Primary surface measurement reported
Sessile-drop contact angle (hydrophobicity) measurements on LIG and nPt-LIG electrode surfaces.
Client Citation Analysis
Batch-to-Batch Variation in Laser-Inscribed Graphene (LIG) Electrodes for Electrochemical Sensing
This study evaluates batch-to-batch variation in laser-inscribed graphene electrodes for electrochemical sensing, using goniometry (contact angle) alongside stereomicroscopy and electrochemical tests (OCP, CV); the contact angle data track hydrophobicity across fabrication batches, test buffers, and after nanoplatinum metallization.
At-a-Glance Summary
How the paper credits the instrument
"Hydrophobicity was analyzed using a Droplet lab DROPOMETER-M (Markham, ON, Canada)." / "Contact angle calculations were based on the polynomial method (non-axisymmetric drop)." / "The instrument camera was used to capture a static picture in sessile droplet mode." — Section 2.4, Goniometry.
How the contact-angle data were used in the study
Contact-angle outputs were used to quantify batch-to-batch variation in LIG hydrophobicity immediately after graphitization, compare wettability across multiple testing solutions (including common biological buffers), and evaluate wettability changes after nanoplatinum metallization.
Replication / reliability statement
"Four unique batches (nine electrodes each) were prepared on individual days, by the same operator." (Section 2.4). Figure 1 reports n = 24 for each violin-plot group and n = 6 electrodes in each batch for batch-average plots, and Section 3.1 describes four batches of six electrodes each.
Paper Details
Title
Batch-to-Batch Variation in Laser-Inscribed Graphene (LIG) Electrodes for Electrochemical Sensing
Authors
Yifan Tang; Geisianny A. Moreira; Diana Vanegas; Shoumen P. A. Datta; Eric S. McLamore
Journal
Micromachines
Year
2024
Volume
15
Pages / Article
874
License
Creative Commons Attribution (CC BY) license
Funding & interests
Funded by NIH/NIAAA U01AA029328, NSF STEPS Center CBET-2019435, and USDA NIFA AFRI 2018-67016-27578. Authors are at Clemson University, MIT Auto-ID Labs, and MGH/Harvard Medical School. The authors declare no conflicts of interest. Droplet Lab appears in no funding, acknowledgement or affiliation statement; the paper names the instrument in its methods (Section 2.4).
Data availability
Cyclic voltammetry data openly available at Zenodo.
What Was Measured
Primary surface / interfacial measurement
Hydrophobicity reported as contact angle (degrees) measured by goniometry using sessile droplets on LIG and nanoplatinum-metallized LIG (nPt-LIG) electrodes.
Supporting measurements
The study also reports LIG characterization using stereomicroscopy, open circuit potential (OCP), and cyclic voltammetry (CV) as part of the batch-variation assessment and electrochemical sensing context, including calculation of oxidation peak current and area between anodic/cathodic curves from CV traces.
Contact angle / hydrophobicity (goniometry)
Droplet lab DROPOMETER-M (Markham, ON, Canada)
Contact angle analysis software
Droplet lab software (version 1.4.0.10)
LIG patterning / graphitization
Universal CO2 laser system (version VLS3.60, Scottsdale, AZ, USA)
Electrodeposition (galvanostatic)
DC power supply (Tektronix, Beaverton, OR, USA)
Electrodeposition (frequency-modulated)
SDG2042X Arbitrary Waveform Function-Generators (Siglent, OH, USA)
pH measurements
Thermo Orion A211 Benchtop pH Meter and calibration standards (Waltham, MA, USA)
Electrochemical characterization (OCP, CV)
MultiPalmSens4 potentiostat (PalmSens BV, GA, Houten, The Netherlands)
Electrochemical testing cells
BASi electrochemical glass cells
Statistical analysis
Rstudio (version 1.1.463)
Electrode pattern design
CorelDraw (Corel Corporation, Ottawa, ON, Canada)
Role of the Dropometer
Hydrophobicity (contact angle) was measured using a Droplet lab DROPOMETER-M by placing a 2 µL aliquot on the working area of the LIG electrode, capturing a static image in sessile droplet mode, and calculating contact angle using a polynomial (non-axisymmetric drop) method. In the software workflow, key image features (e.g., droplet edges/profile of interest) were identified following manufacturer recommendations, and images from each test were archived.
In this study’s batch-variation workflow, the resulting contact-angle data were used to compare hydrophobicity across fabrication batches, across testing solutions (including common buffers), and before/after nanoplatinum metallization.
Bring This Measurement Into Your Lab
If you need to check contact angle consistency across electrode batches or test buffers, we can show you a sessile drop measurement on your samples.
Key Findings
Contact angle did not vary across batches
Under the study's four-batch protocol, contact angle varied by less than 5% within fabrication batches for bare LIG in DI and isotonic bicarbonate, and by 5% for platinum-metallized LIG. The authors conclude: "Contact angle did not vary across batches, but the type of liquid tested did have a significant effect on mean contact angle." The >30% variation reported below occurred when 36 electrodes were fabricated in a single day; the authors note: "Additional studies are required to identify the source of the variation during the LIG manufacturing process."
Baseline LIG wettability in DI
The average contact angle for LIG in DI was reported as 58.6 ± 1.4°, and the authors interpret this as indicating a hydrophilic surface under their test conditions.
Isotonic buffer vs DI comparison
The mean contact angle in 2× isotonic buffer was reported as 59.3 ± 2.6°, and described as not significantly different than DI; within fabrication batches, contact angle variation for non-modified LIG in DI and isotonic bicarbonate was reported as less than 5%.
Buffer-dependent contact-angle shifts and interfacial interpretation
Contact angles for non-modified LIG in HEPES, MES, and Tris were reported as significantly lower than DI, and the authors interpret this as each buffer behaving as a mild surfactant impacting surface tension; within-group variation for these buffer conditions was reported as 6% to 8%.
Fabrication batching and downtime effects on contact-angle variation
When 36 electrodes were fabricated in a single day, reported contact-angle variation was more than 30%. Fabricating and analyzing 36 electrodes as four batches of nine with a 30 min laser downtime between batches was associated with reduced variation (reported as a reduction from 30% to less than 5%), and the authors identify laser maintenance, operational frequency, and batch size as control factors for future protocols.
Nanoplatinum metallization increases contact angle
After metallization with nPt, the contact angle in DI and isotonic carbonate buffer was reported as 78 ± 4°, described as an increase by nearly 20% with a more hydrophobic surface, and varied by 5% within fabrication batches. The authors report the HEPES/MES/Tris contact angles for nPt-LIG as similar (63 ± 2°) and higher than all LIG experiments.
Bare LIG is highly reproducible
Using oxidative peak current, single LIG electrodes varied by less than 2% across batches; the LIG sensor chip by 8%. Peak separation was 205 ± 50 mV for single electrodes and 519 ± 20 mV for the chip.
Platinum metallization trades performance for consistency
Nanoplatinum deposition raised peak current by 150–250 µA, increased capacitance sevenfold, and cut peak separation to 143 ± 3 mV. But batch variation rose to 15–20% within batches and 30–40% across batches. The paper's headline conclusion: "metallization of LIG with nPt improves performance but comes at the expense of increased batch variability."
Figures & Visuals
What it shows
Shows representative goniometry images for four electrode batches (LIG sample with a 2 µL DI droplet) with calculated contact angles overlaid.
What it shows
Violin plots compare contact-angle distributions across testing liquids for non-modified LIG (n = 24 per group), with group subsetting indicated by LSD lettering.
What it shows
Violin plots show how contact-angle distributions shift after nanoplatinum metallization across the same set of testing liquids (n = 24 per group).
What it shows
Batch-average contact angles (with standard deviation error bars) are shown for non-modified LIG (D) and nPt-LIG (E), with n = 6 electrodes per batch.
Why It Matters
The paper frames laser-inscribed graphene as an emerging platform for electrochemical sensing and positions batch-to-batch variability as a practical challenge for scalable device manufacturing. The DROPOMETER-M measured how LIG wettability responds to the liquid in contact with it, and served as a screening check on fabrication consistency. The authors conclude that "contact angle did not vary across batches, but the type of liquid tested did have a significant effect on mean contact angle." The largest batch-to-batch variation in the paper (30–40% across batches) was in the electrochemical response after platinum metallization.
The authors also use contact-angle comparisons across testing buffers (including zwitterionic buffer components) and after nanoplatinum metallization to discuss interfacial behavior in different solutions. The authors state that characterizing hydrophobicity in these buffers "provides key insights into the surface charge of the graphitized/metallized materials."
Expert Perspective
Practical Takeaways
Use the analysis model that performed reliably on LIG in this workflow
The authors report that preliminary Young–Laplace (axisymmetric) fitting showed significant errors (up to 60% for the same sample tested multiple times sequentially), and therefore used the polynomial (non-axisymmetric drop) approach throughout for contact-angle calculations.
Why non-axisymmetric fitting was used on this surface
The paper notes that the LIG "surface chemistry and feature size are highly variable" and that polyimide films "undergo deformation during the graphitization process." The authors state that preliminary Young–Laplace fitting showed significant errors for the LIG surface, which is why the polynomial (non-axisymmetric) method was used for every reported value. The reported values are static sessile drop contact angles.
Fabrication batch structure influenced hydrophobicity consistency
The study reports markedly different contact-angle variation for 36 electrodes fabricated in a single day versus splitting fabrication into multiple batches with laser downtime, and highlights maintenance and operational factors (e.g., lens cleaning, operational frequency, batch size) as protocol controls.
Buffer chemistry changed measured wettability
HEPES, MES, and Tris produced significantly lower contact angles on non-modified LIG than DI, and the authors interpret these shifts in the context of surfactant-like behavior and interfacial effects.
Metallization altered surface wettability
Nanoplatinum metallization increased reported contact angles (78 ± 4° in DI and isotonic carbonate buffer) and shifted contact angles in HEPES/MES/Tris relative to non-modified LIG.
Contact angle was used alongside electrochemical screening for batch-variation assessment
The authors characterize LIG using goniometry together with electrochemical tests (OCP and CV) as part of the overall analysis of batch-to-batch variation for electrochemical sensing applications.
Frequently Asked Questions
What did the DROPOMETER-M measure in this study?
The authors used a Droplet lab DROPOMETER-M to measure static sessile drop contact angles of 2 µL droplets on the working area of bare LIG and nanoplatinum metallized LIG (nPt-LIG) electrodes. Liquids included DI water, MES, Tris, HEPES and 2× isotonic bicarbonate buffer, and angles were calculated with the polynomial (non-axisymmetric drop) method because preliminary Young–Laplace fitting showed significant errors on the LIG surface.
What contact angles did the paper report?
Bare LIG averaged 58.6 ± 1.4° in DI water and 59.3 ± 2.6° in 2× isotonic buffer, which the authors interpret as a hydrophilic surface, while HEPES, MES and Tris gave significantly lower angles. After nanoplatinum metallization the angle in DI and isotonic buffer rose to 78 ± 4°, and the three biological buffers gave similar angles of 63 ± 2°.
What do the contact angle results say about batch-to-batch variation?
The authors report that contact angle varied by less than 5% within batches for bare LIG in DI and isotonic bicarbonate, while the type of test liquid had a significant effect. When 36 electrodes were made in a single day the variation exceeded 30%, and the authors point to laser maintenance, operational frequency and batch size as control factors, noting that further work is needed to identify the source.