Label-free molecular profiling of tear fluid by Raman spectroscopy for neurodegenerative disease differentiation

Tear fluid is an accessible, non-invasive biofluid with strong potential for revealing molecular biomarkers of neurodegenerative diseases. In our previous study, we developed a Raman spectroscopy-based protocol to analyze tear samples from patients with Amyotrophic Lateral Sclerosis (ALS) and healthy controls. Tears (5 μL) were deposited on BaF2 substrates and air-dried under controlled conditions. Raman mapping was performed using a 532 nm laser (6 mW, 1 μm spot size) across the 150--1800 cm−1 spectral range. Distinct spectral features ---including peaks at 1005, 1450, 1575, and 1670 cm−1--- were significantly enhanced in ALS samples, with the 1450 cm−1 C-H deformation band showing up to 80% higher intensity than controls. Building on these findings, we recently extended the protocol to include tear fluid from patients with Parkinson's Disease (PD). Comparative spectral analysis revealed distinct molecular patterns between ALS and PD groups. This tear-focused, label-free approach highlights the potential of Raman spectroscopy for early, non-invasive differential diagnosis in neurodegenerative disorders.