Wearable Breath Sensors with Chip Integrated Mid-Infrared Slow Light Enhanced Absorbance Spectroscopy on Conformal Flexible Substrates

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Omega Optics and the University of Texas, Austin, propose wearable breath alcohol monitoring with a wearable chip-integrated infrared (IR) optical sensor on flexible substrate. Smart sensing is achieved by integrating the devices on flexible substrates with personal clothing. Integrated with Bluetooth on the flexible printed circuit board, the system will enable real time, continuous, remote monitoring, as also personalized warning notifiers for at-risk drivers and drug abusers. The chip-integrated absorption sensing of gases comprises a quantum cascade laser (QCL) and quantum cascade detector (QCD) wafer bonded to silicon passive waveguides in silicon-on- sapphire (SoS) wafer. Enhanced optical absorbance by the guided light is achieved by using an experimentally demonstrated mid-IR holey slotted photonic crystal waveguide (HPCW) in SoS, previously used for detection of chemical warfare simulant triethylphosphate. The principle of enhanced absorption relies on the phenomenon of slow light unique to PCW structures and enhanced optical field intensities in low index narrow slots that combine to increase the effective path length traversed by the guided wave through the sensed gas. In contrast to conventional QCLs and QCDs that rely on bulky electronic drive circuits and benchtop biasing equipment, this proposal transfers experimentally demonstrated printed circuit board based drive elements to a flexible Kapton substrate via demonstrated ink-jet printing techniques. Distributed feedbacks (DFB) QCLs on chip emitting multiple discrete wavelengths centered on =3.4µm and =4.2µm will monitor both ethanol and carbon dioxide (CO2) in breath respectively. Each QCD, corresponding to a QCL, measures light intensity after transduction by the intermediate HPCW. The integrated signal from QCDs generates the absorption spectrum. Change in absorption spectrum identifies the gas qualitatively and quantitatively, notifying wirelessly via Bluetooth to cell phones or remote devices. Our wearable platform can easily detect ethanol with absorption cross-section 2×10-19cm2/molecule, with specificity via absorbance signatures down to 20 parts per billion detection limits, lower than the 100ppb in breath corresponding to 0.02% blood alcohol concentration (BAC) level. The proposed sensing platform together with its potential integration with smart clothing and smart jewelry and accessories, will enable applications beyond breath alcohol monitoring to the monitoring of cancers and infectious diseases, in civilian and industrial air quality monitoring on airborne platforms, and in military, law-enforcement and fire-fighting applications. Our system is readily scalable to other wavelengths that will enable monitoring of other gases and vapors.