Screening of angiotensin converting enzyme inhibitors from natural products via origami microfluidic paper-based analytical devices with colorimetric detection.

We report the screening of angiotensin converting enzyme (ACE) inhibitors on an origami microfluidic paper-based analytical device (μPAD) using colorimetric detection. The hydrolysis product reacts with ninhydrin, resulting in a purple color at the detection zones. Images of the μPADs are captured using a common cell phone and analyzed with Photoshop software. This platform allows six independent colorimetric reactions to take place simultaneously, and the IC values can be obtained in a single run within 22 min. The relative standard deviations of inhibition efficiencies are generally lower than 4.0 % (n = 5). The IC values of captopril and five products from natural plants were obtained and corresponded well with UV methods. The relative deviations between the two methods are within the range of -5 % to +5 %. This work is a proof-of-concept successfully demonstrating the use of μPADs technology to screen enzyme inhibitors from natural products.