Fluorescent Ink Research Articles

Carbon Nanodots: Preparation, Properties, Application (A Review)

Carbon nanodots are a special class of nanoparticles with a size of 1 nm, consisting mainly of carbon and having pronounced fluorescent properties. They have been discovered 20 years ago, and since then have found numerous applications as fluorescent sensors, photocatalysts, fluorescent inks, etc., which has led to the rapid development of methods for their production and study. This review summarizes modern ideas about the synthesis, isolation, optical properties and application of carbon nanodots. The main directions for further research in this area are formulated.

Development of carbon dots‐immobilized fluorescent polylactic acid hydrogel ink toward security authentication

AbstractA self‐healable hydrogel for advanced authentication applications was successfully developed. In the presence of an aqueous solution of ammonium hydroxide as a cheap passivating agent, the hydrothermal carbonization of cellulose diacetate extracted from rice straw yielded nitrogen‐doped carbon dots (NdCD) in a straightforward and ecologically beneficial manner. NdCD achieved a maximum quantum yield of 25.11%. Self‐healing biocomposite inks with different emission properties were created by using different concentrations of NdCD nanoparticles (NPs). In order to create a transparent layer of NdCD@PLA hydrogel, stamps were used to press homogenous films onto paper surfaces. Polylactic acid (PLA) hydrogel was embedded with NPs of NdCD. Self‐healing security hydrogel inks are highly durable. The NdCD@PLA hydrogel is efficiently self‐healable at room temperature. The current NdCD@PLA hydrogel can attach to different surfaces, such as glasses, plastics, and papers. The self‐healable nanobiocomposite was photostable when exposed to UV light. Under UV light, NdCD‐containing nanobiocomposite inks have a bluish color, as proved by both colorimetric parameters and fluorescence spectra. The morphological properties of NdCD were studied by transmission electron microscopy to suggest a particle diameter of 10–15 nm. The morphology of the fluorescent prints was analyzed using a number of different analytical methods. The hydrogel rheology and the mechanical performance of printed papers were tested. The printed films showed excitation and fluorescence bands at 401 and 488 nm, respectively. The present smart ink shows significant promise as a potential industrial production technique to simply produce anti‐counterfeiting prints.Highlights Rice straws were used to prepare nitrogen‐doped carbon dots with a quantum yield of 25.11%. Self‐healable polylactic acid hydrogel was immobilized with N‐doped carbon dots (10–15 nm). Transparent printed films shifted in color to blue (488 nm) when excited at 401 nm. Ultraviolet‐stimulated photochromic authentication prints were prepared. Printed paper demonstrated non‐cytotoxicity, high photostability, and durability.

Termite wings derived N-doped carbon nanodots: applications for Cu2+ sensing, fluorescent ink and flexible polymeric film

Termite wings derived N-doped carbon nanodots: applications for Cu2+ sensing, fluorescent ink and flexible polymeric film

A Strategy for Rapid Synthesis of Carbon Nanodots with Reversible Photoluminescence Switching for Sensitive Dynamic Anti‐Counterfeiting

AbstractCarbon nanodots (CDs) possess exceptional fluorescence properties, which have been extensively studied in the fields of fluorescence detection and anti‐counterfeiting information. However, the exploration of CDs with simple and fast synthesis paths, secure, and efficient encryption properties, remains a challenge. The rapid synthesis of orange CDs (O‐CDs) is reported with a high photoluminescence quantum yield (PLQY) of 57.6% within 10 min at atmospheric pressure using a one‐step pyrolysis method. The O‐CDs exhibit a dual‐emission property, with a blue emission peak at 425 nm and a strong orange emission peak at 590 nm. The dual‐emission peaks of O‐CDs can allow for fast orange/blue switching of fluorescence color with changes in the acid‐base environment. O‐CDs can serve as effective fluorescent probes for pH detection, depending on their fluorescence wavelength and intensity. Additionally, O‐CDs have potential for fluorescence anti‐counterfeiting. When exposed to NH3 gas, O‐CDs fluorescent ink rapidly (1 s) transitions from orange fluorescence to blue fluorescence, and then quickly (4 s) reverts back to orange fluorescence when the gas environment changes to HCl gas atmosphere. Thus, O‐CDs fluorescent inks offer several advantages, including high fluorescence intensity, fast response, recyclability, and lossless encryption/decryption in “on‐off‐on” double encryption anti‐counterfeiting.

Preparation of waterborne anti-counterfeiting ink based on dual luminescent nanohybrids of bacterial cellulose nanocrystals and lanthanide‑nitrogen co-modified GQDs

To address the growing challenge of counterfeit prevention, this study developed a novel anti-counterfeiting ink system based on bacterial cellulose nanocrystals (BCNC) and lanthanide (Er, Yb)‑nitrogen (N) co-dropped graphene quantum dots (GQDs), which exhibited both photoluminescence (PL) and upconversion photoluminescence (UCPL) fluorescent properties as well as excellent rheological characteristics. The Er/Yb/N-GQDs with positive charges were synthesized by a one-step hydrothermal method and subsequently assembled with negatively charged BCNC through electrostatic self-assembly to fabricate a novel nanohybrid, Er/Yb/N-GQDs-BCNC. Raman spectroscopy results indicated an enhancement in the graphitization of GQDs due to lanthanide modification. The TEM results demonstrated a homogeneous distribution of Er/Yb/N-GQDs on BCNC, while XRD, FTIR, and XPS analyses confirmed their physical binding, thus validating the successful synthesis of novel nanohybrids. Then, Er/Yb/N-GQDs-BCNC was introduced into PVA waterborne ink and exhibited dual anti-counterfeiting properties by emitting blue fluorescence at Em 440 nm under Ex 370 nm and green fluorescence at Em 550 nm under Ex 980 nm. Furthermore, the incorporation of BCNC significantly enhanced the thixotropic behavior and yield stress of the PVA waterborne ink. This enhancement made the dual anti-counterfeiting fluorescent ink more suitable for diversified applications on different devices and various substrates, thus providing a novel approach for convenient and rapid information encryption and high security anti-counterfeiting.

Sustainable fabrication of fluorescent carbon quantum dots as an optical amplifier in modern agriculture, anti-counterfeiting, food packing and intelligent pH detection

Carbon quantum dots (CQDs) have received a great deal of attention due to their distinctive luminescent features and exciting potential applications in the fields of agronomy, enhanced anti-counterfeiting, drug tracking and intelligent sensing and detection. The focus of the current effort is on easily transforming toxic, non-biodegradable waste expanded polystyrene foam (WEPS) into extremely luminescent CQDs and investigating their various applications. As a nano-priming agent for Cajanus cajan (L.), the green pigeon pea (GPP), WEPS derived CQDs are used. The outcomes showed that seed priming had beneficial effects at all CQDs concentrations (100–900 mg/L), including accelerated seed germination rate, increased shoot and root length, augmented root vigour, higher chlorophyll content and biomass accumulation in comparison to the control groups. The most crucial data coding can be protected under 365 nm UV light using the optimized CQDs concentration (700 mg/L) blue fluorescent ink. In addition, a straightforward sensing platform with high sensitivity and selectivity is needed for the detection of dual metal ions, as well as one with a "turn-on and turn-off" fluorescence (FL) response. Additionally, a composite film containing well-dispersed CQDs (700 mg/L) in polyvinyl alcohol and strong hydrogen-bond interaction is successfully developed to alleviate the FL quenching caused by CQD aggregation. The resulting film had extraordinary FL performance, good mechanical flexibility and high transparency (transmittance of 90 %). Even more remarkably, this luminescent film showed sensitive pH responsiveness, signifying that when pH is stimulated, the FL intensity changed. A smart pH-detector based on this luminescent film is logically created as a proof-of-concept for real-time sensing and detection of pH changes in human sweat. These results show that WEPS derived CQDs have enormous potential as nano-priming agents for seed germination, seedling development, anti-counterfeiting ink, food packaging and intelligent pH-detector in wearable, real-time health monitoring.

Detection, detoxification, and anti-counterfeiting applications of pullulan-modified nitrogen-doped carbon dots

Nitrogen-doped carbon dots (N-CDs) modified with pullulan were prepared using a hydrothermal method for use in sensing, detoxification, and anti-counterfeiting applications. The excitation-independent N-CDs demonstrated selectivity for hydroquinone and 4-nitrophenol (4-NP) with detection limits of 58 and 13 nM. The N-CD-based detection method was extended to environmental samples such as bottled water, tap water, and river water, and acceptable relative standard deviations (RSDs) and good recoveries were found. In the presence of NaBH4, N-CDs converted the toxic MB to colorless leuco-methylene blue in 10.5 minutes, confirming that the catalytic ability of N-CDs can be evaluated using MB as a model pollutant. With an excellent quantum yield of 31%, the N-CDs had the potential as a fluorescent ink for anti-counterfeiting applications by helping to visualize fingerprints, drawings, and chemical structures under 365 nm UV light while being completely invisible in daylight and sunlight. The N-CDs have significant potential for industrial use as fluorescent inks, detoxification catalysts, and pollutant sensors.

Luminogenic and Bactericidal Studies of an Acrylonitrile-based AIEgen.

We have synthesized an aggregation induced emissive molecule that exhibits promising photophysical characteristics. The aggregating aptitude is demonstrated by binary solvent mixture and it is emissive in both solution and solid state. The luminogenic characteristics are employed in creating fluorescent inks as well as for the detection of nitro antibiotics in biofluids and in solid support. Moreover, the acrylonitrile-based compound is bactericidal tested on E. coli and B. subtilis.

Sustainable latent fingerprint enhancement with ink-free printing and shape memory behavior using Parthenium Hysterophorus-derived carbon dots

We developed a method to produce red fluorescent carbon dots from Parthenium hysterophorus leaves (PCDs) through hydrothermal carbonization. These PCDs exhibit consistent photoluminescence, emitting light regardless of excitation, with a 6.01 ns fluorescence lifetime and a 10.2% quantum yield. They possess a fine size of 4.4 nm, excellent hydrophilicity, and stability in a pH range of 4–11. Leveraging their optical properties, these PCDs function as precise nano-probes for detecting Fe3+ ions, demonstrating a linear correlation within 0 to 50 μM concentrations and a low detection limit of approximately 0.14 μM. Emitting light at about 620 nm, these PCDs remain visible even in daylight. When applied to fingerprints on various substrates and dried, they reveal distinct prints under 365 nm UV light, retaining stability for 24 h. This resilience is attributed to preventing fluorescence reduction, achieved through the coffee-ring effect and electrostatic interactions during drying. Employing deep learning with the YoLOv8 algorithm, fluorescence images of these latent fingerprints (LFPs) exceptionally resemble standard controls. These PCDs serve a dual role as fluorescent ink and nanocomposite films within a PVA matrix, demonstrating potential in anti-counterfeiting applications. This study presents a straightforward method for synthesizing PCDs with intense red luminescence, establishing them as a versatile platform for Fe3+ sensing, flexible fluorescent films, latent fingerprints, and anti-counterfeiting pursuits.

Hydrothermally synthesized fluorescent nitrogen-doped carbon dots for catalytic efficiency and anti-counterfeiting application

Here, Tylophora indica plant extract was utilized to create nitrogen-doped carbon dots by hydrothermal method. The synthesized NDCDs was employed to anti-counterfeiting and enhancing the catalytic activity of Malachite Green dye. The ultraviolet–visible spectroscopy and FT-IR measurements was used to analyze the optical properties and the development of NDCDs as well as the source of Tylophora indica. Using HR-TEM, XRD, and XPS, the structure and elemental contents of the produced NDCDs was investigated. The HRTEM images showed that the NDCDs had a d-spacing of 0.37 nm and an average particle size of 4.3 ± 1 nm. After being subjected to UV light at 365 nm, the produced NDCDs began to glow blue, with a quantum yield (QY) of 16.1 %. The ID and IG ratio values for NDCDs were found to be 0.86. With rate constant values calculated at 0.1830 min−1, respectively, the synthesized NDCDs were found to be a viable catalyst for the Malachite Green (MG) dye reduction process utilizing freshly prepared NaBH4. In addition, the NDCDs solution is used as fluorescent ink. The printed patterns retain their anti-counterfeiting properties even after being heated and stored in an environment for an extended period, indicating the NDCDs stability for prospective anti-counterfeiting applications.

Nitrogen-doped carbon dots for 3D printed smartphone-assisted cascade visual detection of morin and aluminium ion, solid fluorescence ink

With the growing emphasis on health management, individuals increasingly focus on monitoring drug molecular residues and harmful ions. Motivated by the concepts of the intelligent system and quantitative detection, we develop a smartphone-assisted cascade visual sensing device based on nitrogen-doped carbon dots (N-CDs) for in-site quantitative detection of morin and aluminium ion (Al3+). Initially, citric acid and o-phenylenediamine are identified as precursors for N-CDs synthesis via the microwave-assisted hydrothermal treatment. Subsequently, systematic studies reveal that the fluorescence of N-CDs is quenched upon the introduction of morin because of the inner filter effect (IFE). Conversely, the fluorescence recovery phenomenon occurs after the cascade addition of Al3+ since the morin binds with Al3+, resulting in the inhibition of IFE. Simultaneously, the fluorescence recovery of N-CDs enhances the cyan fluorescence emission of morin/Al3+. Based on the fluorescence quenching and recovery behavior, morin and Al3+ can be detected in the ranges of 0.070–50 μM and 0.124–40 μM with low detection limits of 0.070 μM and 0.124 μM, respectively. Furtherly, a smartphone-assisted cascade visual sensing device is designed for in-site quantitative detection of morin and Al3+. Moreover, based on the strong fluorescence and concentration-dependent emission behavior of N-CDs, the multi-color fluorescent ink is developed successfully. This work not only offers an excellent solution for simultaneous detection of morin and Al3+ but also shows numerous opportunities for solid lighting, information encryption and flexible optics.

Excitation-Wavelength- and Time-Dependent Fluorescent Ink Based on RGB Building Blocks for Advanced Anti-Counterfeiting

Excitation-Wavelength- and Time-Dependent Fluorescent Ink Based on RGB Building Blocks for Advanced Anti-Counterfeiting

Paper-based fluorescence sensor array with functionalized carbon quantum dots for bacterial discrimination using a machine learning algorithm

The rapid discrimination of bacteria is currently an emerging trend in the fields of food safety, medical detection, and environmental observation. Traditional methods often require lengthy culturing processes, specialized analytical equipment, and bacterial recognition receptors. In response to this need, we have developed a paper-based fluorescence sensor array platform for identifying different bacteria. The sensor array is based on three unique carbon quantum dots (CQDs) as sensing units, each modified with a different antibiotic (polymyxin B, ampicillin, and gentamicin). These antibiotic-modified CQDs can aggregate on the bacterial surface, triggering aggregation-induced fluorescence quenching. The sensor array exhibits varying fluorescent responses to different bacterial species. To achieve low-cost and portable detection, CQDs were formulated into fluorescent ink and used with an inkjet printer to manufacture paper-based sensor arrays. A smartphone was used to collect the responses generated by the bacteria and platform. Diverse machine learning algorithms were utilized to discriminate bacterial types. Our findings showcase the platform's remarkable capability to differentiate among five bacterial strains, within a detection range spanning from 1.0 × 103 CFU/mL to 1.0 × 107 CFU/mL. Its practicality is further validated through the accurate identification of blind bacterial samples. With its cost-effectiveness, ease of fabrication, and high degree of integration, this platform holds significant promise for on-site detection of diverse bacteria.Graphical abstract

Molecular Engineering toward Broad Color‐Tunable Emission of Pyrene‐Based Aggregation‐Induced Emission Luminogens

AbstractA molecular design strategy for the precise regulation of full‐color‐tunable emission organic luminescence materials is not yet systematically established for pyrene chemistry. To fabricate color‐tunable and highly‐efficiency pyrene‐based emitters, this article presents novel pyrene‐based molecules with donating‐π‐accepting structures, which exhibit bright, relatively narrow‐band FWHM emission, broad color‐tunable from deep blue (439 nm) to orange‐red (599 nm) both in solution and in the solid state. Moreover, the compounds 2a, 2d–g exhibit typical aggregation‐induced emission (AIE) characteristics, with an enhanced fluorescence quantum yield in the solid state. The experimental results indicated that the presence of the sterically bulky meta‐substituted biphenyl adopts an out‐of‐plane twist conformation, which can strengthen the rigidity of the molecular conformation and suppress the intermolecular π–π stacking in the aggregated state, resulting in an enhanced emission in the solid state. The prepared pyrene‐based AIEgens are applied as fluorescent inks to write Chinese characters and art with a vivid pattern. Thus, this article not only presents an efficient molecular strategy to construct pyrene‐based AIEgen with broad color‐tunable emission properties for practical applications, but also display a powerful combination of the strong alliance between the advanced luminescent materials, art and Chinese traditional culture.

Facile Synthesis of Carbonized Polymer Dots and their Applications in Security Inks, Sensing, Light Emitting Diodes, and UV Shielding Films

AbstractCarbonized polymer dots (CPDs) have received much attention in recent years owing to their cost‐effective synthesis, high resistance to photobleaching, environmental friendliness, and excellent biocompatibility. However, the aggregation‐induced fluorescence quenching is a great obstacle to its applications. In this work, the highly fluorescent CPDs are prepared by a facile hydrothermal method assisted by polyethylene glycol (PEG) as the surface passivation agent, where phthalic acid and ethylenediamine are used as carbon and nitrogen source, respectively. Meanwhile, five types of PEG species are applied to prepare five CPDs to investigate PEG on optical properties of the resultant CPDs, among which the best quantum yield reaches 57.0 %. The promising applications of CPDs as fluorescent inks, sensors, light emitting diodes, and UV shielding films have been demonstrated. Overall, our contribution here develops a facile and accessible route for the synthesis of CPDs and further demonstrates its versatile applications.

Greener Approach Supported Nitrogen-Infused Carbon Dots for Biocompatible Cellular Markers and Fluorescent Ink Based Spray-Assisted Fingerprint Analysis

Greener Approach Supported Nitrogen-Infused Carbon Dots for Biocompatible Cellular Markers and Fluorescent Ink Based Spray-Assisted Fingerprint Analysis

Luminescent properties of fluorescent colour water-based ink films

The article presents the luminance results of printouts for eight fluorescent inks intended for various applications, e.g., securing documents and packages, safety signs, or decorative effects. The research involves inks with 30% pigment concentration. The novelty is to show the luminescence depending on the ink film thickness and colour properties. The range of printout ink layer thicknesses is from 0 to 100 μm. The article presents scanning electron images and energy dispersive analysis of tested pigments, spectrofluorometric measures of lifetime, quantum yield, and Stokes shift. It also shows the rheological properties of pigment powder and inks and the optical properties, i.e., colour parameters, transparency, gloss, luminescence intensity, and the fluorescence expressed by the ΔCh, Δb∗, and ΔL∗ parameters. The surface topography and morphology, grain size, pigment shoreline, and roughness of the particles influence the fluorescent effect. The elemental composition, the b∗ colour parameter value in the CIELAB space, and lightness also affect the fluorescence. Pigments with a small grain and a smoother surface, such as chrome, orange, and yellow, shine much better than those with a more significant pigment grain and a rougher structure, such as violet and blue. The topography of pigments also affects their rheological properties and ink rheology. An increase in the ink layer thickness resulted in a decrease in its gloss and transparency values. However, the gloss and transparency do not affect the level of fluorescence, which increases with the ink film thickness to a certain maximum specified for a given ink colour. The equations in the article enable the fluorescent ink users to predict and adjust the appropriate thickness of its layer to obtain desired glowing effects.

Multicolor Fluorescent Inks Based on Lanthanide Hybrid Organogels for Anticounterfeiting and Logic Circuit Design.

With the rapid development of information technology, the encrypted storage of information is becoming increasingly important for human life. The luminescent materials with a color-changed response under physical or chemical stimuli are crucial for information coding and anticounterfeiting. However, traditional fluorescent materials usually face problems such as a lack of tunable fluorescence, insufficient surface-adaptive adhesion, and strict synthesis conditions, hindering their practical applications. Herein, a series of luminescent lanthanide hybrid organogels (Ln-MOGs) were rapidly synthesized using a simple method at room temperature through the coordination between lanthanide ions and 2,6-pyridinedicarboxylic acid and 5-aminoisophthalic acid. And the multicolor fluorescent inks were also prepared based on the Ln-MOG and hyaluronic acid, with the advantages of being easy to write, color-adjustable, and water-responsive discoloration, which has been applied to paper-based anticounterfeiting technology. Inspired by the responsiveness of the fluorescent inks to water, we designed a logic system that can realize single-input logic operations (NOT and PASS1) and double-input logic operations (NAND, AND, OR, NOR, XOR). The encryption of a binary code can be actualized utilizing different luminescent response modes based on the logic circuit system. By adjusting the energy sensitization and luminescence mechanism of lanthanide ions in the gel structure, the information reading and writing ability of the fluorescent inks were verified, which has great potential in the field of multicolor pattern anticounterfeiting and information encryption.

Fluorescent Carbon Dots from Bamboo Stem Waste: Synthesis, Characterization, and Inkjet Printing

AbstractAmong the various anti‐counterfeiting solutions, fluorescent compounds gained attention as challenging to copy solutions because of astute technological improvements. However, fluorescent compound usage in counterfeit detection is limited due to high price of rare earth metals, the low photostability of pigments or organic dyes, and the long‐term toxicity of conventional semiconductor quantum dots. Herein lies the value of carbon dot, a very stable, reasonably priced, and environmentally friendly material with intriguing features. In this work the development of blue fluorescent, N‐doped carbon dots (NCD) from waste bamboo stem cuttings via hydrothermal route is presented as an environmentally friendly approach to reduce the risk of toxic gas evolution from burning of bamboo waste. The carbon dot's practical application in anti‐counterfeit printing was ascertained by comprehending it's superior properties, such as high water solubility, eco‐friendliness, dazzling fluorescence, and surface functionalization through various characterization techniques. Inkjet printing of the designs on paper substrate using the aqueous NCD ink displayed reversible encryption‐decryption ability through variation of pH. The development paves the way for value‐added utilization of waste bamboo cuttings in fluorescent ink production.

Removal of organic amino derivatives from wastewater by using fluorescent nitrogen-doped GQDs under visible light and fluorescence application under ultra violet light

Photocatalysis is one of the most popular organic waste degradation treatments because it can result in the total decomposition of organic pollutants under visible light illumination. Here, we present a metal-free visible-light active catalyst for the effective decomposition of organic aromatic amino derivatives Methylene blue (MB) and Rhodamine B (RB) as model-contaminated dye molecules. Through a one-pot hydrothermal process, blue colour emissive nitrogen-doped graphene quantum dots (N-GQDs) were synthesized from urea and malic acid. The physicochemical characteristic techniques were used to analyze the surface morphology, elemental analysis, surface functional groups, absorption, emission, and band gap of prepared N-GQDs. The effective light absorption properties, transfer of electrons, separation of photoinduced charge carriers, and excellent stability with a band gap of 2.69 eV of synthesized N-GQDs have enabled the degradation of Rh B and MB up to 90 % and 86 % respectively, within 120 min of visible light irradiation. Based on extensive active species trapping experiments, a probable photocatalytic dye degradation mechanism is proposed. These N-GQDs can also be used to make fluorescent ink for imaging and security purposes.