Ligands made of lipoic acid (LA) appended with a polyethylene glycol (PEG) chain have been used in the aqueous phase growth of luminescent gold clusters with distinct emission from yellow to near-IR, using two different routes. In the first route, the gold-ligand complex was chemically reduced using sodium borohydride in alkaline medium, which gave near- IR luminescent gold clusters with maximum emission around 745 nm. In the second method, LA-PEG ligand was photochemically modified to a mixture of thiols, oligomers and oxygenated species under UV-irradiation, which was then used as both reducing agent and stabilizing ligand. By adjusting the pH, temperature, and time of the reaction, we were able to obtain clusters with two distinct emission properties. Refluxing the gold-ligand complex in alkaline medium in the presence of excess ligand gave yellow emission within the first two hours and the emission shifted to red after overnight reaction. Mass spectrometry and chemical assay were used to understand the photo-chemical transformation of Lipoic Acid (LA). Mass spectroscopic studies showed the photo-irradiated product contains thiols, oligomers (dimers, trimers and tetramers) as well as oxygenated species. The amount of thiol formed under different conditions of irradiation was estimated using Ellman’s assay.
We prepared a set of multi-coordinating and reactive amphiphilic polymer ligands and used them for surface-functionalizing magnetic iron oxide nanoparticles. The amphiphilic oligomers were prepared by coupling (via one step nucleophilic addition) several dopamine anchoring groups, polyethylene glycol moieties and reactive groups onto a poly(isobutylene-alt-maleic anhydride) chain. The availability of several anchoring groups in the same ligand greatly enhances the ligand affinity to the nanoparticle surfaces, via multiplecoordination, while the hydrophilic and reactive groups promote colloidal stability in buffer media and allow subsequent conjugation to target biomolecules. The hydrophilic nanoparticles capped with these polymers maintain compact size and exhibit great long term colloidal stability.
We describe the growth and characterization of a set of gold and silver nanoparticles (NPs) as well as fluorescent
nanoclusters (NCs) using one-step reduction (in aqueous phase) of Au and Ag precursors in the presence of modular
bifunctional ligands. These ligands are made of bidentate (lipoic acid) anchoring groups appended with
poly(ethylene glycol) segment, LA-PEG. The particle size can be easily controlled by varying the metal-to-ligand
molar ratio during growth. We found that while high metal-to-ligand molar ratios promote the formation of NPs,
small size and highly fluorescent NCs are exclusively formed when molar excesses of ligands are used. Both sets of
NCs emit in the red to near infrared (NIR) region of the optical spectrum, though the exact location of the emission
depends on the material used. The growth strategy further permitted the in-situ functionalization of the NCs with
reactive groups (e.g., carboxylic acid or amine), which opens up the opportunity to conjugate these materials to
biomolecules using simple to implement coupling chemistries.