Multi-modal biosensing enabled by on-chip nano-corrugated graphene

We present a nano-corrugation graphene (NCGr)-based device, which can support diverse detection strategies. A single NCGr device can exhibit three different modes of biomolecular sensing: electrolyte-gated field-effect transistor (FET) sensing, electrochemical sensing, and sensing based on surface-enhanced Raman spectroscopy (SERS). Each mode produces reliable signals with extremely high sensitivity for DNA hybridization detection (analyte concentrations < 10 fM). The charge-transfer effect is dominant in all NCGr-integrated devices. Electrochemical complex capacitance spectroscopy and electrochemical impedance spectroscopy results indicate the presence of coupled quantum-classical effects (from the band gap opening) in the FET-based device, which govern its Atto-molartDNA concentration, and a nonclassical electrical double layer that reduces the ionic screening. In the electrochemical mode, the NCGr surface behaves catalytically, facilitating long electron transfers in dsDNA “circuits” upon hybridization. The faster penetration of methylene blue into the DNA duplex is confirmed by chronoamperometry, explaining its sensitivity. NCGr can “switch on” the optical sensing ability for SERS and activate its plasmonic behaviour without a heterostructure such as a metal–graphene hybrid or grating structure. The plasmonic signal is geometry dependent; greater changes in the localized electrical field can be observed from the bare surface to the molecular decoration. Finite element method simulations reveal that chemical mechanism dominates over electromagnetic mechanism in the enhancement of SERS and plasmonic devices, indicating that the charge transfer between molecules improves the optical sensing response.