Engineering inertial flow patterns for signal amplification in disc-based protein assays.

Detecting low-abundance proteins is essential in liquid biopsy applications, particularly for extracellular vesicle (EV)-based diagnostics. Here, we introduce RapidEx (Rotationally amplified protein intensity detection of Extracellular vesicles), a disc-fluidic system engineered for highly sensitive protein assays. RapidEx performs two key functions within a single disc cartridge: i) enzymatic chemical reactions for target labeling and ii) efficient washing to enhance signal-to-background contrast. METHODS: The device leverages a unique interplay between disc-specific inertial forces (centrifugal and Coriolis) and membrane-filter flow dynamics. Unlike conventional systems, RapidEx utilizes a low-permeability membrane to redirect fluid laterally during rotation, thereby enhancing washing efficiency and signal-to-noise ratio. The performance of the device was validated through numerical simulation and tyramide-mediated amplification assays. This system processed plasma samples from patients with ovarian cancer (n = 54) and non-cancer controls (n = 28), facilitating EV labeling for a panel of cancer markers. RESULTS: Numerical simulations and experimental validations confirmed that Coriolis-induced lateral flows were found critical to improving labeling and washing efficiency. This synergetic fluidic control with enzymatic chemical reaction enhanced the signal-to-noise ratio, which is >25-fold more sensitive than standard two-step labelling. Applying this platform to clinical samples, protein profiles enabled differentiation between cancer patients and controls and allowed for the identification of platinum therapy resistance in patients prior to chemotherapy treatment. CONCLUSIONS: RapidEx could enable rapid and cost-effective protein-based liquid biopsies, with applications in disease detection and monitoring therapeutic responses.