Unveiling the Long-Lived Emission of Copper Nanoclusters Embedded in a Protein Scaffold

Abstract

Protein-conjugated coinage metal nanoclusters have become promising materials for optoelectronics and biomedical applications. However, the origin of the photoluminescence, especially the long-lived excited state emission in these metal nanoclusters, is still elusive. Here, we unveiled the underlying mechanism of long-lived emission in albumin protein-conjugated copper nanoclusters (Cu NCs) using steady state and time-resolved spectroscopic techniques. Our findings reveal room-temperature phosphorescence (RTP) in protein-conjugated Cu NCs. Time-resolved area-normalized spectra distinguished short-and long-lived components, where the former arises from the singlet state and the latter from the triplet state, thus resulting in RTP. The similarity of the emission spectra at room (298 K) and cryogenic (77 K) temperature ascertains the RTP phenomenon by harvesting the higher-lying triplet states. Time-gated bioimaging of A549 cells using the long-lived emission not only supports RTP emission in the cellular environment but also provides exciting avenues in long-term bioimaging using bovine serum albumin−conjugated Cu NCs.

Recent Advances in Long-Lived Emission in Coinage Metal Nanoclusters: Implications for Optoelectronic Applications

“…Recently, Sharma et al . unveiled the long-lived emission of Cu NCs embedded in bovine serum albumin protein scaffold.…”

“…(C) Time-resolved imaging of A549 cells stained with an aqueous dispersion of BSA–Cu NCs (λ ex = 470 nm, and λ em = 488–800 nm): (i) confocal laser scanning microscopy (CLSM) image with no time delay, (ii) time-gated image after application of a time delay of 0.5 μs, (iii) microsecond time scale photoluminescence lifetime imaging microscopy (PLIM) (scale bar, 10 μm), and (iv) intracellular lifetime histogram of A549 cells stained with BSA–Cu NCs. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

Dual emissive optically active gold nanoclusters endowed with circularly polarized phosphorescence

“…3b). 24 The deconvoluted PL spectra along with the blue shifted PL at lower temperature rule out the possibility of TADF; however, a minor contribution from the mixed singlet–triplet states due to spin-orbital coupling cannot be ruled out and needs further investigation. Selective quenching of the red emission peak in the presence of oxygen further confirms the involvement of the triplet state (Fig.…”

The role of polyethylenimine-functionalized gold nanoclusters carrying plasmid CMTM5 in impeding the malignant progression of prostate cancer cells by promoting EGFR endocytosis

“…An ideal gene delivery system should possess attributes such as biodegradability, non-toxicity, non-immunogenicity, specific targeting, and a reliable capacity to stimulate gene expression [20]. Metal nanoclusters have garnered considerable attention, owing to their extraordinary physical and chemical properties, demonstrating potential applications in optics, catalysts, sensing, targeted imaging, and therapy [21]. Gold nanoclusters (AuNCs), particles with a diameter of less than 2 nanometers, have exhibited immense potential in intracellular delivery and diagnostics, biosensing, bioimaging, drug delivery, and the detection of biomacromolecules (DNA, proteins, enzymes) due to their facile synthesis, high biocompatibility, and robust fluorescent properties [22][23][24][25].…”