Abstract
Gold nanocluster (AuNC) synthesis using a well-distinguished polymer for nanoparticle-mediated drug delivery paves the way for developing efficient theranostics based on pharmaceutically accepted materials. Gelatin-stabilized AuNCs are synthesized and modified by glutathione for tuning the emission spectra. Addition of silver ions enhances the fluorescence, reaching also high quantum yield (26.7%). A simplified model can be proposed describing the nanoclusters' properties-structure relationship based on X-ray photoelectron spectroscopy data and synthesis sequence. Furthermore, these modifications improve fluorescence stability toward pH changes and enzymatic degradation, offering different AuNCs for various applications. The impact of nanocluster formation on gelatin structure integrity is investigated by Fourier transform infrared spectrometry and matrix-assisted laser desorption/ionization time of flight mass spectroscopy, being important to further formulate gelatin nanoparticles (GNPs). The 218 nm-sized NPs show no cytotoxicity up to 600 µg mL-1 and are imaged in skin, as a challenging autofluorescent tissue, by confocal microscopy, when transcutaneously delivered using dissolving microneedles. Linear unmixing allows simultaneous imaging of AuNCs-GNPs and skin with accurate signal separation. This underlines the great potential for bioimaging of this system to better understand nanomaterials' behavior in tissue. Additionally, it is drug delivery system also potentially serving as a theranostic system.
Highlights
They are composed of several up to tens theranostics based on pharmaceutically accepted materials
We proved the effectiveness of gelatin to produce fluorescent AuNCs, introducing different methods for tuning the emission wavelength alongside with the fluorescence intensity
Gold ions reduction-assisted by GSH, in one-pot synthesis, induced 50 nm redshift in the nanoclusters emission alongside with stabilization against pH changes and enzymatic degradation
Summary
Enhancing the fluorescence will be crucial for various bioimaging purposes, especially in tissues. Silver and gold has been considered as a common combination for fabrication of alloy nanoclusters.[49,50] Modification of gold nanoclusters by silver has been reported to enhance the emission.[49,51] By using gelatin and GSH as ligands, it was important to optimize the Ag:Au molar ratio (0.4) to obtain the highest possible fluorescence intensity (Figure S8, Supporting Information). Doping Ag ions after 6 h from the start of the reaction resulted in 2.5-fold increase in fluorescence rather than addition at the start of the reaction (Figure S8, Supporting Information). This might indicate the significance of the different noble metal atoms arrangement in the core for controlling the fluorescence properties of the alloy. TEM images and measured size distributions are shown in Figures S7 and S10 (Supporting Information) of silver-modified and pure gold nanoclusters, respectively
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