A Simple Counting-Based Measurement for Paper Analytical Devices and Their Application.

This work introduces the concept of a counting-based measurement on paper analytical devices (cPADs) to improve the utilization of numerous reactions. The design of cPADs consists of two layers of paper substrates; the first layer contains a central sample zone combined with a radial surrounded by 12 detection zones that are predeposited with the various reagents, and the second layer acts as a connection channel between the sample zone and each detection zone. The solution can vertically flow from the first to the second layer and then move through the area to each subsequent detection zone. The analyte level can be evaluated by counting the number of detection zones that change color from a blank signal. Furthermore, our cPADs exhibit a capability of implementation for a broad series of reactions. Compared to the dPAD technique, some reactions that are possibly difficult to apply in such devices can be wholly enabled in our devices. The final color reaction on cPADs can apparently occur due to its identity. We applied this technique to the monitoring of carbaryl (CBR) and copper ions (Cu2+) using different reactions, including azo-coupling and complexation, respectively. Accordingly, this indicates an excellent result validated using the more traditional methods. Our cPADs can be applied for rapid screening of both CBR and Cu2+ in water samples with outstanding accuracy and precision using a naked-eye measurement by a relatively unskilled person. We offer a simple platform on PADs for rapid screening, combining high cost-effectiveness within a miniaturized platform designed for use with onsite applications, which is thus suitable for several different reactions.

Distance-based ß-amyloid protein detection on PADs for the scanning and subsequent follow-up of Alzheimer's disease in human urine samples.

We report on the first development of a simple distance-based ß-amyloid (Aß) protein quantification using a paper-based device (dPAD) to screen for Alzheimer's disease (AD) and to subsequently follow up on its influence, i.e., clinical dementia. This sensor method is based on the transformation of a free acid form and its binding with a basic form of bromocresol purple (BCP) through its electrostatic interaction with an Aß protein. This sensor can measure the length of color change from yellow to blue-green on a paper strip, with this change proportional to the amount of Aß protein level. We found that the linearity for Aß protein monitoring was in the range from 0.50 to 10.0 ng mL-1, and the subsequent naked-eye detection limit for Aß was 0.20 ng mL-1. This system also provided high reproducibility and with no apparent interference effect for Aß protein analysis in human urine samples. Furthermore, our developed dPAD constituted an accurate and effective device to precisely determine an Aß protein concentration in real samples, with percentage recoveries in the range of 97-103%, and with the highest relative standard deviation of 5.41%. Subsequently, the validation of our assay was assessed by comparison with a commercial ELISA approach, with favorable results. Finally, the proposed dPAD was successfully applied to the determination of an Aß protein in human urine samples and showed more benefits for the unskilled user, such as cost-efficiency, simplicity, low reagent usage, and low time consumption. It is also suitable for point-of-care monitoring.