Tunable Fluorescence Research Articles

Carbon Quantum Dots with Tunable Size and Fluorescence Intensity for Development of a Nano-biosensor.

Carbon quantum dots (CQDs) are a class of nanomaterials known for their remarkable photostability, chemical inertness and biocompatibility. Changing their size, structure, and surface chemistry enable the tuning of their luminescence property, which gives them tremendous potential for various applications. CQDs synthesis typically involves long tedious processes, requiring multiple steps and harsh reaction conditions. Here, a new reliable, economical, and ultra-rapid one-step fabrication method is introduced to obtain CQDs with well-defined and reproducible photoluminescence properties via a simple heat treatment. These solid-state CQDs are homogenous in size and are ready to use without the need for further purification. The size of the fabricated CQDs and their corresponding peak fluorescence intensity are confirmed to be tunable by simple adjustment of the heat treatment conditions. Coupled with their selective fluorescence quenching by metal ions, the clinical potential of CQDs is demonstrated for biosensing applications by designing a new nano-biosensor to assess the quality of stored blood units through hemolysis quantification without disrupting storage conditions. This may pave the way for a new standard in blood bank inventory management.

Facile fabrication of biocompatible carbon dots from egg white by one-step neutralization heat reaction: a capillary array-based fluorimetric strategy for high-throughput detection of total iron ions in fish blood.

Water-soluble and biocompatible protein carbon dots (P-CDs) were simply prepared from egg white by a rapid one-step neutralization heat reaction. Unexpectedly, the thus-fabricated P-CDs could present excitation-dependent tunable fluorescence that could be quenched specifically by Fe3+ and Fe2+ ions with obvious color changes. A high-throughput fluorimetric platform was thereby developed by coating the P-CDs onto a capillary array for detection of total iron ions in fish blood samples, with a linear concentration range of 0.25-60.00 μM and a detection limit of 0.085 μM. Moreover, it can allow for the fast evaluation of total iron ions in fish blood samples, showing recovery efficiencies of 97.25%-99.84%. Such a facile fabrication route for P-CDs from egg white by a rapid neutralization reaction may open a new door for preparing different CDs. More importantly, the developed fluorimetric method may be expected to have wide application in the fields of diagnosis of iron-related diseases, monitoring of environmental water, and ensuring aquatic product safety.

Facile Post‐Processing Approach to Modulate Fluorescent Properties and New Matrix‐Assisted Method to Achieve Solid‐State Luminescence of CDs Based on CTAB Surfactant

AbstractTo realize the practical application of carbon dots (CDs), it is crucial to devise straightforward techniques that can finely modulate the fluorescent properties of CDs. Apart from that, it is imperative to weaken the aggregation‐caused quenching (ACQ) effect, which poses a significant challenge to the utilization of solid‐state CDs. In this work, three CDs named as CDs‐1, CDs‐2, and CDs‐3 are synthesized, and the fluorescence tuning of these CDs is successfully realized, assisted by cetyltrimethylammonium bromide (CTAB) surfactant, because its unique molecular structure is conducive in bolstering fluorescence intensity and adjusting emission wavelength. Furthermore, the luminescence of solid‐state CDs is successfully achieved by employing CTAB as substrate in the matrix‐assisted synthesis of composites CDs‐1@CTAB, CDs‐2@CTAB, and CDs‐3@CTAB. Notably, the photoluminescence quantum yield (PLQY) of CDs‐2@CTAB reaches an impressive value as high as 79.31%, surpassing the value of 70.29% obtained by pristine CDs‐2. The experimental results reveal that CDs@CTAB composites exhibit intriguing afterglow characteristics including room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). This work confirms the versatility of CDs and highlights the significance of surfactant‐assisted strategies in improving the performance of CDs.

Crystallization solvent induced fluorescence tuning by subtle conformational change in a conformationally flexible fluorophore

The fluorophore structural flexibility and ability to display different conformation provides opportunity to develop fluorescent polymorphs that exhibit tunable solid-state fluorescence. In this study, a conformationally flexible organic fluorophore, (4-(diphenylamino)benzaldehyde,...

General and Versatile Nanoarchitectonics for Amino Acid-Based Glasses via Co-Assembly of Organic Counterions.

Amino acid-based biomolecular glasses represent an emerging material to meet the demand for sustainable development. However, most amino acids are difficult to vitrify due to their strong crystallization tendency, limiting further advancements of this field. In this study, we demonstrate that the introduction of counterions effectively suppresses crystallization, as hydrogen bonds within the system stabilize the disordered structures. Based on this, we propose a counterion co-assembly strategy to synthesize a wide range of amino acid-based glasses. This strategy enables the facile fabrication of glass with customizable shapes, high mechanical rigidity, and tunable multicolor fluorescence, ranging from blue to red depending on the excitation wavelength. Furthermore, this strategy allows the integration and enhancement of counterion properties within the glass matrix. Through the co-assembly of phosphorescent counterions, we synthesized a series of long-persistent luminescent glasses with significantly extended afterglow lifetimes. This work presents an effective approach for the synthesis of amino acid-based glasses and provides insights into the development of supramolecular glasses with tailored functionalities.

General and Versatile Nanoarchitectonics for Amino Acid‐Based Glasses via Co‐Assembly of Organic Counterions

Amino acid‐based biomolecular glasses represent an emerging material to meet the demand for sustainable development. However, most amino acids are difficult to vitrify due to their strong crystallization tendency, limiting further advancements of this field. In this study, we demonstrate that the introduction of counterions effectively suppresses crystallization, as hydrogen bonds within the system stabilize the disordered structures. Based on this, we propose a counterion co‐assembly strategy to synthesize a wide range of amino acid‐based glasses. This strategy enables the facile fabrication of glass with customizable shapes, high mechanical rigidity, and tunable multicolor fluorescence, ranging from blue to red depending on the excitation wavelength. Furthermore, this strategy allows the integration and enhancement of counterion properties within the glass matrix. Through the co‐assembly of phosphorescent counterions, we synthesized a series of long‐persistent luminescent glasses with significantly extended afterglow lifetimes. This work presents an effective approach for the synthesis of amino acid‐based glasses and provides insights into the development of supramolecular glasses with tailored functionalities.

An Energy-Tunable Dual Emission Mechanism of the Hybridized Local and Charge Transfer (HLCT) and the Excited State Conjugation Enhancement (ESCE).

Molecular design of dual-fluorescent probes requires precise adjustment of the energy levels of two excited states and the energy barrier between them. While the hybridized local and charge-transfer (HLCT) state has been recently focused as an important excited state for high emission efficiency with a tunable energy level, a dual emission involving the HLCT state has been only achieved with the excited-state intramolecular proton transfer (ESIPT) system. Here, a series of dual-fluorescent molecules involving an HLCT excited state with the excited-state conjugation enhancement (ESCE) motif is presented as the first case. The energy level of the HLCT state has been adjusted by changing substituents and solvents, separately from the ESCE energy level. The HLCT-ESCE molecular design with tunable fluorescence properties proposes a new strategy for the development of advanced fluorescent probes.

The Study of Tunable Excitation Independent and Dependent Photoluminescence Behaviour of P-Functionalized Carbon Dots

In this article, excitation independent and dependent fluorescence properties of surface functionalized carbon dots were studied. The samples were synthesized using a biomass derived Indian gooseberry as carbon precursor via microwave irradiation technique. Concentrated phosphonic acid is utilized as a surface passivator for carbon dots. The formation of spherical carbon dots in the size range of 6 to 12 nm was shown by transmission electron microscopy images. Raman and Fourier transform IR spectroscopies suggest the creation of highly disordered sp3carbon atoms including presence of surface functional groups and interaction of phosphorus with surface of carbon core. From the UV-visible absorption study, absorbance bands at 231 nm and 283 nm attributed to π-π* molecular transitions from carbon core are found. From the photoluminescence measurements, both excitation independent and excitation dependent tunable fluorescence is obtained from ultraviolet to visible (yellow) region of light respectively. The involvement of carbon core electronic states and surface modifier states are responsible for the origin of luminescence and their distinguished nature. The mechanism is discussed and emitted colour are confirmed by CIE plot. The relative quantum yield of the P-functionalized carbon dots is found to be 18.9% with reference to quinine sulfate. The fluorescence in ultra-violet and visible regions is applicable for bioimaging and potential antimicrobial activities.

Design and Construction of an Artificial Light‐Harvesting System Based on Polyacrylic Acid and a Cyanostilbene Derivative

AbstractThe development of materials with tunable fluorescence properties is critical for advancing applications in sensing, imaging, and information encryption. In this study, we synthesized a cyanostilbene derivative (CSA) that combines the benefits of aggregation‐induced emission (AIE) and self‐assembly in water. CSA, featuring a cyanostilbene core and hydrophilic carboxylate groups, exhibits weak fluorescence in solution but forms highly fluorescent nanoaggregates (CSA‐PAA) upon self‐assembly with polyacrylic acid (PAA). By integrating rhodamine 6G (Rh6G) as an energy acceptor, we constructed a light‐harvesting system (CSA‐PAA‐Rh6G) with high Förster resonance energy transfer (FRET) efficiency and tunable emission from green to yellow. This work presents a facile approach for the development of aqueous light‐harvesting systems and shows promise for future applications in tunable luminescent materials.

Beating the Odds with Binuclear N‐Heterocyclic Carbene Metallacycles: A Practical and Efficient Full‐Color Tunable Fluorescence System

AbstractAchieving full‐color emission with just two emitters presents a significant challenge. Two N‐heterocyclic carbene metallacycles (NHC‐M; M ═ Ag, Au) featuring a tetraphenylethene core, combining covalent and coordination bonds are synthesized to restrict rotation within the NHC‐M‐BC (BC = bicyclic) metallacycles and greatly enhanced their quantum yields. The enhancement is accomplished by adjusting the CH3CN/H2O solvent mixture, allowing emission tuning from blue to green for NHC‐Ag‐BC. Further diversification of the emission spectrum, including access to high‐quality white light (CIE coordinates 0.33, 0.34), is facilitated through the addition of sulforhodamine B via fluorescence resonance energy transfer (FRET). The compatibility of NHC‐Ag‐BC with agarose gel extends its applicability to UV‐LEDs chromic coatings, as well as information encryption and anti‐counterfeiting materials. The results underscore the viability of dual‐fluorophore systems for achieving full‐color emission and highlight the potential for developing versatile, multi‐colored functional materials.

Reversible Multi-Color optical switch utilizing tetraphenylethylene and spiropyran Complexes: Applications in advanced information encryption

In this paper, we introduced a strategic methodology to obtain time-resolved encryption utilizing a new technique. This method utilizes a reversible supramolecular optical switch, which is based on complexes consisting of tetraphenylethylene and spiropyran. Notably, these components are separately attached at the focal point of the same cholesterol-based unit, wherein the cholesterol-based unit can provide the essential driving forces to form complexes. A series of complexes were prepared with varying molar ratios (TPE/SP), allowing for the tuning of fluorescence emission. The supramolecular system leverages hydrogen bonding, van der Waals forces, and other non-covalent interactions to orchestrate the collaboration between the fluorophores (tetraphenylethylene) and the photochromic molecule (spiropyran). This coordination results in exceptional photochromic attributes, including rapid response, high contrast, and the capability to regulate fluorescence. The system is capable of achieving tunable dynamic fluorescence emission that transitions from brilliant blue to light purple and finally to red through fluorescence resonance energy transfer (FRET) after successive irradiation periods. Additionally, by fine-tuning the ratio of tetraphenylethylene to spiropyran, different dynamic fluorescence emission can be precisely manipulated. It is rarely reported that complexes accomplish time-dependent fluorescence emission with high-contrast. We are confident that the complexes, grounded on cholesterol unit, hold promise for broader applicability in developing innovative time-dependent fluorescent materials. Such materials can be effectively utilized for time-dependent information encryption, thereby bolstering security measures against unauthorized access.

Sensing the Small Change of Intermolecular Distance in Supramolecular Assembly by Using the Tunable Emission Wavelength of AIE-Active Luminogens.

The distinct molecular states - single molecule, assembly, and aggregate - of two ionic macromolecules, TPPE-APOSS and TPE-APOSS, are easily distinguishable through their tunable fluorescence emission wavelengths, which reflect variations in intermolecular distances. Both ionic macromolecules contain aggregation-induced emission (AIE) active moieties whose emission wavelengths are directly correlated to their mutual distances in solution: far away from each other as individual molecules, maintaining a tunable and relatively long distance in electrostatic interactions-controlled blackberry-type assemblies (microphase separation), or approaching van der Waals close distance in aggregates (macrophase separation). Furthermore, within the blackberry assemblies, the emission wavelength decreases monotonically with increasing assembly size, indicative of shorter intermolecular distances at nanoscale. The emission changes of TPPE-APOSS blackberry assemblies can even be visually distinguishable by eyes when their sizes and intermolecular distances are tuned. Molecular dynamics simulations further revealed that macromolecules are confined in various conformations by controllable intermolecular distances within the blackberry structure, thereby resulting in fluorescence emission with tunable wavelength.

Synergistic Anticancer Effects by Enhancing the G-Quadruplex Binding of Nickel(II) Salphen Complexes through Coupling with S-Doped Carbon Nanodots.

In recent decades, researchers have focused on developing less toxic and more precise cancer therapies. Carbon nanodots (CDs) are among the most promising technologies due to their high biocompatibility, tunable fluorescence, and ability to facilitate photothermal and photodynamic therapy. This study explores the synthesis and characterization of two CDs conjugated with Salphen metal complexes, namely, CDs-PEG-M1 and CDs-PEG-M2, through Sonogashira coupling. Their interaction with G-quadruplex DNA structures (G4s), motifs largely involved in cancer development, was evaluated using various spectroscopic techniques. The results indicate that CDs-PEG-M1 exhibits greater effectiveness in stabilizing G4 structures compared to the metal complex alone or nonfunctionalized CDs. This enhanced stabilization suggests that CDs-PEG-M1 could reduce the concentration of the metal complex needed for potential antitumor applications, thereby minimizing side effects on nontarget tissues. When tested on breast cancer models (MDA-MB-231 as a triple-negative model and MCF-7 as a HER-2 positive model) and on a healthy cell line (HDFa), the CDs-PEG-M1 conjugate reduced cell viability in a concentration- and time-dependent manner, showing greater potency and selectivity against cancer cells compared to virgin CDs and the free M1 complex. This synergistic anticancer effect, driven by the interaction with G4 structures and reactive oxygen species production, underscores the potential of CDs-PEG-M1 as a targeted nanotheranostic tool.

A chitosan-based near-infrared ratiometric fluorescent nanoprobe created by molecular assembly with applications in hypochlorous acid detection in live mouse

Hypochlorous acid (HClO/ClO−) is a key reactive oxidative species (ROS) in the body. The HClO/ClO− concentrations are imbalanced during cancer formation due to the ROS stress response. This paper introduces a novel chitosan-based self-calibration fluorescent nanoprobe (ChCyNil) constructed by molecular assembly for the ratiometric detection of HClO/ClO−. Two chromophores with different fluorescence characteristics and HClO/ClO− sensitivity were labeled on chitosan, and nanoparticles were prepared by a self-assembly strategy for HClO/ClO− detection. ChCyNil exhibits several advantages, such as dual near-infrared emissions at 670 nm and 845 nm, tunable fluorescence intensity, self-calibration fluorescence, and good biocompatibility, improving its accuracy in HClO/ClO− detection. Our study confirmed that ChCyNil exhibits a well-assembled spheroidal nanostructure and good photophysical properties in solution. The fluorescence imaging properties were further proved by detecting endogenous HClO/ClO− produced by LPS/PMA stimuli in cells and zebrafish. In addition, ChCyNil was used to detect the fluorescence behavior of HClO/ClO− in tumors of live mice. The successful design and fabrication of ChCyNil have presented a new strategy for constructing detection tools with improved fluorescence properties for HClO/ClO− in live animals.

Caged AIEgens: Multicolor and White Emission Triggered by Mechanical Activation.

Aggregation-induced emission luminogens (AIEgens) that respond to mechanical force are increasingly used as force probes, memory devices, and advanced security systems. Most of the known mechanisms to modulate mechanoresponsive AIEgens have been based on changes in aggregation states, involving only physical alterations. Instances that employ covalent bond cleavage are still rare. We have developed a novel mechanochemical uncaging strategy to unveil AIEgens with diverse emission characteristics using engineered norborn-2-en-7-one (NEO) mechanophores. These NEO mechanophores were covalently integrated into polymer molecules and activated in both the solution and solid states. This activation resulted in highly tunable fluorescence upon immobilization through solidification or aggregation, producing blue, green, yellow, and orange-red emissions. By designing the caged and uncaged forms as donor-acceptor pairs for Förster resonance energy transfer (FRET), we achieved multicolor mechanofluorescence, effectively broadening the color spectrum to include white emission. Additionally, we computationally explored the electronic structures of activated NEOs, providing insights into the observed regiochemical effects of the substituents. This understanding, together with the novel luminogenic characteristics of the caged and activated species, provides a highly tunable reporter that traces progress with continuous color evolution. This advancement paves the way for future applications of mechanoresponsive materials in areas like damage detection and bioimaging.

Quantum-Inspired Macromolecular Design: Harnessing Quantum Dots for Enhanced Polymer Functionality in Drug Delivery

Quantum dots (QDs) have emerged as transformative nanomaterials in drug delivery due to their unique optical and electronic properties, such as tunable fluorescence, high surface area and size-dependent emission in pharmaceutical origin. When integrated with polymers, this hybrid system offers enhanced functionality for targeted, controlled and stimuli-responsive drug delivery. This review focuses on the synthesis and application of quantum dot-polymer composites in drug delivery, emphasizing their ability to improve drug targeting, sustained release and real-time imaging in therapeutic applications. The multifunctionality of these systems enables personalized medicine approaches, particularly in cancer therapy and neurological disorders. Despite their promising potential, concerns related to toxicity and scalability pose significant challenges for their widespread clinical use. Ongoing research efforts are focused on developing more biocompatible QDs, optimizing the design of polymer-QD hybrids and addressing regulatory hurdles. This review, we believe, provides a comprehensive analysis of current advancements in quantum dot-based drug delivery systems and outlines future directions to overcome the existing limitations and enhance clinical applicability. The integration of quantum dots with polymers represents a significant leap forward in the field of nanomedicine, offering the potential for highly efficient, precise and safe drug delivery platforms.

Configurationally Stepping Confinement Achieved Tunable Chiral Near-Infrared Luminescence Supramolecular Phenothiazine Organic Framework.

Herein, thermally responsive reversible chiral supramolecules are reported, constructed by the chirality transfer from tripeptides to achiral network supramolecular organic frameworks (SOF) based on configurationally stepping confinement, which displayed not only highly selective reversible chirality transfer but also efficient enhanced near-infrared (NIR) luminescence. Taking advantage of macrocyclic confinement, CB[8] separately encapsulated two kinds of tetracationic bis(phenothiazines) derivatives (G1, G2) at 2:1 stoichiometric to form organic 2D SOFs, efficiently enhancing 12.6 fold NIR luminescence and blueshifted from 705 to 680 nm for G1, and redshifted from 695 to 710 nm for G2, respectively. Uncommonly, the tripeptide coassembled with two kinds of achiral noncovalent frameworks (G1/CB[8] or G2/CB[8]) displayed different opposite circular dichroism signals based on different binding modes and affinity, achieving chirality transfer from tripeptide to organic supramolecular assemblies with further enhanced NIR fluorescence up to 46.2 times and the quantum yield (QY) increased from 0.71% to 10.29% for G2/CB[8], showing reversible chirality transfer and tunable NIR fluorescence under thermal stimulus. Therefore, the current research has achieved controllable chirality transfer from tripeptide to the SOFs and the enhancement of tunable NIR fluorescence, which is successfully applied in thermal responsive chiral logic gates, information encryption, and cell imaging.

A multi-dimensional anti-counterfeiting nanocomposite based on fluorescent CDs and Eu-MOFs with dual function for continuous detection of Cu2+ and Bacillus anthracis

Traditional luminescent materials for anti-counterfeiting usually adopt encryption of low-level systems with limited security, which seriously hinders their application in preventing counterfeiting and information leakage. Therefore, it is urgent to develop materials for higher-level anti-counterfeiting. In this work, a stimulus-responsive intelligent luminescent material (AC@CDs-Eu-MOFs) was prepared by co-loading green-fluorescence CDs and red-fluorescence Eu-MOFs on Amino clay (AC). 5D security barcodes, which were easy to observe while difficult to clone, were ulteriorly designed based on the nanocomposite owing to the tunable fluorescence by optical stimulation and chemical stimulus. Owing to the large capacity, low cost, and easy authentication, the 5D security barcodes possess enormous potential in optical data storage and multi-dimensional information encryption. In addition, the chemical stimulus-response enables the nanocomposite achievable in detection of Cu2+ and Bacillus anthracis. Particularly, quantitative determination of copper in environmental water samples could be realized with a detection limit as low as 10.67 nM. Therefore, the material shows potential for detection of environmental pollutants besides advanced anti-counterfeiting.

Surface engineering and concentration-dependent emission activated flexible tunable fluorescence from lignin-based N-doped carbon dots

Achieving the flexible and tunable fluorescence of lignin-based N-doped carbon dots (LCDs) remains a win–win yet challenging strategy. In this study, combining the surface engineering and concentration regulation strategy enabled the flexible adjustment of LCDs fluorescence emission from blue to yellow regions (345 to 560 nm). The surface electron-donor –OH groups not only enhanced the photoluminescence quantum yield (PLQY) to 14.75 % but activated the spectral shift of reduced LCDs (RLCDs). These arose from the reinforced π-electron conjugation and generated new –OH-related extrinsic defects with elevating concentration. Conversely, the electron-withdrawing CO groups participated in the blue-to-green fluorescence modulation. Still, they drastically reduced the PLQY of oxidized LCDs (OLCDs) to 2.13 %, due to the larger particle size and more non-radiative transfer induced by CO groups. Based on these, CDs/PVA films and printed fluorescent patterns with multicolor fluorescence were realized for anti-counterfeiting, and the RLCDs@Al2O3 hybrid facilitated the precise fluorescence fingerprint tracking and recognition. This study provided a facile strategy for enriching and developing novel LCDs with flexible fluorescence for their advanced applications.

Rapid Construction of PVA@CDs/SiO2 Fluorescent/Structural Color Dual-Mode Anti-Counterfeiting Labels via Spray-Coating Method.

A method of sequential spraying of polyvinyl alcohol with carbon quantum dots (PVA@CDs) aqueous suspension and SiO2 aqueous suspension is proposed to rapidly prepare multicolor dual-mode anti-counterfeiting labels. With the optimization of the concentration (15%) of colloidal microspheres in the SiO2 aqueous suspension as well as the spraying process parameters (spray distance of 10 cm, spray duration of 3 s, and assembly temperature of 20 °C), different-sized SiO2 microspheres (168 nm, 228 nm, and 263 nm) were utilized to rapidly assemble red, green, and blue photonic crystals. Furthermore, the tunable fluorescence emission of carbon quantum dots endows the labels with yellow, green, and blue fluorescence. The constructed dual-mode labeling was used to develop an anti-counterfeiting code with dual-channel information storage capabilities and also to create dual-mode multicolor anti-counterfeiting labels on various packaging substrates. This work provides a novel solution for anti-counterfeiting packaging and information storage.