Dual-Mode Encoded Magnetic Composite Microsphere Based on Fluorescence Reporters and Raman Probes as Covert Tag for Anticounterfeiting Applications

Raman encoding for security labels: a review

Owing to its excellent multiplexing ability, high stability, and molecular fingerprint characteristics, Raman encoding has been widely used in security labels for medical safety, jewelry identification and food supervision. Various growing demands have promoted the anti-counterfeiting mode of security labels based on Raman encoding from the classic one that relies on specific patterns to the more secure one that depends on random patterns. As impressive progress has been made in Raman encoding for security labels in recent years, this review attempts to comprehensively cover security labels based on Raman encoding, from label preparation to image verification. For the labels with different anti-counterfeiting modes, the different basic elements they need are summarized, and the role of Raman encoding in different modes is introduced. In addition, security labels based on Raman encoding still have some drawbacks. Therefore, suggestions on how to improve its anti-counterfeiting performance are also discussed, as well as future challenges and prospects.

Communicating Supraparticles to Enable Perceptual, Information-Providing Matter

Materials are the fundament of the physical world, whereas information and its exchange are the centerpieces of the digital world. Their fruitful synergy offers countless opportunities for realizing desired digital transformation processes in the physical world of materials. Yet, to date, a perfect connection between these worlds is missing. From the perspective, this can be achieved by overcoming the paradigm of considering materials as passive objects and turning them into perceptual, information-providing matter. This matter is capable of communicating associated digitally stored information, for example, its origin, fate, and material type as well as its intactness on demand. Herein, the concept of realizing perceptual, information-providing matter by integrating customizable (sub-)micrometer-sized communicating supraparticles (CSPs) is presented. They are assembled from individual nanoparticulate and/or (macro)molecular building blocks with spectrally differentiable signals that are either robust or stimuli-susceptible. Their combination yields functional signal characteristics that provide an identification signature and one or multiple stimuli-recorder features. This enables CSPs to communicate associated digital information on the tagged material and its encountered stimuli histories upon signal readout anywhere across its life cycle. Ultimately, CSPs link the materials and digital worlds with numerous use cases thereof, in particular fostering the transition into an age of sustainability.

Triple-Mode upconversion emission for dynamic multicolor luminescent anti-Counterfeiting

Lanthanide (Ln³⁺) luminescent materials play a crucial role in information security and data storage owing to their excellent and unique optical properties. The advances in dynamic colorful luminescent anti-counterfeiting nanomaterials enable the generation of a high-level information encryption. In this work, a superior thermal, optical wavelength and excitation power triple-mode stimuli-responsive emission color modulation is demonstrated in a lanthanide-doped nanostructured luminescent material. The plentiful emission colors are manipulated by modulating the composition of a fluoride core-shell nanostructure with different Ln³⁺ at different doping concentrations. The nanomaterials display remarkable excitation wavelength/power-dependent color change, along with temperature-dependent color variation in the range from 298 K to 437 K, with a good relative sensitivity S_r of 1.1387% K^-1 at 398 K. The universal optical modulation, combined with the excellent optical and structural stability of the luminescent nanoparticles, renders many advantages for the anti-counterfeiting application. This work explores a universal strategy for the manipulation of triple-mode stimuli-responsive dynamic luminescence and demonstrates its good potential for anti-counterfeiting application.

Exploring the generality of ligands for Silica-Encapsulated nanoclusters as SERS labels

The surface enhanced Raman scattering (SERS) reporters are rather limited, and the Raman peaks still overlap in varying degrees, making SERS multiplex coding a critical bottleneck in the exploration of SERS nanotechnology. Herein, we design a general strategy to expand the SERS probe scope to 26 probes of six types, which can be further expanded within a limited range, with stable performance and structure. By constructing (Au-aggregate)@Ag@silica and (Au-aggregate)@silica nanocomposites, we develop optimal enhancement strategies for each Raman molecules. Mixed signal-ligand SERS probes improve the complexity of Raman spectra and expand the coding capacity. By integrating the strategies, SERS inks are produced and applied in anti-counterfeiting. With these improvements, this work breaks the constrains of probe selection, bringing SERS one step closer to the sensor or anti-counterfeiting application.

Portable, multi-modal Raman and fluorescence spectroscopic platform for point-of-care applications

SIGNIFICANCE

Point-of-care (POC) platforms utilizing optical biosensing strategies can achieve on-site detection of biomarkers to improve the quality of care for patients in low-resource settings.

AIM

We aimed to develop a portable, multi-modal spectroscopic platform capable of performing Raman and fluorescence measurements from a single sample site.

APPROACH

We designed the spectroscopic platform in OpticStudio using commercial optical components and built the system on a portable optical breadboard. Two excitation and collection arms were utilized to detect the two optical signals. The multi-modal functionality was validated using ratiometric Raman/fluorescence samples, and the potential utility was demonstrated using a model bioassay for cardiac troponin I.

RESULTS

The designed spectroscopic platform achieved a spectral resolution of 0.67 ± 0.2 nm across the Raman detection range (660 to 770 nm). The ratiometric Raman/fluorescence samples demonstrated no crosstalk between the two detector arms across a gradient of high molar concentrations. Testing of the model bioassay response showed that the integrated approach improved the linearity of the calibration curve from (R² = 0.977) for the Raman only and (R² = 0.972) for the fluorescence only to (R2 = 0.988) for the multi-modal approach.

CONCLUSION

These findings demonstrate the potential impact of a multi-modal POC spectroscopic platform to improve the sensitivity and robustness necessary for biomarker detection.

Multilevel Anti-Counterfeiting Based on Covert Structural Features Embedded in Femtosecond-Laser-Treated Gold Nanocluster/Graphene Hybrid Layer

The conventional nanoscale anti-counterfeiting scheme, exhibiting limited encoding capacity, faces growing challenges of being falsified with the advent of advanced high-resolution equipment. In this study, we propose a multilevel anti-counterfeiting device based on a femtosecond laser (fs-laser) treated plasmonic gold nanocluster/graphene (AuNC/Gr) hybrid structure integrated with a resonant cavity. The covert structural features encoded in random colored patterns, optical reflection spectra, and Raman spectra constitute three classes of anti-counterfeiting signatures, which originate from the AuNC-covered Gr, which initiates plasmonic and thermal couplings. The attendant inverted thermal distribution is presumed to confine the structural features to the AuNC-Gr interface while leaving no detectable traces on the surface of AuNC/Gr even under advanced high-resolution equipment. Therefore, the proposed approach achieves multilevel anti-counterfeiting accomplishing physically unclonable functions in the form of random colored patterns, reflection spectra, and Raman spectra. As the first report for realizing remarkable optical modulation (i.e., random colored patterns) without any surface trace or damage via fs-laser-AuNC/Gr interaction, our study also discloses the outstanding performance of Gr in fs-laser-induced optothermoplasmonic lithography on near-percolation metal films. Simultaneously, the demonstrated fs-laser-processed plasmonic hybrid structure in conjunction with a resonant cavity is anticipated to expand the encoding capabilities for nanoscale anti-counterfeiting while avoiding the risk of being imitated because of the covert structural features.

Nanocatalyst-Enabled Physically Unclonable Functions as Smart Anticounterfeiting Tags with AI-Aided Smartphone Authentication

Counterfeiting is a worldwide issue affecting many industrial sectors, ranging from specialized technologies to retail market, such as fashion brands, pharmaceutical products, and consumer electronics. Counterfeiting is not only a huge economic burden (>$ 1 trillion losses/year), but it also represents a serious risk to human health, for example, due to the exponential increase of fake drugs and food products invading the market. Considering such a global problem, numerous anticounterfeit technologies have been recently proposed, mostly based on tags. The most advanced category, based on encryption and cryptography, is represented by physically unclonable functions (PUFs). A PUF tag is based on a unique physical object generated through chemical methods with virtually endless possible combinations, providing remarkable encoding capability. However, most methods adopted nowadays are based on expensive and complex technologies, relying on instrumental readouts, which make them not effective in real-world applications. To achieve a simple yet cryptography-based anticounterfeit method, herein we exploit a combination of nanotechnology, chemistry, and artificial intelligence (AI). Notably, we developed platinum nanocatalyst-enabled visual tags, exhibiting the properties of PUFs (encoding capability >10³⁰⁰) along with fast (1 min) ON/OFF readout and full reversibility, enabling multiple onsite authentication cycles. The development of an accurate AI-aided algorithm powers the system, allowing for smartphone-based PUF authentications.

Optically Sensitive and Magnetically Identifiable Supraparticles as Indicators of Surface Abrasion

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.

Colorful Luminescent Magnetic Supraparticles: Expanding the Applicability, Information Capacity, and Security of Micrometer-Scaled Identification Taggants by Dual-Spectral Encoding

(Sub)micrometer-scaled identification (ID) taggants enable direct identification of arbitrary goods, thereby opening up application fields based on the possibility of tracking, tracing, and anti-counterfeiting. Due to their small dimensions, these taggants can equip in principle even the smallest subcomponents or raw materials with information. To achieve the demanded applicability, the mostly used optically encoded ID taggants must be further improved. Here, micrometer-scaled supraparticles with spectrally encoded luminescent and magnetically encoded signal characteristics are reported. They are produced in a readily customizable bottom-up fabrication procedure that enables precise adjustment of luminescent and magnetic properties on multiple hierarchy levels. The incorporation of commonly used magnetic nanoparticles and fluorescent dyes, respectively, into polymer nanocomposite particles, establishes a convenient toolbox of magnetic and luminescent building blocks. The subsequent assembly of selected building blocks in the desired ratios into supraparticles grants for all the flexibility to freely adjust both signal characteristics. The obtained spectrally resolved visible luminescent and invisible magnetic ID signatures are complementary in nature, thus expanding applicability and information security compared to recently reported optical- or magnetic-encoded taggants. Additionally, the introduced ID taggant supraparticles can significantly enhance the coding capacity. Therefore, the introduced supraparticles are considered as next-generation ID taggants.

Spray-Drying and Atomic Layer Deposition: Complementary Tools toward Fully Orthogonal Control of Bulk Composition and Surface Identity of Multifunctional Supraparticles

Spray-drying is a scalable process enabling one to assemble freely chosen nanoparticles into supraparticles. Atomic layer deposition (ALD) allows for controlled thin film deposition of a vast variety of materials including exotic ones that can hardly be synthesized by wet chemical methods. The properties of coated supraparticles are defined not only by the nanoparticle material chosen and the nanostructure adjusted during spray-drying but also by surface functionalities modified by ALD, if ALD is capable of modifying not only the outer surfaces but also surfaces buried inside the porous supraparticle. Simultaneously, surface accessibility in the porous supraparticles must be ensured to make use of all functionalized surfaces. In this work, iron oxide supraparticles are utilized as a model substrate as their magnetic properties enable the use of advanced magnetic characterization methods. Detailed information about the structural evolution upon individual ALD cycles of aluminium oxide, zinc oxide and titanium dioxide are thereby revealed and confirmed by gas sorption analyses. This demonstrates a powerful and versatile approach to freely designing the functionality of future materials by combination of spray-drying and ALD.

Aggregation induced emission based active conjugated imidazole luminogens for visualization of latent fingerprints and multiple anticounterfeiting applications

Aggregation-induced emission based organic heterocyclic luminogens bearing conjugated electronic structures showed much attention due to its excellent fluorescence in aggregation state. In this communication, a novel conjugated blue light emitting imidazole molecule is synthesized by one pot multicomponent reaction route is reported for the first time. The prepared molecule exhibits a strong fluorescence in aggregation state with exceptional properties, such as high purity, inexpensive, eco-friendly, large scale production, high photostability, etc. By considering these advantages, a new fluorescence based platform has been setup for in-situ visualization of latent fingerprints and its preservation by spray method followed by Poly(vinyl alcohol) masking. A clear and well defined fluorescence fingerprint images are noticed on variety of surfaces by revealing level 1-3 ridge features upon ultraviolet 365 nm light exposure. The dual nature of binding specificity as well as excellent fluorescence properties permits the visualization of latent fingerprints for longer durations (up to 365 days) with superior contrast, high sensitivity, efficiency, selectivity and minimal background hindrance. We further fabricated unclonable invisible security ink for various printing modes on valuable goods for protection against forging. The developed labels are displaying uniform distribution of ink and exceptional stability under various atmospheric environments. The development of long preservative information using aggregation-induced emission based luminogen opens up a new avenue in advanced forensic and data security applications.

The untapped potential of magnetic nanoparticles for forensic investigations: A comprehensive review

With a growing interest in precise and sensitive diagnosis for criminal investigations, nanoparticles (NPs) have intrigued scientific minds working in the field of forensic science due to their exceptional properties. Magnetic nanoparticles (MNPs) have emerged as a powerful tool for improving forensic analysis due to their super magnetic behavior combined with smaller dimensions. MNP-based applications can benefit criminologists to solve criminal mysteries with greater precision and pace. This review highlights the different types of MNP-based applications and their developmental and implicational aspects of forensic science. It also renders insight into the future prospects of a splendid blend of nanotechnology and forensic science, leading to a better scientific analysis.

A Single Magnetic Particle with Nearly Unlimited Encoding Options

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.

Reduced Self-Aggregation and Improved Stability of Silica-Coated Fe3O4/Ag SERS-Active Nanotags Functionalized With 2-Mercaptoethanesulfonate

Nanocomposites combining magnetic and plasmonic properties are very attractive within the field of surface-enhanced Raman scattering (SERS) spectroscopy. Applications presented so far take advantage of not only the cooperation of both components but also synergy (enhanced properties), leading to multi-approach analysis. While many methods were proposed to synthesize such plasmonic-magnetic nanoparticles, the issue of their collective magnetic behavior, inducing irreversible self-aggregation, has not been addressed yet. Thus, here we present a simple and fast method to overcome this problem, employing 2-mercaptoethanesulfonate (MES) ions as both a SERS tag and primer molecules in the silica-coating process of the previously fabricated Fe3O4/Ag nanocomposite. The use of MES favored the formation of silica-coated nanomaterial comprised of well-dispersed small clusters of Fe3O4/Ag nanoparticles. Furthermore, adsorbed MES molecules provided a reliable SERS response, which was successfully detected after magnetic assembly of the Fe3O4/Ag@MES@SiO2 on the surface of the banknote. Improved chemical stability after coating with a silica layer was also found when the nanocomposite was exposed to suspension of yeast cells. This work reports on the application of 2-mercaptoethanesulfonate not only providing a photostable SERS signal due to a non-aromatic Raman reporter but also acting as a silica-coating primer and a factor responsible for a substantial reduction of the self-aggregation of the plasmonic-magnetic nanocomposite. Additionally, here obtained Fe3O4/Ag@MES@SiO2 SERS nanotags showed the potential as security labels for the authentication purposes, retaining its original SERS performance after deposition on the banknote.

The Role of Suspension Array Technology in Rapid Detection of Foodborne Pollutants: Applications and Future Challenges

Food safety is an important livelihood issue, which has always been focused attention by countries and governments all over the world. As food supply chains are becoming global, food quality control is essential for consumer protection as well as for the food industry. In recent years, a great part of food analysis is carried out using new techniques for rapid detection. As the first biochip technology that has been approved by the Food and Drug Administration (FDA), there is an increasing interest in suspension array technology (SAT) for food and environmental analysis with advantages of rapidity, high accuracy, sensitivity, and throughput. Therefore, it is important for researchers to understand the development and application of this technology in food industry. Herein, we summarized the principle and composition of SAT and its application in food safety monitoring. The utility of SAT in detection of foodborne microorganisms, residues of agricultural and veterinary drugs, genetically modified food and allergens in recent years is elaborated, and the further development direction of SAT is envisaged.

Plasmon-coupled microcavity aptasensors for visual and ultra-sensitive simultaneous detection of Staphylococcus aureus and Escherichia coli

Septicemia and bacteremia are serious infections in the bloodstream. Thus, time-saving and ultra-sensitive pathogenic bacteria detection is highly required. Herein, we constructed gold nanoparticle-modified polystyrene microspheres (Au/PS) as plasmon-coupled microcavities to realize simultaneous detection of Staphylococcus aureus and Escherichia coli based on a fluorescence and surface-enhanced Raman spectroscopy (SERS) dual-mode method. Fluorescence imaging, serving as a means for assistant validation and rapid screening, was carried out to achieve qualitative and semi-quantitative determination, which gave us visual information of the existence and distribution of the target bacteria. Meanwhile, SERS test was conducted to realize ultra-sensitive quantitative detection. The evanescent wave aroused from total internal reflection in PS microcavities coupled with the localized electromagnetic field from surface plasmons of gold nanoparticles to improve light-matter interaction synergistically, leading to an enhancement factor of 2.25 × 10¹¹ for SERS sensing. The whole measurement was carried out in a typical sandwich assay of "capture probe-target bacteria-signal probe." As a result, calibrated concentration response curves demonstrated the sensitive quantitative detection with the limit of detection (LOD) of 3 cfu/mL for S. aureus and 2 cfu/mL for E. coli. This rapid, ultra-sensitive, and visual sensing method was further developed for dual-bacteria detection in the whole blood samples.

Multiplexed SERS Barcodes for Anti-Counterfeiting

Forged signature threatens the authenticity of personal identity. Here, an effective SERS anti-counterfeiting system is designed for personal signatures. Mixed ligands improve the complexity of Raman spectra and expand the coding capacity. Fourteen distinct combinations are created from mere five ligands, and great expansion is possible with modest expansion of the ligand library. On the other hand, the (Au-aggregate)@Ag@PSPAA nanostructure significantly increases the surface-enhanced Raman scattering (SERS) intensity and stability so that excellent performance is achieved in SERS detection. By integrating these strategies, SERS inks are produced and applied in signature anti-counterfeiting. The resulting spectra are converted to barcodes that are readily detected through a smart phone APP. With these improvements, this work brings SERS one step closer toward practical applications in signature anti-counterfeiting.

Optical Nanomaterials and Enabling Technologies for High-Security-Level Anticounterfeiting

Optical nanomaterials have been widely used in anticounterfeiting applications. There have been significant developments powered by recent advances in material science, printing technologies, and the availability of smartphone-based decoding technology. Recent progress in this field is surveyed, including the availability of optical reflection, absorption, scattering, and luminescent nanoparticles. It is demonstrated that advances in the design and synthesis of lanthanide-doped upconversion nanoparticles will lead to the next generation of anticounterfeiting technologies. Their tunable optical properties and optical responses to a range of external stimuli allow high-security level information encoding. Challenges in the scale-up synthesis of nanomaterials, engineering of assessorial devices for smart-phone-based decryption, and alignment to the potential markets which will lead to new directions for research, are discussed.

Gap-enhanced Raman tags for physically unclonable anticounterfeiting labels

Anticounterfeiting labels based on physical unclonable functions (PUFs), as one of the powerful tools against counterfeiting, are easy to generate but difficult to duplicate due to inherent randomness. Gap-enhanced Raman tags (GERTs) with embedded Raman reporters show strong intensity enhancement and ultra-high photostability suitable for fast and repeated readout of PUF labels. Herein, we demonstrate a PUF label fabricated by drop-casting aqueous GERTs, high-speed read using a confocal Raman system, digitized through coarse-grained coding methods, and authenticated via pixel-by-pixel comparison. A three-dimensional encoding capacity of over 3 × 1015051 can be achieved for the labels composed of ten types of GERTs with a mapping resolution of 2500 pixels and quaternary encoding of Raman intensity levels at each pixel. Authentication experiments have ensured the robustness and security of the PUF system, and the practical viability is demonstrated. Such PUF labels could provide a potential platform to realize unbreakable anticounterfeiting.

Upconversion Nanoparticles@Carbon Dots@Meso-SiO2 Sandwiched Core-Shell Nanohybrids with Tunable Dual-Mode Luminescence for 3D Anti-Counterfeiting Barcodes

Development of advanced fluorescent materials for constructing a secure and unclonable encryption is urgently required; however, their application in anti-counterfeiting applications is a great challenge. In this work, we proposed and synthesized a new type of upconversion nanoparticles@carbon dots@meso-SiO₂ nanohybrids by integrating two fluorescent materials of lanthanide-doped NaYF₄ upconversion nanoparticles (UCNPs) and carbon dots (CDs) into mesoporous silica (mSiO₂) to produce a novel sandwichlike core-shell structure and a dual-mode fluorescence from UCNPs and CDs. By tailoring the UCNP core of different upconversion luminescence, all three kinds of dual-mode luminescent UCNPs@CDs@mSiO₂ nanohybrids exhibited typical RGB upconversion luminescence under a 980 nm laser and blue downconversion luminescence under a 365 nm UV light. Due to strong the hydrophilic nature of the nanohybrids, they can be further fabricated into environmentally benign luminescent inks for creating highly secured, fluorescent-based, three-dimensional anti-counterfeiting barcodes via inkjet printing. The resultant UCNPs@CDs@mSiO₂ inks with a dual-mode and tunable luminescence nature endow the inkjet-printing barcodes with an extremely high encoding capacity and high security. Such dual-mode fluorescent inks and barcodes are simple to fabricate, easy to view, efficient for coding, and difficult to clone, thus making them promising nanomaterials for anti-counterfeiting applications.

A sintered graphene/titania material as a synthetic keratoprosthesis skirt for end-stage corneal disorders

An artificial cornea or keratoprosthesis requires high mechanical strength, good biocompatibility, and sufficient wear and corrosion resistance to withstand the hostile environment. We report a reduced graphene oxide-reinforced titania-based composite for this application. Graphene oxide nanoparticles (GO) and liquid crystalline graphene oxide (LCGO) were the graphene precursors and mixed with titanium dioxide (TiO₂) powder. The composites reinforced with reduced GO or LCGO were produced through spark plasma sintering (SPS). The mechanical properties (Young's modulus and hardness), wear behaviour and corrosion resistance were studied using nanoindentation, anoidic polarization, long-term corrosion assay in artificial tear fluid and tribology assay in corroboration with atomic force microscopy and scanning electron microscopy. Biocompatibility was assessed by human corneal stromal cell attachment, survival and proliferation, and DNA damages. Sintered composites were implanted into rabbit corneas to assess for in vivo stability and host tissue responses. We showed that reduced graphene/TiO₂ hybrids were safe and biocompatible. In particular, the 1% reduced LCGO/TiO₂ (1rLCGO/TiO₂) composite was mechanically strong, chemically stable, and showed better wear and corrosion resistance than pure titania and other combinations of graphene-reinforced titania. Hence the 1rLCGO/ TiO₂ bioceramics can be a potential skirt biomaterial for keratoprosthesis to treat end-stage corneal blindness. STATEMENT OF SIGNIFICANCE: The osteo-odonto-keratoprosthesis (OOKP) is an artificial cornea procedure used to restore vision in end-stage corneal diseases, however it is contraindicated in young subjects, patients with advanced imflammatory diseases and posterior segment complications. Hence, there is a need of an improved keratoprosthesisskirt material with high mechanical and chemical stability, wear resistance and tissue integration ability. Our study characterized a reduced graphene oxide-reinforced titania-based biomaterial, which demonstrated strong mechanical strength, wear and corrosion resistance, and was safe and biocompatible to human corneal stromal cells. In vivo implantation to rabbit corneas did not cause any immune and inflammation outcomes. In conclusion, this invention is a potential keratoprosthesis skirt biomaterial to withstand the hostile environment in treating end-stage corneal blindness.

Spy Must Be Spotted: A Multistimuli-Responsive Luminescent Material for Dynamic Multimodal Anticounterfeiting and Encryption

The development of luminescent materials for anticounterfeiting and encryption is of great importance. Herein, we develop a multistimuli-responsive luminescent material, Na₂CaGe₂O₆:Pb²⁺/Er³⁺, and use it to print luminescent images. The photoluminescence and upconversion luminescence of these images show different patterns and colors under different stimuli. The photostimulated luminescence (PSL) of the printed images causes dynamic changes in appearance and is accordingly applied for dynamic multimodal anticounterfeiting on banknotes. The PSL of these luminescent images is also applied in a virtual war scenario to demonstrate that the dynamic PSL-encrypted information in the fabricated image is sufficiently safe even in extreme cases and that spies will be detected. These results can inspire us with more creative security designs based on this luminescent material.

Supraparticles: Functionality from Uniform Structural Motifs

Under the right process conditions, nanoparticles can cluster together to form defined, dispersed structures, which can be termed supraparticles. Controlling the size, shape, and morphology of such entities is a central step in various fields of science and technology, ranging from colloid chemistry and soft matter physics to powder technology and pharmaceutical and food sciences. These diverse scientific communities have been investigating formation processes and structure/property relations of such supraparticles under completely different boundary conditions. On the fundamental side, the field is driven by the desire to gain maximum control of the assembly structures using very defined and tailored colloidal building blocks, whereas more applied disciplines focus on optimizing the functional properties from rather ill-defined starting materials. With this review article, we aim to provide a connecting perspective by outlining fundamental principles that govern the formation and functionality of supraparticles. We discuss the formation of supraparticles as a result of colloidal properties interplaying with external process parameters. We then outline how the structure of the supraparticles gives rise to diverse functional properties. They can be a result of the structure itself (emergent properties), of the colocalization of different, functional building blocks, or of coupling between individual particles in close proximity. Taken together, we aim to establish structure-property and process-structure relationships that provide unifying guidelines for the rational design of functional supraparticles with optimized properties. Finally, we aspire to connect the different disciplines by providing a categorized overview of the existing, diverging nomenclature of seemingly similar supraparticle structures.

Preparation and RGB upconversion optic properties of transparent anti-counterfeiting films

Advanced anti-counterfeiting labels have aroused an intensive interest in packaging industry to avoid the serious issue of counterfeit. However, the preparation and cost of the existing labels associated with the drawbacks, including the complex and high-cost equipment, limit the protection of the authenticity of goods. Herein, we developed a series of anti-counterfeiting labels based on multicolor upconversion micro-particles (UCMPs) inks via straightforward and low-cost solutions, including spin-coating, stamping and screen printing. The UCMPs were synthesized through a facile hydrothermal process and displayed tunable red (R), green (G) and blue (B) color by doping different lanthanide ions, which are Er³⁺/Tm³⁺, Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ in NaYF₄ hosts, respectively. The optimal UCMPs inks were deposited on a flexible polyethylene terephthalate (PET) substrate to obtain transparent anti-counterfeiting labels possessing higher transmittance, stronger upconversion fluorescence intensity and good photostability. Under ambient conditions, the patterns and films were transparent, but could exhibit multicolor light under 980 nm laser excitation. They can be used as anti-counterfeiting labels for die-cutting packages to further elevate the security of goods. The tunable and designable transparent anti-counterfeiting labels based on RGB UCMPs inks exhibit the merits of low-cost, easy-manufacture and versatility, underlying the practical application in the field of anti-counterfeiting.

Catalytic coupling reaction mechanism of 4-nitrobenzenethiol on silver clusters: a density functional theoretical study

The catalytic coupling reaction mechanism of the transformation from 4-nitrobenzenethiol (4-NBT) to 4,4'-dimercaptoazobenzene (4,4'-DMAB) on a silver cluster was studied by density functional theory. Reactants, intermediates, transition states and products were optimized with the B3LYP method using the 6-311 + G(d,p) basis set (Ag using the pseudo potential basis set of LanL2DZ). Transition states and intermediates were confirmed by the corresponding vibration analysis and intrinsic reaction coordinates (IRC). Consistent with literature reports, the key point of the transformation from 4-NBT absorbed on the surface of Ag₅ clusters to 4,4'-DMAB is the elimination of two O atoms on the amino group. Meanwhile, the catalytic coupling reaction of 4-nitrobenzenethiol on a silver cluster is easy to carry out under irradiation. The possibility of "inter system channeling" (ISC) between different potential energy surfaces in the coupling reaction of 4-NBT is further discussed. The irradiation has an auxiliary catalytic effect on the coupling reaction. Our research results can explain the observed experimental phenomena. Graphical abstract Catalytic coupling reaction mechanism of the transformation from 4-nitrothiophenol (4-NBT) to 4,4'-dimercaptoazobenzene (4,4'-DMAB) on silver clusters studied by density functional theory.

Optimizing Melamine Resin Microspheres with Excess Formaldehyde for the SERS Substrate

Influence of the excess monomer within the synthetic reaction solution of melamine resin microspheres (MFMSs) on the surface-enhanced Raman spectroscopy (SERS) enhancement from Rhodamine 6G (R6G) was investigated, where the R6G was adsorbed on the silver nanoparticles (AgNPs) that were loaded on the MFMSs. Surface characteristics of the MFMSs were modified by the excess monomer (i.e., the excessive melamine or formaldehyde) through its terminal overreaction, which can be simply controlled by some of the synthetic reaction conditions, thus further allowing us to optimize the assembly of the loaded AgNPs for the SERS detection. These SERS substrates incorporating the optimized MFMSs with the excess formaldehyde can also be used for tracing analyses of more environmental and food contaminants.

Luminescent, Fire-Resistant, and Water-Proof Ultralong Hydroxyapatite Nanowire-Based Paper for Multimode Anticounterfeiting Applications

Counterfeiting of valuable certificates, documents, and banknotes is a serious issue worldwide. As a result, the need for developing novel anticounterfeiting materials is greatly increasing. Herein, we report a new kind of ultralong hydroxyapatite nanowire (HAPNW)-based paper with luminescence, fire resistance, and waterproofness properties that may be exploited for anticounterfeiting applications. In this work, lanthanide-ion-doped HAPNWs (HAPNW:Ln³⁺) with lengths over 100 μm have been synthesized and used as a raw material to fabricating a free-standing luminescent, fire-resistant, water-proof paper through a simple vacuum filtration process. It is interesting to find that the luminescence intensity, structure, and morphology of HAPNW:Ln³⁺ highly depend on the experimental conditions. The as-prepared HAPNW:Ln³⁺ paper has a unique combination of properties, such as high flexibility, good processability, writing and printing abilities, luminescence, tunable emission color, waterproofness, and fire resistance. In addition, a well-designed pattern can be embedded in the paper that is invisible under ambient light but viewable as a luminescent color under ultraviolet light. Moreover, the HAPNW:Ln³⁺ paper can be well-preserved without any damage after being burned by fire or soaked in water. The unique combination of luminescence, fire resistance, and waterproofness properties and the nanowire structure of the as-prepared HAPNW:Ln³⁺ paper may be exploited toward developing a new kind of multimode anticounterfeiting technology for various high-level security antiforgery applications, such as in making forgery-proof documents, certificates, labels, and tags and in packaging.

A neutral dinuclear Ir(iii) complex for anti-counterfeiting and data encryption

A neutral dinuclear Ir(iii) Schiff base complexPIBIPhas been synthesized and shown to exhibit both piezochromic luminescence (PCL) and aggregation induced emission (AIE) behaviour.