Scientists design portable fluorescent sensor for vitamin B12 food testing

Chinese researchers have developed a new fluorescent sensor that could present a simpler alternative to measuring vitamin B12 in food through laboratory tests. The scientists at Liaocheng University propose that this new method could be adapted to a simple paper strip or cotton swab. 

The team notes that the most common measuring techniques, including chromatography and electrochemical analysis, often require complex instruments, lengthy sample handling, or precise conditions. Many fluorescence probes also remain tied to laboratory spectrometers.

To streamline the process, they developed boron- and nitrogen-co-doped carbon dots (B, N-CDs) that emit bright blue fluorescence under ultraviolet light but become significantly dimmer in the presence of vitamin B12.

They transferred this “sensing chemistry” from a liquid assay onto filter-paper strips and a specially designed cotton-swab sensor. These two formats are intended to make the detection step faster, cheaper, and easier to use outside conventional instrument-heavy workflows, note the study authors.

“The work shows how carbon-dot fluorescence can be adapted into visually readable portable sensors without sacrificing sensitivity or selectivity,” the team highlights. “The current real-food workflow still involves laboratory sample pretreatment before measurement, so further simplification will be important for truly field-ready testing.”

The authors also outline practical next steps, including replacing the laboratory ultraviolet (UV) lamp with a compact battery-powered UV-LED and adding smartphone-based image analysis for automated quantification.

Designing a fluorescent signal

Given vitamin B12’s essential role in maintaining health, there is a significant need to develop simple, sensitive, and rapid analytical methods. Currently, common analytical methods include chromatography and electrochemical voltammetry, highlight the study authors.

However, they flag limitations for chromatography, such as requiring complex instruments, cumbersome pretreatment, and long analysis time. Moreover, electrochemical methods are prone to problems such as electrode contamination and insufficient selectivity.

In their paper published in Biomedical Analysis, they explain that, when vitamin B12 is present, the nutrient binds directly to the carbon dots, dimming their blue light in a process that they call static fluorescence quenching.

Given vitamin B12’s essential role in maintaining health, there is a significant need to develop simple, sensitive, and rapid analytical methods.In laboratory tests, the sensor measured vitamin B12 across different concentrations — detecting levels as low as 0.02 μM — and remained virtually unaffected by other B vitamins, amino acids, sugars, or common biomolecules.

Several chemical analyses confirmed that the light dims in direct proportion to the amount of vitamin B12 present, which makes the material a promising candidate for precise biochemical testing.

Transitioning to paper strips and swabs

To translate the screening method into portable formats, the team infused filter paper with B, N-CDs, and designed a cotton-swab device that delivers the fluorescent probe to a specific area during use.

The swab format was designed to combine sample collection, transfer, mixing, and signal readout in one disposable device.

When exposed to 365 nm UV light, both test formats darkened as the amount of vitamin B12 went up. For the paper strip test, measuring the ratio of green-to-blue color intensity allowed researchers to directly track vitamin B12 concentrations between 0 and 80 μM in a straight, predictable line.

When stored either at room temperature or refrigerated at 4°C, both the test strips and cotton swab sensors maintained reliable fluorescence signals and vitamin B12-sensing performance for at least 20 days.

To test the accuracy of the new method, researchers added known amounts of vitamin B12 to egg yolk and goat liver food samples. The test successfully detected nearly 100% of the added vitamin — matching the precision of high-performance liquid chromatography (HPLC) — demonstrating that real food ingredients do not disrupt its readings.

The introduction of this new screening method is particularly timely, as research by the supplement brand NOW previously revealed discrepancies between nutritional products’ vitamin B12 potency claims and their actual levels, based on a sampling of 25 different brands purchased on Amazon. Notably, 11 brands exceeded their label claim of potency, with six testing more than 120%.