A dual-mode paper-based microfluidic chip for protamine detection

Timely and accessible fertility screening remains a challenge for male reproductive health, where privacy and convenience are often critical. Here, we present a dual-mode paper-based microfluidic device for the rapid detection of protamine—a key biomarker of sperm quality. The device combines distance-based migration and colorimetric readouts by leveraging electrostatic interactions between polydiacetylene-antibody (PDA-Ab) vesicles and APTMS-modified paper. This approach allows rapid, instrument-free, and privacy-preserving detection, making it suitable for point-of-care fertility screening. Upon interaction with protamine, PDA-Ab vesicles undergo a chromatic transition from blue to purple and display enhanced migration due to electrostatic repulsion. The device exhibited a exponential response in migration distance ( R ² = 0.94) and a gradual increase in absorbance at 640 nm across the 0–3 mg/mL protamine range. The optimized 1 % 3-aminopropyltrimethoxysilane (APTMS)-modified substrate ensured signal clarity and reproducibility. Visual differentiation of protamine concentrations was achieved within 10 min, requiring no instrumentation. This low-cost, easy-to-use platform supports semi-quantitative protamine analysis and is well suited for point-of-care fertility screening. The dual-readout format enhances reliability and offers strong potential for home-based reproductive health monitoring.