor chromophore in the FRET process. The FRET-mediated process caused a 2.3-fold increase in O-1(2) generation compared to that obtained with Ag-7(MBISA)(6) NCs alone. This study establishes a general and simple strategy for improving the PDT activity of metal NC-based photosensitizers.
- 出版日期2018
