Ag@poly(m-phenylenediamine)-Ag core-shell nanoparticles: one-step preparation, characterization, and their application for H2O2 detection

We have recently found that the direct mixing of m-phenylenediamine (MPD) and AgNO3 aqueous solutions at room temperature leads to Ag@poly(m-phenylenediamine) (Ag@PMPD) core-shell nanoparticles (Langmuir, 2011, 27, 2170). In this study, we characterize such core-shell nanoparticles in more detail by X-ray diffraction and IR techniques and further demonstrate that the size of the core and whole particle as well as the ratio of the shell thickness to the core size can be tuned by the molar ratio of MPD to Ag. Furthermore, the PMPD shell can be further used as a reductant to reduce Ag+ into small Ag nanoparticles (AgNPs) which are embedded in the PMPD matrix, leading to nanoparticles with a Ag core and a small AgNP-embedded PMPD shell (Ag@PMPD-Ag core-shell nanoparticles). The Ag core, although buried in the central part of the resultant nanoparticle, can still catalyze the reduction of H2O2, but the embedded AgNPs in the PMPD matrix exhibit superior catalytic performance. With these Ag@PMPD-Ag core-shell nanoparticles, we constructed an enzymeless H2O2 sensor with a fast amperometric response time of less than 2 s, a linear range of 0.1 to 170 mM and a detection limit of 2.5 mu M at a signal-to-noise ratio of 3.