Dual spectroscopic detection of THz energy modes of critical chemical compounds

"Raman plus X" dual-modal spectroscopy technology for food analysis: A review

Raman spectroscopy, a nondestructive optical technique that provides detailed chemical information, has attracted growing interest in the food industry. Complementary spectroscopic methods, such as near-infrared (NIR) spectroscopy, nuclear magnetic resonance (NMR), terahertz (THz) spectroscopy, laser-induced breakdown spectroscopy (LIBS), and fluorescence spectroscopy (Flu), enhance Raman spectroscopy's capabilities in various applications. The integration of Raman with these techniques, termed "Raman plus X," has shown significant potential in agri-food analysis. This review highlights the latest advances and applications of dual-modal spectroscopy methods combining Raman spectroscopy with NIR, NMR, THz, LIBS, and Flu in food analysis. Key applications include detecting harmful contaminants, evaluating food quality, identifying adulteration, and characterizing structure. The synergistic use of Raman-based dual-modal spectroscopy provides more comprehensive information and improves modeling accuracy compared to single techniques. The review also explores the role of data fusion in multisource spectral analysis and discusses challenges and prospects of "Raman plus X," including the development of integrated hardware and advanced data fusion algorithms. These advancements aim to streamline multisource data analysis, offering valuable insights to select appropriate analytical methods for practical applications in the food industry.

Graphene-Enhanced Refreshable Metasurface Expands Analytes of THz Label-Free Sensing and Achieves Picogram Limit of Detection

THz sensing offers unique advantages including strong penetrability, low photon energy, and specific recognition of biomolecules and chemicals. However, current label-free THz sensors all operate below 1 THz, severely limiting applications as many drugs and chemicals vibrate at higher THz frequencies. Moreover, the THz detection of analytes at picogram levels is challenging. Here, a modern graphene-enhanced THz metasurface label-free sensor is presented. Its tunable resonance from ∼1.8 to 2.6 THz matches the fingerprint resonant frequencies of various analytes not currently detectable by label-free THz sensing. Quantitative detection of trace 1,3-DNB (absorbing at ∼2.52 THz) is first achieved with a maximum reflectance sensitivity of ∼10% pmol-1 and a detection limit of 42 pg. The sensor can also be refreshed, minimizing cost and being more environmentally friendly. Our strategy expands application scenarios of label-free THz sensing, enhancing its potential in fields such as the pharmaceutical industry, environmental monitoring, and security.

Spectroscopic and imaging considerations of THz-TDS and ULF-Raman techniques towards practical security applications

Nitrogen-containing high-energy organic compounds represent a class of materials with critical implications in various fields, including military, aerospace, and chemical industries. The precise characterization and analysis of these compounds are essential for both safety and performance considerations. Spectroscopic characterization in the far-infrared region has great potential for non-destructive investigation of high energetic and related compounds. This research article presents a comprehensive study of common organic energetic materials in the far-infrared region (5-200 cm-1), aiming to enhance security measures through the utilization of cutting-edge spectroscopic techniques. Broadband terahertz time-domain spectroscopy and ultra-low frequency Raman spectroscopy are employed as powerful tools to probe the vibrational and rotational modes of various explosive materials. One of the key objectives of this present work is unveiling the characteristic spectral features and optical parameters of five common nitrogen based high energy organic compounds towards rapid and accurate identification. Further, we have explored the potential of terahertz reflection imaging for non-contact through barrier sensing, a critical requirement in security applications. Based on the spectral features obtained from the spectroscopic studies and using advanced imaging algorithms we have been able to detect these compounds under various barriers including paper, cloth, backpack, etc. Subsequently, this study highlights the capabilities of the two techniques offering a pathway to enhance their utility over a wide range of practical security applications.