Preparation of pH-responsive AgNPs/polymer nanohybrids with controllable metal-enhanced fluorescence behavior

• pH responsive silver/polymer nanohybrids with switchable metal enhanced fluorescence were synthesized by the immobilization of fluorescent polymer onto silver nanoparticles (AgNPs) via Ag–S coordination interaction.
• pH responsive polymer is as the bridge with length regulation between fluorophores and Ag.
• Polymers with different polymerization degree reached maximal fluorescent intensity in different pH value.
• When the degree of polymerization (DP) of polymer was 150, the maximal MEF was obtained.

Fabrication of metal-enhanced fluorescence (MEF) system with stimuli responsive “soft” shells is an efficient means to achieve tunable MEF behavior. In this article, pH responsive fluorophores modified polyacrylic acid (PAA) with tunable chain length was synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization using a rhodamine B (RB) functionalized RAFT agent, followed by the immobilization onto silver nanoparticles (AgNPs) via Ag–S coordination interaction to afford core–shell nanohybrids with AgNPs core, PAA shell and RB fluorophores on the surface. TEM and XPS analysis revealed that the polymer was successfully linked onto AgNPs surface. Our results revealed that the fluorescent intensity of AgNPs/polymer core–shell nanohybrids was sensitive extremely to the environmental pH values. All the maximal fluorescence intensities were observed at around pH 2, but slightly different. The maximal fluorescent intensity at pH 2 increased with the increasing polymer chain length first and then decreased. When the degree of polymerization (DP) of polymer was designed at 150, the maximal MEF was obtained. The size change of the core–shell nanohybrids with different environmental value was also supported by DLS analysis, which also manifested that the tunable MEF behavior was sensitive to the distance between the AgNPs and fluorophores. These pH responsive AgNPs/polymer core–shell nanohybrids may envision potential applications in drug delivery, sensors and nanodevices.

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