Abstract
Metallic nanoparticles with different physical properties have been screen printed as authentication tags on different types of paper. Gold and silver nanoparticles show unique optical signatures, including sharp emission bandwidths and long lifetimes of the printed label, even under accelerated weathering conditions. Magnetic nanoparticles show distinct physical signals that depend on the size of the nanoparticle itself. They were also screen printed on different substrates and their magnetic signals read out using a magnetic pattern recognition sensor and a vibrating sample magnetometer. The novelty of our work lies in the demonstration that the combination of nanomaterials with optical and magnetic properties on the same printed support is possible, and the resulting combined signals can be used to obtain a user-configurable label, providing a high degree of security in anti-counterfeiting applications using simple commercially-available sensors.
Highlights
According to the International Chamber of Commerce the impact of counterfeiting is estimated at 5%–7% of world trade, worth an estimated $600 billion a year [1]
The good hydrodynamic stability of the as-prepared magnetite nanoparticles can be appreciated in the optical image of their colloidal dispersion in TEG given in figure 1(A)
The highresolution TEM photograph of figure 1(C) allows to appreciate the high crystallinity of the nanoparticles, with lattice fringe spacing of 2.96 Å, very close to the d value for cubic Fe3O4 [220] planes (2.97 Å) [35], and figure 1(D) shows the particle-size distribution obtained from TEM observations, which is centered at 7.9 ± 1.4 nm
Summary
According to the International Chamber of Commerce the impact of counterfeiting is estimated at 5%–7% of world trade, worth an estimated $600 billion a year [1]. Besides the above described optical signaling nanostructured materials, magnetic nanoparticles are used as tags to provide characteristic magnetic signatures in different patterns that are readable with commercially-available giant magnetoresistive sensors Their use as anti-counterfeiting signatures able to be deposited using ink jet printers was postulated more than ten years ago [21]. We have chosen single-phase, spherical nanoparticles without (or with minimal) functionalization (gold, silver and magnetite) and applied them on different paper supports by a standard screen printing method The combination of these nanoparticles can provide optical and magnetic signals on the same tagging act, i.e., multiple tags can be screen printed on the same spot, and their responses can be independently detected. Other aspects relevant to potential application such as the influence of the paper support and the ability of the labels to withstand accelerate weathering conditions after tagging have been studied
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