Hydrogel Bead-Based Assay for the Measurement of Protein Biomarkers in Saliva

We report a novel poly-(ethylene) glycol (PEG) hydrogel bead-based assay that permits measurement of protein biomarkers in complex samples such as saliva without sample processing and with limits of detection and dynamic range that are comparable or better than the current gold-standard, enzyme-linked immunosorbent assay (ELISA) without requiring detection antibodies and enzyme amplification. Additionally, in comparison to ELISA, the analysis time is >2 times shorter and the workflow is simpler. The PEG-based hydrogel beads preconcentrated protein biomarkers by covalent capture and in parallel removed interferent proteins by molecular weight cutoff without being affected by salts. The captured proteins were fluorescently labeled during their photochemical release from hydrogel beads. The released proteins were bound to immobilized antibodies and fluorescence was measured to determine their concentrations. Using the reported hydrogel beads, we measured proteins such as interleukin 6 (IL6) and interleukin 8 (IL8) at pg/mL concentrations in 200 μL of unprocessed saliva in ∼100 min. We applied the hydrogel beads to measure IL6 and IL8 in minimally stimulated saliva of oral lichen planus (OLP) patients and healthy individuals.