2D Colloidal Crystals Based SERS Sensors for NH3 Detection

This work demonstrates Au Nanoparticles (NPs) decorated onto partial embedded PS 2D colloidal crystals embedded in the flexible PDMS matrix by RF-sputtering technique for surface enhanced Raman spectroscopy (SERS) NH3 sensor. The surface morphology and optical properties of Au NPs decorated over 2D PS colloidal crystals (CC) on flexible substrate is investigated by scanning electron microscopy (SEM) and UV-visible spectroscopy. The sensitivity of the Au NPs/ 2D CC/PDMS system for NH3 detection is investigated by the SERS techniques. A significant increase in the SERS intensity is observed as a function of NH3 concentration from 100 to 1000 ppm for the synthesized sensors system. The noticeable change in the SERS intensity with the exposure of the NH3 gas is attributed to the change in the electric near-field due to the Au NPs aggregation or distance as well as change in the dielectric of the surrounding medium. The SERS intensity exhibit a dependence on the change in refractive index/dielectric constant by NH3 gas molecules, and are linked to coupling effects between surface plasmon resonance (SPR) on the corrugated Au NPs islands and the hot spot formed by 2D PS CC assembly. The proposed Au NPs/ 2D CC/PDMS sensor system is capable for single molecule detection of gaseous precursors.