Microfluidic paper-based analytical devices(μPADs)represent a growing class of low-cost,user-friendly and disposable technology designed for point-of-use applications,which use porous cellulose to store reagents and capillary action for fluid transportation.Here,we describe a simple,rapid,low cost,visual cocaine detection method that combines glucoamylase-trapped aptamer-cross-linked hydrogel for molecular recognition and signal amplification with the μPAD for portable readout.An aptamer-cross-linked hydrogel trapped with glucoamylase is formed in a PCR tube with a capillary inserted in the rubber cover.Upon target introduction,the hydrogel collapses to release glucoamylase,which catalyzes the hydrolysis of amylose in the sample to produce a large amount of glucose.With a simple folding of the μPAD,the sample wicks to the inlet and diffuses to each reaction reservoir in parallel which contains KI,horse radish peroxidase and glucose oxidase(KI/HRP/GOx),allowing mixing of the glucose to react with the reagents in the reservoir.As a result,hydrogen peroxide is produced and then reduced by HRP while colorless iodide is oxidized to distinctive brown iodine.Through color gradient changes based on different concentrations of cocaine,semiquantitative analysis is achieved by naked eyes and quantitation can be obtained by analyzing the change of color via cloud computing.Moreover,μPADs are efficiently fabricated by wax patterning and are disposable after detection.The determination of cocaine in urine samples is also performed to demonstrate the applicability of this device for complex biological samples.We believe that the method reported here provides a new platform of low cost,ease of use,portable and visual detection of a wide range of targets.