Synthesis of highly fluorescent gold nanoclusters and their use in sensitive analysis of metal ions

Abstract

As a promising fluorescent material, gold nanoclusters (Au NCs) have been used for biosensing and imaging. In metal ion sensing, the fluorescence of Au NCs is usually quenched in the presence of ions, but the reaction mechanism has not been clarified. In this work, mercaptan acids (3-mercaptopropanoic acid (3-MPA), 6-mercaptohexanoic acid (6-MHA), 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHA)) were used as reductants and ligands to synthesize fluorescent Au NCs. The Au NCs had a core containing 18 atoms capped by 18 (3-MPA) or 10 (6-MHA, 11-MUA, 16-MHA) ligand molecules. The Au NCs prepared in this work had higher fluorescence quantum yields than those reported previously and the fluorescence showed a red-shift when varying the chain length of the mercaptan acids. It was found that in presence of ions (Mo(vi), Hg(ii)), the fluorescence of the Au NCs is dependent upon the ligands. The Au NCs with 3-MPA and 6-MHA ligands were sensitive to Mo(vi) and Hg(ii), while the Au NCs capped with 11-MUA and 16-MHA ligands were not sensitive to the ions. Various characterization techniques, including transmission electron microscopy, matrix-assisted laser-desorption ionization time of flight mass spectrometry, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy and thermogravimetric analysis, were used to investigate the components and electronic structure of the clusters, as well as the emission and excitation properties before and after the reaction with metal ions. The structure of the Au NCs after the reaction with Mo(vi) and Hg(ii) was also studied. It was found that Mo(vi) and Hg(ii) both reacted with the gold atoms at the core site, but the reaction mechanisms were different.

Highly Luminescent Gold Nanocluster Frameworks

“…Comparison between the Au 4f photoelectron spectra (Figure e), Au 4f7/2 peaks appear at 83.8 and 83.9 eV for GNCs and GNCFs respectively. The results confirm the existence of a precisely similar chemical environment of gold atoms both in GNCs and GNCFs, containing Au (0) and Au (I) species . The nanocluster is, therefore, constructed by a metal core assembled with Au (0) atoms, surrounded by Au (I)‐GSH species around its surfaces.…”

“…The results confirm the existence of a precisely similar chemical environment of gold atoms both in GNCs and GNCFs, containing Au (0) and Au (I) species. [24] The nanocluster is, therefore, constructed by a metal core assembled with Au (0) atoms, surrounded by Au (I)-GSH species around its surfaces. The high-resolution Sn 3d photoelectron spectra of GNCFs (Figure 3f) display the peaks at 487.3 ± 0.3 and 495.7 ± 0.2 eV corresponding to Sn 3d5/2 and Sn 3d3/2 respectively, indicating the presence of Sn 4+ , [25] possibly due to oxidation during sample preparation (drying) for XPS.…”

Enhanced Cellular Uptake of H-Chain Human Ferritin Containing Gold Nanoparticles

“…The absorbance profile of these samples at 55 shows the coelution of AuNPs with the first protein elution peak (8.5-8.6 mL), corresponds to the fraction containing oligomeric ferritin species. On the other han lack of absorption at A550nm in the ferritin monomer elution (second elution peak, 11.4 mL) suggests that this peak contains apoferritin or ferritin containing nanoclusters, which are fluorescent and are undetectable by absorbance measure [15,48,49]. A semiquantitative analysis of the peak areas from protein chromatograms in F 3 suggests that nanoparticle synthesis in ferritin induces changes that alter the m mer/oligomer ratio present in the initial apoferritin sample (Table 2).…”

“…The absorbance profile of these samples at 550 nm shows the coelution of AuNPs with the first protein elution peak (8.5-8.6 mL), which corresponds to the fraction containing oligomeric ferritin species. On the other hand, the lack of absorption at A 550nm in the ferritin monomer elution (second elution peak, 11.2-11.4 mL) suggests that this peak contains apoferritin or ferritin containing gold nanoclusters, which are fluorescent and are undetectable by absorbance measurements [15,48,49].…”

Bio-Mediated Synthesis of Nanoparticles for Fluorescence Sensors

“…Besides, some of these heavy metals, even at a low concentration level, are highly poisonous to human health as a result of accumulation in organs. 42,105,[114][115][116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][131] Therefore, numerous NIRemitting AuNCs have been employed as a platform to monitor whether the level of heavy metal ions surpasses the suggested limits (Table 3). Inorganic anions, such as cyanide (CN -), sulfide (S 2-), and (nitrite) NO 2-, retain the damaging influence on ecological systems as well as human health.…”