Instrument-free quantitative detection of alkaline phosphatase using paper-based devices

Almost all the existing assay methods for alkaline phosphatase (ALP) require expensive analytical instruments and well-trained users to achieve quantitative results. This work initially describes a quantitative ALP assay that integrates low-cost microfluidic paper-based analytical devices (μPADs) with an instrument-free length-measuring readout. The detection motif of length measurement is based on the starch-mediated wettability change of the μPAD from hydrophilic to hydrophobic. Under optimal conditions, this new method is quantitatively sensitive to ALP levels in buffer samples ranging from ∼0.075 to 5 U mL−1, with a visual detection limit of 0.075 U mL−1. The satisfactory recovery results of assaying several human serum samples additionally prove its practicability. The proposed method needs only a ubiquitous cheap ruler to realize quantitative analysis, thus making it a simple, cost-efficient, and promising alternative tool for potential broad applications in the diagnosis of ALP-relevant diseases or assessment of ALP functions in biological systems especially in resource-poor settings.