Counterfeiting can be a high-tech crime that necessitates high-tech solutions; now, researchers have produced a nontoxic luminescent security ink that could help in the fight against increasingly sophisticated counterfeiting schemes. This research is presented in the journal Advanced Photonics Research.
Every day consumers, companies, and governments are directly impacted by increased amounts of counterfeiting, and it can affect a wide range of goods and products. From banknotes, official documentation, and consumer electronics to medicine, health records, and medical devices, counterfeit items can significantly impact people’s lives and even risk their health.
Since the start of the Covid-19 pandemic, there have been numerous issues with counterfeiting, including the illegal supply and trade of fake N95 medical face-masks to bogus health and vaccination certificates. All of these can endanger the lives of health workers and the general population by doing nothing to protect against the spread of the SARS-Cov-2 virus.
Furthermore, the counterfeiting of other important documentation such as passports, ID cards, and educational qualifications can undermine both the integrity of civil society as well as having national and international security issues. Counterfeiters are also becoming more advanced when forging banknotes and currency, which has an impact on the economy.
(a,b) Cross-sectional SEM and c,d) 3D AFM images of the PVDF/Na[Eu(tta)4] (left column) and PVDF/[Bmim][Eu(tta)4] composites (right column), respectively. Image Credit: Correia, D.M, Advanced Photonics Research
Advancing Luminescent Inks
Therefore, as counterfeiters are consistently developing new methods anticounterfeiting measures must remain ahead of the curve. Luminescent inks have been an attractive development for some time in this area due to their ability to spontaneously emit light without the need for a heat source.
To apply luminescent inks to an authentic product, document, or article for security functionality requires a printing process, and as such the inks must demonstrate a series of key features: high stability, capacity to disperse luminescent nanomaterials, be cost-effective, and the ability to print on a diverse range of different surfaces.
However, most of the materials conventionally used in these inks can be generally unstable and toxic. The team led by Veronica de Zea Bermudez, professor of Materials Chemistry at the University Trás-os-Montes and Alto Douro, Portugal, have thus indicated that their luminescent ink is both stable and non-toxic: “we present the production of a nontoxic luminescent security ink with high photo-, thermal, and chemical stability, and strong red emission upon excitation with a commercial LED,” Bermudez stated.
Therefore, the inks would be theoretically safe for applying to medical equipment including face-masks and can be exposed to varying intensities of light which is advantageous when scanning the inks for optical authentication using both white light and 365 nm LED lights.
Poly(Vinylidene Fluoride)-Based Advantages
To achieve a low-cost and eco-friendly ink that was stable enough for printing, the team synthesized an amalgam with a base of poly(vinylidene fluoride) mixed with a homemade luminescent ionic fluid. For comparison purposes, the team also used ink which only incorporated the homemade solution.
The results of the experiment demonstrated exciting potential for the poly(vinylidene fluoride)-based ink, which exhibited the potential to expand the range of anti-counterfeiting applications using anti-counterfeiting inks.
Part of this is owing to a technological advantage that the poly(vinylidene fluoride)-based ink has, which is the ability to be modified and tuned for specific applications. “While the production of PVDF copolymers is well known, the possibility of changing the IL cation and anion chemical composition offers a wide range of possibilities,” says Bermudez.
Therefore, these inks have two significant advantages: 1. They avoid sedimentation and non-homogeneity as they do not contain additional emitting micro/nanoparticles; 2. The volatility is reduced to zero as a result of the presence of IL.
What this means in simple terms is that these poly(vinylidene fluoride)-based inks are well-suited for the rapid preparation of high-resolution, complex designs via ink-jet printing methods. This makes them cost-effective and highly stable throughout the entire printing process and reproducible in continuous or drop-on-demand processes.
The team also tested the inks when exposed to various wet solutions including ethanol, which could potentially decay or remove the ink. However, the poly(vinylidene fluoride)-based ink showed no changes in luminescence intensity when exposed to ethanol.
Moreover, the pattern or design that the ink was printed in also remained fully intact. This is a noteworthy development for protecting and authenticating medical equipment and devices that may be routinely exposed to disinfectant sprays or liquids that contain ethanol.
The researchers did suggest that additional work can be done to fully explore the tuning of the chemical-physical properties of the inks, which could offer even more application potential in the future.
a) Digital images of the PVDF/[Bmim][Eu(tta)4] film taken before and after the chemical exposure under 365 nm UV light, at different ethanol immersion times (30–90 min). b) Optical authentication test of a N95 brand personal protection mask by means of a screen-printed luminescent tag based on PVDF/[Bmim][Eu(tta)4] security ink under exposure to white light (left) and to a 365 nm LED (right). Image Credit: Correia, D.M, Advanced Photonics Research
They also stated that in future developments the emitter concentration could be reduced to the minimum level as to “not jeopardize the luminescence intensity.”
This study represents clear progress in the increasingly challenging field of producing anti-counterfeiting inks, and opens up new application potentials as a result of the unique and advantageous characteristics of poly(vinylidene fluoride)-based ink.
Correia, D.M., Polícia, R., Pereira, N., Rial Tubio, C., Cardoso, M., Botelho, G., Ferreira, R.A.S., Lanceros-Méndez, S. and de Zea Bermudez, V. (2021), Luminescent Poly(vinylidene fluoride)-Based Inks for Anticounterfeiting Applications. Adv. Photonics Res. 2100151. https://onlinelibrary.wiley.com/doi/10.1002/adpr.202100151