Application of metal-organic frameworks for sensing of VOCs and other volatile biomarkers

Volatile organic compounds (VOCs) are present in the mixture of gases found in the exhaled human breath. Since their occurrence in the breath may indicate the presence of a disease, some VOCs are referred to as "biomarkers." One of the most interesting types of gas sensors which have been thoroughly explored for VOCs detections is based on metal-organic frameworks (MOFs), which are crystalline porous coordination polymers assembled by following reticular chemistry rules. The aim of this review is to present a comprehensive summary of the latest MOF-derived composites that have been employed as VOCs biomarkers' sensors. The study will first focus on reviewing the role of VOCs as disease biomarkers and then on the most prevalent methods used for analyte sensing by MOFs, including optical, electromechanical, and electrical sensing. The successive section examines some of the most recent reports on the use of five typical MOF families for sensing VOCs relevant as disease biomarkers. The basic structural features of these MOFs and their fundamental working principles as gas sensors will be highlighted in each sub-section through selected examples, emphasizing at the same time the correlation between the MOFs structure and functionalities, and their sensing properties. Finally, the study will be concluded with a discussion about a new class of MOFs called bio-MOFs, and their potentialities in VOCs sensing.