An optical sensor includes a sample cell through which a fluid flows, an optical sensor formed by an optical emitter and an optical detector. The system uses a thermoelectric cooler to maintain a case temperature of the module at about 50\xb0 C. The panel-fixing portion is adapted to engage with the mounting panel, such that the elastic device can be mounted on the mounting panel, and the mounting panel is adapted to engage with the internal face, such that the elastic portion can expand or contract as a function of whether the door is opened or closed. The working electrode may be any electrode compatible with the media, including noble metals, carbon, or combinations thereof.