Contents
Material Wettability, Wicking and Microfluidics

Paper Microfluidic and Lateral Flow Wicking Control: Contact Angle Checks for Barriers, Channels and Process Changes

Paper devices work only when barriers repel the sample and channels wick it. A timed water contact angle on each barrier material and after each fabrication change shows whether the surface still wets the way the device needs.

Who this is for: Paper microfluidic and lateral flow developers, diagnostic R&D teams and university sensor labs.

Where it fits: Barrier material selection, fabrication process changes, incoming paper checks and the methods section of a paper.

What it does not do: It does not measure flow time, leak resistance or assay performance; run those tests alongside it.

Method
Sessile drop water contact angle at fixed read times on barriers and paper
Standard
No standard covers paper device barriers; TAPPI T 458 style fixed time readings on paper are supported, ISO/TS 14778 only partly
Setup
About 2 minutes
Book a 15 minute demo Request a quote
microfluidic-paper-based-analytical-device
Why it matters

What wetting checks showed in published paper devices

158° held, 144° leaked

water contact angles of two permanent marker barriers on filter paper; the green ink held dyed water for 4 minutes, the black ink leaked.

Oyewunmi, Safiabadi Tali, Jahanshahi-Anbuhi, Chemosensors 8(4):97, 2020 (Dropometer)

94.9° vs 81.5°

water and 1.5% Triton X-100 on wax printed paper; that 13° gap was enough to make wax act as a valve with 1.6 to 20 minute delays.

Meng et al., Lab on a Chip, 2021

±25%

tolerance on lateral flow membrane capillary flow time, for grades from 75 ± 19 to 180 ± 45 seconds per 4 cm.

MilliporeSigma Hi-Flow lateral flow membrane specifications

Sources: Oyewunmi O. D., Safiabadi Tali S. H., Jahanshahi-Anbuhi S., Chemosensors, 2020; Meng et al., Automatic flow delay through passive wax valves for paper based analytical devices, Lab on a Chip, 2021; MilliporeSigma lateral flow membranes product page. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this paper device wetting check does and what it does not

A quick reference for diagnostic and sensor teams checking fit before reading further.

Evidence Box

Problem this solves

Barriers that leak, channels that stop wicking and fabrication changes that quietly change how paper wets.

Standards

TAPPI T 458 reads water contact angle on paper at fixed times; ASTM D724 was withdrawn in 2009. ISO/TS 14778 needs faster early time capture than the Dropometer camera. None covers microfluidic barriers.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

A Concordia University sensor lab checked three fabrication methods with Dropometer water contact angle across three papers and two theses, 2020 to 2025.

Customer publication

A Sensors and Actuators B study read Parafilm at 108 ± 5° before and 109 ± 5° after CO2 laser cutting, n = 3, and kept its laser settings.

Honest limit

A high angle does not prove a barrier holds. In the Concordia ink study, a leak test settled which inks to use.

Who this is for

What paper device wetting question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Device developer

You choose barrier materials and change fabrication steps. A contact angle on each new barrier, before and after each step, shows whether the step changed the surface.

Pair every barrier reading with a leak test.

Lateral flow process engineer

You run strips, pads and membranes from several lots. A timed contact angle on incoming paper or pads flags a wetting change before it shows up as slow or uneven flow.

Membranes that wick at once read near zero; trend wicking time instead.

University sensor lab

Students change inks, wax, laser settings and treatments every term. One locked method keeps their contact angles comparable and their methods sections complete.

Report drop volume and read time; many papers leave them out.
Fit check

Is this the right check for your paper device?

It measures how water wets barrier materials and paper at fixed times. It does not measure flow or the assay.

Good fit if

You compare barrier materials such as wax, inks, Parafilm or sizing.
You change a fabrication step and need to know if wetting changed.
You treat paper or electrodes to restore wicking.
You need wetting values with spread for a paper.
Students share one instrument and need one method.

Less relevant if

You need flow time on nitrocellulose; use a timed flow test.
Your paper absorbs the drop before the first frame.
You need early time values per ISO/TS 14778 at 50 frames per second or faster.
You need assay sensitivity; contact angle is upstream of that.
Summary

How contact angle supports paper microfluidic and lateral flow work

The answer in under a minute.

Measure water contact angle on every barrier material and on the paper behind it, at fixed read times, before and after each fabrication change. A barrier should stay strongly hydrophobic over the read; the channel or test zone should keep wicking. Confirm the choice with a leak or flow test before you lock the process.

The Dropometer contact angle kit runs the measurement. The Concordia University case study shows a paper sensor lab checking marker inks, laser cut Parafilm and printed electrodes, and the Parafilm heating laser cutting study reports the before and after check in its methods. The TAPPI T 458 and ASTM D724 page covers fixed time readings on paper, and our biotechnology guide and contact angle measurement guide explain more.

Expert Quote

Expert perspective on wetting in a capillary

A contact angle is a thermodynamic property: fix the liquid and the solid and the same angle appears whether the drop sits on a plate or climbs a capillary.

Dr. Alidad Amirfazli

Professor, Department of Mechanical Engineering, York University; Co-founder, Scientific Advisor, Droplet Lab

The problem

Why paper devices fail when wetting changes

Paper and lateral flow devices move liquid by capillary action, and the Lucas Washburn relation says wicking distance grows with the square root of time and with the cosine of the contact angle. A more hydrophobic paper wicks more slowly, and a barrier that is not hydrophobic enough lets the sample through. Nitrocellulose membranes are naturally hydrophobic and need a minimum amount of surfactant to wet, so small changes in treatment change flow. Membrane makers specify capillary flow time with a tolerance of about 25%, and run it at 45 to 55% relative humidity. Paper microfluidic barriers are usually judged by a dye leak test, which shows a failure but not how close a barrier is to failing. Fabrication adds risk: wax spreads about 275 µm into paper when heated, laser cutting and heat can change a barrier surface, and dried inks can make paper behind an electrode hydrophobic. Without a number for each surface, a change in materials or process shows up only when devices leak, flow slowly or give weak signals.

Sample leaks across a barrier or bleeds at the edges.
Flow is slow, uneven or stops before the test zone.
Colour develops unevenly across the detection zone.
A printed electrode gives almost no signal.
A new paper lot or process step changes results without a clear cause.
Troubleshooting

Why paper devices wet the wrong way and what to check

Why:

  • The barrier material does not cover the fibres fully, so the sample finds a path through.

How to detect:

  • The barrier angle is lower or falls over the read, and dyed water crosses it in a leak test.

Corrective action:

  • Choose barrier materials that stay high over the read and pass a leak test, as the Concordia ink study did.

Why:

  • Heat, laser cutting or solvents can change roughness and chemistry at the barrier surface.

How to detect:

  • The barrier angle shifts between pristine material and material after the step.

Corrective action:

Measure before and after each step with the same method. The Parafilm laser cutting study found no measurable change and kept its settings.

Why:

  • Dried inks or binders can make the paper behind an electrode or zone hydrophobic.

How to detect:

  • The back of the paper under the ink reads high, near 108° in one printed electrode study, and the zone will not wick.

Corrective action:

  • Treat or redesign so the channel side stays hydrophilic, then confirm with the angle and the signal.

Why:

  • Sizing, fillers and coatings vary between grades and lots and change how fast paper absorbs water.

How to detect:

  • The angle at a fixed time, or the change between two times, shifts on incoming paper.

Corrective action:

Check incoming lots at fixed times, as the TAPPI T 458 method does, and keep a retained reference sheet.

Why:

  • Paper takes up moisture and barrier materials age, so wetting can change before use.

How to detect:

  • Values track room humidity or storage time.

Corrective action:

  • Condition samples and record humidity and temperature with every reading.

Why:

Drop volume and read time change results on porous paper. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

  • The same material reads differently between students or sessions.

Corrective action:

Lock volume and read times and check a flat control against our contact angle reference values.

Not sure a fabrication change altered wetting?

Send samples from before and after the change, and we will measure them on a call.

Book a 15 minute demo
Lab records

What a paper device wetting record contains

Each check produces a record you can file with the device build and cite in a methods section.

Material

Paper grade and lot, barrier material and how it was applied.

Process step

Which step was checked, with settings such as oven time or laser power.

Method settings

Drop volume, read times, humidity and temperature.

Readings

Angle per spot at each read time, mean and spread, with n.

Confirming test

Leak test, flow time or signal for the same samples.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure on paper devices

Barrier

Water contact angle on the barrier at a fixed early time

Why it matters: It shows how strongly the barrier repels the aqueous sample.

How to interpret: Higher and steadier is better. In the Concordia ink study, green and blue inks read 158° and 151° at 10 s and held dyed water; red and black at 145° and 144° leaked.

When it is not enough: It does not prove the barrier holds; run a leak test.

Time

Barrier angle over the read, such as 10 s to 60 s

Why it matters: A barrier that slowly absorbs will fail during a long assay.

How to interpret: A flat curve means a stable barrier. A falling angle means the sample is getting in.

When it is not enough: Assays longer than your read window need a longer leak test.

Process

Angle before and after a fabrication step

Why it matters: It shows whether heating, cutting or printing changed the surface.

How to interpret: A change smaller than the spread is no measurable change; 108 ± 5° to 109 ± 5° is one published example.

When it is not enough: It does not show changes in pore structure under the surface.

Channel

Angle or wicking time on the channel side

Why it matters: The channel and test zone must keep wicking for the sample to reach them.

How to interpret: A drop that soaks in at once is what a channel needs. A high angle on the channel side is a fault.

When it is not enough: Very fast wicking leaves no angle to read; record the time to absorb instead.

Validation

Validated measurement approach for paper devices

How the Dropometer itself has been validated, and how a paper sensor lab used it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer evidence from a paper sensor lab

Concordia University's Jahanshahi-Anbuhi lab used Dropometer water contact angle in three papers and two theses from 2020 to 2025: to choose marker ink barriers with a leak test, to confirm laser cutting left Parafilm unchanged, and with SEM and FTIR to explain a weak printed electrode signal.

Read the citation analysis
QC Protocol

How to check wetting on paper device materials

Six steps per material or process change. Keep every step identical between samples.

1

Condition

Store paper and barrier samples in the same room conditions and record humidity and temperature.

2

Prepare

Cut flat coupons of each barrier and each side of the paper; for process checks, cut matched samples before and after the step.

3

Mount

Hold the coupon flat without touching the test area.

4

Measure

Place a locked drop volume and read at fixed times, such as 10 s and 60 s. The TAPPI T 458 page covers fixed time readings.

5

Confirm

Run a leak or flow test on the same build. Our capillary number entry explains how flow and wetting interact.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the paper microfluidic wetting SOP

A two page SOP you can adapt for your devices, with the method lock, barrier and process rules, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Contact angle measurement with the Dropometer

Example output

Example paper device wetting log

Example data only. Your values will differ with paper grade, barrier material and read time.

How to read this log

Barrier A stayed high from 10 s to 60 s and held in the leak test. Barrier B started lower, fell over the read and leaked. The laser step changed the barrier by less than the spread. The channel read zero because the drop wicked at once, which is what a channel needs. The back of the printed zone read high, which explains a dry zone. Our page on polymer microfluidic channel wettability covers closed channels.

Example paper device wetting log

Sample Angle at 10 s (°) Angle at 60 s (°) Spread (°) Leak or flow test Decision
Barrier A on filter paper 155 153 3 Held 4 min Use
Barrier B on filter paper 140 128 6 Leaked Reject
Barrier A after laser step 154 152 4 Held 4 min Keep step
Channel, untreated paper Wicked at once Wicked at once n/a Flow reached zone Pass
Paper behind printed zone 110 108 3 Zone stayed dry Treat and retest

Example data, not customer data. Water drops of a fixed volume; read at 10 s and 60 s; n = 3 per sample.

Signal order

The order to check signals on paper device wetting

Check these in order. Each one rules out a cause before you look at the next.

1

Conditioning

Rules out humidity and storage differences.

2

Reference coupon

Confirms the session reads as before.

3

Barrier angle over time

Shows whether the barrier repels and keeps repelling.

4

Channel side

Shows the channel still wicks.

5

Leak or flow test

Confirms what the angles mean for the device. Our page on hydrogel wettability covers absorbing surfaces.

FAQ

Common questions about paper microfluidic and lateral flow wetting

Questions diagnostic and sensor teams ask about contact angle on paper.

In the Lucas Washburn relation, wicking distance depends on pore size and on the cosine of the contact angle. A higher angle means slower wicking, as capillary flow models show. For a fixed paper grade, a change in contact angle is one of the few things that changes wicking speed.

There is no single value. In one Dropometer study, marker barriers at 158° and 151° held dyed water for 4 minutes, while barriers at 145° and 144° leaked. Wax printed paper read about 95° and still blocked water. Set your own limit from barriers that pass a leak test for your assay time.

Often only briefly. Treated membranes wick a drop within moments, so there is little or no angle to read. For lateral flow membranes, capillary flow time in seconds per 4 cm is the usual specification. Contact angle is more useful on barriers, backings, pads and untreated or blocked material.

No standard covers paper microfluidic barriers. TAPPI T 458 reads water contact angle on paper at fixed times, and ASTM D724 was withdrawn in 2009. ISO/TS 14778 needs image capture at 50 frames per second or faster, which the Dropometer camera does not reach, so treat it as partial alignment only.

Measure matched samples before and after the step with the same drop volume and read time. A change smaller than the spread means no measurable change. The Parafilm laser cutting study read 108 ± 5° before and 109 ± 5° after, and kept its settings.

Published results disagree. One study found no change in wicking speed from 30% to 85% relative humidity, while membrane makers test flow time at 45 to 55% and warn that very dry air causes static. Record humidity and temperature with every reading so you can tell later.

Dried ink or binder can make the paper behind the electrode hydrophobic, so the sample never reaches it. Measure the back of the paper as well as the electrode face. In one Concordia study, a water treatment kept the paper wicking and the peak current rose from about 4 to about 305 µA.

Business impact

What changes when you check wetting at each fabrication step

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with a wetting check at each step

Metric Before Dropometer With Dropometer Indicative Benchmark
Barrier selection Chosen by trial builds Angle over time plus a leak test Green 158° and blue 151° held; red 145° and black 144° leaked (Concordia, Chemosensors 2020)
Process changes Assumed not to affect wetting Before and after check on each step Parafilm 108 ± 5° to 109 ± 5°, settings kept (Sensors and Actuators B, 2023)
Weak signal diagnosis Trial and error Angle on both sides of the paper Peak current 4 ± 2 to 305 ± 18 µA after treatment (Electrochimica Acta, 2025)
Methods reporting Drop volume and timing often missing Full method recorded per sample No published benchmark; track it on your own projects

See the measurement on your own paper devices

Send a barrier and a channel sample. We will show the readings on a call.

Book a 15 minute demo

Estimate saved device builds from earlier wetting checks

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Paper device build estimate

Estimate saved device builds from earlier wetting checks.

Each Dropometer unit is US$5,000; the default models one unit.
Your own cost of materials and time for one build that fails a leak or flow test.
Coupon preparation, contact angle measurement and recording.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Candidates saved per month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What contact angle cannot tell you about a paper device

Honest limits, so you know when to reach for another test.

A high angle does not prove a barrier holds.
Fast wicking paper absorbs drops before an angle can be read.
Values on paper depend on read time and drop volume.
The camera runs at 10 frames per second, too slow for ISO/TS 14778 early time capture.
It does not measure flow time on nitrocellulose.
Surface angle does not show pore size or wax depth.

Contact angle shows how water wets a barrier or paper surface at fixed times. Flow time, leak resistance, pore structure and assay performance need their own tests.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related wicking workflows

These pages cover the paper wetting standards, customer evidence and the checks that sit beside this one.

Standard

TAPPI T 458 and ASTM D724

Fixed time water contact angle on paper.

View use case

Standard

ISO/TS 14778

Optical water contact angle on paper and board.

View use case

Standard

TAPPI T 558

Wettability and absorbency with an automated tester.

View use case

Case study

Concordia University

Three fabrication methods checked with water contact angle.

View use case

Published paper

Engineered detection zone on paper microfluidics

Parafilm before and after laser cutting.

View use case

Published paper

Dual modal assay kit for water hardness

Marker ink barriers chosen with contact angle and a leak test.

View use case

Related use case

Material wettability, wicking and microfluidics

All wettability and wicking use cases in one place.

View use case

Related use case

Polymer microfluidic channel wettability

Wetting in PDMS and thermoplastic channels.

View use case

Related use case

Hydrogel and biomaterial wettability

Contact angle on absorbing, hydrated surfaces.

View use case

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
Washburn, E. W. The dynamics of capillary flow. Physical Review 17(3):273, 1921. https://journals.aps.org/pr/issues/17/3
2.
Kalish, B., Tan, M. K., Tsutsui, H. Modifying wicking speeds in paper based microfluidic devices by laser etching. Micromachines 11(8):773, 2020. https://www.mdpi.com/2072-666X/11/8/773
3.
Martinez, A. W., Phillips, S. T., Butte, M. J., Whitesides, G. M. Patterned paper as a platform for inexpensive, low volume, portable bioassays. Angewandte Chemie International Edition 46(8):1318 to 1320, 2007. https://www.gmwgroup.harvard.edu/publications/patterned-paper-platform-inexpensive-low-volume-portable-bioassays
4.
Carrilho, E., Martinez, A. W., Whitesides, G. M. Understanding wax printing: a simple micropatterning process for paper based microfluidics. Analytical Chemistry 81(16):7091 to 7095, 2009. https://www.gmwgroup.harvard.edu/file_url/1267
5.
Strong, E. B. et al. Fabrication of miniaturized paper based microfluidic devices (MicroPADs). Scientific Reports 9:7, 2019. https://link.springer.com/10.1038/s41598-018-37029-0
6.
Meng, Chen, Zhu, Li, Ye, Ho, Chen. Automatic flow delay through passive wax valves for paper based analytical devices. Lab on a Chip, 2021, with supplementary Table S4. https://pubs.rsc.org/en/content/articlelanding/2021/lc/d1lc00638j
7.
EMD Millipore. Rapid lateral flow test strips: considerations for product development (manufacturer handbook). https://perfqws.sigmaaldrich.com/deepweb/assets/sigmaaldrich/marketing/global/documents/332/608/tb500en00em-rapid-lateral-flow-test-strips.pdf
8.
MilliporeSigma. Lateral flow membranes: capillary flow time specifications (manufacturer product page). https://www.sigmaaldrich.com/SK/en/products/clinical-diagnostics/lateral-flow-membranes
9.
Dissanayake et al. Predicting the wicking rate of nitrocellulose membranes from recipe data. Analytical Sciences 40:907 to 915, 2024. https://link.springer.com/article/10.1007/s44211-024-00540-8
10.
Walji, N., MacDonald, B. D. Influence of geometry and surrounding conditions on fluid flow in paper based devices. Micromachines 7(5):73, 2016. https://www.mdpi.com/2072-666X/7/5/73
11.
Safiabadi Tali, S. H., Hajimiri, H., Sadiq, Z., Jahanshahi-Anbuhi, S. Engineered detection zone to enhance color uniformity on paper microfluidics fabricated via Parafilm heating laser cutting. Sensors and Actuators B: Chemical 380:133324, 2023. See our citation analysis. https://dropletlab.com/validation/citations/analysis/engineered-detection-zone-to-enhance-color-uniformity-on-paper-microfluidics-fabricated-via-parafilm-heating-laser-cutting/
12.
Oyewunmi, O. D., Safiabadi Tali, S. H., Jahanshahi-Anbuhi, S. 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. Chemosensors 8(4):97, 2020. See our citation analysis. https://dropletlab.com/validation/citations/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/
13.
Oyewunmi, O. D. Development of a dual modal microfluidic paper based analytical device for the quantitative and qualitative detection of the total hardness of water. MASc thesis, Concordia University, 2020. See our citation analysis. https://dropletlab.com/validation/citations/analysis/development-of-a-dual-modal-microfluidic-paper-based-analytical-device-for-the-quantitative-and-qualitative-detection-of-the-total-hardness-of-water/
14.
Concordia University case study: seven years, three fabrication methods. See the case study. https://dropletlab.com/validation/case-studies/concordia-paper-microfluidics-contact-angle/
15.
ISO/TS 14778:2021. Paper and board: measurement of water contact angle by optical methods. https://www.iso.org/standard/66468.html
16.
TAPPI T 458 cm-24. Surface wettability of paper (angle of contact method). https://imisrise.tappi.org/TAPPI/Products/01/T/0104T458.aspx
17.
TAPPI T 558. Surface wettability and absorbency of sheeted materials using an automated contact angle tester. https://imisrise.tappi.org/TAPPI/Products/01/T/0104T558.aspx
18.
ASTM D724-99(2003). Surface wettability of paper (angle of contact method). Withdrawn 2009, no replacement. https://store.astm.org/d0724-99r03.html
19.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
20.
Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects. https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
21.
Droplet Lab validation papers
22.
Customer publications that cite the Dropometer
23.
Contact angle measurement guide
24.
Biotechnology guide