Abstract
A dip-and-read microfluidic paper-based analytical device (µPAD) was developed for the qualitative and quantitative detection of the total hardness of water. To create well-defined hydrophobic barriers on filter paper, a regular office printer and a commercially available permanent marker pen were utilized as a quick and simple technique with easily accessible equipment/materials to fabricate µPAD in new or resource-limited laboratories without sophisticated equipment. After a wettability and barrier efficiency analysis on the permanent marker colors, the blue and green ink markers exhibited favorable hydrophobic properties and were utilized in the fabrication of the developed test devices. The device had five reaction and detection zones modeled after the classification given by the World Health Organization (WHO), so qualitatively it determined whether the water was ‘soft’, ‘moderately hard’, ‘hard’, or ‘very hard’ by changing color from blue to pink in about 3 min. The device was also used to introduce an alternative colorimetric reaction for quantitative analysis of the water hardness without the need for ethylenediaminetetraacetic acid (EDTA) and without compromising the simplicity and low cost of the device. The developed µPAD showed a calculated limit of detection (LOD) of 0.02 mM, which is at least 80% less than those of commercially available test strips and other reported µPADs, and the results of the real-world samples were consistent with those of the standard titration (with EDTA). In addition, the device exhibited stability for 2 months at room and frigid condition (4 °C) and at varying harsh temperatures from 25 to 100 °C. The results demonstrate that the developed paper-based device can be used for rapid, on-site analysis of water with no interferences and no need for a pipette for sample introduction during testing.
Highlights
Water is a valuable resource for humanity
We (6) investigated the greatly improved limit of detection of the sensor (0.02 mM), which is at least 80% lower than that of commercially available test strips and other reported μPADs for the detection of total water hardness
The design (Figure 2a) contains five detection (D) and reaction zones (R): four for the different classes of water hardness, including soft (S), moderately hard (MH), hard (H), and very hard (VH) and one for a control (C) section that is used for the quantification
Summary
Water is a valuable resource for humanity. The various usage of water knows no bounds—from industrial usage to domestic and drinking purposes, to agricultural purposes, which in the end supply food for humanity. The common means of determining the level of hardness of water have been the traditional titration method, ion selective electrode analysis [8], inductively coupled plasma atomic emission spectroscopy (ICP-OES) [9], and Raman spectroscopy characterization [10] These methods, though giving accurate results, require bulky instruments and apparatus, need an external power source and a large amount of sample for operation, and do not allow for dynamic and point-of-use testing. The previously reported sensor needed an auxiliary tool (pipette) for sample introduction during testing, which could lead to errors due to human interaction Our study tackled these shortcomings by (1) fabricating a paper sensor that determined the total hardness of water both qualitatively and quantitatively in just one test (dual-mode detection).
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