The terahertz electromagnetically induced transparency-like metamaterials for sensitive biosensors in the detection of cancer cells.

A kind of novel biosensor based on the electromagnetic induced transparency like (EIT-like) metamaterials (MMs) have been proposed. It demonstrates that the symmetry-breaking double-splits ring resonators can realize the EIT-like plasmonic resonance, the according transparency window occurs at 1.67 THz. The coupled oscillators model illustrates that with the increase of asymmetry degree of double splits, the coupling between bright and dark mode is enhanced. Consequently, the non-radiative damping γ2 grows from 1.45 to 1.85 THz and coupling coefficient κ from 3.46 to 4.49 THz2, while the radiative damping γ1 decreases from 11.5 to 9 THz. Such EIT-like MMs were evaluated in simulation as the refractive index sensors, which the theoretical sensitivity was calculated to 455.7 GHz/RIU (RIU, Refractive Index Unit) under 11 μm-thick analyte layer. Meanwhile, the dependence of full width at half maximum (FWHM) on analyte thickness was also studied. In experiments, it is found that the frequency shift Δf increases from 50 to 90 GHz when the oral cancer cells (HSC3) concentration improves from 1 × 105 to 7 × 105 cells/ml. The maximum experimental sensitivity approaches 900 kHz/cell ml-1 at 7 × 105 cells/ml. Additionally, the apoptosis of cancer cells under the effect of anti-cancer drug was investigated. It shows that with the increase of anti-cancer drug concentration from 1 to 15 μM and the extension of drug action duration from 24 to 72 h, the Δf changes from 140 to 70 GHz and 140-40 GHz, respectively. Besides, the corresponding FWHM also increases from 237.9 to 305.4 GHz and 237.8-337.6 GHz. The results measured by MMs biosensors and biological method exhibit a relatively good agreement, showing a great potential for cells measurement with the sensitive biosensors based on the EIT-like MMs.