Feasibility of non-invasive measurement of cardiac biomarkers using mid-infrared spectroscopy: finite element analysis and experimental validation

Attenuated total reflectance mid-infrared (ATR-MIR) spectroscopy provides a quick and efficient way to identify protein-specific absorption spectra, making it a promising technique for the non-invasive detection of cardiac biomarkers that are thought to be direct indicators of major cardiovascular events. However, there are still questions about the effectiveness of ATR-MIR in identifying various critical cardiac biomarkers and the detection depth of evanescent waves. This study employs finite element simulations to examine the optical path of attenuated total reflectance (ATR) and the detection depth of evanescent waves. To simulate a subcutaneous tissue environment, a polydimethylsiloxane (PDMS) reagent bath, a high-density melamine sponge, and a poly(ethylene terephthalate) (PET) film are used to assess the ability of MIR spectroscopy to detect cardiac biomarkers at different depths. The findings reveal that the absorption spectra of cardiac troponin I (cTnI), N-terminal pro-B-type natriuretic peptide (NT-proBNP), and C-reactive protein (CRP) show distinct characteristic peaks in the amide I and amide II bands with high specificity. At a depth of about 15 μm, the peak amplitude shows a strong correlation with the biomarker concentration. Even at a depth of 80 μm, the absorption spectrum of cTnI still displays significant characteristic peaks, confirming its ability to detect subcutaneous superficial cardiac biomarkers. This research underscores the considerable potential of ATR-MIR spectroscopy for the non-invasive detection of subcutaneous cardiac biomarkers, which could aid in the development of wearable devices for monitoring cardiovascular health, ultimately contributing to the prevention, diagnosis, and treatment of cardiovascular diseases.