Fluorescent Ink Research Articles

Upcycling Waste: Citrus limon Peel-Derived Carbon Quantum Dots for Sensitive Detection of Tetracycline in the Nanomolar Range.

In this work, a sustainable method was developed for the production of water-soluble carbon quantum dots employing a green approach. The synthetic protocol was employed using the microwave pyrolysis technique, while lemon peel served as a carbon precursor. Fabrication of highly fluorescent lemon-peel-derived CQDs (LP-CQDs) having inherent nitrogen functionality was validated by X-ray photoelectron spectroscopy, FTIR, X-ray diffraction, Raman spectroscopic analysis, and TEM techniques. The average particle size of fabricated LP-CQDs was 4.46 nm. LP-CQDs yielded a remarkable quantum yield of 49.5%, which displayed excellent salinity, photostability, storage time, conditions, and pH stability. LP-CQDs displayed encouraging results for tetracycline (TC) detection using a PL turn-off approach. The sensitivity of LP-CQDs toward TC was seen in a nanomolar range having a detection limit of 50.4 nM. Method validation was comprehensively studied to ensure the precision of the nanosensor. A complete analysis of different photophysical parameters of LP-CQDs was performed with TC to gain a deeper understanding of the sensing mechanism. Fabricated LP-CQDs showed fluorescence quenching toward TC, elucidated by the inner filter effect (IFE) mechanism. The synthesized nanoprobe demonstrated a lesser detection limit with a broad linear range, enabling facile, cheap, environmentally friendly, and fast detection of TC. Practicality of the detection method was assessed through analysis of real samples, resulting in satisfactory recovery percentage and relative standard deviation with respect to the developed probes. Furthermore, LP-CQDs were used as fluorescent inks and to fabricate paper-based fluorescent strips. This study lays the door for the sensing platform of LP-CQDs toward detection of TC, which may impact the potential role of environmental sustainability.

Synthesis of oil-soluble carbon dots via pyrolysis and their diverse applications in doxycycline detection, fluorescent ink and film

The overuse of doxycycline poses a risk for ecological environment. Advanced materials such as anti-counterfeiting and photovoltaic materials are urgently needed to develop innovative strategies for exploiting solar cells and protecting valuable products. Herein, oil-soluble CDs (o-CDs) were successfully fabricated from citric acid, tris-base and oleylamine as precursors via pyrolysis method. The o-CDs with uniform size distribution exhibited a high quantum yield of 0.48 and excellent photostability. The fluorescence of o-CDs was rapidly quenched by doxycycline at room temperature without further modification. Optimal conditions were selected to construct a fluorescence probe with high selectivity and good sensitivity to detect doxycycline. Interestingly, the probe achieved two linear ranges of 0.85––16.7 µM and 16.7––33.4 µM with a low detection limit of 0.26 µM. Furthermore, inner filter effect (IFE) was dominated in the process in which doxycycline interact with the oxygen-containing groups of o-CDs. This sensing platform has been further successfully applied to the detection of doxycycline in milk with recovery rates of 96.8%- 102.7% and relative standard deviations of 0.98%- 1.02%, suggesting that the novel probe has the potential to be applied in real samples. Moreover, o-CDs directly serve as fluorescence ink and work as fluorescence film using PVA as matrix because of strong fluorescence in the solid state, indicating that they have potential applications in anti-counterfeiting and photovoltaic materials. This is the first report that oil-soluble CDs via pyrolysis is applied in the detection of doxycycline in milk. Importantly, this work provides efficient strategies for the construction of anti-counterfeiting and photovoltaic materials.

Synthesis of Temperature Sensing Nitrogen-Doped Carbon Dots and Their Application in Fluorescent Ink.

With the discovery of research, many properties of carbon dots are getting better and better. People have taken advantage of this and utilized them interspersed in various fields. In the present study, water-soluble nitrogen-doped carbon dots (N-CDs) with excellent optical and fluorescence thermal properties were prepared by the hydrothermal method using 4-dimethylaminopyridine and N,N'-methylenebisacrylamide as precursors. Co2+ has a selective bursting effect on the fluorescence of N-CDs. The fluorescence of N-CDs is selectively burst by Co2+, and the high sensitivity is good in the range of 0-12 μM with a detection limit of 74 nM. In addition, the good temperature response (reversible and recoverable fluorescence in the temperature range of 20~90 °C) and excellent optical properties of the N-CDs also make them new potentials in the field of fluorescent inks and temperature sensing.

Host-Guest Complexes of Pillar[5]arene as Components for Supramolecular Light-Harvesting Systems with Tunable Fluorescence.

A guest molecule containing a short alkyl spacer between the tetraphenylethylene group and the methylpyridinium group was designed and synthesized. After complexation with a water-soluble pillar[5]arene, the resulting host-guest complex can further self-assemble into fluorescence-emitting nanoparticles in water. By loading a commercially available dye Rhodamine 6G into the nanoparticles, an efficient artificial light-harvesting system with high donor/acceptor ratios (>400/1) was successfully constructed. The obtained systems show considerable antenna effects with values of more than 10 times. The system also exhibits tunable fluorescence emission behavior and can be used as a fluorescent ink for information encryption.

Photostable yellow emissive carbon dots for iron-mediated reversible sensing of biothiols and cellular imaging

The different levels of biothiols in cells can not only screen cancer cells but also play a selective role in killing cancer cells. Therefore, accurate monitoring of biothiol in cancer cells is of great research significance. Herein, novel yellow emission CDs (Y-CDs) were prepared by a simple hydrothermal method using 2, 5-dihydroxyterephthalic acid (DHTA) as precursors. The Y-CDs as a highly efficient dual-mode sensor could detect Fe3+ and biothiols by colorimetric and fluorescence signals. Especially, with the addition of L-Cysteine, the quenched fluorescence could be quickly restored within 2 min and the detection limit was as low as 31.65 nM. Additionally, this sensor was utilized to sense biothiols in actual samples and living cells due to its eminent biocompatibility. Finally, the Y-CDs were successfully applied not only as fluorescent ink for message encryption but also as a portable solid hydrogels sensor for the detection of Fe3+ and biothiols. Therefore, these results suggested that Y-CDs could serve as a promising sensor for Fe3+ and biothiol detection in early cancer screening.

Functionalization of cellulose carbon dots with different elements (N, B and S) for mercury ion detection and anti-counterfeit applications

Mercury ion (Hg2+), as one of the most toxic heavy metal ions, accumulates easily in the environment, which can generate potential hazards to the ecosystem and human health. To effectively detect and remove Hg2+, we fabricated four types of carbon dots (CDs) using carboxymethyl nanocellulose as a carbon source doped with different elements using a hydrothermal method. All the CDs exhibited a strong fluorescence emission, excitation-dependent emission and possessed good water dispersibility. Moreover, the four fluorescent CDs were used for Hg2+ recognition in aqueous solution, where the CDs-N exhibited better sensitivity and selectivity for Hg2+ detection, with a low limit of detection of 8.29 × 10−6 mol/L. It was determined that the fluorescence quenching could be ascribed to a photoinduced charge-transfer processes between Hg2+ and the CDs. In addition, the CDs-N were used as a smart invisible ink for anti-counterfeiting, information encryption and decryption. Furthermore, the CDs-N were immersed into a cellulose (CMC)-based hydrogel network to prepare fluorescent hydrogels capable of simultaneously detecting and adsorbing Hg2+. We anticipate that this research will open possibilities for a green method to synthesize fluorescent CDs for metal ion detection and fluorescent ink production.

Sustainable and highly-stable carbon dots from cellulose as a fluorescent reference for visual ratiometric pH detection

Fluorescent materials, including organic molecules and quantum dots, usually respond to the environmental changes, such as acidity and basicity. It is challenging to construct highly-stable fluorescent materials. In this work, we fabricated novel carbon dots (CDs) with a high stability and a high quantum yield by using a solvothermal process, in which cellulose was the green precursor and 1-allyl-3-methylimidazolium chloride (AmimCl)/N,N-dimethylformamide (DMF) was the solvent. The resultant CDs had the cationic imidazolium groups on their surface. As a result, they exhibited the excellent fluorescence stability in strong-acidic, strong-basic and high salt solutions. In addition, the CDs also presented a good resistance to the photobleaching under strong UV irradiation conditions. The highly stable CDs can be utilized as a fluorescent reference to significantly improve the responsiveness of the fluorescent materials. For example, the CDs were combined with cellulose acetate fluorescein isothiocyanate (CA-FITC) to obtain a series of ratiometric probes, which can visually detect pH values with a higher sensitivity. Furthermore, based on the outstanding processability and formability of cellulose derivatives, the CDs/CA-FITC was easily fabricated into responsive fluorescent coatings, films, and inks, indicating a huge potential in visual detection, solid-state luminescence, and anti-counterfeiting.

Benzofuran derived pH-responsive AIEgens: Design, synthesis and applications in monitoring the urea content in soil and food quality evaluation

The stimuli-responsive luminescent materials have received special attention because of the modulable physical or chemical properties under the influence of external stimuli such as pH, temperature, light, heat, pressure, and so on. Therefore, such materials have potential applications in mechano-sensing devices, security inks, memory devices, data storage, deformation detectors, and so on. We present here the design and synthesis of three pH-responsive luminogens L1-L3 with aggregation-induced emissive properties built over the benzofuran scaffold. The AIE active luminogens L1-L3 demonstrated reversible fluorescence switching when exposed to Trifluoroacetic acid (TFA) fumes followed by Triethylamine (TEA) or NH3 fumes. The pH-sensitive fluorescence behavior of L2 has been successfully used in developing fluorescent inks for anti-counterfeit applications, as well as to construct paper strip-based detecting tools for qualitatively detecting the urea content in the soil and evaluating the ripeness/maturity of the packed fruits (grapes) in a non-destructive manner. Furthermore, both L1 and L2 were found to be highly biocompatible and well internalized within the cytoplasm of MDA-MB-231 cancer cells, with very high fluorescence intensity.

Controlling molecular assembly on time scale: Time-dependent multicolor fluorescence for information encryption

Dynamic assembly on time scale is common in biological systems but rare for artificial materials, especially for smart luminescent materials. Programming molecular assembly in a spatio-temporal manner and resulting in white-light-including multicolor fluorescence with time-dynamic features remains challenging. Herein, controlling molecular assembly on time scale is achieved by integrating a pH-responsive motif to a transient alkaline solution which is fabricated by activators (NaOH) and deactivators (esters), leading to automatic assembly on time scale and time-dependent multicolor fluorescence changing from blue to white and yellow. The kinetics of the assembly process is dependent on the ester hydrolysis process, which can be controlled by varying ester concentrations, temperature, initial pH, stirring rate and ester structures. This dynamic fluorescent system can be further developed for intelligent fluorescent materials such as fluorescent ink, three-dimension (3D) codes and even four-dimension (4D) codes, exhibiting a promising potential for information encryption.

Green synthesis of boron-doped carbon dots from Chinese herbal residues for Fe3+ sensing, anti-counterfeiting, and photodegradation applications

Carbon dots (CDs), especially from biomass doped with heteroatoms, have drawn increasing attention owing to their versatility in potential applications. In this work, boron-doped CDs derived from Chinese herbal residues (B@HRCDs) were fabricated through a simple, green, one-step solvothermal method, resulting in B@HRCDs with a uniform size of 2.8 nm. The synthesized B@HRCDs were characterized using Fourier transform infrared spectroscopy, UV–visible spectroscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, and Fluorescence techniques. As prepared, the B@HRCDs demonstrated a bright fluorescence with a quantum yield of 4.0% and displayed exceptional selectivity towards Fe3+. In vitro experiments, they did not exhibit cytotoxicity against BV2 cells. The synthesized B@HRCDs were used as a sensitive nanoprobe for the detection of free Fe3+ in the range of 0–80 μM with a minimum limit of detection (LOD) of 1.08 μM. Based on their biocompatibility and negligible cytotoxicity, B@HRCDs were also shown to be useful for intracellular Fe3+ detection applications. When fluorescent ink was applied to bond paper, the patterns were clearly visible under UV light, indicating that B@HRCDs can be used for message encryption. Finally, it was further shown that the degradation rate of indigo carmine after 5 h of sunlight irradiation was 91% in the presence of B@HRCDs and decreased to 61% after 5 cycles, which indicates that the B@HRCDs have favorable photocatalytic activity and photostability. It is thus believed that this strategy achieves the reuse of herbal residues and proposes a low-cost, green method for the synthesis of CDs with Fe3+ sensing, anti-counterfeiting, and photodegradation functions.

Erasable, Rewritable, And Reprogrammable Dual Information Encryption Based on Photoluminescent Supramolecular Host-Guest Recognition And Hydrogel Shape Memory.

Information encryption technologies are very important for security, health, commodity, and communications, etc. Novel information encryption mechanisms and materials are desired to achieve multi-mode and re-programmable encryption. Here, wedemonstrate a supramolecular strategy to achieve multi-modal, erasable, reprogrammable, and reusable information encryption by reversibly modulating fluorescence. A butyl-naphthalimide with flexible ethylenediamine functionalized β-cyclodextrin (N-CD) is utilized as fluorescent responsive ink for printing or patterning information on polymer brushes with dangling adamantane group grafted on responsive hydrogels. The photoluminescent naphthalimide moiety is bonded to β-CD and entrapped in the cavity. Its fluorescence is highly weakened in β-CD cavity and recovers after being expelled from the cavity by a competing guest molecule to emit bright green photoluminescence under UV. Experiments and theoretical calculations suggest π-π stacking and ICT as the primary mechanism for the naphthalimides assembly and fluorescence, which can be quenched through insertion of conjugated molecules and recover by removing the insert. Such reversible quenching and recovering are used to achieve repeated writing, erasing, and re-writing of information. Wefurther combine supramolecular recognition and hydrogel shape memory to achieve reversible dual-encryption. This study provides a novel strategy to develop smart materials with improved information security for broad applications. This article is protected by copyright. All rights reserved.

Rapid Preparation of Long-Wavelength Emissive Carbon Dots for Information Encryption Using the Microwave-Assisted Method.

The synthesis of long-wavelength emission fluorescent carbon dots is not common, and it is even more difficult to quickly synthesize within 10 min. In this experiment, yellow, orange, and red B, N codoped fluorescent carbon dots were successfully synthesized using a microwave-assisted method with o-phenylenediamine as the carbon-nitrogen source, boric acid as the boron source, and potassium chloride as the catalyst in just 7 min. Based on the different contents of B, N element doping, there are differences in their surface structures, resulting in differences in the luminescence properties of the synthesized carbon dots. Long-wavelength carbon dots can avoid interference from the blue fluorescence of filter papers and have a clearer display in information encryption. Therefore, three types of carbon dots were mixed with PVP to produce fluorescent inks, and anticounterfeiting and encryption patterns were designed on the filter paper, displaying different fluorescence information under sunlight and UV light. In addition, the rich fluorescent colors were combined ingeniously to enable secondary encryption of information in the form of binary codes that increase the difficulty of decoding. These indicate that the three synthesized long-wavelength carbon dots have good application prospects in information encryption.

Green synthesized carbon dots as antibiotics sensor and fluorescent ink

Nearly all antibiotics cause significant health issues and environmental risks due to their unrestricted intake and delayed consumption. So, their detection and removal are of great concern. In this work, a novel Coleus zeylanicus leaves-derived nitrogen doped carbon dot (NCDs) based sensor was developed for the detection of antibiotics. The NCDs were synthesized via cost effective hydrothermal method. The NCDs with amorphous nature have an average size of 2.59 nm and a surface charge of -30.89 mV and exhibited excellent stability towards various experimental conditions. The NCDs worked as a fluorescent probe for levofloxacin (LEV) detection and an electrochemical sensing probe for the detection of amoxicillin (AMX). The fluorescence of NCDs was enhanced by LEV, and the limit of detection is obtained as 0.06 µM. The NCDs detected AMX with a LOD of 0.03 nM. Additionally, the effectiveness of NCDs in sensing levofloxacin and amoxicillin was confirmed in spiked water samples. Also, the role of NCDs as fluorescent ink was explored. In light of the findings of this study, it could be possible to find new ways to address environmental issues using carbon dots from sustainable sources.

Design of polarity-dependence orange emission multifunctional carbon dots for water detection and anti-counterfeiting

In this work, polarity-dependence orange emission multifunctional carbon dots (o-CDs) were designed for water detection in organic solvents and anti-counterfeiting. The o-CDs were readily fabricated by a one-step hydrothermal method with citric acid and p-aminoazobenzene as precursors. The o-CDs possess bright orange fluorescence, good photochemical stability, and polarity-dependence characteristic. With the increase of polarity, the emission peak of o-CDs gradually red-shifted. Meanwhile, with the increase of water content in organic solvent, the fluorescence intensity of o-CDs decreased significantly and the emission peak position gradually red-shifted. This is due to the specific water-fluorophore interaction (particularly hydrogen bond effects), part of o-CDs gathered, making the carbonized cores suffer from π–π stacking and reduced the transition energy gap. Based on this, a fluorescence sensing platform with satisfactory recoveries and relative standard deviation was constructed to detect water content in real alcohol solvents. Furthermore, the o-CDs were further designed into fluorescent ink and prepared fluorescent flexible films, realizing information encryption and solid-state fluorescence. This work opens up a possibility for the development of polarity-dependence orange emission nanomaterial based on CDs for water detection, anti-counterfeiting, and solid-state fluorescence.

Conventional Non-Fluorescent Polymers: Unconventional Security Inks for Data Storage and Multidimensional Photonic Cryptography.

Traditional security inks relying on fluorescent/phosphorescent molecules are facing increasing risks of forgery or tampering due to their simple readout scheme (i.e., UV-light irradiation) and the advancement of counterfeiting technologies. In this work, a multidimensional data-encryption method based on non-fluorescent polymers via a "lock-key" mechanism is developed. The non-fluorescent invisible polymer inks serve as the "lock" for data-encryption, while the anti-rigidochromic fluorophores that can distinctively light up the polymer inks with programed emissions are "keys" for decryption. The emission of decrypted data is prescribed by polymer chemical structure, molecular weight, topology, copolymer sequence, and phase structure, and shows distinct intensity, wavelength, and chirality compared with the intrinsic emission of fluorophores. Therefore, the data is triply encrypted and naturally gains a high-security level, e.g., only one out of 20000 keys can access the only correct readout from 40000000 possible outputs in a three-polymers-based data-encryption matrix. Note that fluorophores lacking anti-rigidochrimism cannot selectively light up the inks and fail in data-decryption. Further, the diverse topologies, less well-defined structures, and random-coiled shapes of polymers make it impossible for them to be imitated. This work offers a new design for security inks and boosts data security levels beyond the reach of conventional fluorescent inks.

Heteroatom doped carbon dots from green sources as metal ion sensor and as fluorescent ink

In this study, novel eco-friendly nitrogen-doped carbon dots (NCDs) were prepared via a green, efficient, and one-pot synthesis method from Sida cordifolia root as the carbon source and triethylene tetraamine as the nitrogen source for the detection of metal ions. The amorphous, nanosized carbon dots with 17.8 % quantum yield exhibited exceptional stability towards different experimental conditions. These NCDs acted as a nanoprobe for the sensing of Co(II) and Cu(II) via fluorescence and electrochemical techniques, respectively. These blue fluorescent carbon dots detects Co(II) with a detection limit as low as 0.11 μM and Cu(II) with 0.03 nM. The inner filter effect (IFE) acted as the primary fluorescence quenching mechanism. Also, the developed sensor could detect metal ions in different water samples. Moreover, NCDs were used as fluorescent security ink for writing and drawing. The findings of this study open up a new platform for the effective and reliable sensing of metal ions.

Synthesis of multicolor fluorescent carbon dots from zanthoxylum bungeanum and their application in fluorescent anti-counterfeiting ink

Multicolor fluorescent carbon dots (CDs) have wide application prospects in many fields. Presented herein reported a synthesis of multicolor fluorescent CDs using zanthoxylum bungeanum as a carbon precursor. By changing the nitrogen sources, blue, green, and red fluorescent carbon dots (B-CDs, G-CDs, and R-CDs) with stable optical properties and high quantum yields (QY) were synthesized. Their emission wavelengths are 492 nm, 523 nm, and 601 nm respectively and their QYs were measured to be 13.1%, 11.2%, and 9.8%, respectively. These CDs exhibit good salt resistance, photobleaching resistance, and chemical stability. These characteristics make them suitable for various applications, particularly in the field of anti-counterfeiting fluorescent ink. This study provides an economic and efficient strategy for synthesizing multicolor fluorescent CDs derived from natural products, highlighting the potential for producing multicolor CDs and enhancing their application value.

Effect of precursors on ZnO nanoparticles to enhance the level-III ridge details of LFPs and anti-counterfeiting applications

Comparative analysis for the combustion-based synthesis of zinc oxide nanoparticles (NPs) utilizing various precursors of zinc was reported. l-ascorbic acid extraction was used as a fuel for the combustion process. The sizes, morphologies, structural details and purity of samples were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). XRD pattern matches with the standard JCPDS card of ZnO with good crystallite size. The average crystallite size of the NPs was confirmed the nano-regime. Variations in morphological structures and the energy band gap variation with the change in precursors was reported. Using a powder-dusting technique, on separate surfaces, level-III features of the fingerprints produced by these NPs without any background noise. The suggested powder composition was easy to make and effective for producing latent finger prints on a variety of dry and wet surfaces. In the area of counterfeit prevention, the fluorescent ink has several potential applications. Invisible security ink was developed for anti-counterfeiting applications based on the UV fluorescence feature of ZnO NPs. The fluorescent invisible security ink for screen printing was evaluated and proved to be stable on a variety of microporous papers. The new strategy adopted here lowers the cost of ink by using rare earth free ZnO NPs.

Mechano- and solvato-fluorochromic chalcone and its water-based flexo-ink for anticounterfeit applications

Pigments with unique optical features are always sought after in realizing superior security features to protect authentic documents/products against forgery. The present study reports the synthesis of triphenylamine-naphthalene chalcone (TPA-NC) with fascinating optical features: solvato-fluorochromism, mechano-fluorochromism, and aggregation-induced emission. The flexo print obtained on UV dull paper using water-based eco-friendly UV fluorescent ink with TPA-NC as pigment displayed good adhesion, resistance to abrasion, light fastness, and favourable electrical parameter values, which could be well utilized in security documents and developing OTFTs in banknotes to prevent them from being forged. Moreover, the printed paper samples could impart superior features including solvent fugitiveness, penetrating fluorescence, and mechanical stimuli responsive variations in emission color for achieving multilevel security. The security ink prepared using the thermally stable and biocompatible TPA derivative could generate a robust platform for tamper-detection, validation of genuine documents/products and in marking technology. Moreover, an ultra-high radio frequency identification (RFID) antenna is designed to resonate at 2.35 GHz. The hybrid arrangement has steady radiation characteristics for electronic anticounterfeiting applications.

Synthesis of high-performance carbon dots from laurel leaves and their application in anti-counterfeit ink

Green-emitting carbon dots (G-CDs) with high quantum yield were successfully synthesized through a one-step bottom-up approach, utilizing laurel leaves as the carbon precursor, o-phenylenediamine (OPD) as the nitrogen source, and N,N-dimethylacetamide (DMAC) as the solvent. Structural characterizations unveiled the presence of abundant nitrogen-containing functional groups on the surface of G-CDs, significantly influencing their luminescent properties. The excitation and emission wavelengths of G-CDs were determined to be 467 nm and 508 nm, respectively, with a quantum yield of up to 49.9 %. Moreover, the emissions of G-CDs were found to be dependent on the excitation wavelength, suggesting a potential correlation between luminescence and particle size. Notably, the stability assessment demonstrated excellent salt resistance and strong photostability of the G-CDs. A brief discussion on the practical application of G-CDs in anti-counterfeit fluorescent ink highlighted their potential in this filed. This study presents a green synthesis strategy for producing high-performance carbon dots, reducing reliance on chemical reagents, lowering synthesis costs, and mitigating environmental pollution.