Surface modification on silver nanoparticles for enhancing vapor selectivity of localized surface plasmon resonance sensors

This study focuses on localized surface plasmon resonance (LSPR) sensors employing silver nanoparticles that were surface functionalized with various thiolate self-assembled monolayers (SAM) to provide chemical selectivity for detection of volatile organic compounds (VOCs). Changes in the LSPR spectrum of silver nanoparticles were measured as the response signal. One unmodified and three surface-modified nanoparticle LSPR sensors generated distinguishable patterns for tested organic vapors with different functional groups. The sensor responses were rapid and reversible for all tested vapors. The detection limits of the LSPR sensor were as low as 18-30 ppm for heptanone, depending on the surface modification of Ag nanoparticles. SAM modification not only altered chemical affinity of the surface, but also moderately improved the detection limit without lengthening the response time. Surface modification using thiolates with refractive indices higher than condensed VOC neither reduced nor reversed the sensor response. Mechanisms for this phenomenon are also discussed.