Abstract-Terahertz biosensing based on bi-layer metamaterial absorbers toward ultra-high sensitivity and simple fabrication

Applied Physics Letters

Hong Zhou, Cheng Yang, Donglin Hu, Dongxiao Li, Xindan Hui, Feng Zhang, Ming Chen,  Xiaojing Mu,

Overview of (a) the proposed CPH absorber, (b) CS absorber, and (c) CCS absorber with the biomolecular analyte attached on the nanostructure surface. (a-a′), (b-b′), and (c-c′) show the corresponding cross-sectional views in (a), (b), and (c). The cross-sectional views of electric field distribution in the z-direction in (d) the CPH absorber, (e) CS absorber, and (f) CCS absorber.

https://aip.scitation.org/doi/abs/10.1063/1.5111584

Metamaterial absorbers have proven their ability to sense in the terahertz domain. However, the sensitivity is always limited by the poor spatial overlap between the analyte and the localized enhanced electromagnetic field. Here, we try to tackle this challenge by utilizing an absorber with a bilayer cross-shaped plate-hole structure to ingeniously excite hot-spots covering the analyte. As a result, the sensitivity is significantly improved, theoretically about 7 and 18 times higher than that of the conventional cross-shaped absorber and its complementary cross-shaped absorber, respectively. We then experimentally demonstrate its ability to quantitatively detect biotin with a sensitivity of 153 GHz/μM, higher than that of previously reported biotin sensors. Additionally, the polarization-independent nanostructure decreases the design and fabrication complexity and maintains high reflection at a wide range of incident angles over ±50°. These findings open up opportunities for metamaterial absorbers to realize ultrasensitive biosensing in the fingerprint region of the terahertz regime.

This work was supported by the National Natural Science Foundation of China (Grant Nos. 51605060 and 81430053), Fundamental Research Funds for the Central Universities (No. 2018CDPTCG0001-5), National Key Research and Development Program of China (Grant No. 2016YFB0402702), and Chongqing municipality key research and development program of China (Grant No. cstc2017rgzn-zdyfX0041).

Abstract-Ultrasensitive sensing with three-dimensional terahertz metamaterial absorber

Siyu Tan, Fengping Yan, Wei Wang, Hong Zhou, Yafei Hou,

http://iopscience.iop.org/article/10.1088/2040-8986/aab66e/pdf

Planar metasurfaces and metamaterial absorbers have shown great promise for label-free sensing applications at microwaves, optical and terahertz frequencies. The realization of high-quality-factor resonance in these structures is of significant interest to enhance the sensing sensitivities to detect the minute frequency shifts. We propose and demonstrate in this manuscript an ultrasensitive terahertz metamaterial absorber sensor based on three-dimensional split ring resonator absorber with a high quality factor of 60.09. The sensing performance of the proposed absorber sensor was systematically investigated through detailed numerical calculations and a maximum refractive index sensitivity of 34.40% RIU-1 was obtained. Furthermore, the absorber sensor can maintain a high sensitivity for a wide range of incidence angles up to 60° under TM polarization incidence. These findings would improve the design flexibility of the absorber sensors and further open up new avenues to achieve ultrasensitive sensing in terahertz regime.
© 2018 IOP Publishing Ltd

Abstract-Simultaneous measurement of refractive index and conductivity based on metamaterial absorber

Wei Wang1, Fengping Yan2.  Siyu Tan3, Luna Zhang4, Zhuoya Bai5, Dan Cheng6, Hong Zhou7 and Yafei Hou

http://iopscience.iop.org/article/10.1088/2040-8986/aa8fc1

An algorithm for the metamaterial sensors to simultaneously measure the refractive index and conductivity of the analyte is introduced. To verify the algorithm, a square ring metamaterial absorber is numerically calculated as a specific example in the terahertz frequency. Firstly, the sensing performances of the absorber on the refractive index (RI) and conductivity are evaluated separately. Then the relationship expressions between dual variables (frequency shift (FS) and amplitude modulation (AM)) and two arguments (RI and conductivity) can be obtained through mathematical fitting process. By reversely solving this equations set, the conductivity and RI of the analyte can be expressed as another equations set that can be solved easily. The proposed algorithm offers an effective method to determine RI and conductivity of the analyte by measuring the AM and FS of the reflection dip of the absorber sensor. To validate the effectiveness and accuracy of the algorithm, the FS and AM obtained from the simulations are plugged into the reverse equations set. Then the calculated n and σ are compared to their responding original values. The maximum percentage error between them are both less than 0.83%, which are small enough to illustrate the rightness of the proposed method.