Layer-by-Layer Structured AuNP Sensors for Terpene Vapor Detection

A localized surface plasmon resonance (LSPR) sensor based on self-assembled Au nanoparticle (AuNP) multilayers is developed for the detection of volatile terpenes that are considered to be biomarker gases during the growth process of plants. The sensor is fabricated by an alternate deposition of a bifunctional dithiol cross-linker and AuNPs. UV-vis spectra, atomic force microscopy images, and scanning electron microscope images of AuNP multilayers are investigated to analyze their LSPR spectra and refractive index sensitivity to terpene vapors. The results show that the optical properties of NP multilayers are jointly decided by the molecular length and chemical nature of dithiol linkers. The electric field coupling of AuNPs occurred in inter- and intra-layers determined by the refractive index sensitivity (RIS) of the sensor. The normalized RIS of the AuNP multilayer is about three times higher than that of the monolayer. The responses of AuNP multilayer sensors to changes in terpene vapor concentration are rapid, reversible, and reproducible.