The tag consists of tiny magnetic DNA particles encapsulated in a silica casing and mixed with the oil.
It was tested for the barcoding of products including food grade oil (extra virgin olive oil), to verify the authenticity.
Researchers said the method is equivalent to a label that cannot be removed.
Food industry potential
Robert Grass, lecturer in the Department of Chemistry and Applied Biosciences at ETH Zurich, said that the greatest potential for the use of invisible labels is in the food industry.
Silica particles are found in ketchup and orange juice and iron oxide is permitted as a food additive E172.
To ensure that the particles can be detected in the oil the researchers magnetised the tag.
The iron oxide is responsible for the magnetic properties, while the surrounding silica matrix acts as protective barrier and confers heat stability and surface functionality, said the researchers.
DNA could be recovered from the particles upon dissolution in fluoride-containing solution and analyzed by qPCR and Sanger sequencing.
The method made it possible to detect adulteration because if the concentration of nanoparticles does not match the original value, another oil must have been added.
A proper tag must be dispersible in the final fluid but also invisible and still detectable.
The particles added at the place of origin could be extracted from the oil and analysed, enabling a definitive identification of the producer.
Tagging technologies include magnetic inks, fluorescent labels, photochromic and thermochromic inks, isotopic tracers and Raman-active components. Polypeptides and nucleic acids have been used as tags.
Chromatographic and spectroscopic techniques are currently used to gain insight into the modifications involved but results are often unsatisfactory since it is not always possible to discriminate components added/substituted, said the study.
DNA analytics, magneticseparation and silica encapsulation can be combined to get read outs at 1ppb and low-cost tracers for the marking of oil-based items.
Iron oxide nanoparticles were produced by a conventional co-precipitation method under ambient conditions.
Lab experiments showed that the tags dispersed well in the oil and did not show visual changes, they also remained stable when heated and came through an accelerated ageing trial (65°C for 35 days, equivalent to storage at real time for two years), without substantial losses.
Source: ACS Nano
Online ahead of print, DOI: 10.1021/nn4063853
“Magnetically Recoverable, Thermostable, Hydrophobic DNA/Silica Encapsulates and Their Application as Invisible Oil Tags”
Authors: Michela Puddu, Daniela Paunescu, Wendelin J. Stark, and Robert N. Grass