Utilizing diversified properties of monolayer protected gold nano-clusters to construct a hybrid sensor array for organic vapor detection

The present study demonstrated improvement in the vapor recognition rate of a sensor array employing monolayer-protected gold nano-clusters (MPCs) by combining two different MPC transduction properties. The number of sensors was increased by using the same set of MPC materials on different platforms and combined them as a hybrid array. Resistive changes in MPC film due to the insufficient swelling of inter-particle distance, which resulted from nature of absorbed vapor and surface thiolates, provided information in addition to the mass increases during vapor sorption. Quartz crystal microbalance (QCM) was used as the mass-change transducer and MEMS-fabricated interdigit electrode was used as the resistive transducer. Four different thiolate ligands were used to cap the gold core for diversification of the chemical selectivity. Fifteen organic vapors with various functional groups were tested for QCM and chemiresistor (CR) presence. Cluster analysis indicated that the arrays of QCMs and CRs show different selectivity for these 15 VOCs. Linear discriminant analyses (LDA) showed that single-compound identification rates within the response data library of 15 VOCs were 87.7% for the 4-QCM array, 82.1% for the 4-CR array, and 96.1% when a hybrid array of 8-sensors was used. This result proves that different properties of the same MPC can be used as different sensors to increase sensor numbers, and, therefore, to improve recognition rates via a hybrid platform.