Flexible chemiresistor sensors: thin film assemblies of nanoparticles on a polyethylene terephthalate substrate

Abstract

The thin film assembly of metal nanoparticles on flexible chemiresistor (CR) arrays represents an intriguing way to address the versatility of chemical sensor design. In this work, thin film assemblies of gold nanoparticles in size range of 2–8 nm diameters with high monodispersity (unlinked or linked by molecular mediators) were assembled on a CR array with a polyethylene terephthalate (PET) substrate to demonstrate the flexible chemiresistor characteristics of the nanostructured materials. The correlation between the relative change in electrical conductivity and the change in dielectric medium constant in response to flexible wrapping of the device demonstrated the viability of manipulating the electrical responses in terms of wrapping direction. The responses of the devices in response to volatile organic compounds (VOCs) were analyzed in terms of particle size, interparticle properties, and substrate–film interactions. For molecularly linked films with small particle size and large interparticle spacing, which is characterized by a high percentage of organics and linker molecules, the relatively low electrical conductivity renders the change in interparticle spacing able to play a dominant role in the sensor response to VOCs with small dielectric constants. The combination of a high percentage of linker molecules in the thin film assembly and a high dielectric constant for the VOCs was found to produce a negative response characteristic. In contrast, the response characteristic for the unlinked film via weak interparticle interactions was dominated by the change in interparticle spacing regardless of the percentage of organics in the nanostructure. The delineation between these factors and the sensing characteristics is useful in enabling a rationale design of the nanostructures on flexible chemiresistors.