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Acetone in human breath gas has been established as a biomarker for type-1 diabetes (T1D). Non-invasive breath gas analysis for diabetes diagnostics using breath acetone as a biomarker depends on the availability of a portable, fast-response and sensitive acetone detection device. So far such an instrument is not available yet. We report on the first acetone detection device using cavity ringdown spectroscopy and evaluate its performance prior to breath gas testing. Taking advantage of the coincidence of the largest absorption cross-section of acetone in the UV being at 266 nm with the availability of the palm-size 266 nm laser source, we construct a portable ringdown acetone detection device. The high quality single mode laser beam allows us to simplify the optical design for coupling the laser beam into the cavity, which consists of a pair of high reflectivity mirrors (R = 99.87%) separated by 45 cm. The ringdown signal observed by a miniature detector is processed by a laptop computer. The instrument performance on sensitivity, response time and sampling methods is evaluated using acetone diluted in deionized water in the concentration range of 6 drops l−1 to 0.5 drop l−1. The device operating with two different sampling methods is investigated and shows different measurement sensitivities and response times. The minimum detectable concentration of acetone sample solutions is 0.5 drop l−1 or 7.9 µg l−1, which corresponds to a gas concentration of 0.49 ppmv derived from the measured absorbance (based on 1-σ). The typical measuring time in the second sampling method, including the times for the sample introduction, the purge of the gas cell and the data processing, is less than 50 s. Since the average concentration of acetone in healthy human breath gas is approximately 0.79–1.4 ppmv, this instrument has sufficient sensitivity to detect breath acetone with elevated concentrations. Issues in future developments towards an instrument suitable for breath gas testing are discussed.

We present a new method to develop fibre Bragg grating (FBG)-based temperature sensors using the fibre grating loop ringdown (FGLRD) technique. With this novel approach, temperature is sensed by measuring the wavelength-dependent optical loss resulting from the temperature variations incurred in the FBG. The sensor incorporates a standard telecommunications diode laser and an inexpensive photodetector and achieves rapid temperature measurements in a time domain (measuring the ringdown time). Apparent advantages of this method over the current FBG-OSA approach include the high measurement resolution and low instrument costs. A temperature sensor (type I) using a standard off-the-shelf single-mode bare FBG as the sensing element has been developed and it achieved an absolute measurement resolution of 0.18 °C (based on 3-σ) limited by the precision of the temperature calibration source used in the experiment. To the best of our knowledge, this is the highest measurement resolution of an FBG-based temperature sensor using a standard bare FBG. Additionally, the general applicability of the method has also been evaluated by constructing a temperature sensor (type II) using a long period grating. Discussions on the advantages and limitations of the FGLRD method as compared with the current FBG-OSA scheme are presented.

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