Ionic liquid-assisted synthesis of multicolor luminescent silica nanodots and their use as anticounterfeiting ink

Intrinsic dual emissive insulin capped Au/Ag nanoclusters as single ratiometric nanoprobe for reversible detection of pH and temperature and cell imaging

pH and temperature are two important characteristics in cells and the environment. These, not only in the well-done regulation of cell functions but also in diagnosis and treatment, have a key role. Protein-protected bimetallic nanoclusters are abundantly used in the building of biosensors. However, insulin-stabilized Au-Ag nanoclusters with dual intrinsic emission have not been investigated yet. In this work, Dual emissive insulin templated Au-Ag nanocluster (Ins(Au/Ag)NCs) were first synthesized in a simple and green one-put manner. The two emission wavelengths of, as-prepared NCs centered at 410 and 630 nm, excited in one excitation wavelength (330 nm). These two emission peaks were assigned to the di-Tyrosine cross-linked formation and bimetallic nanoclusters respectively. Further analysis displayed that each emission band of Ins(Au/Ag)NCs responded to one variable whilst another peak remained constant; For blue and red emission wavelengths, pH dependency and thermo-responsibility were observed respectively. As-prepared nanoprobe with the intrinsic dual emissive feature was used for ratiometric determination of these parameters, each with a discrete response from another. The linear range of 6.0-9.0 for pH and 1 to 71 °C for temperature was obtained, which comprises the physiological range of pH and temperature and afforded intracellular sensing and imaging capability. As-prepared NCs probe show excellent biocompatibility and cell membrane permeability, and so were successfully applied as direct ratiometric pH and temperature probes in HeLa and HFF cells. More interestingly, this dual emissive nanoprobe is capable of distinguishing cancer cells from normal ones.

A Strategic Approach to Design Multi-Functional RGB Luminescent Security Pigment Based Golden Ink with Myriad Security Features to Curb Counterfeiting of Passport

Authentication and verification of the most important government issued identity proof, i.e. passport has become more complex and challenging in the last few decades due to various innovations in ways of counterfeiting by fraudsters. Here, the aim is to provide more secured ink without altering its golden appearance in visible light. In this panorama, a novel advanced multi-functional luminescent security pigment (MLSP) based golden ink (MLSI) is developed that provides an optical authentication and information encryption features to protect the legitimacy of the passport. The advanced MLSP is derived from the ratiometric combination of different luminescent materials to form a single pigment which emits red (620 nm), green (523 nm) and blue (474 nm), when irradiated via 254, 365 and 980 nm NIR wavelengths, respectively. It also includes magnetic nanoparticles to generate magnetic character recognition feature. The MLSI has been fabricated to examine its printing feasibility and stability over different substrates using the conventional screen-printing technique against harsh chemicals and under different atmospheric conditions. Hence, these advantageous multi-level security features with golden appearance in visible light is a new breakthrough toward curbing the counterfeiting of passport as well as bank cheques, government documents, pharmaceuticals, military equipment, and many more.

Nitrogen-rich silicon quantum dots: facile synthesis and application as a fluorescent "on-off-on" probe for sensitive detection of Hg2+ and cyanide ions

The sensitive and reliable detection of Hg²⁺ and CN^- as harsh environmental contaminants are of great importance. In view of this, a novel "on-off-on" fluorescent probe based on nitrogen-rich silicon quantum dots (NR-SiQDs) has been designed for sensitive detecting Hg²⁺ and CN^- ions in aqueous media. NR-SiQDs were synthesized by a facile, one-step, and environment friendly procedure in the presence of 3-aminopropyl trimethoxysilane (APTMS) and ascorbic acid (AA) as precursors, with L-asparagine as a nitrogen source for surface modification. The NR-SiQDs exhibited strong fluorescence emission at 450 nm with 42.34% quantum yield, satisfactory salt tolerance, and superior photo- and pH-stability. The fluorescence emission was effectively quenched by Hg²⁺ (turn off) due to the formation of a non-fluorescent stable NR-SiQDs/Hg²⁺ complex while after the addition of cyanide ions (CN^- ), Hg²⁺ ions can be leached from the surface of the NR-SiQDs and the fluorescence emission intensity of the quenched NR-SiQDs fully recovered (turn on) due to the formation of highly stable [Hg (CN)₄ ]^2- species. After optimizing the response conditions, the obtained limits of detection were found to be 53 nM and 0.46 μM for Hg²⁺ and CN^- , respectively. Finally, the NR-SiQDs based fluorescence probe was utilized to detect Hg²⁺ and CN^- ions in water samples and satisfactory results were obtained, suggesting its potential application for environmental monitoring.

Design of novel lanthanide-doped core-shell nanocrystals with dual up-conversion and down-conversion luminescence for anti-counterfeiting printing

Development of advanced luminescent nanomaterials and technologies is of great significance for anti-counterfeiting applications in global economy, security, and human health, but has proved to be a great challenge. In this work, we design, synthesize, and characterize mono-disperse, dumbbell-shaped lanthanide-doped NaYF₄@NaGdF₄ core-shell nanoparticles (CSNPs) with dual-mode fluorescence by coating the NaGdF₄:Ln'³⁺ shell onto NaYF₄:Ln³⁺ core nanospheres via a two-step oleic acid mediated thermal decomposition process. Different from the conventional synthesis method to produce spherical nanoparticles, the epitaxial growth of the NaGdF₄:Ln'³⁺ shell onto the nanosphere cores and the lattice mismatch between β-NaGdF₄ and β-NaYF₄ nanocrystals enable the formation of dumbbell-shaped CSNPs, as evidenced by the morphological evolution of CSNPs and as explained by the Ostwald ripening growth mechanism. By tailoring different doped lanthanide ions in the core and the shell, the resultant CSNPs exhibit tunable but different up-/down-conversion luminescence under the irradiation of a 980 nm laser and 254 nm UV light, respectively. Finally, these hydrophilic CSNPs are further fabricated into environmentally benign luminescent inks for inkjet printing to create a variety of dual-mode fluorescent patterns (peacock, temple, and a logo of "Hunan University of Technology") on different paper-based substrates (A4 paper, envelope, and postcard). Our dual-mode light-responsive CSNPs, along with an easy fabrication method, provide a simple and promising material and technique for anti-counterfeiting applications.

Facile synthesis of Silicon quantum dot-Gadolinium: A potential fluorescent/T1-T2 multimodal imaging agent

Highly stable and multifunctional fluorescent quantum dots are particularly attractive in practical applications. Here, a new kind of ultra-small-sized silicon quantum dot-gadolinium (SiQD-Gd) was successfully fabricated by a newly-designed facile hydrothermal growth and chelating method. The obtained SiQD-Gd exhibited outstanding water dispersibility, stability and good fluorescent property with the quantum yield of 11.6%. SiQD-Gd displayed a low cytotoxicity in normal cell lines (HELF, HEK293F) and tumor cell lines (H1299, A549). Meanwhile, SiQD-Gd showed excellent magnetic resonance response with r₁ relaxation rate of 10.5 mmol L^-1·s^-1 and r₂ relaxation rate of 47.5 mmol L^-1·s^-1, which are 2.5 and 7.4 times enhanced comparing to that of the commercial MR agent Magnevist. In vivo studies showed significant contrast enhancement effect of its T₁- and T₂-weighted MR imaging. In addition, in vivo fluorescent imaging for mice and zebrafish indicated its potential applications in fluorescent tracking. Thus, the excellent multimodal imaging capacity and biocompatibility of SiQD-Gd make it a potential imaging agent for clinic applications.

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.

Hexamethylenetetramine: an effective and universal nitrogen-doping reagent to enhance the photoluminescence of carbon nanodots

Guidelines of how to select nitrogen-doping reagents for enhancing photoluminescence of carbon nanodots are proposed by taking hexamethylenetetramine as a typical example.

Is nano ZrO2 a better photocatalyst than nano TiO2 for degradation of plastics?

The environmental accumulation of plastic is a huge problem due to its low degradability.

Synthesis and properties enhancement of metal nanoclusters templated on a biological molecule/ionic liquids complex

Two biological template molecules and two short-chain imidazolium ionic liquids with amphipathy were selected to synthesize four different types of metal nanoclusters, which were templated on a biological molecule/imidazolium ionic liquids complex.

Future prospects of luminescent nanomaterial based security inks: from synthesis to anti-counterfeiting applications

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.

Stöber strategy for synthesizing multifluorescent organosilica nanocrystals

We first report the Stöber synthesis of diamond-structured fluorescent organosilica nanocrystals (OSNCs) with finely tunable fluorescence (460–625 nm).