###### Abstract  
Small and compact mid-infrared devices are of increasing importance, as there are several applications demanding on-site and real-time measurements in harsh real-world scenarios. The RobustATR, an innovative infrared attenuated total reflectance (IR-ATR) accessory, has been developed and tested with exemplary analytes integrating a single-wavelength Fabry-Perot quantum cascade laser as light source for testing the feasibility of a potentially miniaturized overall sensor design. Successful direct coupling of the laser radiation via substrate-integrated hollow waveguide (HWBG) coupling elements to the sensor interface could be shown, whereby exemplary analytes of environmental and medical relevance were tested, revealing the future potential for real-world applications. infrared attenuated total reflection; IR-ATR; quantum cascade laser; QCL; substrate-integrated hollow waveguide; HWBG; chem/bio sensor; IR sensor; handheld device; mid-infrared; MIR; IR spectroscopy; harsh environment; medical applications +
Footnote †: journal: Applied  
as well as the required in-field robustness are needed. In harsh environments and in-field scenarios, reliable measurements of shock and vibration stability along with reasonable sensor response times provide close to real-time information [5, 14, 15]. Not only must the sensor size and weight be taken into account, but the marine environment itself may also be challenging. Corrosion processes are certainly enhanced due to the presence of electrolytes--in particular, chloride ions--and amplified by the presence of living organisms or dissolved gases. Hence, sensor devices suitable for applications in marine environments should, in addition to the required performance metrics, be corrosion- and temperature-resistant, facilitating extended deployment periods [16]. Ethanol, serving as an exemplary environmentally relevant analyte in the present study, is a small molecule used in a wide variety of application scenarios. For example, ethanol is used as a high-performance fuel in internal combustion engines. If ethanol is burned, fewer pollutants are emitted, when compared to gasoline [17]. Adding a small amount of ethanol into petroleum is a common strategy leading to enhanced engine fuel efficiency and reduced gasoline consumption. Furthermore, ethanol is considered a 'green chemical' which may be produced from grains and sugar or lingo-cellulosic biomass [18], and may also be derived from biological systems via dark fermentation of marine alga. Another natural source of ethanol is derived from microalgae that may fixate CO\({}_{2}\), which beneficially leads to a decrease of atmospheric CO\({}_{2}\), providing ethanol in turn [19]. Interestingly, naturally grown seaweed used for natural pigments and phycocolloids (i.e., sugar polymers) may also be used for sugar hydrolysis, and consecutively for ethanol production, with a constant net balance of CO\({}_{2}\)[20]. Methanol is less flammable compared to gasoline and--as a biofuel--certainly competitive with ethanol. It is a key intermediate for liquid fuels, and may also reduce the number of air pollutants upon combustion [21, 22]. Although methanol is known to be toxic to humans, a small amount of methanol is already present in the human body, and a concentration of up to 500 mg per day to adult humans is considered non-harmful. Methanol is also naturally released in the environment due to the decomposition of plants and animals [22]. Besides environmental application scenarios, healthcare is another important field that requires portable and robust analytical devices, e.g., for the non-invasive and real-time identification of diseases and their biomarkers [23]. As an example, tryptophan is an indispensable amino acid that cannot be produced by mammals and has to be supplied by dietary protein. About 600 to 900 mg of tryptophan should be consumed on a daily basis [24, 25]. As an exemplary molecule, tryptophan was selected for the present study.