CO₂‑Responsive Polymer-Functionalized Au Nanoparticles for CO₂ Sensor

Abstract

Metallic nanoparticles (NPs) coated with stimuli-responsive polymers (SRPs) exhibit tunable optical properties responding to external stimuli and show promising sensing applications. We present a new CO₂-responsive polymer, poly­(<i>N</i>-(3-amidino)-aniline) (PNAAN), coated gold NPs (AuNPs) synthesized by directly reducing HAuCl₄ with a CO₂-responsive monomer <i>N</i>-(3-amidino)-aniline (NAAN). The amidine group of PNAAN can be protonated into a hydrophilic amidinium group by dissolved CO₂ (dCO₂). This induces the PNAAN to swell and detach from the AuNP surface, resulting in AuNP aggregation and color change. By monitoring the UV absorbance change of AuNPs, a sensitive dCO₂ sensor with a linear range of 0.0132 to 0.1584 hPa and a limit of detection (LOD) of 0.0024 hPa is developed. This method shows dramatic improvement in sensitivity and convenience of sample preparation compared with the previously reported dCO₂ sensor