The effect of ligand-ligand interactions on the formation of photoluminescent gold nanoclusters embedded in Au(i)-thiolate supramolecules.

In this study, we prepared photoluminescent l-cysteine (Cys)-capped gold nanoclusters (Cys-Au NCs) via NaBH4-mediated reduction of aggregated coordination polymers (supramolecules) of -[Cys-Au(i)]n-. The -[Cys-Au(i)]n- supramolecules with interesting chiral properties were formed through simple reactions of chloroauric acid (HAuCl4) with Cys at certain pH values (pH 3-7). The -[Cys-Au(i)]n- polymers could self-assemble into -[Cys-Au(i)]n- supramolecules with irregular morphologies and diameters larger than 500 nm through stacked hydrogen bonding and zwitterionic interactions between Cys ligands and through Au(i)Au(i) aurophilic interactions in solutions with pH values ≤7. The photoluminescent Au NCs (quantum yield = 11.6%) dominated by a Au13 core were embedded in -[Cys-Au(i)]n- supramolecules after NaBH4-mediated reduction. The optical and structural properties of Cys-Au NCs/-[Cys-Au(i)]n- nanocomposites were investigated, revealing that the interaction between Cys ligands plays a critical role in the self-assembly of -[Cys-Au(i)]n- supramolecules and in the formation of photoluminescent Cys-Au NCs embedded in the supramolecules. To further demonstrate that the photoluminescence properties and structures of the nanocomposites are mediated by the intermolecular forces of thiol ligands, other thiol ligands (l-penicillamine, l-homocysteine, 3-mercaptopropionic acid, and l-glutathione) and a ligand-crosslinking agent [bis(sulfosuccinimidyl) suberate; BS3] were used. We concluded that the electrostatic interactions, hydrogen bonding and steric effects dominate the polymer self-assembly into thiol-ligand-Au(i) supramolecules and thus the formation of Au NCs. Our study provides insights into the bottom-up synthesis of photoluminescent Au NCs from thiol-ligand-Au(i) complexes, polymers, and supramolecules. The hybrid Au NCs/-[Cys-Au(i)]n- nanocomposites can potentially be employed as drug carriers and bioimaging agents.

Analyses of functional polymer-modified nanoparticles for protein sensing by surface-assisted laser desorption/ionization mass spectrometry coupled with HgTe nanomatrices.

In this study, we employed HgTe nanostructure-based matrices (nanomartrices; NMs) for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) for the analyses of polyethylene glycol (PEG) derivatives as well as thiol-PEG-modified gold nanoparticles (PEG-Au NPs). Relative to common organic matrices, the use of HgTe NMs as the matrix for SALDI-MS resulted in more highly efficient analyses of PEG derivatives, in terms of sensitivity and reproducibility. The symmetric MS profiles of PEG (Mw: ca. 8000 Da) obtained through HgTe NMs/SALDI-MS analysis revealed the absence of polymer degradation during this process. Under optimal conditions, the HgTe NMs/SALDI-MS system enabled the detection of PEG sample as low as 100 pg and with molecular weights of up to approximately 42,000 Da. We also used this approach for the analyses of PEG-Au NPs in which various functional groups (carboxymethyl, amine, biotin) were present at the PEG termini, revealing that the combination of SALDI-MS and HgTe NMs have great potential for use in the characterization of modified polymer-ligands on nanomaterials. We also demonstrated the PEG-Au NPs can be coupled with HgTe NMs/SALDI-MS for characterization of biorecognition events. After avidin, the target protein, had been selectively captured by the biotin-PEG-Au NPs, we found that the desorption/ionization efficiency of biotin-PEG from the Au NP surface was suppressed; accordingly, this novel SALDI-MS approach allows rapid detection of avidin with high specificity and sensitivity. Au NP surfaces functionalized with other functional-PEG ligands might also allow amplification of signals from other biological interactions.