Paper BI-TuP11
Flash Networking Poster: Exhaled Breath Analysis of Ammonia Gas using Colorimetric Attenuated Total Reflectance Spectroscopy

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

The identification of exhaled breath volatile organic compounds represents a metabolic biosignature with the potential to recognize some diseases. There are various techniques to analyze exhaled breath gases, as spectrometry, gas chromatography, and spectroscopy. The recent trend towards breath analysis instruments has led to the development of fully integrated prototypes of point-of-care devices.

In this research we develop a miniature sensor using attenuated total reflectance spectroscopy to detect breath gases in the range of hundreds ppb. A 0.2 mm thick, 20 mm wide, 65 mm long, fused silica plate with 60° beveled edges (Shin-Etsu Quartz Products, Inc.) was used as the internal reflection element (IRE).¹ The IRE surface was coated with the chemical sensor specific to one of the gases from the breath, embedded in a polymer, using a layer-by-layer electrostatic assembly method. The evanescent light produced by multiple total internal reflections penetrates a few tens of nanometers in the film leading to a high detection sensitivity.

For ammonia gas detection Poly(diallyldimethylammonium chloride) (PDDA, Mw: 200000-350000, 20 wt% in H₂O) and tetrakis(4-sulfophenyl)porphyrin (TSPP, Mw: 934.99) were used as polymer and chemical sensor, respectively.^2,3 The detection consists in measuring the decrease of light intensity of the Soret band of the porphyrin molecule around 483 nm under the chemical reaction with ammonia. First we recorded absorption spectra through the IRE using a broadband visible light source and a spectrograph for different film conditions and ammonia concentrations. Then the broadband light source and the spectrograph were replaced with a 450 nm light emitting diode (LED) and a photodiode (PD). The ammonia sensing capability of the porphyrin film was tested in both liquid and gas phases and a 500 ppb detection limit was found. We studied the ammonia gas detection limit in dependence with the number of layers of the chemical sensor and the polymer deposited on the IRE surface. AFM measurements show the surface modifications after the ammonia gas adsorption on the chemical sensor film. Stability, reversibility, and the humidity influence will be discussed.

¹M. A. Bratescu, et al., Attenuated total reflectance spectroscopy of coumarin organosilane molecules adsorbed on a fused silica surface, Applied Surface Science, 257, 1792, 2010.

²K. S. Suslick, et al., An optoelectronic nose for the detection of toxic gases, Nature Chemistry, 1, 562, 2009.

³S. Korposh, et al., Sensor and Materials, 21, 179, 2009.