Fig. 1. Graphene plasmon biosensor. (a) Schematic of the graphene plasmon sensor. Monolayer protein was deposited on top of the GNR array fabricated on 700 nm thick MgF2 supported on Si substrate. Incident IR light excites plasmon resonance across the GNR: S, source; D, drain. (b) SEM image of a GNR array with a ribbon width (W) of 100 nm and a period width (P) of 140 nm. (c) The electric transfer curve (green curve) and carrier density (red line) of the double layered graphene/MgF2 sensor. The black arrow is the CNP.

Fig. 2. Comparison between double layered graphene plasmon and single layer graphene plasmon. (a) Experimental extinction spectra comparison between single layer graphene and double layered graphene at Vg=−8V. Ribbon width, 100 nm; period, 140 nm. (b) Simulated near-field enhancement distribution |E/E0| at the edge of single layer graphene (1000cm−1) and double layered graphene (1350cm−1) GNRs at their resonant frequencies. (c) Simulated extinction spectra of double layered GNR with EF, single layer graphene with |EF| and 2|EF|. Fermi level EF=0.2, 0.3, 0.4, 0.5 eV. (d) Near-field enhancement distribution |E/E0| along the white dashed line in (b), EF=0.3eV; mobility is using 600cm2/(V·s).

Fig. 3. Enhanced IR spectroscopy of nanoscale proteins. (a) Extinction spectrum of the GNR (ΔCNP=−15V) after the protein layer formation (red curve). The pristine extinction spectrum of a 9 nm thick protein layer is shown as the black curve. The pink vertical lines indicate the vibrational fingerprints of backbone (A and B), while the orange ones correspond to the side chain and endpoint (C and D). (b) Partially representative molecular structure of BSA, containing a peptide bond, a carboxyl-terminal end, and a side chain (CH3 is taken as an example); vibrational fingerprints of BSA and their positions in (a). ν, stretching vibration; υs, symmetric stretching vibration; δ, in-plane bending vibration; δas, asymmetric in-plane bending vibration. “+” denotes the coupling between different vibration modes, and the former contributes more than the latter. (c) Extinction spectra of the GNR after the protein layer formation at different gate voltages (solid lines). The baselines derived from the pristine plasmon extinction spectra are shown as dashed lines. (d) The plasmonic enhanced signal at different effective gate voltages were obtained by subtracting the corresponding baseline from each measured extinction curve in (c).