High-Sensitive Terahertz Biosensors

Abstract

The objective of rapid and reliable biochemical measurement outside the laboratory for detection of analytes in broad area of agricultural, environmental, defense, and medical applications is high in demand. The aim is to exploit the biological reagents with simple integration of bioreceptor, electrical measurement, and data acquisition unit into a monolithic device. Recently, biosensors have emerged as a hybrid functional system capable of determining a broad spectrum of analytes at a very low level of concentration. The biosensors have drawn significant attention for their capability of label-free detection of biological elements like tissues, antibodies–antigen, cell receptors, enzymes, nucleic acids, etc. Thus, the biosensor array can save the time and requirement of expensive equipment during their outdoor uses and subsequently deploy to control the spread of disease during the pandemic, a rise of pollution, and instant blood glucose measurement without the need for a sophisticated laboratory. The demand for biosensors is rising with rapid technological advancements and miniaturization of diagnostic devices. Thus, the global biosensor market exceeded USD 19.6 billion in 2019. Recently, terahertz (THz) technology has drawn significant attention among the bioresearch fraternity due to its label-free, contactless, and nondestructive approach for optical detection of biological element, biomedical imaging, pharmaceutical, and many others. The THz spectrum is roughly in the frequency range of 300 GHz to 10 THz. The vibrational frequencies of the various biological macromolecules such as the nucleic acids, DNA, RNA, and proteins lie in the THz frequency range, enabling contact-free, label-free, and nondestructive detection of biomolecules using the THz spectroscopy and imaging. The THz is a promising tool for biosensor application since the radiation energy of the THz wave is low; thus, it has lesser chance to damage the biomolecules. There is a strong intermolecular interaction between THz wave and biomolecules, as several vibrational and rotational modes exist within the THz spectrum range. The strong confinement of electromagnetic fields in the metamaterials within the THz range allows the minute detection of dielectric change, leading to high sensitivity. Moreover, the ingredients and composition in the materials can be easily detected due to their different absorption and reflection features in the THz range. Above all, the THz technology allows a CMOS compatible microfabrication process and standard lithography to realize high-sensitive microstrip waveguides, metallic mesh, and parallel plate microcavity-based sensors. In this chapter, we have mainly focused on the fundamentals of terahertz biosensors and discussed recent advancements in the microfabrication process of THz biosensors, various methods of interaction with biomolecules and detection. The future scope to enhance the reliability and sensitivity of THz biosensors has also been discussed.