Abstract
We theoretically and experimentally demonstrate a label-free terahertz biosensor with ultrahigh sensitivity and distinctive discretion. By constructing a metal-air-metal (MAM) metamaterial perfect absorber (MPA) with a metallic paired-ring resonator array, a hollow microfluidic channel, and a backed reflector, a novel dual-band absorptive sensing platform is proposed in the THz range. The near field coupling by dipole-induced trapped modes and the magnetic momentum caused a vertical to transverse power flux that dramatically enhanced the electromagnetic field on top of the metasurface and in the microfluidic channel, respectively. Both the resonant modes exhibit perfect absorption and produce ultrahigh normalized sensitivities of 0.47/RIU (refractive index unit, RIU) and 0.51/RIU at 0.76 THz and 1.28 THz, respectively. Compared with conventional microfluidic sensors, the salient advantages of our design are the perfect spatial overlap for light-matter interaction and polarization insensitivity. Characterized by THz time domain spectroscopic absorption quantification measurements with different concentrations of bovine serum albumin (BSA), the proposed sensor exhibits promising applications in microfluidic biosensing.
Highlights
Attributed to its large molecular fingerprint recognition, low photon energy and high penetration characteristics, terahertz spectroscopy has emerged as a promising technique for studying chemical and bio-molecules [1,2]
In 2015, L.Cong compared the sensitivity of terahertz MMs absorber and metasurface with the same resonator, the results show that the figure of merit (FOM) was increased by an order of magnitude because the Fabry-Perot cavity significantly enhanced the EM field concentration in the absorber [22]
In contrast to the conventional sensors which lack of a highperformance THz biosensing with aqueous solution, we overcome the limitation of water absorption by confining the analyte-aqueous solution in the micron-volumetric fluidic chamber, integrated on the highly concentrated resonant metamaterial perfect absorber (MPA) cavity
Summary
Attributed to its large molecular fingerprint recognition, low photon energy and high penetration characteristics, terahertz spectroscopy has emerged as a promising technique for studying chemical and bio-molecules [1,2]. A large overlap with greatly confined cavity resonance of the MPA, resulting ultra high sensitivity detection, has aroused widespread concerns in the research field of terahertz sensing [20]. Two trapped-mode induced sharp transverse resonances were engineered for ultrahigh sensitivity by combining the fundamental ring-shaped dipole mode and the meta-mirror magnetic coupling mode These two near unity absorption peaks occur at 0.76 THz and 1.28 THz, which give birth to the intensely confined EM field in the micofluidic channel and the distinctive SNR along with minute dielectric variation. The trapped mode resonators confine electromagnetic fields in extremely subwavelength space and allow for the enhanced interaction overlap between the BSA solution and terahertz waves, while minimizing the water absorption loss. In the proposed MPA sensor, the microfluidic channel is fully overlapped with the resonant field, leading to strong electromagnetic interaction with analyte. The radiative damping rate of the resonant mode can be significantly reduced by the transverse resonance, which is controlled by engineering the deep-subwavelength height of the microfluidic channel, leading to near 100% absorption
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