Acid-Triggered Self-Assembled Egg White Protein-Coated Gold Nanoclusters for Selective Fluorescent Detection of Fe³⁺, NO₂^–, and Cysteine

Abstract

Herein, we present a simple and economical synthesis for the first multianalyte probe able to selectively quantify the concentrations of Fe3+, NO2 –, and cysteine. It comprises H+-triggered self-assembled gold nanoclusters (AuNCs@EW/H+, AuEHs), showing enhanced red fluorescence at 640 nm. The AuEH is a good fluorescent nanosensor for Fe3+ and NO2 – with detection limits of 1.40 and 2.82 nM, respectively. Iron detection, through fluorescence quenching, occurs because of nanocluster aggregation elicited by the complexation of Fe3+ with amino acids on the surface of AuEH; nitrite detection likely proceeds through fluorescence quenching via the disassembly of the nanoclusters following irreversible oxidation by nitrite. This selectivity is good enough that it can be used to quantify the nitrite concentration in commercially available processed meat. Cysteine detection occurs through the restoration of fluorescence of iron-quenched samples; similar molecules including homocysteine and glutathione are unable to restore fluorescence, showing the specificity of the interaction. Applications, including as a detecting ink and as a biocompatible probe, show promise because of the lack of observable toxicity of the AuEHs, demonstrating their promise as specific and sensitive biosensors.

Luminescent metal nanoclusters: Biosensing strategies and bioimaging applications

“…prepared H + ‐triggered self‐assembled Au NCs (AuEH) based on egg white‐functionalized Au NCs. [122] These AuEH can be used as probes for the detection of multianalytes. One of the analytes is Fe 3+ that can trigger the aggregation of AuEH by the complexation of Fe 3+ with amino acids on the surface of AuEH.…”

Metal Nanoclusters as Biomaterials for Bioapplications: Atomic Precision as the Next Goal

“…Copyright 2020 Elsevier B.V. (d) Synthesis of the AuEH and a profile of its sensing behavior toward Fe 3+ , NO 2 – , and Cys. Reproduced with permission from ref . Copyright 2020 American Chemical Society.…”

“…On the contrary, the Cu 2+ ions can highly interact with the surface ligand and generate large-size Cu 2+ –Au NCs, which induces aggregation and results in fluorescence quenching. Li and co-workers synthesized egg white protein-protected Au NCs, and its fluorescent performance is selectively sensitive to Fe 3+ and NO 2 – with detection limits of 1.40 and 2.82 nM, respectively . They found that the fluorescence quenching by iron is due to the interaction between Fe 3+ and the carboxyl and amino group of the surface protein, inducing the aggregation of Au NCs to form lager particles, Figure b .…”

“…Li and co-workers synthesized egg white protein-protected Au NCs, and its fluorescent performance is selectively sensitive to Fe 3+ and NO 2 – with detection limits of 1.40 and 2.82 nM, respectively . They found that the fluorescence quenching by iron is due to the interaction between Fe 3+ and the carboxyl and amino group of the surface protein, inducing the aggregation of Au NCs to form lager particles, Figure b . They proposed that nitrite-induced fluorescence quenching is due to an irreversible oxidation leading to the disassembly of NCs .…”

“…92 They found that the fluorescence quenching by iron is due to the interaction between Fe 3+ and the carboxyl and amino group of the surface protein, inducing the aggregation of Au NCs to form lager particles, Figure 5b. 92 They proposed that nitrite-induced fluorescence quenching is due to an irreversible oxidation leading to the disassembly of NCs. 92 Overall, metal NCs show great potential in future applications because the assays for ion detection which rely on the optical changes are easy to operate, and the changes can be quantified with excellent detection limits.…”