Compact mid-infrared fiber probe for in vivo multi-compound monitoring demonstrated using ex vivo human skin

Simultaneous monitoring of multiple biomarkers in tissues is critical for biomedical applications. However, few existing platforms enable concurrent in vivo detection. This study presents a compact mid-infrared transflection optical fiber probe for label-free, simultaneous monitoring of three physiologically relevant biomarkers - ethanol, glucose, and lactate. The probe comprises two silver halide fibers - one with an angled tip and one gold-coated as mirror - housed in polyetheretherketone tubing and surrounded by a semi-permeable membrane. With an outer diameter of only 1.1 mm, this is the smallest mid-infrared transflection probe reported to date. Coupled with a quantum cascade laser, the probe achieves ~1 mM detection limits for the three compounds. Peak deconvolution was deployed to resolve overlapping spectral features, enabling quantification of individual compounds in mixtures. Validation was performed in ex vivo human skin against microdialysis. Additionally, monitoring of the concentration changes for all three compounds in the skin was demonstrated.