Microsensor arrays for breath analysis M. Righettoni, Angiola Forleo 2 , L. Francioso 2 , Pietro Siciliano 2 and Sotiris E. Pratsinis 1 1 Particle Technology Laboratory, ETH Zurich, CH-8092 Zurich, Switzerland righettoni@ptl.mavt.ethz.ch 2 Institute for Microelectronics and Microsystems, IMM-CNR, IT 73100 Lecce, Italy Abstract: Breath analysis, an innovative non-invasive diagnostic technique, bears the potential of drastically reducing the costs of medical diagnostics offering a simple alternative to standard blood analysis. Here, a flame spray pyrolysis (FSP) reactor was used for synthesis and direct deposition of nanostructured metal oxide (MO x ) films onto microsensor substrates. These sensors were assembled in an array and tested simultaneously for different analytes requiring low power consumption to heat the sensor to the operating target temperature. The sensors had varying responses to the different analytes depending on sensing material (e.g. SnO 2 , WO 3 , ZnO), facilitating improvements on the selectivity of specific analytes (e.g. acetone, methanol, isoprene). Key words: metal oxide, flame spray pyrolysis, microsensors, selectivity. Introduction Human breath analysis is an emerging field of medical diagnostics that promises rapid, noninvasive monitoring and even detection of illnesses [1]. Fully integrated gas sensors made of nanoparticle films are a key technological development for advancing portability and performance of breath analysis devices [2]. The requirements for application of exhaled breath analysis in clinical routine are still challenging. Moreover, the development of small hand-held devices able to provide reliable and continuous real-time measurement of important breath markers such as acetone is desirable. Chemo- resistive gas sensors made of nanostructured metal oxide semiconductors offer a promising alternative [2] to more sophisticated chemical detection devices such as gas chromatography (GC), proton-transfer-reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS).These sensors have a lower limit of detection (LOD) in parts-per-billion concentrations to most reducing or oxidizing analytes[3] and can be miniaturized and integrated in gas microsensors [4] at low cost [3]. Additionally, lower power consumption can be achieved that is a key parameter in order to make these devices portable. A major shortcoming, however, is their poor selectivity to specific analyte in the presence of interfering gases. This problem has been resolved partly by careful materials engineering (e.g. control of crystal phases, addition of dopants), use of filters in the devices (e.g. to control the relative humidity) and the arrangement of several sensors in arrays (e.g. electronic noses). Recently, the application of electronic noses to detect diseases was proposed and investigated in more detail [5]. Some researchers have shown the ability of these devices to identify bacteria, infections, and other diseases [6]. Experimental A flame spray pyrolysis (FSP) reactor was used in combination with a water-cooled substrate holder for synthesis and direct deposition of different MO x nanostructured films onto microsensors substrate array [7].Each sensor consisted of a 1.5 x 1.5 mm substrate, with a platinum heater embedded having a 440 x 440 μm active area and requiring only about 500 mW to heat up at 350 °C. The flame-made & directly deposited sensing films were mechanically stabilized by in situ annealing with a particle free flame [4]. Flame settings are described more in detail elsewhere [2].The crystal size and phase composition were characterized by X-ray diffraction (XRD). Prior to sensing tests, the sensors were kept in an oven at 500 °C for 5 hours at ambient pressure to stabilize the nanoparticle size and avoid further sintering during sensor measurements. For gas sensing tests, the devices were soldered onto a commercial TO-39 socket and were hosted in a test chamber. The micro- sensors were heated at different operating DOI 10.5162/IMCS2012/P2.0.2 IMCS 2012 – The 14th International Meeting on Chemical Sensors 1261