In the course of globalization, tracking of material supply chains and product protection against counterfeiting is a topic of increasing relevance. The labeling of raw materials or product components with encoded microstructures may therefore ensure their reliable and tamper-proof identification. In this work, luminescent lanthanide doped calcium fluoride nanoparticles with characteristic optical properties are assembled to micrometer-sized supraparticles via spray-drying. By wise selection of these nanoscale building blocks, it is possible to create spectrally encoded microparticles. Their code relies on the relative emission intensities of the different luminescent nanoparticles and their concentration ratios within the supraparticle. Due to this strategy, we offer a nanoscale modular approach for an easily adjustable and simple creation of ratiometric luminescence-encoded microparticles for the tamper-proof marking of objects.
Communicating objects are demanded for product security and the concepts of a circular economy or the Internet of Nano Things. Smart additives in the form of particles can be the key to equip objects with the desired materials intelligence as their miniaturized size improves applicability and security. Beyond their proposed identification by optical signals, magnetic signals deriving from magnetic particles can hypothetically be used for identification but are to date only resolved roughly. Herein, a magnetic particle‐based toolbox is reported, that provides more than 77 billion (77 × 109) different magnetic codes, adjustable in one single particle, that can be read out unambiguously, easily, and quickly. The key towards achieving the vast code variety is a hierarchical supraparticle design that is inspired by music: similarly to how the line‐up variation of a musical ensemble yields distinguishable overtones, the variation of the supraparticle composition alters their magnetic overtones. By minimizing magnetic interactions, customizable signals are spectrally decoded by the simple method of magnetic particle spectroscopy. A large number of chemically adjustable magnetic codes and the possibility of their remote, contactless detection from within materials is a breakthrough for unexploited labeling applications and pave the way towards materials intelligence.
Product identification tags are of great importance in a globalized world with increasingly complex trading routes and networks. Beyond currently used coding strategies, such as QR codes, higher data density, flexible application as well as miniaturization and readout indication are longed for in the next generation of security tags. In this work, micron‐sized supraparticles (SPs) with encoded information (ID) are produced that not only exhibit multiple initially covert identification levels but are also irreversibly marked as “read” upon readout. To achieve this, lanthanide doped CaF2 nanoparticles are assembled in various quantity‐weighted ratios via spray‐drying in presence of a broad‐spectrum stealth fluorophore (StFl), yielding covert spectrally encoded ID‐SPs. Using these as pigments, QR codes, initially dominated by the green fluorescence of the StFl, could be generated. Upon thermal energy input, these particle‐based tags irreversibly switch to an activated state revealing not only multiple luminescent colors but also spectral IDs. This strategy provides the next generation of material‐based security tags with a high data density and security level that switch information upon readout and can be, therefore, used as seal of quality.
Many surfaces of man-made objects are equipped with a coating. The coating fulfills specific functions, for instance, as easy-to-clean, [1] scratch-resistant, [2] antireflexive, [3] or antimicrobial [4] agent. These functional properties are usually achieved via molecular building blocks, by nanoparticulate coating additives or by imprinting a surface texture. A certain degree of "smartness" can also be achieved by combining several additives [5,6] which may turn a surface into a gas sensor, [7] a corrosion protection layer, [8] or a self-healing layer. [9] Although there have always been solutions to identify deformations in components, such as in metals [10] or polymer parts, [11] the detection of damages within a surface coating which is only a few micrometers thick still remains a challenge. [12] Such a "scratch-detecting" surface indicator must be cheap, easy to manufacture, easy to detect and should be applicable to any type of surface. Some additives for bulk materials have already been presented which are able to detect scratches and repair them directly. [13] A disadvantage of these systems is, however, that they only do work in a bulk material and not in a coating of a few microns thickness. In this study, we report on shear stress indicators in the form of so-called supraparticles that can be used as damage detectors in thin coatings. These indicator supraparticles are micron-sized, hierarchically structured particles and are composed of nanoparticles. The great advantage of such supraparticles is that a number of very different properties can be combined by assembling different nanoparticle building blocks which carry specific attributes (e.g., magnetism, fluorescence, catalytic activity, etc.). [14] Forced assembly of nanoparticles can be achieved by spray-drying. This process is well-known and well established, for instance, in the pharmaceutical or food industry, to obtain dry powder products (such as granular drugs or instant coffee). [15] Complex architectures can be achieved by repeating this process: In a first spray-drying cycle, supraparticles can be formed from a nanoparticle dispersion. Within a second spray-drying cycle, the supraparticles resulting from the first spray-drying cycle can be coated with other nanoparticles to ultimately obtain core-shell supraparticles.
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