Enhanced one-photon and two-photon excited luminescence of polymer-stabilized AuAg nanoclusters aggregates
Introduction
Gold nanoclusters are nanoparticles composed of a few, up to a few hundred gold atoms in a core, stabilized with ligands with a well-defined gold to ligand stoichiometry [1,2]. In thiol-stabilized nanoclusters Au0 in the core is surrounded by so called staples, i.e. repeating AunSRn+1 units [1,2]. Contrary to bigger gold nanoparticles (bigger than 3 nm in diameter), nanoclusters do not exhibit surface plasmon resonances, but present molecule-like optical properties. Recently, processes of aggregation of nanoclusters attracted a broad interest among researchers and several approaches to obtain the aggregates were proposed, which generally can be divided into solvent induced aggregation [3,4], aggregation on the interface (e.g., oil-water [5]) and ion induced aggregation [6]. From the fabrication point of view, it is particularly interesting to find the proper matrix for nanoclusters self-assembly. Much effort has been put into the examination of DNA [7], liquid crystal matrix [8], various polymers [[9], [10], [11]] and metal organic frameworks (MOFs) [12]. Nevertheless, the precise control of the agglomeration still presents a challenge and each of the mentioned matrices has its disadvantages.
Nanocluster superstructures seem to be an attractive alternative for conventional drug-delivery systems based on polyethylene glycols (PEGs) and their derivatives. Known for low toxicity and biocompatibility, nanoclusters can be efficiently used to target disease areas like tumor tissues without extra detriment for an organism [13,14]. Their drug-delivery capability in cell cultures was confirmed for cationic-polymer stabilized AuSG NCs aggregates [11]. Moreover, aggregation was shown to improve optical properties of the nanoparticles, for instance to increase the photoluminescence intensity [15,16]. This appears particularly desirable if we take into account low PL quantum yields of most noble metal nanoclusters.
Here, we present systematic studies of the aggregation process in silver-doped gold nanoclusters, with particular emphasis on the impact of aggregation on the linear and nonlinear optical properties of the NCs. Self-assembling of water-soluble glutathione-capped NCs is demonstrated and methods of the structures stabilization by a polymer addition is described. This simple approach enables one to obtain seven times stronger PL intensity of polymer-stabilized aggregates, in comparison to gold - silver NCs without a polymer, and an order of magnitude higher PL in comparison with gold NCs.
Section snippets
Chemicals
All of the chemicals were commercially available and used without further purification. Gold(III) chloride trihydrate (HAuCl4·3H2O, 99.999%), silver nitrate (AgNO3, ≥99.0%), glutathione (GSH, ≥98.0%), poly(allylamine hydrochloride) (PAH, Mw ~15,000) and poly(sodium methacrylate) (PMAA, Mw ~18,500) were purchased from Aldrich. Deionized water with the resistivity of 18 μS/cm was used in the studies.
Instrumentation
The UV–Vis absorption spectra and the fluorescence spectra were measured in 10 mm quartz cuvettes
Au:Ag nanoclusters
The gold and silver-doped gold nanoclusters (AuAg NCs, synthetic silver: gold ratio between 1:10 and 1:54) were synthesized as described in Refs. [[17], [18], [19]]. Then the samples were characterized with one-photon spectroscopy methods. For all the measurements, aqueous solutions at concentration 0.25 mg/mL were prepared. Regardless of the silver content in the whole series the number and localization of the absorption and PL bands remained constant. The absorption spectrum showed a clear
Conclusion
We fabricated water–soluble AuAg NCs and observed spontaneous aggregation of the nanoclusters into spheres of average diameter up to 1500 nm. The Ag:Au ratio 1:40.5 presented the narrowest size distribution with the average diameter equal to 500 nm. The increasing Ag:Au ratio resulted in increasing nanoclusters QY, whereas the spontaneous aggregation of NCs did not have direct impact on their optical properties. As the NCs are charged negatively in pH = 7, they easily interacted with a cationic
CRediT authorship contribution statement
Magdalena Waszkielewicz: Investigation, Writing - original draft, Visualization. Joanna Olesiak–Banska: Conceptualization, Writing - original draft, Supervision. Marek Grzelczak: Methodology, Supervision, Writing - review & editing. Ana Sánchez–Iglesias: Methodology, Supervision, Writing - review & editing. Anna Pniakowska: Investigation, Writing - review & editing. Marek Samoc: Conceptualization, Funding acquisition, Writing - review & editing.
Acknowledgment
This work was supported by the National Science Centre under grant DEC-2013/10/A/ST4/00114, by KNOW – Center of Excellence in Biotechnology project, and by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Science and Technology.
References (25)
- et al.
Nanoparticles for multi-modality cancer diagnosis: simple protocol for self-assembly of gold nanoclusters mediated by gadolinium ions
Biomaterials
(2017) - et al.
Dual targeting luminescent gold nanoclusters for tumor imaging and deep tissue therapy
Biomaterials
(2016) - et al.
DNA liquid crystals doped with AuAg nanoclusters: one-photon and two-photon imaging
J. Mol. Liq.
(2018) - et al.
Atomically precise clusters of noble metals: emerging link between atoms and nanoparticles
Chem. Rev.
(2017) - et al.
Atomically precise colloidal metal nanoclusters and nanoparticles: fundamentals and opportunities
Chem. Rev.
(2016) - et al.
Enhanced emission of polyethyleneimine-coated copper nanoclusters and their solvent effect
J. Phys. Chem. C
(2015) - et al.
From aggregation-induced emission of Au(I)–Thiolate complexes to ultrabright Au(0)@Au(I)–Thiolate core–shell nanoclusters
J. Am. Chem. Soc.
(2012) - et al.
In situ formation and ordered assembly of gold nanoclusters to nano-ribbons at the oil/water interface
J. Mater. Chem.
(2011) - et al.
DNA assembled metal nanoclusters: synthesis to novel applications
RSC Adv.
(2016) - et al.
Self-Assembly of silver and gold nanoparticles in a metal-free phthalocyanine liquid crystalline matrix: structural, thermal, electrical and nonlinear optical characterization
Chemistry
(2016)
The solvent effect on the luminescence of silver nanoclusters
Phys. Chem. Chem. Phys.
Stimuli-responsive nanogel composites and their application in nanomedicine
Chem. Soc. Rev.
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