Product Milestone: Towards Low‑Input 2D Proteomics: 3D‑Printed Immobilized pH Gradient (IPG) Carbon Microbead Arrays for First‑Dimension Isoelectric Focusing
- 6 days ago
- 5 min read
Proteomics keeps pushing toward smaller and smaller samples: tiny biopsies, rare cell populations, and
now true single-cell workflows. But one part of the workflow has not kept pace nearly as well—prefractionation.
Today, many labs still rely on immobilized pH gradient (IPG) gel strips for first dimension isoelectric focusing (IEF). IPG strips work extremely well for microgram-scale proteomics. They provide stable pH gradients and high-resolution charge separation. The problem arises when you need to move those focused proteins into an orthogonal method or hyphenated platform (LC–MS, nanoLC–MS, etc.). Cutting or eluting bands from a gel is labor-intensive, and for nanogram–picogram inputs, it can result in the loss of a significant fraction of the sample.
We set out to solve that.
Why we built an alternative to IPG strips
The core challenge is simple: can we keep the charge-based separation power of IEF, but in a format that’s:
More compatible with low input samples
Easier to interface with microwells and microfluidics
Better matched to modern LC–MS based workflows
That led us to a different kind of IEF substrate: 3D-printed, immobilized-pH-gradient carbon microbead arrays, which we call NanoPak C IPG.
Instead of a continuous polyacrylamide strip, NanoPak C IPG uses individual carbon microbeads. Each bead is ampholyte-blended and carries an immobilized pH gradient. Using additive manufacturing, we print these beads into two-dimensional and three-dimensional patterns on a substrate. Each bead effectively becomes a localized IEF “spot” at a defined pH window.
How NanoPak-C-IPG works
The workflow has three main components.
1) Ampholyte blended carbon microbeads
We start with a viscous suspension of natural micrographite, a liquid crosslinker, and ampholytes (weakly acidic and basic buffering groups).
A microfluidic co nozzle generates microdroplets, which are cured at 90 °C to form solid carbon microbeads.
By adjusting synthesis conditions, we can tune bead size (tens to hundreds of micrometers) and assign distinct pH gradient profiles (e.g., pH 4–6, 6–8, 8–9).
2) 3D printed IEF microbead arrays
We prepare a printable “ink” by mixing NanoPak C IPG beads with tetradecane and a small amount of benzoyl peroxide as a crosslinker.
An off-the-shelf micro extrusion bioprinter deposits this ink into programmed 2D and 3D patterns on a substrate.
UV curing locks the beads together and to the substrate, giving us mechanically robust 1D chains and 2D/3D arrays with defined spacing and geometry.
3) IEF prefractionation and LC analysis
The printed array is mounted in a custom IEF holder with hydration channels and electrodes.
In an applied electric field, proteins migrate and focus on the beads at pH values that match their isoelectric points.
Individual beads (each representing a specific pH window) are aspirated into microwells, proteins are eluted with T PBS, and the eluates are injected onto all carbon NanoPak C RP HPLC columns for second dimension separation and detection at 280 nm.
In other words, we’ve turned the IPG strip into a printed, bead-based IEF microarray that interfaces directly with microwells and LC.
What we tested: a three-protein model system
For this first white paper, we focused on a simple, interpretable system: a three-protein mixture in which each protein falls within a different pI range.
Proteins: phycocyanin, hemoglobin, cytochrome c
Known pI ranges:
Phycocyanin: pI 4–5
Hemoglobin: pI 7–8
Cytochrome c: pI 8–9
We printed arrays using NanoPak C IPG beads covering three pH windows:
pH 4–6
pH 6–8
pH 8–9
Bead sizes were 40 µm and 100 µm, and we worked at low total protein loads (around 1 ppm, with sample volumes of 1–10 µL depending on bead size).
Key results
From a practical lab perspective, three findings stand out.
1) The beads behave as local IEF capture sites.
We see pI-directed fractionation: each protein is captured on beads corresponding to its expected pH window, then recovered and resolved downstream by RP HPLC.
2) High extraction efficiencies at small volumes.
Under the conditions tested:
100 µm beads achieved >90% extraction efficiency.
40 µm beads achieved >85% extraction efficiency.
Here, “extraction efficiency” is defined as the fraction of loaded protein recovered in the eluted and chromatographically detected fractions.
3) Open format for low-input workflows.
The device retains a microwell-like form factor and an open configuration. That makes it easier to interface with single-cell isolation formats, small tissue biopsies, or nanopipette-based sampling compared with enclosed microfluidic channels.
Taken together, these data support the idea that NanoPak C IPG arrays can perform effective first-dimension IEF prefractionation at low sample amounts, while aligning naturally with microwell- and LC-based workflows.
Where this fits in the proteomics landscape
We do not view NanoPak C IPG as a universal replacement for IPG strips. IPG gels are mature, well understood, and excellent for many bulk proteomics applications.
Instead, NanoPak C IPG is designed for situations where:
Sample is scarce (nanogram–picogram levels, single-cell or near-single-cell).
Integration with microwell plates, microfluidic isolation, or custom geometries matters.
A direct hand-off from IEF to LC on all carbon media is attractive (e.g., for certain bottom-up workflows).
Because the microbeads and printing process are tunable, we can envision arrays optimized for specific pH ranges, capacities, or device layouts—something that’s difficult to achieve with fixed commercial strips.
What’s next
The white paper focuses on proof of principle: we show that ampholyte-blended carbon microbeads can be 3D-printed into tunable IEF arrays and that they can pre-fractionate and recover proteins with high extraction efficiency under low-input conditions.
Our next steps include:
Benchmarking against commercial IPG strips under matched conditions.
Expanding to more complex protein mixtures, including post-translational modified species.
Automating microbead handling to remove the manual transfer step.
Integrating NanoPak-C-IPG and NanoPak-C All Carbon HPLC into a more seamless, low-input 2D separation platform.
Learn more
If you’d like the full technical details—including synthesis conditions, printing protocol, IEF setup, and RP HPLC methods—you can download the white paper here:
For inquiries or collaborations, or if you are interested in evaluating NanoPak-C all-carbon microbeads, please contact our technical team at inquiry@millennialscientific.com, call us at 855 388 2800, or fill out our online contact form at www.millennialscientific.com/contact.
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2. R.T. Kelly, Single-Cell Proteomics: Progress And Prospects, Molecular & Cellular Proteomics 19(11) (2020) 1739-1748.
3. K. Chandramouli, P.-Y. Qian, Proteomics: Challenges, Techniques And Possibilities To Overcome Biological Sample Complexity, Human Genomics And Proteomics : Hgp 2009 (2009)
4. J. Liu, C. Hansen, S.R. Quake, Solving The “World-To-Chip” Interface Problem With A Microfluidic Matrix, Analytical Chemistry 75(18) (2003) 4718-4723.
