Supraparticles with a Magnetic Fingerprint Readable by Magnetic Particle Spectroscopy: An Alternative beyond Optical Tracers

Abstract

Marking and identification of materials is becoming increasingly important due to complex global resource and supply chains. Luminescent particle‐based markers have come to the forefront due to their small dimensions and their ability to be integrated in diverse materials. However, light‐absorbing materials can hardly be marked by these particles, thus leading to insufficient recycling rates of, e.g., black plastics. In this work, microparticles with a unique magnetic fingerprint are tailored by modification of their nanoparticle building blocks. This fingerprint tailoring is achieved either by combination of magnetic building blocks with nonmagnetic ones in the supraparticles or, alternatively, by surface modification of the building blocks. An easy‐to‐use device, based on the principle of magnetic particle spectroscopy (MPS), is established to resolve the magnetic fingerprint information. This facilitates the employment of magnetic supraparticles as markers for product tracking and identification. As a proof of concept, it is shown that such particles enable the marking of black plastic.

A Single Magnetic Particle with Nearly Unlimited Encoding Options

“…[21,22] In 2019, an approach to achieve six distinguishable magnetic fingerprints, by utilizing one magnetic nanoparticle type, was reported by our group. [23] Very recently, 29 different magnetic compositions were decoded by an automated decoding algorithm. [24] We understand the fingerprint of magnetic materials as their intrinsic signature, while the deliberate adjustment thereof should be denoted as magnetic codes.…”

“…[23,25] As magnetic signals can be transmitted through many materials that would not allow optical information to pass, such particles could be integrated within and not only on top of the surface of arbitrary objects, thus protecting the information against environmental harm but also against obvious detection and thus counterfeiting. [23,26] If such a magnetic particle marker could be achieved, it would equip materials with intelligence in many fields: it could further reduce the number of counterfeit products, which yield global annual damages of almost 500 billion US$ (2.5 % of global imports), [27] enable the identification and recycling of dark plastics, [23,[28][29][30] or permit the tracking-as well as monitoring-of goods and value chains, and finally could render quality control of materials and processes possible (Figure 1). [19] Although such a magnetic marker technology seems very promising, until now it is commonly accepted that too few magnetic codes are resolvable from magnetic markers, preventing research to achieve it.…”

Supraparticles for Sustainability

“…[ 215 ] In terms of SPs for recycling, only one publication from our group was found to date where SPs were described to contribute to recycling, indicating high capabilities for future contributions in this field. [ 216 ] Therein, a magnetic SP is suggested to enable sorting and identification of dark plastics. By variation of the composition, different magnetic fingerprints are resolved via magnetic particle spectroscopy ( Figure a).…”

“…(a) Reproduced with permission. [ 216 ] Copyright 2019, Wiley‐VCH GmbH & Co. KGaA. (b, [ 220 ] c) [ 221 ] Reproduced with permission.…”

Reversible magnetism switching of iron oxide nanoparticle dispersions by controlled agglomeration

“…Recent work indicated that magnetic particle spectroscopy (MPS) can sensitively detect changes induced by agglomeration of individual magnetic nanoparticles. [6][7][8] Due to the method's fast measurement speed and easily congurable measurement setup, it is potentially promising to in situ gain a better understanding of dynamically agglomerating magnetic particles in dispersion. 9 With respect to future applications, being able to precisely tailor agglomeration and thus magnetic properties of nanoparticles could be utilized to improve the efficiency of hyperthermia.…”