Gold/Silver-Polymer Hybrid Nanostructures as Thermoreversible Optical Sensors and Probes for the Quantification Radical
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Gold/Silver-Polymer Hybrid Nanostructures as Thermoreversible Optical Sensors and Probes for the Quantification Radical Compounds Eun Chul Cho, Ju A La, Sora Lim, and Ji Eun Song Department of Chemical Engineering, Hanyang University, Seoul, 133-791, South Korea ABSTRACT We present gold (Au) and silver (Ag) nanoparticles (NPs) could be used not only for stimuliresponsive optical sensors but also for the quantification of radical compounds when these nanoparticles are suitably combined with polymeric materials. When Au NPs are assembled 2dimensionally on the surface of hydrogel NPs which respond to temperatures, the hybrid NPs displayed thermoreversible multiple color switching. Accordingly, optical bandwidths of the hybrid NPs are reversibly changed with temperatures: with hybrid NPs assembled with 51 nm Au NPs, prominent optical signals are recorded at 900 nm at 50 oC while most of extinction signals are shown below 600 nm at room temperatures. In addition, we demonstrate the modification of Ag NPs’ surfaces (nanocubes and nanospheres) with polyelectrolytes (either positive or negative) could extend the quantifiable detection ranges of radical compounds. Through the surface modification of Ag NPs, the polyelectrolytes protect the Ag NPs by probably either retarding (forming diffusion barriers) or preventing (blocking/entrapping/scavenging) the arrival of radicals to Ag NPs or both. The roles of the polyelectrolytes are demonstrated by using radical compounds produced from tetrahydrofuran and H2O2. From the results, we could obtain calibration curves for the wide-range quantification of radical compounds. INTRODUCTION To date, so many excellent works have been reported for the applications of gold (Au) and silver (Ag) nanoparticles (NPs) to various fields. Meanwhile, combination of plasmonic NPs with functional polymers can further shed light on the characteristics of NPs. On the basis of our recent two published papers, Chem. Mater. 26, 3272 (2014); Anal. Chem. 86, 6675 (2014) [1,2], we present here Au and Ag NPs could be used not only for stimuli-responsive optical sensors but also for the quantification of radical compounds when these nanoparticles are suitably combined with polymeric materials to form hybrid nanostructures. Firstly, we first present Au-hydrogel hybrid colloids as optical sensors in which multiple colors (maximum four colors: wine ↔ violet ↔ dark blue ↔ faint blue) are switching reversibly in response to temperature changes. Next, we present the modification of Ag NPs’ surfaces (nanocubes and nanospheres) with polyelectrolytes (either positive or negative) provides Ag NPs with opportunities for plasmonic-based wide-range quantification of radical compounds. The results are discussed on the basis of the references. RESULTS AND DISCUSSION Au-hydrogel hybrid NPs as plasmonic-based thermochromism We used spherical Au NPs and thermoresponsive hydrogel colloids for the construction of hybrid NPs. Four types of spherical Au NPs (15, 33, 43, 51 nm in diameter) were synthesized in
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