Heat Treatment-Based One-Step Preparation of Highly Concentrated, Well-Stable Silver Colloids that Can Form Stable Films on Bare Electrodes for H2O2 Detection

A simple thermal process for the one-step preparation of highly concentrated (up to 0.21 M) but well-stable silver colloids with a bimodal size distribution is developed for the first time, carried out by directly heating an aqueous solution of concentrated AgNO3 and poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co- (1-vinylpyrrolidone)] (PQ11), a kind of cationic polyelectrolyte, at 100 °C without the extra introduction of other reducing agents and protective agents. Time-dependent UV-vis spectra were collected to gain further insight into the Ag nanoparticles (AgNPs) formation process. Most importantly, it is found that the colloidal solution can form stable films on bare electrode surfaces and the AgNPs contained therein exhibit notable catalytic activity toward the reduction of H2O2, leading to a H2O2 sensor with a fast amperometric response time of less than 2 s. The linear detection range is estimated to be from 100 μM to 150 mM (r = 0.9995), and the detection limit is estimated to be 1.8 μM at a signal-to-noise ratio of 3.