Terahertz sensors for next generation biomedical and other industrial electronics applications: A critical review

Terahertz (THz) sensors have emerged in recent years as an innovative technique for studying biological and chemical materials in a non-destructive, label-free and non-contact manner. The interaction between analyte and THz wave is very weak when detecting analytes such as DNA/RNA, proteins and other tiny biomolecules because the wavelength of THz wave is large and does not correspond to the scale of analyte. Therefore, there is an immediate requirement to look into a novel, extremely sensitive, and specialized biosensing technique appropriate for the THz band in order to detect trace analytes accurately. This article critically reviews the significance of THz-sensors for biosensing, chemical sensing, disease detection, dielectric & refractive index (RI) sensing, temperature sensing and strain sensing. Split ring resonators (SRR), metamaterial absorbers (MMA), plasmonic gratings, Fano-resonators, photonic crystal resonators (PCR), meta surfaces and plasmonic waveguides are the popular sensing structures that can be adopted in the development of THz-sensors. Quality factor (Q-factor), sensitivity and figure of merit (FoM) are the key factors which can be used for measuring the performance of THz-sensors with both transmissive or reflective mode of operation.