# Effect of Working Atmospheres on the Detection of Diacetyl by Resistive SnO2 Sensor
## 1 Introduction  
Gas sensors are of great interest due to their numerous applications and the possibility for a real-time analysis of several analytes [1, 2, 3]. Among these, resistive gas sensors exhibit attractive advantages compared with other gas sensors, such as fast and accurate gas detection, flexibility, low cost and small size [4]. The development of high-performance resistive gas sensors requires suitable gas-sensing materials in terms of both physical and chemical properties, such as morphology, crystalline structure, specific surface area and active sites. Since, as is well known, these characteristics all affect the performance of gas sensors, exploring and developing innovative materials has received attention in scientific research in recent years [5]. Attention is concentrated on the development of nanostructured materials, endowed with better sensing properties if compared to the same bulk material, such as carbon-based materials (in the form of carbon dots, nanotubes and graphene) [6, 7, 8, 9], polymeric fibers (hybrid nanofibers) [10, 11] and metal oxides semiconductor (MOS, as nanospheres, nanowires and nanosheets) [12, 13, 14, 15, 16, 17]. Indeed, the large surface areas of nanomaterials ensure more active sites, enabling fast charge transfers and efficient gas-sensitive reactions [4]. Due to their widespread use in a variety of applications, in the recent years time-consuming, complex, and expensive traditional techniques have been substituted by these types of sensors. It has been especially evident in the field of volatile organic compound (VOC) detection, where traditional techniques, such as chromatography-mass spectrometry [18, 19, 20, 21], generally lack ease of use, need specialized personnel and elaborate protocols,and are characterized by high cost of the devices and insufficient flexibility. When early warning and quality monitoring applications are requested, resistive sensors are valuable alternatives. Indeed, in some specific applications, VOCs, such as diacetyl, need to be continuously monitored [22]. During the alcoholic fermentation processes of wine, beer and distilled beverages, diacetyl is naturally produced in small quantities, and it confers a characteristic butter-like aroma [23; 24; 25; 26; 27]. However, high diacetyl concentration (\(>\)5 mg/L) imparts an undesirable flavor indicating an alteration in the production or storage process. The time-monitoring of diacetyl concentrations can contribute to identifying and characterizing the quality of products [22]. Moreover, during this process, the so-called alcoholic fermentation, carbon dioxide and ethanol are produced too, and the influence of the atmosphere composition was reported to be fundamental in diacetyl detection and monitoring [28]. Till now, few works reported the detection of gaseous diacetyl mainly by means of complex array sensors [27; 29; 30]. [PERSON] et al. used variously-doped SnO\({}_{2}\) and CeO\({}_{2}\) to detect diacetyl among other volatile compounds [27], whereas PPy-V\({}_{2}\)O\({}_{5}\) and PPy-ZnO nanocomposite fibers were successfully used by [PERSON] et al. to discriminate the presence of diacetyl in fermented products [29]. [PERSON] et al. used an array of conducting polymers mounted on an electronic chip to discriminate between peers and to recognize the presence of volatile compounds, such as diacetyl [30]. In this work, tin oxide (SnO\({}_{2}\)) is used to develop a high-performance resistive MOS sensor for the detection of VOCs [17; 31], diacetyl in particular, thanks to the peculiar electrical properties of its microsphere structure [13]. The detection of diacetyl is performed by sampling the head space above the liquid solutions at different diacetyl concentrations (0.2-3.2 mg/L). The sensor has been tested using both aqueous and alcoholic (5% ethanol) diacetyl solutions in different carrier/regeneration gases, able to reproduce the typical alcoholic fermentation environment, rich in carbon dioxide (CO\({}_{2}\)) and poor of oxygen.