Tailor-made mesoporous SiO2/Au thin film with a substitutable interface for highly sensitive and selective room-temperature gas detection of VOCs

Trace amounts of volatile organic compounds (VOCs) were detected in Au chip interfaces modified with mesoporous SiO2 nanomaterials by using a surface plasmon resonance (SPR) technique. With Kretchmann-configuration SPR, it was possible to detect interactive and specific signal changes between a SiO2/Au gas-sensor surface and acetone, formaldehyde, and methane gases at room temperature. A dielectric spacing layer on Au was expanded and SPR signals were amplified by the mesoporous SiO2 nanoparticles with a large surface area and surface properties that were easily modified with specific ligands and became highly sensitive to, and selective for, the target gas molecules. A phosphonitrilic chloride trimer (PNCT), a universal self-assembled monolayer (SAM), and post-treatment for simple substitutions of ligands equipped the surfaces of SiO2 nanoparticles with targeted receptors, which resulted in the sensitive and selective detection of acetone to CH3-, formaldehyde to NH2-, and methane to Cl-functional groups. The chips modified with each functional group had a response time of about 2 s for concentrations of each gas that ranged from 0.2 to 3.0 ppm. The sensors modified with the functional groups showed limit of detection (LOD) values of 0.3, 0.6, and 0.5 ppm, respectively, which exceeded the Occupational Safety and Health Administration (OSHA) regulations, and limit of quantification (LOQ) values of 0.9, 1.8, and 1.6 ppm. Relative humidity of 45 ∼ 84 % under ambient air had negligible influence on the baseline signals in this SPR gas-sensing system. These sensors have the potential to monitor VOCs in both environmental and indoor settings.