Healthcare facilities produce millions of tons of waste annually, with a significant portion consisting of diagnostic plasticware. Here, we introduce a new detection platform that completely replaces traditional assay plates with a piece of membrane, offering a much greener and more sustainable alternative. The membrane, integrated within the portable vortex fluidic device (P‐VFD), enables rapid detection of a clinically relevant protein biomarker, urinary p75ECD. This biomarker is utilized to evaluate the prognosis, disease severity, and progression of amyotrophic lateral sclerosis (ALS). This assay has a limit‐of‐detection (LOD) of 4.03 pg, which is comparable to the plate‐based assay (2.24 pg) and has been optimized through a full factorial design of experiments (DOE). P‐VFD has great potential in quantifying p75ECD in human biofluids and can significantly reduce the assay time to 5 min compared to the current plate‐based p75ECD ELISA assay (3 days), with at least a 4.4‐fold reduction in the usage of the detection antibody.