Microwave-assisted synthesis of water-soluble, fluorescent gold nanoclusters capped with small organic molecules and a revealing fluorescence and X-ray absorption study

Abstract

Colourless solutions of blue light-emitting, water-soluble gold nanoclusters (AuNC) were synthesized from gold colloids under microwave irradiation using small organic molecules as ligands. Stabilized by 1,3,5-triaza-7-phosphaadamantane (TPA) or L-glutamine (GLU), fluorescence quantum yields up to 5% were obtained. AuNC are considered to be very promising for biological labelling, optoelectronic devices and light-emitting materials but the structure-property relationships have still not been fully clarified. To expand the knowledge about the AuNC apart from their fluorescent properties they were studied by X-ray absorption spectroscopy elucidating the oxidation state of the nanoclusters' gold atoms. Based on curve fitting of the XANES spectra in comparison to several gold references, optically transparent fluorescent AuNC are predicted to be ligand-stabilized Au5(+) species. Additionally, their near edge structure compared with analogous results of polynuclear clusters known from the literature discloses an increasing intensity of the feature close to the absorption edge with decreasing cluster size. As a result, a linear relationship between the cluster size and the X-ray absorption coefficient can be established for the first time.

Label-free photoelectrochemical cytosensing via resonance energy transfer using gold nanoparticle-enhanced carbon dots

“…26 After conjugating the C-dots with the AuNPs-Cys, the characteristic absorption peak of the AuNPs-Cys bathochromically shifted from 525 nm (curve b) to 550 nm (curve c) and the absorption intensity reduced which might be due to the formation of the J-type aggregate nucleated in C-dots 35 and the relatively low content of AuNPs-Cys nanoparticles in C-dots-AuNPs-Cys conjugates, indicating the formation of the C-dots-AuNPs-Cys. 37,38 After conjugating the C-dots with AuNPs-Cys, an emission peak was observed at 450 nm, while the PL emission intensity decreased significantly compared with the C-dots alone (curve c), which is consistent with enhanced charge separation and electron transfer of the C-dots. 1B).…”

Hybrid nanomaterial: biocolloidals

“…Encapsulation of fluorescent dyes is one of the most important roles of SiO 2 NPs for bioimaging purposes. Huge loads of fluorophore molecules can be encapsulated in SiO 2 particles to act as a superfluorescent NPs (Kainz et al, 2010;Pergantis et al, 2012;Tan et al, 2012;Zhu et al, 2014;Helmbrecht et al, 2015;Luo et al, 2015). On the other hand, this encapsulation is also applicable to NPs that are not biocompatible.…”

“…Also, the multifunctionality gained by biomolecule hybridization allows IONPs to be used in magnetic nanotherapy, tumor targeting, and medical imaging as theranostic applications for personalized treatments. If the sizes of ferromagnetic substrates are smaller than the size of magnetic domains, supermagnetism happens on the nanoscale (Ho et al, 1990;Heo et al, 2009;Herold et al, 2012;Hermanson, 2013;Helmbrecht et al, 2015). Superparamagnetism (SP) takes place in the single magnetic domain.…”

“…Nonhydrolytic synthesis (sol-gel technique) is another method of fabrication that uses capping agents (Kajihara and Yao, 2000). There are other less common synthetic routes, such as solvothermal, oxidation (De Azevedo et al, 2006), hydrothermal (Sun et al, 2005;Xing et al, 2015), chemical vapor deposition (Lee et al, 2007), physical vapor deposition (Johnson and Walsh, 2011), electrodeposition, sonochemical, and microwave-assisted synthesis to fabricate TiO 2 NPs (Chen TH et al, 2008;Yallappa et al, 2013;Ali et al, 2015;Amiri et al, 2015;Helmbrecht et al, 2015). The techniques used for the hybridization of biomolecules to their surfaces have been examined and partially summarized in reports (Pieranski, 1983).…”

“…One of the widely employed types of nanomaterials with diameters between 1 and 100 nm are iron oxide NPs (IONPs). Much attention was drawn to their significant features, which make IONPs very suitable for potential technologic applications in materials engineering and biological sciences (Griesser et al, 2002;Harris, 2004;Fudouzi and Sawada, 2006;Gioux et al, 2010;Gabudean et al, 2012;Giorgetti et al, 2012;Frank et al, 2013;Garg et al, 2013;Gatto et al, 2013;Hasany et al, 2013;Ghosh and Collie, 2014;Gonella and Dai, 2014;Hashemizadeh and Huyeh, 2014;Hassan and Singh, 2014;Gui et al, 2015;Guisbiers et al, 2015;Harris et al, 2015;Helmbrecht et al, 2015;Garg, 2016). Since they are relatively nontoxic to human organs, magnetite and maghemite are selected to be used in biomedical applications.…”