Several gas molecules of environmental and domestic significance exhibit a strong deep-UV absorption. Therefore, a sensitive and a selective gas detector based on this unique molecular property (i.e., absorption at a specific wavelength) can be developed using deep-UV absorption spectrophotometry. UV absorption spectrometry provides a highly sensitive, reliable, self-referenced, and selective approach for gas sensing. This review article addresses the recent progress in the application of deep-UV absorption for gas sensing owing to its inherent features and tremendous potentials. Applications, advancements, and challenges related to UV emission sources, gas cells, and UV photodetectors are assessed and compared. We present the relevant theoretical aspects and challenges associated with the development of portable sensitive spectrophotometer. Finally, the applications of UV absorption spectrometry for ozone, NO₂, SO₂, and aromatic organic compounds during the last decades are discussed and compared. A portable UV absorption spectrophotometer can be developed by using LEDs, hollow core waveguides (HCW), and UV photodetectors (i.e., photodiodes). LED provides a portable UV emission source with low power input, low-intensity drifts, low cost, and ease of alignment. It is a quasi-chromatic UV source and covers the absorption band of molecules without optical filters for absorbance measurement of a target analyte. HCWs can be applied as a miniature gas cell for guiding UV radiation for measurement of low gas concentrations. Photodiodes, on the other hand, offer a portable UV photodetector with excellent spectral selectivity with visible rejection, minimal dark current, linearity, and resistance against UV-aging.

A simple deep-ultraviolet (UV) absorption spectrophotometer based on ultraviolet light-emitting diode (UV LED) was developed for the detection of air-borne toluene with a good sensitivity. A fiber-coupled deep UV-LED was employed as a light source, and a spectrometer was used as a detector with a gas cell in between. 3D printed opto-fluidics connectors were designed to integrate the gas flow with UV light. Two types of hollow core waveguides (HCW) were tested as gas cells: a glass capillary tube with aluminum-coated inner walls and an aluminum capillary tube. The setup was tested for different toluene concentrations (10–100 ppm), and a linear relationship was observed with sensitivities of 0.20 mA·U/ppm and 0.32 mA·U/ppm for the glass and aluminum HCWs, respectively. The corresponding limits of detection were found to be 8.1 ppm and 12.4 ppm, respectively.

Deep-UV absorption spectrometry for detection of toxic airborne gases, for instance, Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) has drawn considerable attention owing to its high sensitivity and reliability. However, the development of a deep-UV absorbance detector having good sensitivity, portability, and a low-volume gas cell with applicability for a micro Gas Chromatography (μGC) is challenging. Herein we present a novel, self-referenced, and portable deep-UV absorbance detector with a microliter (275 μL) gas cell having minimal dead volume. It has excellent compatibility with μGC for detection of individual BTEX components in a mixed sample at a sub-ppm level. The design consists of the latest, portable, and cost-effective optical and electronic components, i.e., deep-UV LED, hollow-core waveguide, and photodiodes. The detector directly measures the absorbance values in volts using an integrated circuit with a log-ratio amplifier. The prototype was tested with direct injection of toluene-N₂ (1.5 ppm to 50 ppm) and good linearity (R² = 0.99) with a limit of detection of 196 ppb was obtained. The absorbance detector with μGC setup was tested with a BTEX mixture in N₂ at different GC column temperatures. All the BTEX species were sequentially separated and detected with an individual peak for a concentration range of 2.5 ppm to 10 ppm.