The Glass Column That Separates a Colour and Reads Its Fingerprint at the Same Time
A green candy coating is usually two dyes pretending to be one. Telling them apart normally means an HPLC-MS lab. This pocket-sized glass column does the separation and the identification — with light.
Colour sells food, and where natural colour fades, colorants go in — sometimes the cheap, illegal, industrial kind swapped for an approved food dye. Catching that adulteration means two hard jobs: separating the mixed colorants and identifying each one. The standard tools — HPLC, mass spectrometry, NMR — do it well but are expensive, bulky and lab-bound. Surface-enhanced Raman scattering (SERS) can fingerprint a dye cheaply and portably, but on its own it cannot untangle a mixture: overlapping spectra blur together. A 2026 study in the Microchemical Journal from Tamkang University fuses the two — putting the separation and the SERS onto one alumina column.
The Obstacle
SERS is a superb fingerprinting tool, but a real food colour is often a blend, and blended spectra are ambiguous — a green is yellow-plus-blue, a brown is several dyes at once. To resolve a mixture you need a separation step first, which usually means a whole chromatography instrument bolted in front of the Raman. Prior “SERS + separation” schemes needed HPLC hardware and major re-engineering of the SERS process. The unmet need: a single, cheap device that separates the colorants and provides the SERS enhancement in place, so each component can be read as it resolves.
The Innovation
The trick is to make alumina powder do two jobs at once. The team modifies alumina sequentially: first with a fluorine-free water-repellent (WRP) on a surfactant bilayer to make it lipophilic — turning it into a reversed-phase stationary phase — and then impregnates it with citrate-capped silver nanoparticles to make it a native SERS sensor. Packed into a disposable glass Pasteur pipette, this dual-function powder becomes a VAD-SERS column: load a colour at the top, elute with a green water/acetone mobile phase, and the components migrate to different heights — each visible band then read in situ by SERS on the RAMaker (532 nm). Because you can see the colours and fingerprint them on the same column, the authors name it Visualization-Augmented Deconvolutional SERS (VAD-SERS). (Chen, Yu, Yu, Wang & Huang; Microchemical Journal, 2026, 224, 117923; DOI 10.1016/j.microc.2026.117923.)
Key Results
The column proves itself four ways: the modified alumina really is a SERS sensor, it separates and reads a dye mixture, it catches adulteration, and it deconvolutes the colours of real candy.
The SERS Stationary Phase Works
A probe molecule gives a strong SERS signal only once the alumina is fully modified — bare alumina and the lipophilic-but-silver-free powder stay quiet, while the silver-nanoparticle-loaded stationary phase lights up. The dual-function powder is genuinely a native SERS sensor, not just a separation medium.
Separating a Three-Dye Mixture, Reading Each Band
A 1:1:1 mixture of three industrial dyes (Red HS, Yellow HGS, blue ASMQ) loaded onto one column resolved into distinct colour bands at different migration distances; every band was identified both visually and by SERS. Even a green band from overlapping yellow and blue could be deconvoluted as the sum of Yellow HGS and ASMQ.
Catching Adulteration
In a mimic of a common fraud — spiking a legal food colorant with a cheaper industrial dye of similar colour — each spiked solution resolved into two bands on the column, directly evidencing the adulteration, and the adulterant was identified by scanning its band.
Deconvoluting a Green (and Brown) Candy
Analysing commercial candies, VAD-SERS split the green coating into Tartrazine + Brilliant Blue and the brown coating into Allura Red + Tartrazine + Brilliant Blue — unambiguous component identification that solution-phase SERS alone could not deliver. It even detected Tartrazine down to ~0.2 µg on-column, a dye that is otherwise hard to see by SERS.
And it is cheap. A full analysis used ≤1 mL of water-based mobile phase, the columns stayed usable for at least six weeks of storage, and a preliminary preparative run recovered over 80% of a loaded dye on a reusable column.
Why ProTrusTech Is Featuring This Research
The identification half of VAD-SERS is Raman/SERS on the RAMaker — a Raman microscope with a 532 nm laser reading each separated band directly on the glass column, backed by the platform’s 355/532 nm multi-wavelength capability. The authors also point to Raman mapping as the route to extend the method to colourless targets and preparative scale — squarely in the RAMaker’s wheelhouse. It is a creative demonstration of Raman moving into the separation, not just after it.
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Why This Matters
Food-colour regulation is tightening while cheap analysis tools lag. A single, disposable glass column that separates and SERS-fingerprints colorants — for pennies of solvent, no HPLC, no MS — is a realistic field/QC tool for spotting illegal dye adulteration. The underlying idea — a stationary phase that is also the SERS substrate — is general, and the authors flag extensions to preparative separation and to colourless analytes via Raman mapping. It joins ProTrusTech’s food-safety SERS features.
What’s Next
- Quantitative validation (calibration, recovery, LODs) across a broader colorant panel.
- Preparative-scale columns and reuse/recycling of the SERS stationary phase.
- Extending to colourless analytes via Raman mapping along the column.
Working on SERS assays, food-safety screening, or separation-coupled Raman — and need a multi-wavelength Raman microscope and mapping? Get in touch with our team.
Key Takeaways
- VAD-SERS makes an alumina column that is both a reversed-phase separation medium and a native SERS sensor — separation + identification in one cheap glass column.
- It resolves and identifies mixed industrial dyes, flags adulteration (each spiked colour splits into two bands), and deconvolutes real candy greens and browns into their component dyes (Tartrazine to ~0.2 µg on-column).
- Cheap (≤1 mL mobile phase), storable (≥6 weeks), reusable (>80% preparative recovery); identification is Raman/SERS on the RAMaker (532 nm; 355/532 multi-wavelength).
