Silver/gold core/shell nanowire monolayer on a QCM microsensor for enhanced mercury detection

Abstract

The formation of a silver nanowire monolayer (Ag NWML) galvanically replaced with gold (Au) directly on the electrodes of a quartz crystal microbalance (QCM) transducer for non-spectroscopic based elemental mercury (Hg⁰) vapor sensing is reported in this study. The modification of Ag NWML to Ag/Au alloyed (Ag/Au NWML) structures through galvanic replacement (GR) reaction was found to enhance the sensitivity and selectivity of the sensors. Following GR reaction, the morphology of the Ag nanowires was found to change without deforming the monolayer packing arrangement. Interestingly, the selectivity of the sensor toward Hg⁰ vapor was increased by increasing the Au concentration during the GR reaction. The Ag/Au NWML based sensor which was modified using a 2 mM Au solution was found to produce 3 times higher sensitivity compared to the Au control QCM as well as having more than 95% accuracy and >90% repeatability. This was found to be due to the formation of Ag/Au alloys (Ag/Au NWML) with active sites that had a high affinity toward Hg⁰ vapor.