Probing How Various Metal Ions Interact with the Surface of QDs: Implication of the Interaction Event on the Photophysics of QDs

Abstract

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 2+ 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 2+ , 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 2+ causes the FE. In FT-IR experiments, a prominent peak at 670 cm −1 , corresponding to Cd−S stretching vibrations, indicates strong ground-state interactions between the −SH of GSH and Cd 2+ ions. Moreover, a decrease in the diffusion coefficient of QDs in the presence of Cd 2+ ions during fluorescence correlation spectroscopy (FCS) studies further substantiates the removal of GSH by Cd 2+ 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 2+ . More importantly, these results also suggest that Cd 2+ can effectively be used for enhancing the fluorescence quantum yield of thiol-capped QDs such as GSH@ZAIS.

Realization of a Model-Free Pathway for Quantum Dot–Protein Interaction Beyond Classical Protein Corona or Protein Complex

“…The shorter decay component (τ 1 ∼3.8 ns) belongs to the band edge emission; the intermediate (τ 2 ∼38 ns) and longer (τ 3 ∼242 ns) decay components are due to the trap/defect state emission. 59 In presence of BSA, the τ 1 , τ 2 , and τ 3 of ZAIS QD increase to 4.60, 41.11, and 243.6 ns, respectively. Taking into account the relative contribution of lifetime components, a closer look indicates that (τ 1 × b 1 ) increases from 1.01 to 1.10 ns, while (τ 2 × b 2 ) decreases from 11.45 to 11.51 ns, and (τ 3 × b 3 ) increases from 106.48 to 114.49 ns.…”

Defect-Mediated Charge Carrier Recombination of Zinc–Silver–Indium Sulfide QDs in the Presence of Naphthoquinone Derivatives: An Insight into the Interfacial Surface Dynamics

“…It can be observed that the fluorescence intensity of QD has been quenched by ∼80% in the presence of NQ, ∼85% in the presence of ANQ, and ∼90% in the presence of HNQ. We note here that depassivation of the surface ligand of QD by naphthoquinones can be ruled out due to the bulky nature of these naphthoquinones. , Moreover, aggregation of QDs in the presence of these analytes cannot also be the cause of fluorescence quenching as no change of emission maxima of QD in the presence of analytes has been observed. , The fluorescence response of all the three analytes has been shown in Figure S7. It is pertinent to take a note here that, upon addition of ANQ/HNQ to QD, no significant increase in the fluorescence intensity of the acceptor units in respective systems also establishes that no appreciable EET process takes place between the QD and the acceptor units that are used in the present study.…”

Interfacial Nucleation Mechanism of Water-Soluble Ag–In–S Quantum Dots at Room Temperature and Their Visible Light Catalytic Performance

“…The competition mechanism gradually tends to the sulfur source, forming a gradually completed growth process and forming AIS QDs. 48 The interfacial reaction nucleation mechanism of the sulfur source and hydroxide competing cations at the interface of the complex needs certain conditions to be realized. First, there is no high temperature to provide the power for ion nucleation, so the selection of the sulfur source is particularly important.…”

“…Under the action of this competitive mechanism, with the continuous consumption of the hydroxide outside the complex in precursor solution, the sulfur source has the opportunity to nucleate and grow with cations. The competition mechanism gradually tends to the sulfur source, forming a gradually completed growth process and forming AIS QDs . The interfacial reaction nucleation mechanism of the sulfur source and hydroxide competing cations at the interface of the complex needs certain conditions to be realized.…”