Rapid Tear Proteomics via In-Capillary Digestion for Biomarker Discovery

Tear fluid is emerging as a valuable resource for biomarker discovery, but its low sample volume and dynamic composition pose significant challenges for analytical testing. Most tear proteomics studies have focused on samples collected with Schirmer strips, while capillary tube collection has received less attention. To address these challenges, we developed a novel in-capillary trypsin digestion workflow that requires as little as 0.5 μL of tear fluid for bottom-up shotgun proteomics. This method uses liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify a higher number of proteins with enhanced efficiency compared to previously reported methods, which typically required 5-10 μL of pooled tear fluid. Using the same microcentrifuge tube for both tear collection and sample processing, this streamlined workflow simplifies sample handling and minimizes both sample loss and experimental errors associated with sample transfer. This method also efficiently reduced sample processing time to under 2 hours prior to overnight trypsin di-gestion, compared to the 5-8 hours required by other methods. With this workflow, we identified 500-800 proteins per 0.5 μL sample without the need for fractionation, allowing for at least three technical replicates. This optimized workflow greatly enhances the efficiency of tear proteomics for biomarker discovery.