One-droplet saliva detection on photonic crystal-based competitive immunoassay for precise diagnosis of migraine

Migraine exhibits a substantial prevalence worldwide. The current diagnostic criteria rests exclusively on clinical characteristics without any objective and reliable means. The calcitonin gene-related peptide (CGRP), as a biomarker for distinguishing migraine, undergoes swift degradation, featuring a half-life of under 10 min, which poses a significant challenge to the point-of-care testing of CGRP in clinical application. Here, a photonic crystal (PC)-based biochip has been developed to detect CGRP via the fluorescence competition assay. The chip integrates the functionalities of fluorescence enhancement and hydrophilic-hydrophobic patterning enrichment, enabling rapid and sensitive detection of CGRP. After investigating the optimal enhancement distance of fluorescence near PCs, the chip allows CGRP detection using <30 mu L of saliva at room temperature within 10 min. A minimum detection limit of 0.05 pg/mL is achieved. Furthermore, CGRP concentrations in the saliva of 70 subjects have been tested by PC biochips. The results exhibit strong concordance with the enzyme-linked immunosorbent assay (ELISA), demonstrating a linear correlation coefficient of R2 of 0.97. This sensitive detection of markers within such a short duration surpasses the capacities of ELISA, which paves the way for establishing a precise diagnostic framework integrating clinical phenotypes and biomarkers for migraine.