Abstract
Gold nanoclusters (AuNCs) have attracted extensive attention as light-emissive materials with unique advantages such as high photostability, large Stoke shifts and low toxicity. However, a better understanding of their solid-state photoluminescence properties is still needed. Herein, we investigated for the first time the intrinsic photoluminescence properties of lyophilized bovine serum albumin stabilized AuNCs (BSA-AuNCs) via fluorescence lifetime imaging microscopy (FLIM) studies performed under both one and two photon excitations (OPE and TPE) on individual microflakes, combined with fluorescence spectroscopic investigations. Both in solution and solid-state, the synthesized BSA-AuNCs exhibit photoluminescence in the first biological window with an absolute quantum yield of 6% and high photostability under continuous irradiation. Moreover, under both OPE and TPE conditions, solid BSA-AuNCs samples exhibited a low degree of photobleaching, while FLIM assays prove the homogeneous distribution of the photoluminescence signal inside the microflakes. Finally, we demonstrate the ability of BSA-AuNCs to perform as reliable bright and photostable contrast agents for the visualization of cancer tissue mimicking agarose-phantoms using FLIM approach under non-invasive TPE. Therefore, our results emphasize the great potential of the as synthesized BSA-AuNCs for ex vivo and in vivo non-invasive NIR imaging applications.
Highlights
Metal nanoclusters (NCs) are a class of extremely small and versatile nanomaterials (1–5 nm) exhibiting unique chemical and optical properties
In this work, we investigate, for the first time, the intrinsic PL of lyophilized bovine serum albumin (BSA)-stabilized AuNCs and demonstrate the persistence of one-photon excitation (OPE) and two-photon excitation (TPE) PL properties in solid samples
The final aim of our study was to provide the first demonstration of using BSA-AuNCs as fluorescence contrast in a simulated ex vivo environment using the TPE-fluorescence lifetime imaging microscopy (FLIM) method, as a novel proof of concept for AuNCs-based NIR tissue imaging approach
Summary
Metal nanoclusters (NCs) are a class of extremely small and versatile nanomaterials (1–5 nm) exhibiting unique chemical and optical properties. They are composed of a few and up to 200 atoms, having a size comparable to the Fermi wavelength, and are protected by an organic molecular ligand enriching them with molecular-like properties such as large Stoke shift and tunable intrinsic photoluminescence (PL) (Akyüz et al, 2020), similar to upconversion nanocrystals (Wang et al, 2021a; Wang et al, 2021b). There is a lack of studies on the properties of AuNCs, BSA-AuNCs, in solid-state. Such studies could ensure a better understanding of the PL process occurring in AuNCs inside complex heterogeneous cellular environment, when exploited in biomedical applications
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