Interfacial Interaction Monitoring and Constitutional Isomer Discrimination Using a Graphene-Integrated Terahertz Metasurface

Monitoring and discrimination of molecular behavior in isomers remain a longstanding challenge due to similar chemical compositions, although they have functionally critical differences. Due to the consistent demand for molecular design/structural analysis in research fields and reaction/quality control in industrial fields, the identification of isomeric pairs is essential. However, conventional analytical techniques, including nuclear magnetic resonance and mass spectrometry, require destructive processes or large-scale sample volumes, limiting their applicability to on-chip or simple analysis with accessibility. Here, we propose a graphene-integrated terahertz metasurface platform that enables nondestructive and on-chip constitutional isomer discrimination, along with monitoring over interfacial molecular behavior with a nanogram scale limit of detection. By covering a graphene layer onto a nanoslot cavity array of the metasurface, a floated graphene monolayer can be utilized as an active probing pad with the assistance of extreme terahertz field confinement. With high sensitivity toward the interfacial state of the graphene surface, constitutional isomers with different electronic properties can be comprehensively distinguished via both the graphene-analyte interaction rate and the graphene conductivity change. The proposed platform features label-free isomer discrimination and interfacial interaction monitoring through a one-shot process implemented within a 6 mm square compact metasurface using under 20 μL of sample solution. This configuration benefits from compatibility for electrical measurement in addition to optical analysis in a nondestructive manner, with promising potential for molecular isomer characterization and behavior tracking.