The Role of Spectroscopy in Airport Security Screening

By Owais AliReviewed by Lexie CornerSep 16 2024

Spectroscopy provides a powerful and adaptable method for detecting and identifying hazardous materials, explosives, and contraband, contributing to enhanced security measures in air travel. This article outlines the use of various spectroscopic techniques in airport security, focusing on their advantages and recent advancements.

Image Credit: GoodStudio/Shutterstock.com

Overview of Spectroscopy Techniques Used in Airport Security

Various advanced spectroscopy techniques are employed in airport security to enhance threat detection and passenger safety. Each offers unique advantages, collectively forming a multi-layered approach to improve the effectiveness of screening operations.

Fourier Transform Infrared (FTIR)

FTIR spectroscopy analyzes materials by passing infrared radiation through a sample and detecting the absorbed and transmitted light. The resulting spectrum, obtained via the Fourier transform, acts as a molecular 'fingerprint,' revealing unique patterns specific to each material.

This enables rapid and accurate detection of hazardous substances and explosives based on their distinct infrared signatures.^1,2

Raman Spectroscopy

Raman spectroscopy provides a non-destructive and rapid method for identifying chemical substances by analyzing their molecular vibrations. It uses laser light to produce spectra that reveal the chemical composition of materials, even through transparent containers.

This technique can detect chemicals in various environments, including liquids, without sample preparation. It complements FTIR by analyzing chemicals with weak infrared spectra that are challenging to measure with FTIR alone, enhancing the accuracy and speed of security screenings.^1,3

Nuclear Quadrupole Resonance (NQR) Spectroscopy

NQR spectroscopy detects nuclei with a non-spherical charge distribution by measuring how their electric quadrupole moment interacts with the electric field gradient from surrounding electrons. This interaction produces unique resonance frequencies sensitive to the molecular structure, resulting in distinct spectral signatures for different materials.

For instance, in explosives like RDX, different crystal packing geometries produce NQR frequencies that differ by approximately 100 kHz, making NQR an invaluable tool for precise material identification in security applications.⁴

How Are These Spectroscopic Techniques Used in Airport Security?

Flammable Liquid or Chemical Detection

FTIR spectroscopy is used to scan liquids and containers, collecting infrared absorption spectra that reflect their chemical composition. For instance, water-based beverages show strong absorption peaks around 950 nm, while flammable liquids like ethanol and gasoline exhibit distinct IR signatures.

Similarly, acids, bases, and hydrogen peroxide solutions have characteristic IR absorption features. By analyzing these spectral profiles, FTIR systems quickly identify whether a liquid is safe or poses a potential threat, enabling security personnel to respond accordingly.⁵

The Thermo Scientific™ Gemini™ Analyzer is a renowned handheld FTIR device used in airports for detecting narcotics, unknown chemicals, and explosives. It can efficiently identify over 15,000 substances in under 30 seconds, offering complementary and confirmatory testing within a single portable unit.⁶

Non-Nitrate Explosives and Hazardous Chemicals Detection

Raman spectroscopy complements FTIR in airport security by quickly identifying a wide range of chemicals, including non-nitrate-based explosives like acetone peroxide (TATP), through their unique molecular "fingerprints."

Its non-invasive capability allows for the analysis of sealed containers, such as beverage bottles, without opening them, reducing the risk to security personnel and passengers.

Raman's low sensitivity to water further enables it to detect chemicals in aqueous solutions, expediting the screening process and enhancing security measures by efficiently identifying hazardous materials.¹

Agilent's Raman spectrometer Insight200M system is widely used in international airports, offering fast, accurate screening for all container types, including metals, with a scan time of just 6 seconds and an ultralow false alarm rate.⁷

NQR for Nitrate Explosives Detection

NQR detects hazardous materials by identifying nitrogen-containing compounds (explosives) through their unique electric quadrupole moments. Since nitrogen-14 has a non-spherical charge distribution, NQR can differentiate between explosive and non-explosive materials based on distinct spectral lines corresponding to their chemical environment and crystalline structure.

This technique is particularly effective for identifying explosives in luggage by detecting specific NQR frequencies unique to different compounds.⁴

Advantages of Using Spectroscopic Techniques

The use of spectroscopic techniques in airport security offers several key advantages. Non-invasive screening methods, such as Raman and FTIR, allow for the analysis of container and luggage contents without physical inspection or opening, thereby reducing the risk of exposure to hazardous materials and preserving passenger privacy.

These techniques deliver near-instantaneous results, facilitating rapid screening and minimizing false alarms, enhancing the security process's efficiency and reliability. Additionally, their versatility enables the detection of various substances, including explosives, flammable liquids, and hazardous chemicals, effectively identifying potential threats.^1,4,5

Recent Research and Developments

Recent advancements in spectroscopy technology have further enhanced its utility in airport security applications. The development of portable, user-friendly instruments, such as handheld Raman and IR spectrometers, has made it possible to integrate these technologies seamlessly into the security screening process.

THz-Wave Spectroscopy for Real-Time Detection of Explosive Vapors

One notable innovation is the use of tunable terahertz (THz)-wave absorption spectroscopy for the real-time detection of hazardous gases in the air surrounding passengers. This technique uses unique absorption fingerprints of trace gases in the THz-wave region to quickly identify low concentrations of explosive vapors or other dangerous substances.

A study published in Optics Express integrated a frequency-tunable THz-wave generator with compact multipass gas absorption cells, achieving the detection of explosive gases at concentrations as low as 0.2 ppm. The researchers also developed a portable prototype with a 6-meter-path-length multipass cell for walk-through security screening, offering near-instantaneous results and improving security and passenger flow.⁸

Submicron Analysis of Trace Explosives in Fingerprints

In a study published in Analytical Chemistry, researchers used optical-photothermal infrared (O-PTIR) spectromicroscopy to detect high explosives, such as PETN, RDX, C-4, and TNT, within fingerprints deposited on various surfaces like glass slides and tables. The study employed the mIRage IR microscope in non-contact, far-field reflection mode to achieve submicron spatial resolution.

This technique provided high-resolution, non-destructive analysis, detecting particles smaller than 1 µm (~7 pg) without sample alteration. In addition, the collected spectra are searchable and interpretable using institutional and commercial IR databases, eliminating the need for mathematical modeling.⁹

Conclusion

Ongoing advancements in spectroscopic technologies and innovative data processing methods are expected to enhance security screening processes significantly. As the aviation industry continues to face evolving threats, spectroscopy will play an increasingly important role in maintaining efficient passenger travel while upholding high security standards.

Discover More: Advanced Filters for Raman Spectroscopy with a Focus on Biomedical Applications

References and Further Reading

1. Crocombe, RA., Leary, PE., Kammrath, BW. (Eds.). (2021). Portable Spectroscopy and Spectrometry, Applications. John Wiley & Sons. https://doi.org/10.1002/9781119636489
2. Thermo Fisher Scientific. (n.d) Thermo Scientific FTIR spectrometer and microscope resources. [Online] Thermo Fisher Scientific. Available from: https://www.thermofisher.com/us/en/home/industrial/spectroscopy-elemental-isotope-analysis/molecular-spectroscopy/fourier-transform-infrared-spectroscopy.html
3. Agilent. (2024). An Introduction to the Fundamentals of Raman Spectroscopy. [Online] Agilent. Available from: https://www.agilent.com/en/support/molecular-spectroscopy/raman-spectroscopy/what-is-raman-spectroscopy-faq-guide
4. Horace-Herron, KL., Masna, NVR., Bhunia, S., Mandal, S., Ray, S. (2024). Nuclear Quadrupole Resonance for Substance Detection. IEEE Access. https://doi.org/10.1109/ACCESS.2024.3438877
5. Itozaki, H. (2020). Near infrared inspection technology of bottled explosive liquid in airports. NIR news. https://doi.org/10.1177/096033601988928
6. Thermo Fisher Scientific. (2019). Case Study - Stemming the flow of narcotics in Turkey with Gemini handheld analyzers. [Online]. Thermo Fisher Scientific. Available from: https://assets.thermofisher.com/TFS-Assets/CAD/Application-Notes/gemini-analyzer-case-study-istabul-airport.pdf
7. Agilent. (2024). Raman Aviation Security Systems - Insight200M Liquid Explosive Detection System. [Online] Agilent. Available from: https://www.agilent.com/en/product/molecular-spectroscopy/raman-spectroscopy/raman-aviation-security-systems/cobalt-insight200m-the-bottle-screener-for-liquid-aerosols-gels
8. Takida, Y., Nawata, K., Minamide, H. (2021). Security screening system based on terahertz-wave spectroscopic gas detection. Optics Express. https://doi.org/10.1364/OE.413201
9. Banas, A., et al. (2020). Detection of high-explosive materials within fingerprints by means of optical-photothermal infrared spectromicroscopy. Analytical Chemistry. https://doi.org/10.1021/acs.analchem.0c00938

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.