Client Citation Analysis
The Dropometer measured static water contact angle on Parafilm before and after laser ablation (Chapter 3) and on screen printed paper electrodes, front and back, with and without water treatment (Chapter 4). It did not measure any sensor output. Channel widths, color uniformity, glucose response, cyclic voltammetry, impedance, SEM and FTIR all came from other tools.
Water contact angle in degrees, reported as mean ± SD: 108 ± 5° and 109 ± 5° on Parafilm (n = 3), 108 ± 2° on the untreated electrode backside, and 112 ± 6° versus 110 ± 5° on the front electrode surface.
Can low cost fabrication routes (Parafilm heating with laser cutting, and do it yourself screen printing) give paper sensors that wick properly and read precisely, and what stops liquid reaching printed electrodes?
Laser cutting did not change Parafilm wettability. Printed carbon ink turned the paper under the electrodes hydrophobic, and rinsing with water while the ink was still wet kept the paper hydrophilic, which lifted the oxidation peak current from 4 ± 2 µA to 305 ± 18 µA.
A doctoral thesis on low cost paper sensors where water contact angle checked two fabrication steps.
Water contact angle measured with a Dropometer on Parafilm before and after laser ablation, and on printed electrode regions of paper electrochemical devices (ePADs) before and after water treatment.
A micrometer measured laminate thickness; an optical microscope and ImageJ measured channel and barrier widths; a scanner and ImageJ quantified color uniformity. A PalmSens4 potentiostat ran cyclic voltammetry; the thesis does not name the instrument used for chronoamperometry and impedance. SEM (Phenom ProX G5) and FTIR (Nicolet iS20) checked structure and chemistry.
Water contact angle on Parafilm and on printed electrode regions of ePADs
Thickness of Parafilm laminated paper
Ablation of paper channels and cutting of vinyl screen printing masks
Cross section of laminated channels
Cyclic voltammetry on ePADs (chronoamperometry and impedance also run; instrument not named for those)
Fiber and graphite flake morphology of untreated and water treated ePADs
Chemical groups on the electrode backside before and after drying
In Chapter 3 the team used a Dropometer to check one risk of their Parafilm heating and laser cutting method: that the laser might damage the hydrophobic Parafilm backing. They ablated a 2.5 × 2.5 cm patch of paper and measured water contact angle on the exposed Parafilm.
The angle stayed the same within error: 108 ± 5° on pristine Parafilm and 109 ± 5° after ablation (n = 3). The authors read this as the laser settings cutting the paper with minimal impact on the Parafilm.
In Chapter 4 the Dropometer measured the electrode region of screen printed paper devices. On the untreated backside the droplet sometimes sat on the paper at 108 ± 2° instead of soaking in. Water treated devices stayed hydrophilic and kept wicking.
On the front electrode surface the angle barely moved: 112 ± 6° untreated and 110 ± 5° water treated. So the treatment changed the paper under the ink, not the ink surface itself. SEM, FTIR and electrochemistry supplied the rest of the explanation.
The contact angles supported the authors' explanation for the weak signal of untreated electrodes: in some devices water could not pass through hydrophobic paper to reach them. Together with SEM, FTIR and impedance data, this helped the authors attribute the 75 fold gain to restored wicking rather than a change in the ink.
Checking whether a printing, coating or laser step has changed how water wets your substrate? Measure it before and after with the Dropometer.
Parafilm read 108 ± 5° before and 109 ± 5° after laser ablation of the paper (n = 3), so the backing kept its hydrophobic barrier role.
On untreated devices the backside electrode region reached 108 ± 2°, and in some cases the droplet never entered the paper.
The front electrode surface read 112 ± 6° untreated and 110 ± 5° water treated, while the treated backside stayed hydrophilic and wicked.
From other instruments: twice washed devices gave 305 ± 18 µA oxidation peaks versus 4 ± 2 µA untreated, and charge transfer resistance fell from over 40 kΩ to 0.14 kΩ.
From other tools: Parafilm laminated channels held liquid with barriers as narrow as 172 ± 15 µm, and printed electrodes reached 286 ± 31 µm resolution.
Two figures in the thesis contain Dropometer images or values. The thesis has no Creative Commons licence, so we link to the published versions instead of reproducing them.
Panel A shows water drops on Parafilm before and after laser ablation, with Dropometer values of 108 ± 5° and 109 ± 5°. Thesis © S. H. Safiabadi Tali 2025; published version in Sensors and Actuators B: Chemical (licence not stated in the thesis). Figure number in the journal article may differ.
Supporting figure on water contact angle measurements of untreated and water treated ePADs, made with the Dropometer. Thesis © S. H. Safiabadi Tali 2025; published version in Electrochimica Acta (licence not stated in the thesis). Likely in the article's supplementary file.
Paper sensors only work if liquid reaches the right place. Contact angle is a quick way to test whether a fabrication step has changed that.
Carbon inks carry hydrophobic components that can seal the paper under an electrode. A contact angle check on the backside shows this before any electrochemistry is run.
Laser steps can change surface roughness and chemistry. Measuring the barrier material before and after confirms the step left it intact.
Ties a weak sensor signal to a wetting cause
Separates paper wettability from electrode surface wettability
Verifies a laser step left the hydrophobic barrier intact
The front electrode surface and the paper behind it behaved differently. Measuring only one side would have hidden the cause.
The authors combined contact angle with SEM, FTIR and impedance before drawing a conclusion about mechanism.
It measured water contact angle on Parafilm before and after laser cutting, and on the electrode region of screen printed paper devices. Every sensor performance number in the thesis came from other instruments.
No measurable change was found. Pristine Parafilm read 108 ± 5° and laser exposed Parafilm read 109 ± 5°, with three replicates each.
Untreated devices had hydrophobic paper under the ink, so the sample could not reach the electrodes. Water treatment kept the paper wicking, while SEM, FTIR and the front surface angles showed the ink itself was largely unchanged.
Yes. Chapter 3 appeared in Sensors and Actuators B: Chemical in 2023, and Chapter 4 in Electrochimica Acta in 2025.
Use the formal reference below when citing the original thesis.
Safiabadi Tali, S. H. (2025). Development of portable and easy-to-use chemo/biosensors [Doctoral thesis, Concordia University]. No DOI or repository link stated in the thesis.
Safiabadi Tali, PhD thesis, Concordia University, 2025. No DOI (thesis)