Application of a Terahertz System Combined with an X-Shaped Metamaterial Microfluidic Cartridge

Abstract

Terahertz (THz) radiation has attracted wide attention for its ability to sense molecular structure and chemical matter because of a label-free molecular fingerprint and nondestructive properties. When it comes to molecular recognition with terahertz radiation, our attention goes first towards the absorption spectrum, which is beyond the far infrared region. To enhance the sensitivity for similar species, however, it is necessary to apply an artificially designed metamaterial sensor for detection, which confines an electromagnetic field in an extremely sub-wavelength space and hence receives an electromagnetic response through resonance. Once the resonance is caused through the interaction between the THz radiation and the metamaterial, a minute variation might be observed in the frequency domain. For a geometric structure of a metamaterial, a novel design called an X-shaped plasmonic sensor (XPS) can create a quadrupole resonance and lead to sensitivity greater than in the dipole mode. A microfluidic system is able to consume reagents in small volumes for detection, to diminish noise from the environment, and to concentrate the sample into detection spots. A microfluidic device integrated with an X-shaped plasmonic sensor might thus achieve an effective and highly sensitive detection cartridge. Our tests involved not only measurements of liquid samples, but also the performance of a dry bio-sample coated on an XPS.

Keywords: metamaterials; microfluidics; terahertz radiation.

Figure 1

(a) Scale of an XPS, of linewidth 100 μm, length 250 μm and period 450 μm. (b) x-component of electric field distribution in a quadrupole resonance. (c) A simulation result shows a resonant dip at frequency 0.4186 THz.

Figure 2

Fabrication: (a) XPS metamaterial; (b) SU8 mold; (c) PDMS microfluidic layer; (d) finished product (detection cartridge).

Figure 3

(a) Illustration of detection mechanism; the THz radiation penetrates the entire cartridge. (b) Internal setup in the chamber (TeraPulse 4000). (c) Setup of optical components inside the equipment.

Figure 4

Effect of four XPS designs in an actual situation; all perform best in direction 90°.

Figure 5

Simulation for microfluidic cartridge. (a) X-component of electric field distribution in a quadrupole resonance. (b) A simulation result shows a resonant dip at 0.20 THz. (c) An experimental result shows a resonant dip at 0.17 THz.

Figure 6

Spectrum of IPA solution at five concentrations: (a) Original signal with fluctuation; (b) Post-processing signal to eliminate interference; (c) Refractive index of the entire device, the value increases as the water ratio rises.

Figure 7

Trial of measurement of glucose aqueous solution from 0% to 0.5% with no tendency of variation.

Figure 8

Detection of cancer cell on XPS of two designs; the red shift has extent 7.47 GHz in design C for both cells.