Fluorescence Turn-On Antioxidant Recognition by Interface-Mediated Radical Termination ofl-Cysteine-Capped Gold Nanoclusters

Abstract

Selective antioxidant recognition plays a critical role in various scientific and clinical fields, however, development of straightforward detection mechanisms and reduction of technique operation are still barriers nowadays. For example, convenient detection of epigallocatechin gallate (EGCG), the most effective antioxidant among all tea catechins, is highly sought but is severely limited due to the lack of appropriate indicators. To overcome the aforementioned obstacles and to provide more adequate processes that can be employed in antioxidant detection, specific analyte targeting and efficient signal reporting are necessary for the platform design. In this work, a fluorescence "turn on" strategy based on gold nanocluster (AuNC) interface-mediated radical scavenging for selective antioxidant detection is reported. This approach utilizes Lcysteine capped AuNCs with great fluorescence stability as the reporter, where the presence of reactive oxygen species (ROS) generated from the Fenton reaction results in obvious fluorescence quenching. The introduction of antioxidants, that is, EGCG molecules, interestingly, neutralizes the ROS by initiating direct electron and hydrogen atom transfer to eliminate the unpaired free radicals. Besides, the phenolic OH groups and the gallate ring of EGCG also provide a selective and efficient complexation orientation toward Fenton reaction metal ions, where ROS generation is consequently prohibited. This dual-effect phenomenon recovers the originally ROS quenched AuNC fluorescence, which is dependent upon the introduced EGCG quantity. Relying on this fluorescence turn on strategy, the current platform delivers a low detection limit of 1.20 μM with excellent selectivity toward EGCG under the presence of other interfering species. Meanwhile, this approach also provides great accuracy on detecting total antioxidant capacity in commercial green tea samples. This antioxidant fluorometric turn on design therefore gives a more straightforward route on EGCG detection, and its specific recognition capability is very suitable for practical real sample analysis.

One-Step Laser Nanostructuration of Reduced Graphene Oxide Films Embedding Metal Nanoparticles for Sensing Applications

“…For the Au­(III)@GO before the laser treatment, two solved components at BEs of 85.6 and 89.2 eV corresponding to the Au 4f 7/2 (Au 3+ ) and Au 4f 5/2 (Au 1+ ) electron doublet, respectively, are observed (Figure S4D). ,, Despite the fact that the cation used is the Au­(III), the presence of Au­(I) can be attributed to the GO coordination ability through cation-π and electrostatic interactions. ,,− A slight presence of zerovalent Au(0) was detected by XPS at 83.7 eV, which can be attributed to the intrinsic chemistry of the GO rich in vacant electrons, electron doublets, and electronegative functional groups potentially able to reduce the Au 3+ to Au 0 , promoting the production of Au nanoseeds. ,, After the laser (Figure G), the AuNP formation is suggested by the BE shift toward lower values . The two sharp and asymmetric peaks recorded at 84.0 and 87.7 eV, with a spin–orbit splitting value of 3.7 eV, are characteristic of the Au(0). ,, …”

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection

“…As demonstrated in Figure , obvious fluorescence emissions corresponding to Au, Ag, and Cu reveal nanocluster formation on the MOF-patterned surface. Au nanoclusters (AuNCs) , and Ag nanoclusters (AgNCs) give the most intense emission at 519 nm (under 495 nm excitation), while Cu nanoclusters (CuNCs) deliver a strong emission at 569 nm (under 555 nm excitation). Other than the short-lived CuNC fluorescence, due to rapid oxidation without protection from capping agents (Video S1), fluorescence signals from AgNC and AuNC on this surface are stable for up to 2 weeks under ambient conditions.…”

“…To realize this design, Au, Ag, and Cu are independently tested on the platform supported by cubicshaped ZIF-8 MOFs. In these experiments, a ZIF-8 MOFdecorated surface is immersed into metal ion precursor solutions with an upside-down orientation to avoid gravimetric sedimentation, followed by the addition of sodium borohy- 62,63 and Ag nanoclusters (AgNCs) 64 give the most intense emission at 519 nm (under 495 nm excitation), while Cu nanoclusters (CuNCs) 65 deliver a strong emission at 569 nm (under 555 nm excitation). Other than the short-lived CuNC fluorescence, due to rapid oxidation without protection from capping agents (Video S1), fluorescence signals from AgNC and AuNC on this surface are stable for up to 2 weeks under ambient conditions.…”

Sustainable Exscalar Monodispersed Gold Nanoparticles with Enhanced Dispersion Stability and Biocompatibility for Theragnostics

“…Noble gold nanoparticles (AuNPs) have gained tremendous potential both in academia and industry for various applications, including catalysis, sensing, photonics, analytics, surface-enhanced Raman scattering, photochemistry, optoelectronics, energy conversion, and biomedicine, as contrast agents in X-ray computed/photoacoustic topography, , and in vaccine development . Benefiting from their unique morphology-dependent optical and electronic properties due to localized surface plasmon resonance, vibrant AuNP chromophores could be designed .…”