# A Prototype of a Portable Gas Analyzer for Exhaled Acetone Detection
## 1 Introduction  
Exhaled human breath consists of several different compounds, including volatile organic compounds (VOCs), which are continuously generated in the human body and are partially emitted via exhaled breath, through the skin, and by urine and feces [1; 2; 3]. VOCs are mainly in the ppm-ppt (part per million to part per trillion) range, thus, laboratory methods are used for their detection in breath, such as GC-MS (gas chromatography-mass spectrometry) [4; 5], PTR-MS (proton transfer reaction-mass spectrometry) [6; 7], IMS-MS (ion-mobility spectrometry-mass spectrometry) [8; 9], and SIFT-MS (selected ion flow tube-mass spectrometry) [10; 11]. Over the last 40 years, almost 3500 different VOCs have been detected in the human breath [12], and a single breath consists of around 500 various VOCs [13]. The biomarkers present in the exhaled breath are used to indicate several diseases, including lung cancer [14; 15], asthma [16; 17], chronic obstructive pulmonary disease [18; 19], breast cancer [20; 21], diabetes [22; 23], etc. The total number of diseases that can be detected or controlled by exhaled breath analysis is still unknown [24]. Exhaled human breath analysis has been developing for many years with the utilization of several different methods and techniques, for example, exhaled nitric oxide (FeNO) is currently used in clinical practice. However, it took 12 years from when the first report [25] about an increased level of NO in bronchial asthma was published until the first medical use of FeNO analysis in routine clinical practice. Another example is exhaled breath condensate (EBC) measurements. EBCis a promising source of biomarkers of lung disease; however, it is not a biomarker, but rather a matrix in which biomarkers may be identified [26]. The first papers concerning possible medical applications for EBC were published in early 1980, but a publication boom started in 2006, and the number of papers has increased in each subsequent year. After the American Thoracic Society (ATS) and the European Respiratory Society (ERS) developed guidelines for EBC collection and measurement, such measurements started to be commonly applied in asthma and COPD (Chronic obstructive pulmonary disease) diagnoses. One of the global diseases that is the cause of millions of deaths per year is diabetes. This is a chronic disease that occurs either when the pancreas does not produce enough insulin or when the body cannot effectively use the insulin it produces. Insulin is a hormone that regulates blood sugar. Hyperglycemia, or raised blood sugar, is a common effect of uncontrolled diabetes and, over time, leads to serious damage to many of the body's systems, especially the nerves and blood vessels. Based on actual data provided by the World Health Organization (WHO), 422 million adults have diabetes, and it is projected that diabetes will be the seventh leading cause of death by 2030 [27]. The conventional method for glucose monitoring is based on blood glucose measurements, and it has been used in clinical practice for at least 50 years. Moreover, it has been observed that patients with diabetes tend to have higher acetone levels in their breath than non-diabetics [28]. Due to its increased levels, acetone can be regarded as a biomarker of this disease. The number of people with diabetes increases every year. The exhaled acetone is usually within the range of 0.2-0.9 ppm for non-diabetics, and in the range of 1.25-2.5 ppm for people with diabetes [29]. Some references show that the acetone level can increase up to 25 ppm for type-1 diabetes [30]. The development of gas sensors technology has enabled the possibility to fabricate acetone sensors with sensitivities in the ppm range. The latest achievements in this field are reviewed and discussed in [31; 32; 33]. In this paper, we present for the first time, to the best of our knowledge, a prototype of a portable gas analyzer for exhaled acetone detection.