Primary surface measurement reported
Water contact angle of HPLC grade water on permanent-marker–treated Whatman® Grade 4 filter paper was measured.
Client Citation Analysis
Dual-Modal Assay Kit for the Qualitative and Quantitative Determination of the Total Water Hardness Using a Permanent Marker Fabricated Microfluidic Paper-Based Analytical Device
This paper develops a permanent-marker–fabricated microfluidic paper-based analytical device (µPAD) for total water hardness testing and uses water contact angle measurements, together with leakage analysis, to select permanent marker inks for hydrophobic barrier formation on paper.
At-a-Glance Summary
Dropometer attribution in the paper
Contact angle measurements were performed using “a device called a Dropometer (Droplet Smart Tech Incorporation, Toronto, ON, Canada),” with images analyzed using the installed “Sessile” mobile application.
How the surface-tension / contact-angle data were used in the study
The authors used water contact angle (alongside leakage analysis) to compare four permanent marker colors and select inks with favorable hydrophobic barrier performance for µPAD fabrication.
Replication / reliability statement
Each bar in the reported contact angle comparison represents the mean of three individual experiments ± standard deviation.
Paper Details
Title
Dual-Modal Assay Kit for the Qualitative and Quantitative Determination of the Total Water Hardness Using a Permanent Marker Fabricated Microfluidic Paper-Based Analytical Device
Authors
Oyejide Damilola Oyewunmi; Seyed Hamid Safiabadi-Tali; Sana Jahanshahi-Anbuhi
Journal
Chemosensors
Year
2020
Volume
8
Pages / Article
97
License
Creative Commons Attribution (CC BY) license
7.3
Scopus metrics (Elsevier / Scopus rating 2024)
Scopus metrics (Elsevier / Scopus rating 2024)
CiteScore subject ranks (CiteScore 2024)
- Q1 - Chemistry: Analytical Chemistry (40/160)
- Q1 - Chemistry: Physical and Theoretical Chemistry (45/187)
3.7
Journal Impact Factor (Clarivate JCR)
3.8
Journal Impact Factor (Clarivate JCR)
Journal Impact Factor (Clarivate JCR)
JCR category rank
- Q2 - Instruments and Instrumentation;
- Q2 - Chemistry, Analytical;
- Q2 - Electrochemistry
What Was Measured
Primary surface / interfacial measurement
Water contact angle of HPLC grade water on permanent-marker–treated Whatman® Grade 4 filter paper was used to compare marker ink hydrophobicity.
Supporting measurements
Elution (wicking) velocity was determined for multiple Whatman paper grades by dipping paper strips into HPLC grade water and observing wicking versus time at room atmospheric conditions. Leakage analysis was used to compare barrier performance of devices fabricated with different marker colors. The µPAD outputs were also evaluated via colorimetric response for qualitative and quantitative determination of total water hardness.
Contact angle
Dropometer (Droplet Smart Tech Incorporation, Toronto, ON, Canada); Sessile mobile application
µPAD pattern printing
Hewlett-Packard LaserJet P4015× Printer (EconoMode setting)
Statistical analysis
GraphPad Prism 8 software
Quantitative readout (image-based)
smart-phone or mobile scanner; ImageJ software
Temperature stability testing
oven (Thermo ScientificTM PrecisionTM Compact Gravity Convention, ThermoFisher Scientific, Mississauga, ON, Canada); conditioned laboratory refrigerator (4 °C)
Role of the Dropometer
The Dropometer was used to measure the water contact angle on paper surfaces treated with permanent marker inks. The Whatman® Grade 4 filter paper was cut into 2 cm × 2 cm squares, the four marker colors (blue, green, red, black) were applied, and HPLC grade water was dispensed via the sample application syringe onto each treated square sheet. Images were captured and analyzed using the installed Sessile mobile application to obtain contact angle results.
In the study workflow, the Dropometer contact angle results were used to compare marker ink hydrophobicity and support the selection of marker colors for creating hydrophobic barriers in the fabricated µPAD.
Bring This Measurement Into Your Lab
If you screen inks or coatings for hydrophobic barriers on paper, we can show you a sessile drop contact angle workflow on your samples.
Key Findings
Marker color changed water contact angle on treated paper
After 10 s, the reported contact angles were 144 deg. (black), 151 deg. (blue), 145 deg. (red), and 158 deg. (green) on Whatman® Grade 4 filter paper.
Hydrophobic strength ranked highest for green and blue inks
Based on water contact angle, the authors reported the hydrophobic strength order as green marker > blue marker > red marker ≈ black marker.
Contact angle behavior remained similar over a 60 s observation window
An investigation of contact angles over 60 s showed similar results to those at 10 s, which the authors interpret as the pigments retaining hydrophobicity over time.
Contact angle supported ink selection for hydrophobic barrier fabrication
Using water contact angle together with leakage analysis, the authors selected the green and blue markers for creating hydrophobic barriers in the µPAD.
Figures & Visuals
What it shows
Shows contact angle measurement over time for black, blue, red, and green markers on Whatman® Grade 4 filter paper upon exposure to drops of HPLC grade water (including measurement at 10 s and mean measurement over 60 s).
What it shows
Shows leakage outcomes for devices fabricated with different marker colors after dipping into colored HPLC grade water, used to support selection of green and blue inks.
What it shows
Shows elution velocity of distilled water in different paper grades and supports the choice of Whatman® Grade 4 filter paper for faster wicking.
Why It Matters
The paper’s fabrication approach relies on forming well-confined hydrophilic channels on paper using hydrophobic barriers created by permanent marker inks. Within that workflow, the contact angle measurements provide a quantitative wettability comparison across marker colors applied to the chosen paper substrate.
By pairing contact angle results with leakage analysis, the authors used surface wetting behavior to inform practical fabrication decisions (marker color selection) that affect barrier performance in the µPAD used for total water hardness determination.
Expert Perspective
Practical Takeaways
Dropometer contact angle as an ink-screening step
The study uses Dropometer-measured water contact angle to compare hydrophobicity across four permanent marker ink colors applied to Whatman® Grade 4 filter paper.
Time-based readout for wetting behavior
Contact angles were reported at 10 s after droplet deposition and also evaluated over 60 s to compare short-time and time-extended behavior.
Pair contact angle with leakage analysis for barrier performance
The fabrication workflow combines contact angle measurements with leakage analysis (colored HPLC grade water dipping) to select marker colors for hydrophobic barriers.
Substrate choice ties to wicking performance
Paper grade selection was informed by elution (wicking) velocity measurements prior to finalizing the substrate used for the µPAD.
Frequently Asked Questions
What did the Dropometer measure in this paper?
The authors used a Dropometer (Droplet Smart Tech Incorporation) to measure the contact angle of HPLC grade water on 2 cm × 2 cm squares of Whatman Grade 4 filter paper coated with blue, green, red or black permanent marker. Images were analysed with the Sessile mobile application, and each result is the mean of three experiments ± standard deviation.
What contact angles were reported?
Measured 10 s after the droplet was placed, the contact angles were 144° for black, 151° for blue, 145° for red and 158° for green marker (Figure 3b). Readings over 60 s were similar, which the authors take to mean the pigments retain their hydrophobicity over time, and they rank hydrophobic strength as green, then blue, then red and black at about the same level.
How did contact angle feed into the device design?
The authors combined the contact angle results with a leakage test in which devices were dipped in coloured HPLC grade water for 4 min; green and blue marker devices showed no leakage, while red and black leaked. Green and blue markers were therefore used for the hydrophobic barriers of the µPAD. The water hardness readout itself is colorimetric and does not use contact angle.