Negative-Pressure-Actuated Microfluidics: A Dual-Mode Point-of-Care Sensor for Allergen-Specific IgE in Interstitial Fluid

This study reports an integrated dual-signal microfluidic immunosensor for point-of-care detection of ovalbumin-specific IgE (OVA-sIgE) in interstitial fluid. A pH-responsive composite material, ZIF-8 encapsulating phenolphthalein and surface-conjugated with antimouse OVA-sIgE (ZIF-8@PP∼Abs), was synthesized and characterized. Structural and elemental analyses confirmed the successful synthesis and antibody functionalization, while the composite retained strong alkaline-triggered colorimetric response due to ZIF-8 decomposition and subsequent phenolphthalein release. Carbon dots (CDs) show concentration-dependent fluorescence, which is effectively quenched by ZIF-8@PP∼Abs. A paper-based chip coimmobilized with CDs and OVA antigen enabled simultaneous colorimetric and fluorescent detection. The colorimetric pathway operates as a "turn-on" system through alkaline-induced color change, while the fluorescent pathway functions as a "turn-off" system via CDs quenching by ZIF-8@PP∼Abs. Quantitative analysis using the green channel─identified as the most sensitive through RGB decomposition─showed linear responses across 0.06-8.00 ng/mL OVA-sIgE, with detection limits of 0.026 ng/mL (colorimetric) and 0.032 ng/mL (fluorescence). The dual-signal design, featuring built-in cross-verification, demonstrates high reliability through favorable spike-and-recovery results. ROC analysis shows AUC values of 0.9999 for both signals, with a significant reduction in false positives. To achieve operational integration, a custom-designed negative-pressure-driven microfluidic chip was developed, incorporating all necessary steps into a negative-pressure valve-controlled microfluidic chip. The chip demonstrated robust fluid handling, repeatable operation, and user-friendly functionality. The integrated sensor exhibited excellent selectivity, strong anti-interference capability against common interstitial fluid constituents. This work presents a practical, accurate, and reliable platform for decentralized allergy testing, merging advanced nanomaterials, dual-mode transduction, and microfluidic engineering.