Plasmonic Crystal-Based Gas Sensor Toward an Optical Nose Design

This paper presents a high-sensitivity gas sensor based on plasmonic crystal incorporating a thin layer of graphene oxide (GO). The plasmonic crystal consists of a periodic array of polymeric nanoposts with gold (Au) disks at the top and nanoholes in an Au thin film at the bottom. The thin GO layer coated atop the plasmonic crystal is the gas absorbent material for the sensor. Gas adsorption of GO modifies the refractive index of the plasmonic structure and returns a shift in the resonance wavelength of the surface plasmon polariton excited at the GO coated Au surface. The differences in target gas species and their adsorption in GO lead to a difference in the resonance shift. To identify the gas species in a complex gas mixture, a sensor array is designed with different sensing elements coated with different thicknesses of GO. The optical responses of the different sensing elements to a gas mixture are analyzed using principal component analysis (PCA)-based pattern recognition algorithm. The PCA separates the sensor responses to different species of gases, providing specificity of the device. The proposed sensor demonstrates a refractive index sensitivity of 449.63 nm/RIU. In addition, volatile organic compounds, such as ethylene, methanol that serve as plant health indicators and ammonia that plays a key role in the ecosystem, are detected by the sensor. A change in a gas concentration results in a differing amount of adsorbate and correlated shift in the resonance wavelength of the device. The GO coated sensor exhibits sensitivities of 0.6 pm/ppm to gaseous ethylene, 3.2 pm/ppm to methanol, and 12.84 pm/ppm to ammonia. The integration of plasmonic sensing element arrays with varying GO thicknesses to modulate the gas adsorption, offers a promising approach to detect different gas species in a single test.