# Reduced Graphene Oxide-Metalloporphyrin Sensors for Human Breath Screening  
[PERSON]  
1 Department of Computer Science and Genome Center, University of California, Davis, CA 95616, USA;  
[EMAIL_ADDRESS] (A.E. ); [EMAIL_ADDRESS] (I.T. )1 Department of Computer Science and Genome Center, University of California, Davis, CA 95616, USA;
To tackle these challenges, nanomaterial-based VOC breath sensors have been developed [9]. Based on their characteristics, nanomaterial-based VOC sensors can be categorized as colorimetric [16], acoustic [17], and electrochemical [18; 19; 20]. They can either be specific to a single VOC or cross-sensitive to multiple VOCs [21]. [PERSON] et al. used a cross-sensitive colorimetric sensor array that was assembled with nanoporous dimeric metalloporphyrins to detect eight VOCs in the exhaled breath of lung cancer patients, with a response time of 3 min [22]. In another study, [PERSON] et al. coated a single-walled carbon nanotube-based thin film on a quartz crystal microbalance (QCM) device to create an array of cross-sensitive QCM sensors [17]. Their acoustic VOC sensors were able to discriminate six different VOCs (ethanol, methanol, isopropanol, acetone, ethyl acetate, and toluene) of public health relevance [17]. Electrochemical sensors, including metal oxide semiconductors (MOS) and chemiresistive sensors, measure electrical property changes in the sensing material under the exposure of sensing VOC analytes. [PERSON] et al. used an array of carbon black-based chemiresistive sensors for detecting lung cancer with 71.4% sensitivity and 91.9% specificity [20]. [PERSON] et al. assembled a selective MOS sensor using copper oxide (CuO\({}_{2}\))-functionalized graphene sheets (FGS) for hydrogen sulfide (H\({}_{2}\)S) detection [19]. The CuO\({}_{2}\)-FGS sensor detected a low H\({}_{2}\)S concentration (5 ppb) with a sensor sensitivity of 11%. Nanomaterial-based VOC sensors have been successfully used for disease detection in breath samples for lung cancer [23; 24], breast cancer [25], liver cirrhosis [26], head and neck cancer [27], diabetes [28], _Clostridium difficile_ infection [29], chronic kidney disease [30], Alzheimer's disease, and Parkinson's disease [31], among others. Current challenges in nanomaterial VOC sensors include miniaturization, large-scale production, operation at room temperature, accuracy, sensitivity, and specificity [32; 33]. Each sensor type may have different advantages and limitations: colorimetric sensors are low cost but can only be used once due to the irreversible color change [34]; acoustic sensors may be sensitive and lose accuracy due to an undesirable frequency shift [35]; electrochemical MOS sensors have shown high sensitivity to VOC detection [19], but they require a high operating temperature (T \(>\) 300 \({}^{\circ}\)C) and have high power consumption [33; 36]. Some of these challenges can be addressed using carbon nanomaterials, such as carbon nanotubes, carbon black, graphene, and reduced graphene oxide, due to their low power consumption, high surface-volume ratio, high electron mobility, and high capability of gas adsorption [33; 37]. The complexity of fabrication methods and insufficient detection accuracy of VOC sensors remain outstanding challenges that hinder their clinical utility [33]. Here, we present a carbon nanomaterial VOC sensor, based on reduced graphene-oxide (RGO)/metalloporphyrin, that is easy and inexpensive to manufacture, and which can accurately detect VOCs related to a variety of diseases that are usually present in human breath. We fabricated an RGO-metalloporphyrin-sensing array using a drop casting method and characterized it using scanning electron microscopy (SEM) and energy dispersive spectra (EDS). The sensing array was then exposed to three disease-related breath VOCs (acetone, ammonia, and isopropanol) and carbon monoxide.