Interband plasmon-enhanced optical absorption of DNA nucleobases through the graphene nanopore

Plasmonic Biosensors Based on Deformed Graphene

Rapid, accurate, and label-free detection of biomolecules and chemical substances remains a challenge in healthcare. Optical biosensors have been considered as biomedical diagnostic tools required in numerous areas including the detection of viruses, food monitoring, diagnosing pollutants in the environment, global personalized medicine, and molecular diagnostics. In particular, the broadly emerging and promising technique of surface plasmon resonance has established to provide real-time and label-free detection when used in biosensing applications in a highly sensitive, specific, and cost-effective manner with small footprint platform. In this study we propose a novel plasmonic biosensor based on biaxially crumpled graphene structures, wherein plasmon resonances in graphene are utilized to detect variations in the refractive index of the sample medium. Shifts in the resonance wavelength of the plasmon modes for a given change in the RI of the surrounding analyte are calculated by investigating the optical response of crumpled graphene structures on different substrates using theoretical computations based on the finite element method combined with the semiclassical Drude model. The results reveal a high sensitivity of 4990 nm/RIU, corresponding to a large figure-of-merit of 20 for biaxially crumpled graphene structures on polystyrene substrates. We demonstrate that biaxially crumpled graphene exhibits superior sensing performance compared with a uniaxial structure. According to the results, crumpled graphene structures on a titanium oxide substrate can improve the sensor sensitivity by avoiding the damping effects of polydimethylsiloxane substrates. The enhanced sensitivity and broadband mechanical tunability of the biaxially crumpled graphene render it a promising platform for biosensing applications.

DNA sequencing by Förster resonant energy transfer

We propose a new DNA sequencing concept based on nonradiative Förster resonant energy transfer (FRET) from a donor quantum dot (QD) to an acceptor molecule. The FRET mechanism combined with the nanopore-based DNA translocation is suggested as a novel concept for sequencing DNA molecules. A recently-developed hybrid quantum/classical method is employed, which uses time-dependent density functional theory and quasistatic finite difference time domain calculations. Due to the significant absorbance of DNA bases for photon energies higher than 4 eV, biocompatibility, and stability, we use Zinc-Oxide (ZnO) QD as a donor in the FRET mechanism. The most sensitivity for the proposed method to DNA is achieved for the Hoechst fluorescent-dye acceptor and 1 nm ZnO-QD. Results show that the insertion of each type of DNA nucleobases between the donor and acceptor changes the frequency of the emitted light from the acceptor molecule between 0.25 to 1.6 eV. The noise analysis shows that the method can determine any unknown DNA nucleobases if the signal-to-noise ratio is larger than 5 dB. The proposed concept and excellent results shed light on a new promising class of DNA sequencers.