Electrochemiluminescent Metallopolymer−Nanoparticle Composites: Nanoparticle Size Effects

Metallopolymer−gold nanocomposites have been synthesized in which the metal complex−Au nanoparticle (NP) mole ratio is systematically varied by mixing solutions of 4-(dimethylamino) pyridine protected gold nanoparticles and a [Ru(bpy)₂PVP₁₀]²⁺ metallopolymer; bpy is 2,2′-bipyridyl and PVP is poly-(4-vinylpyridine). The impact of changing the gold nanoparticle diameter ranging from 4.0 ± 0.5 to 12.5 ± 1 nm has been investigated. The photo induced emission of the metallopolymer undergoes static quenching by the metal nanoparticles irrespective of their size. When the volume ratio of Au NP−Ru is 1, the quenching efficiency increases from 38% to 93% on going from 4.0 ± 0.5 to 12.5 ± 1 nm diameter nanoparticles while the radius of the quenching sphere remains unaffected at 75 ± 5 Å. The conductivity of thin films is initially unaffected by nanoparticle incorporation until a percolation threshold is reached at a mole ratio of 4.95 × 10⁻² after which the conductivity increases before reaching a maximum. For thin films of the nanocomposites on electrodes, the electrochemiluminescence intensity of the nanocomposite initially increases as nanoparticles are added before decreasing for the highest loadings. The electrochemiluminescence intensity increases with increasing nanoparticle diameter. The electrochemiluminescence (ECL) emission intensity of the nanocomposite formed using 12.5 nm particles at mole ratios between 5 × 10⁻³ and 10 × 10⁻³ is approximately 7-fold higher than that found for the parent metallopolymer. The application of these materials for low cost ECL-based point of care devices is discussed.