Enhanced electrochemiluminescence and charge transport through films of metallopolymer-gold nanoparticle composites

Water-soluble 4-(dimethylamino) pyridine (DMAP) stabilized gold nanoparticles (DMAP-AuNP) were synthesized by ligand exchange and phase transfer (toluene/water). The DMAP-AuNPs are positively charged with the core diameter of 4 ± 1 nm. Metallopolymer-gold nanocomposites were prepared by mixing gold nanoparticles and [Ru(bpy)₂PVP₁₀](ClO ₄)₂, in water at different mole ratios; bpy is 2,2′-bipyridyl and PVP is poly (4-vinylpyridine). The photoluminescence emission intensity of the metallopolymer decreases with increasing AuNP loading and approximately 57% of the emission intensity is quenched when the Au NP:Ru mole ratio is 14.8 × 10^-2. The rate of homogeneous charge transfer through thin layers of the nanocomposite deposited on glassy carbon electrodes increases with increasing nanoparticle loading. The homogeneous charge transport diffusion coefficient, D_CT, for the composite (AuNP:Ru mole ratio 13.2 × 10^-2) is (2.8 ± 0.8) × 10^-11 cm² s^-1 and is approximately 3-fold higher than that found for the pure metallopolymer. Significantly, despite the ability of the metal nanoparticles to quench the rutheniumbased emission, the electrochemiluminescence of the nanocomposite with a AuNP:Ru mole ratio of 4.95 × 10^-2 is approximately three times more intense than the parent metallopolymer. This enhancement arises from the increased rate of charge transport that leads to a greater number of excited states per unit time while minimizing the quenching effects. The implications of these findings for the design of electrochemiluminescent sensors are discussed.