Terahertz Imaging and Spectroscopy in Cancer Diagnostics:A Technical Review

Terahertz(THz)waves are electromagnetic waves with frequency in the range from 0.1 to 10 THz.THz waves have great potential in the biomedical field,especially in cancer diagnosis,because they exhibit low ionization energy and can be used to discern most biomolecules based on their spectral fingerprints.In this paper,we review the recent progress in two applications of THz waves in cancer diagnosis:imaging and spectroscopy.THz imaging is expected to help researchers and doctors attain a direct intuitive understanding of a cancerous area.THz spectroscopy is an efficient tool for component analysis of tissue samples to identify cancer biomarkers.Additionally,the advantages and disadvantages of the developed technologies for cancer diagnosis are discussed.Furthermore,auxiliary techniques that have been used to enhance the spectral signal-to-noise ratio(SNR)are also reviewed.

Hexagonal arrangement of phospholipids in bilayer membranes

The phospholipid membrane plays a key role in myriad biological processes and phenomena, and the arrangement structure of membrane determines its function. However, the molecular arrangement structure of phospholipids in cell membranes is difficult to detect experimentally. On the basis of molecular dynamic simulations both in a non-destructive way and at native environment, we observed and confirmed that the phospholipids self-assemble to a hexagonal arrangement structure under physiological conditions. The underlying mechanism was revealed to be that there are hexagonal arrangement regions with a lower free energy around each lipid molecule. The findings potentially advance the understanding of biological functions of phospholipid bilayers.

Terahertz spatial sampling with subwavelength accuracy

A simple terahertz(THz)spatial sampling method offers kilohertz(kHz)level sampling rates and greatly preserves the energy of a THz pulse,which enables THz imaging detection with a high signal-to-noise ratio,micron-grade accuracy,and subwavelength resolution.

Terahertz Spectroscopy for Accurate Identification of Panax quinquefolium Basing on Nonconjugated 24(R)-Pseudoginsenoside F_(11)

Panax quinquefolium is a perennial herbaceous plant that contains many beneficial ginsenosides with diverse pharmacological effects.24(R)-pseudoginsenoside F_(11)is specific to P.quinquefolium,a useful biomarker for distinguishing this species from other related plants.However,because of its nonconjugated property and the complexity of existing detection methods,this biomarker cannot be used as the identification standard.We herein present a stable 24(R)-pseudoginsenoside F_(11)fingerprint spectrum in the terahertz band,thereby proving that F_(11)can be detected and quantitatively analyzed via terahertz spectroscopy.We also analyzed the sample by high-performance liquid chromatography-triple quadrupole mass spectrometry.The difference between the normalized data for the two analytical methods was less than 5%.Furthermore,P.quinquefolium from different areas and other substances can be clearly distinguished based on these terahertz spectra with a standard principal component analysis.Our method is a fast,simple,and cost-effective approach for identifying and quantitatively analyzing P.quinquefolium.

Linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces

In this Letter, we demonstrate a linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces, which integrated the frequency selectivity of a split ring resonator metasurface and the polarization selectivity of a metallic grating surface. Since the double-layer can reduce the loss, and the Fabry- Perot like resonant effect between the two layers can improve the conversion efficiency, this converter can rotate the incident y-polarized terahertz wave into an x-polarized transmitted wave with relatively low loss and high efficiency. Experimental results show that an average conversion efficiency exceeding 75% from 0.25 to 0.65 THz with the highest efficiency of 90% at 0.43 THz with onlv -2 dB loss has been achieved.