In recent decades, THz metamaterials have emerged as a promising technology for biosensing by extracting useful information (composition, structure and dynamics) of biological samples from the interaction between the THz wave and the biological samples. Advantages of biosensing with THz metamaterials include label-free and non-invasive detection with high sensitivity. In this review, we first summarize different THz sensing principles modulated by the metamaterial for bio-analyte detection. Then, we compare various resonance modes induced in the THz range for biosensing enhancement. In addition, non-conventional materials used in the THz metamaterial to improve the biosensing performance are evaluated. We categorize and review different types of bio-analyte detection using THz metamaterials. Finally, we discuss the future perspective of THz metamaterial in biosensing.

Metasurfaces are usually planar structures and do not possess intrinsic chirality and therefore hardly generate optical activity. Here we realized a tunable optical activity in a terahertz wave through a microfluid-based soft metasurface. The meta-atom is a chiral structured microchannel made of soft polydimethylsiloxane and injected with the liquid metal Galinstan. A microfluid pressure system is bonded to the metasurface to reconfigure all meta-atoms simultaneously. By pumping glycerol liquid into the pressure system, the metasurface is deformed from a planar structure to a three dimensional one, which manifests intrinsic chirality for optical activity realization. By controlling the injected glycerol volume, a polarization rotation from 0°to 14° at 0.19 THz is demonstrated. The soft metasurface with tunable optical activity can be flexibly applied in various applications such as polarization microscopy, bio-detection and material analysis, etc.

Ultrasensitive refractive index (RI) sensing based on novel Vernier-effect demodulation through a single fiber Fabry–Perot interferometer (FFPI) is proposed and demonstrated. A core-offset fiber pair is used as an FFPI for RI sensing. An artificial reference spectrum (ARS) obtained by modulating and extracting a sensing spectrum twice is demonstrated. The Vernier effect is realized by superimposing the sensing spectrum with the ARS. By optimizing the cavity length of the FFPI and the free spectrum range (FSR) of the ARS, an ultrahigh sensitivity of 133948.33 nm/refractive index unit (RIU) with a magnification factor of 118.38 in the RI range of 1.3340~1.3354 is obtained. The magnification factor based on the ARS can be conveniently adjusted. Furthermore, the proposed scheme is suitable for various interferometric sensing applications.

Metamaterials interact with incident electromagnetic waves through their consisting subwavelength metamolecules. In this paper, we reported a reconfigurable metamaterial which tunes its THz response experimentally from a single mode resonance at 2.99 THz to a dual mode resonance at 2.94 THz and 2.99 THz. The reconfiguration is realized through a micromachined actuator, and the tunability is achieved by breaking the symmetry of the metamolecule. An abrupt change in the transmission is experimentally observed when the gap between two metallic structures is closed, and a decrease in transmission from 40% to 5% at 2.94 THz is obtained. Such a tunable metamaterial promises widespread applications in optical switches, filters, and THz detectors.

In this paper, we proposed a reflective metasurface which controls the phase delay of the electromagnetic (EM) wave through geometric phase manipulation. By coding the metasurface unit cells in different orientation angles, an orbital angular momentum (OAM) wave can be obtained through the metasurface reflection. A broadband reflective OAM wave with mode l = −1 was demonstrated which was experimentally observed from 8.3 GHz to 11.6 GHz. The mode spectrum of OAM wave was analyzed and the spectrum weight was about 0.82 through numerical calculation and about 0.47 through experimental measurement for the mode l = −1. The realization of this broadband OAM wave has the potential application to improve the OAM wave based communication capacity.