A Portable UV-LED Dual-Nafion Microfluidic Platform for Label-Free Trace Protein Preconcentration and Absorbance Detection

Sensitive label-free detection of low-abundance proteins requires both effective on-chip preconcentration and a compact, low-noise optical readout for use outside conventional laboratories. Here, we present a portable UV-LED dual-Nafion microfluidic platform that integrates a 280 nm UV-LED, a chromium-coated slot collimator, a dual-Nafion ion concentration polarization (ICP) preconcentrator, and a miniature spectrometer within a 3D-printed enclosure. The symmetric dual-Nafion geometry on a UV-transparent quartz substrate confines the ICP enrichment zone to a fixed 120 × 500 µm interrogation window, enabling spatially stable, label-free on-chip absorbance monitoring at 280 nm. Using bovine serum albumin (BSA) as a model protein, the platform showed a linear absorbance response over 0–60 µM (R2 = 0.9933) and a static-loading limit of detection of 0.91 µM. Under a 30 V bias in 0.3 mM phosphate-buffered saline, representative 60 min experiments produced apparent enrichment factors of approximately 41, 4.5 × 103, and 1.6 × 104 at initial BSA concentrations of 1 µM, 10 nM, and 1 nM, respectively. At 10 pM, a reproducible, voltage-dependent absorbance increase was detected with three independent chips, whereas the 0 V and BSA-free controls remained below the detection threshold. The platform provides a practical approach for label-free trace-protein analysis and a potential upstream module for biomarker-specific assays.