Fluorescent gold clusters synthesized in a poly(ethyleneimine) modified reverse microemulsion

Area of Science:

• Nanomaterials Science
• Polymer Chemistry
• Colloid Science

Background:

• Reverse microemulsions offer controlled environments for nanoparticle synthesis.
• Polyelectrolytes like poly(ethyleneimine) (PEI) can influence nanoparticle formation and properties.
• Gold clusters and nanoparticles exhibit unique optical and electronic properties.

Purpose of the Study:

• To synthesize gold clusters and nanoparticles in a polyelectrolyte-modified reverse microemulsion.
• To investigate the role of poly(ethyleneimine) (PEI) as a reducing, stabilizing, and templating agent.
• To characterize the size, optical, and fluorescent properties of the synthesized gold species.

Main Methods:

• Formation of gold nanoparticles and clusters within a water/oil microemulsion using PEI.
• Synthesis via simple mixing of two microemulsion systems containing PEI and gold chloride.
• Characterization using UV-vis spectroscopy, fluorescence spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and asymmetric flow field flow fractionation (AF-FFF).

Main Results:

• UV-vis spectroscopy revealed two absorption maxima, indicating distinct particle fractions at 360 nm (gold clusters) and 520 nm (gold nanoparticles).
• Fluorescence properties confirmed the formation of gold clusters (<2 nm).
• Characterization confirmed the presence of both gold nanoparticles (>5 nm) and fluorescent gold clusters (<2 nm) after solvent evaporation, with AF-FFF identifying two distinct cluster fractions.

Conclusions:

• Poly(ethyleneimine) (PEI) effectively acts as a reducing, stabilizing, and templating agent in reverse microemulsions for gold cluster and nanoparticle synthesis.
• The method allows for the formation and stabilization of both gold nanoparticles and fluorescent gold clusters.
• The synthesized gold clusters exhibit distinct optical and fluorescent properties, with potential for further applications.