Highly Sensitive Biomolecule Sensing Exploiting Graphene Assisted THz Resonators

Abstract

In this research, we show a novel approach for sensing of single-strand DNA (ssDNA) in a few femto-mole levels using low energy photon of terahertz (THz) electromagnetic waves. Combining of THz resonance structure and suspended graphene monolayer can provide unprecedentedly increased sensitivity in sensing of such small biomolecules even with enormous scale difference between THz wavelength and DNA nucleotides. We show remarkable signal differences between four different ssDNA chains based on single nucleobases in a quantitative trait which have not been easily succeeded under earlier THz studies1. Since DNA is very small and has a tiny difference in molecular structures for four species, the DNA on sensing chips even with nanoslot array does not interact well with the THz waves. However, DNA onto the graphene layer changes THz transmittance slightly, basically related to the changed electronic structure of graphene by doping effect. The measured transmission is then amplified by the nanoslot array. As well-known, the nanoslot antenna acts as a cavity, increasing absorption cross-section of molecules effectively through the THz E-field enhancement around the slot, can be summarized as, σA ∝ρ (Eslot/Hslot), where σA is absorption cross-section of the target absorber (in this work, DNA or DNA+graphene system), ρ is a density of states of an analyte molecule, and E and H are the amplitude of the electric and magnetic field attributed from the slot.