Development of a Semiquantitative Barcode Readout Approach for Paper-Based Analytical Devices (PADs) for Enzymatic HO and Glucose Detection.

The integration of barcode technology with smartphones on paper-based analytical devices (PADs) presents a promising approach to bridging manual detection with digital interpretation and data storage. However, previous studies of 1D barcode approaches have been limited to providing only a "yes/no" response for analyte detection. Herein, a method of using barcode readout for semiquantitative signal detection on PADs has been achieved through the integration of barcode technology with a distance-based measurement concept on PADs. To demonstrate the feasibility of this concept, a PAD fabrication strategy incorporating barcodes was explored, using the enzymatic reaction between horseradish peroxidase (HRP), 3,3'-diaminobenzidine (DAB), and HO as a model system. The enzyme-catalyzed polymerization of DAB to polyDAB in the presence of hydrogen peroxide results in the appearance of color observable by the naked eye inside a paperfluidic channel, with the color-changed length depending on the HO concentration. At the same time, the barcode pattern displayed as a result of this distance-based color evolution overlaid with a paper-based barcode layer can be read using a smartphone application. Parameters affecting the signal readout performance were studied. The developed device can be used to detect HO concentrations in the range of 0.25 to 10 mM within 90 min with 79.6% of barcode signals correctly readable. Additionally, results from different smartphone models showed a consistent reading performance (78.4-79.6%). Finally, the quantification of glucose levels in artificial urine samples was demonstrated. This developed PAD signaling strategy offers end-users more simplicity and can be used as a standalone device or in conjunction with other digital devices.