A dual-Nafion microfluidic preconcentrator with integrated label-free UV absorbance detection on a quartz substrate.

A dual-Nafion microfluidic preconcentrator with integrated label-free ultraviolet absorbance detection on a quartz substrate is presented for stable electrokinetic protein enrichment and real-time monitoring. The device employs a symmetric dual-membrane architecture to spatially confine the ion-concentration-polarization enrichment zone, thereby suppressing axial migration and improving operational stability compared with conventional single-Nafion configurations. Integration of a UV-transparent quartz substrate and a chromium-defined optical window enables background-suppressed, on-chip absorbance detection at 280 nm without fluorescent labeling. Device performance was characterized using bovine serum albumin as a model protein under controlled electrokinetic conditions, where real-time absorbance measurements demonstrated stable enrichment behavior over a wide concentration range, yielding enrichment factors of approximately 39-fold, 3960-fold, and 4380-fold from initial concentrations of 1 µM, 10 nM, and 1 nM, respectively, within 30 min of operation. Compared with a previously reported single-Nafion glass-based device, the dual-Nafion platform exhibits enhanced enrichment efficiency and extends reliable operation into the low-nanomolar regime. These results highlight the advantages of combining a symmetric dual‑Nafion architecture with quartz‑based, label‑free UV absorbance detection for reproducible electrokinetic preconcentration, and demonstrate the feasibility of using this integrated platform as a front‑end module for downstream biosensing and analytical systems.