Ultrasensitive Plasmonic Detection of Molecules with Graphene

Graphene plasmons can couple with vibrations in both extended and local systems, for example, phonons in polar crystals and molecular vibrations in polymers. These interactions are characterized by plasmon-induced transparency features within the plasmon infrared absorption profile. Detection enhancement made possible by graphene-based plasmon-induced transparency has been demonstrated in both polymer and protein films and has shown to offer superior detection capabilities compared to conventional metal dipole plasmonic sensors. Here, we demonstrate the detection of molecular vibrations in minute, residual molecular quantities of solid- and gas-phase molecules down to 50 zeptomol/μm2 using graphene plasmonic sensing platforms. Plasmon-induced transparency enhancement is shown to be sensitive to both the specific molecular coordination of the measured vibrations and to the distribution of modes within the measured vibrational bands. This work could lead to the development of functionalization-free, chemical-specific, large-area, signal-enhancement platforms for infrared spectroscopy.