Optically Sensitive and Magnetically Identifiable Supraparticles as Indicators of Surface Abrasion

Abstract

Identifying and ensuring the integrity of products plays an important role in today's globalized world. Miniaturized information taggants in the packaging surface are therefore required to monitor the product itself instead of applying external labels. Ideally, multiple types of information are stored in such additives. In this work, micrometer-sized core−shell particles (supraparticles) were developed to provide material surfaces with both an identifier and a surface abrasion indication functionality. The core of the supraparticles contains iron oxide nanoparticles that allow identification of the surface with a spectral magnetic code resolved by magnetic particle spectroscopy. The fluorescent silica nanoparticles in the supraparticle shell can be abraded by mechanical stress and resolved by fluorescence spectroscopy. This provides information about the mechanical integrity of the system. The application as surfaces, that contain several types of information in one supraparticle, was demonstrated here by incorporating such bifunctional supraparticles as additives in a surface coating.

Spray‐Dried Photonic Balls with a Disordered/Ordered Hybrid Structure for Shear‐Stress Indication

“…[ 31 ] Thereby, the high order on the surface is interrupted by indentations (Figure S2c, Supporting Information). In order to form spherical supraparticles in general, which is a necessary but not sufficient condition to achieve photonic balls, the addition of a surface functionalization (like amino silanes on the silica nanoparticle surface [ 4 ] ) or a salt (such as CaCl 2 [ 3 ] ) is suggested in literature. These modifications slightly destabilize the nanoparticle dispersion, which avoids the formation of a crust at the outermost layers of the droplet that forms during spray‐drying.…”

“…Regarding the spray-dryer device parameters such as feed rate, temperature, flying speed (aspirator), and nozzle-type, there are already several studies showing their influence on the sphericity of the resulting supraparticles. [3,4,9,26,33] Based on these reports, the ideal parameters were selected as following: inlet temperature of 140 °C (resulting in an outlet temperature of around 80 °C), aspirator power at 75%, ultrasonic nozzle power at 5 W, vacuum at −30 mbar, 2 mm tube, and pump rate at 15%. Only if all parameters are optimized in a way as detailed in the Experimental Section, ultimately spray-dried photonic balls with the desired structure can be obtained.…”

“…These photonic shearstress indicators may find application as mechanical indicators in 3D printing or may allow the creation of smart surfaces. [3][4][5]…”

“…[ 2 ] It has recently been shown that optical supraparticles, i.e., particles consisting of organic dye‐carrying nanoparticles, can reliably detect shear stress by an optical signal response. [ 3–6 ] However, the use of organic molecules as optical probes brings along disadvantages, such as chemical instability (e.g., photo‐bleaching) and cross‐sensitivities toward other environmental influences such as temperature or humidity. [ 7 ] This is why the use of materials providing their color not through molecular chemistry (as with pigments and organic dyes) but through their physical structure and thus, a color response only to mechanical triggers, would be favorable.…”

Recording Temperature with Magnetic Supraparticles

“…MPS was reported to be a promising tool for magnetic signals detection in a spectrally resolved manner out of materials in (milli)seconds [27,28] using geometrically customizable sensors that can be utilized by untrained personnel. [29] Furthermore, a self-referenced signal detection permits us to obtain reliable information independent of external influences, such as readout sensitivity or the presence of diamagnetic or paramagnetic materials.…”