Development of Pipetteless Paper-Based Analytical Devices with a Volume Gauge

In this work, we propose a new design for paper-based analytical devices (PADs) that eliminate the need to use a micropipette for sample introduction. With this design, a PAD is equipped with a distance-based detection channel that is connected to a storage channel that indicates the volume of a sample introduced into the PAD. The analyte in the sample solution reacts with a colorimetric reagent deposited into the distance-based detection channel as the sample solution flows into the storage channel where the volume is measured. The ratio of the lengths of the detection channel and that of the storage channel (D/S ratio) are constant for a sample containing a certain concentration, which is independent of the introduced volume. Therefore, the PADs permit volume-independent quantification using a dropper instead of a micropipette because the length of the storage channel plays the role of a volume gauge to estimate the introduced sample volume. In this study, the D/S ratios obtained with a dropper were comparable to those obtained with a micropipette, which confirmed that precise volume control is unnecessary for this PAD system. The proposed PADs were applied to the determinations of iron and bovine serum albumin using bathophenanthroline and tetrabromophenol blue as colorimetric reagents, respectively. The calibration curves showed good linear relationships with coefficients of 0.989 for iron and 0.994 for bovine serum albumin, respectively.