text: Sensors for the detection of ammonia as a potential biomarker for health screening The presence of ammonia within the body has long been linked to complications stemming from the liver kidneys and stomach These complications can be the result of serious conditions such as chronic kidney disease CKD peptic ulcers and recently COVID 19 Limited liver and kidney function leads to increased blood urea nitrogen BUN within the body resulting in elevated levels of ammonia in the mouth nose and skin Similarly peptic ulcers commonly from H pylori result in ammonia production from urea within the stomach The presence of these biomarkers enables a potential screening protocol to be considered for frequent non invasive monitoring of these conditions Unfortunately detection of ammonia in these mediums is rather challenging due to relatively small concentrations and an abundance of interferents Currently there are no options available for non invasive screening of these conditions continuously and in real time Here we demonstrate the selective detection of ammonia using a vapor phase thermodynamic sensing platform capable of being employed as part of a health screening protocol The results show that our detection system has the remarkable ability to selectively detect trace levels of ammonia in the vapor phase using a single catalyst Additionally detection was demonstrated in the presence of interferents such as carbon dioxide CO sub 2 sub and acetone common in human breath These results show that our thermodynamic sensors are well suited to selectively detect ammonia at levels that could potentially be useful for health screening applications 