School of Chemical Sciences, National Institute of Science Education and Research (NISER), Jatni, Khurda, Bhubaneswar 752050, Odisha, India.
Homi Bhabha National Institute (HBNI), Mumbai 400 094, India.
Langmuir. 2021 Jun 15;37(23):6995-7007. doi: 10.1021/acs.langmuir.1c00548. Epub 2021 May 28.
With an aim to understand the mechanism of interaction between quantum dots (QDs) and various metal ions, fluorescence response of less-toxic and water-soluble glutathione-capped Zn-Ag-In-S (GSH@ZAIS) QDs in the presence of different metal ions has been investigated at both ensemble and single-molecule level. Fourier transform infrared (FT-IR) spectroscopy has also been performed to obtain a molecular level understanding of the interaction event. The steady-state data reveal no significant change in QD emission for alkali and alkaline earth metal ions, while there is a decrease in fluorescence intensity for transition metal (TM) and some heavy transition metal (HTM) ions. Interestingly, a significant fluorescent enhancement (FE) (19-96%) of QDs is found for Cd ions. Time-resolved fluorescence studies reveal that all the three decay components of QDs decrease in the presence of first-row TM ions. However, in the case of Cd, the shorter component is found to increase while the longer one decreases. The analysis of data reveals that photoinduced electron transfer is responsible for fluorescence quenching of QDs in the presence of first-row TM ions and destruction/removal of trap/defect states in the case of Cd causes the FE. In FT-IR experiments, a prominent peak at 670 cm, corresponding to Cd-S stretching vibrations, indicates strong ground-state interactions between the -SH of GSH and Cd ions. Moreover, a decrease in the diffusion coefficient of QDs in the presence of Cd ions during fluorescence correlation spectroscopy (FCS) studies further substantiates the removal of GSH by Cd from the surface of QDs. The optical output of this study demonstrates that ZAIS can be used for fluorescence signaling of various metal ions and in particular selective detection of Cd. More importantly, these results also suggest that Cd can effectively be used for enhancing the fluorescence quantum yield of thiol-capped QDs such as GSH@ZAIS.
为了理解量子点 (QD) 与各种金属离子相互作用的机制，在体相和单分子水平上研究了低毒且水溶性谷胱甘肽包裹的 Zn-Ag-In-S (GSH@ZAIS) QD 在不同金属离子存在下的荧光响应。傅里叶变换红外 (FT-IR) 光谱也用于获得对相互作用事件的分子水平理解。稳态数据显示，碱金属和碱土金属离子对 QD 发射没有显著影响，而过渡金属 (TM) 和一些重过渡金属 (HTM) 离子则会降低荧光强度。有趣的是，发现 Cd 离子对 QD 有显著的荧光增强 (FE) (19-96%)。时间分辨荧光研究表明，所有三种 QD 衰减分量在第一行 TM 离子存在下都会减少。然而，在 Cd 的情况下，发现较短的分量增加，而较长的分量减少。数据分析表明，光诱导电子转移是导致第一行 TM 离子存在时 QD 荧光猝灭的原因，而 Cd 则导致陷阱/缺陷态的破坏/去除，从而导致 FE。在 FT-IR 实验中，在 670 cm 处出现一个明显的峰，对应于 Cd-S 伸缩振动，表明 GSH 的 -SH 与 Cd 离子之间存在强烈的基态相互作用。此外，在荧光相关光谱 (FCS) 研究中，Cd 存在时 QD 的扩散系数降低进一步证实了 Cd 从 QD 表面去除 GSH。这项研究的光学输出表明，ZAIS 可用于各种金属离子的荧光信号，特别是 Cd 的选择性检测。更重要的是，这些结果还表明，Cd 可以有效地用于增强巯基包裹的 QD（如 GSH@ZAIS）的荧光量子产率。
