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. 2022 Jun 13;12(6):408.
doi: 10.3390/bios12060408.

Terahertz Metamaterial Sensor for Sensitive Detection of Citrate Salt Solutions

Xinxin Deng  1   2 , Yanchun Shen  3 , Bingwei Liu  4 , Ziyu Song  1 , Xiaoyong He  1 , Qinnan Zhang  1 , Dongxiong Ling  1 , Dongfeng Liu  2 , Dongshan Wei  1
Affiliations

Terahertz Metamaterial Sensor for Sensitive Detection of Citrate Salt Solutions

Xinxin Deng et al. Biosensors (Basel). .

Abstract

Citrate salts (CSs), as one type of organic salts, have been widely used in the food and pharmaceutical industries. Accurate and quantitative detection of CSs in food and medicine is very important for health and safety. In this study, an asymmetric double-opening ring metamaterial sensor is designed, fabricated, and used to detect citrate salts combined with THz spectroscopy. Factors that influence the sensitivity of the metamaterial sensor including the opening positions and the arrangement of the metal opening ring unit, the refraction index and the thickness of the analyte deposited on the metamaterial sensor were analyzed and discussed from electromagnetic simulations and THz spectroscopy measurements. Based on the high sensitivity of the metamaterial sensor to the refractive index of the analyte, six different citrate salt solutions with low concentrations were well identified. Therefore, THz spectroscopy combined with a metamaterials sensor can provide a new, rapid, and accurate detection of citrate salts.

Keywords: citrate salt; frequency shift; metamaterial sensor; refractive index; terahertz spectroscopy.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic diagrams of the asymmetric metal ring unit with two openings at a changing angle of Δθ (a) and the asymmetric metal ring array at a rotation angle of φ = 40° (b). The THz wave TE incidence is indicated in the inset of (a).
Figure 2
Figure 2
Transmission spectra of the metamaterial sensor with different changing angles (a) and with different rotation angles (b).
Figure 3
Figure 3
Optical microscope image of the sensor.
Figure 4
Figure 4
(a) Transmission spectra of the simulated metamaterial sensor covered by analytes with different refractive indices at h = 20 μm; (b) variation in the resonant peak frequency shift with the refractive index of the analyte; (c) transmission spectra of the simulated metamaterial sensor covered by analytes with different thicknesses at n = 1.8; (d) variation in the resonant peak frequency shift with the thickness of the analyte.
Figure 5
Figure 5
Measured and simulated THz transmission spectra of the blank sensor without analytes.
Figure 6
Figure 6
Transmission spectral curves of the blank sensor and the sensor covered with six different CSs.
Figure 7
Figure 7
Refractive indices of CSs measured by THz–TDS system.
See this image and copyright information in PMC

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