Metallophilic Bond‐Induced Quenching of Delayed Fluorescence in Au₂₅@BSA Nanoclusters

Abstract

The metallophilic bond is a weak interaction between closed‐shell ions and has been widely used a probe for various sensing of toxic chemicals for environmental safety concerns. Here, the interaction between Au nanoclusters (NCs) and metallic ions (mercury (Hg2+) and copper (Cu2+) ions) is explored using steady‐state and time‐resolved luminescence and transient absorption measurements. For Hg2+ ions, the delayed fluorescence (DF) of bovine serum albumin (BSA) protected Au25 (Au25@BSA) NCs is quenched via an effective triplet state electron transfer through the metallophilic bond. However, the Cu2+ ions do not alter the DF in Au25@BSA NCs because of the absence of the metallophilic interaction. Furthermore, for Au8@BSA and Au10@histidine, in which there are no Au+ ions on the surface, the fluorescence is not quenched by Hg2+ ions. Such a novel triplet electron transfer process through metallophilic bonds are observed and reported for the first time. The reduction of the reverse intersystem crossing is the crucial for Hg2+ ion sensing in the fluorescent Au25@BSA NCs.

Fluorescent Metallic Nanoclusters: Electron Dynamics, Structure, and Applications

“…In the case, the pnotoexcited electrons in the singlet excited state transfer into the triplet state (ISC) and then the triplet electrons are effectively trapped by Hg ions; which results selectively in the quenching of the delayed fl uorescence, as shown in Figure 19 . [ 81 ] The timeresolved fl uorescence/absorption measurement confi rms that such an electron transfer results in an anomalous quenching of delayed fl uorescence in Au 25 @BSA ( Figure 20 . Using rate equations, they simulated the dynamic processes and showed a consistent fl uorescence evolution in Au 25 @BSA.…”

“…It is interesting to note, an exceptional electron transfer of triplet state was observed by Yu et al through metallophilic bond between Au 25 @BSA and Hg ions. In the case, the pnotoexcited electrons in the singlet excited state transfer into the triplet state (ISC) and then the triplet electrons are effectively trapped by Hg ions; which results selectively in the quenching of the delayed fluorescence, as shown in Figure . The time‐resolved fluorescence/absorption measurement confirms that such an electron transfer results in an anomalous quenching of delayed fluorescence in Au 25 @BSA ( Figure .…”

“…[ 77a ] Using time-resolved fl uorescence, they observed the lifetime reduction of the excited state and drastic quenching of fl uorescence and thus demonstrated an effi cient fl uorescence resonance energy transfer (FRET) from the dansyl donor to the core of Au 25 NCs, as shown in Figure 18 www.particle-journal.com www.MaterialsViews.com REVIEW protein (lactoferrin) and the Au clusters by performing lifetime measurements by the TCSPC technique. [ 77a , c ] It is interesting to note, an exceptional electron transfer of triplet state was observed by Yu et al [ 81 ] through metallophilic bond between Au 25 @BSA and Hg ions. In the case, the pnotoexcited electrons in the singlet excited state transfer into the triplet state (ISC) and then the triplet electrons are effectively trapped by Hg ions; which results selectively in the quenching of the delayed fl uorescence, as shown in Figure 19 .…”

“…[ 118 ] Other than Aubased NCs, Yuan et al designed a new sensor based on highly luminescent Ag + NCs for Hg 2+ ions detection (detection limit <5 × 10 −9 M ). [ 1c ] Yu et al [ 81 ] elucidated the mechanism for selectively probing Hg 2+ using of Au 25 NCs that an ultrafast electron transfer occurs from the triplet state of the Au 25 Also, BSA-protected Cu NCs were introduced in a protein matrix for the use of potential sensor of Pb 2+ ion at part-per-million concentrations. [ 119 ] In addition to the metal ions detection, BSA-templated Au NCs were proposed by Xu and co-workers [ 120 ] as a probe for protease detection through the determination of trypsin in real urine samples.…”

Effect of quencher, denaturants, temperature and pH on the fluorescent properties of BSA protected gold nanoclusters

“…They observed that, Hg 2+ quenches the delayed fluorescence of BSA Au 25 nanocluster via triplet state electron transfer through metallic bond. However, the Cu 2+ do not alter the delayed fluorescence in BSA Au 25 [18]. There are other numerous reports on the BSA Au clusters for spectroscopic investigations and biochemical applications [2,3,19–23].…”