Construction of emission-tunable nanoparticles based on a TICT-AIEgen: impact of aggregation-induced emission versus twisted intramolecular charge transfer

A TICT-AIE activated dual-channel fluorescence-on probe to reveal the dynamics mechanosensing of lipid droplets during ferroptosis

Mechanical forces play a crucial role in cellular processes, including ferroptosis, a form of regulated cell death associated with various diseases. However, the mechanical aspects of organelle lipid droplets (LDs) during ferroptosis are poorly understood. In this study, we designed and synthesized a fluorescent probe, TPE-V1, to enable real-time monitoring of LDs' viscosity using a dual-channel fluorescence-on model (red channel at 617 nm and NIR channel at 710 nm). The fluorescent imaging of using TPE-V1 was achieved due to the integrated mechanisms of the twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE). Through dual-emission channel fluorescence imaging, we observed the enhanced mechanical energy of LDs triggering cellular mechanosensing, including ferroptosis and cell deformation. Theoretical calculations confirmed the probe's behavior, showing that high-viscosity media prevented the rotation processes and restored fluorescence quenching in low viscosity. These findings suggest that our TICT-TPE design strategy provides a practical approach to study LDs' mechanical properties during ferroptosis. This development enhances our understanding of the interplay between mechanical forces and LDs, contributing to the knowledge of ferroptotic cell death and potential therapeutic interventions targeting dysregulated cell death processes.

Ultrabright Acrylic Polymers with Tunable Fluorescence Enabled by Imprisoning Single TICT Probe

Bright and colorful fluorescent polymers are ideal materials for a variety of applications. Although polymers could be made fluorescent by physical doping or chemical binding of fluorescent units, it is a great challenge to get colorful and highly emissive polymers with a single fluorophore. Here the development of a general and facile method to synthesize ultrabright and colorful polymers using a single twisted intramolecular charge transfer (TICT) probe is reported. By incorporating polymerizable, highly fluorescent, and environmental sensitive TICT probe, a series of colorful acrylic polymers (emission from 481 to 543 nm) with almost 100% fluorescence quantum yields are prepared. Like the solvatochromic effect, functional groups within side chains of acrylic polymers (including alkyl chain, tetrahydrofurfuryl group, and hydroxyl group) provide varied environmental polarity for the incorporated fluorophore, resulting in a series of colorful polymeric materials. Benefiting from the excellent photophysical properties, the polymers show great potential in encryption, cultural relics protection, white light-emitting diode bulb making, and fingerprint identification.

Tunable Fluorescence via Self-Assembled Switching of AIE-Active Micelle-like Nanoaggregates

Chemical structures bearing a combination of aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT) properties attracted the attention of many researchers. Recently, there is an increasing demand to pose tunable AIEE and ICT fluorophores that could present their conformation changes-related emission colors by adjusting the medium polarity. In this study, we designed and synthesized a series of 4-alkoxyphenyl-substituted 1,8-naphthalic anhydride derivatives NAxC using the Suzuki coupling reaction to construct donor-acceptor (D-A)-type fluorophores with alkoxyl substituents of varying carbon chain lengths (x = 1, 2, 4, 6, 12 in NAxC). To explain the observation that molecules with longer carbon chains revealed unusual fluorescence enhancement in water, we study the optical properties and evaluate their locally excited (LE) and ICT states by solvent effects combined with Lippert-Mataga plots. Then, we explored the self-assembly abilities of these molecules in water-organic (W/O) mixed solutions and observed the morphology of its nanostructure using a fluorescence microscope and SEM. The results show that NAxC, x = 4, 6, 12 show different degrees of self-assembly behaviors and corresponding aggregation-induced emission enhancement (AIEE) progresses. At the same time, different nanostructures and corresponding spectral changes can be obtained by adjusting the water ratio in the mixed solution. That is, NAxC compounds present different transitions between LE, ICT and AIEE based on the polarity, water ratio and time changes. We designed NAxC as the structure-activity relationship (SAR) of the surfactant to demonstrate that AIEE comes from the formation of micelle-like nanoaggregates, which causes a restriction of the transfer from the LE state to the ICT state, and micelle formation results in a blue-shift in emission and enhances the intensity in the aggregate state. Among them, NA12C is most likely to form micelles and the most obvious fluorescence enhancement, which will switch over time due to the nano-aggregation transition.

A ratiometric fluorescent tag based on dual-emissive hydrophobic carbon dots for in-situ monitoring of seafood freshness

A ratiometric fluorescent tag based on dual-emissive hydrophobic carbon dots (H-CDs) with well volatile base nitrogens (VBNs)-response was fabricated, offering the in-situ, real-time, and visual evaluation of seafood freshness. The presented H-CDs aggregates exhibited a sensitive response to VBNs, with a limit of detection of 7 μM and 137 ppb for spermine and ammonia hydroxide, respectively. Subsequently, a ratiometric tag was successfully fabricated by depositing dual-emissive CDs on cotton paper. Upon the treatment with ammonia vapour, the presented tag exhibited highly recognizable colour variations from red to blue under UV light. In addition, the cytotoxicity was explored by CCK8 assay, and the results proved the nontoxicity of the presented H-CDs. To our knowledge, this is the first ratiometric tag based on dual-emissive CDs with aggregation-induced emission properties for recognition of VBNs and seafood freshness in a real-time and visual manner.

Construction of a TICT-AIE-Integrated Unimolecular Platform for Imaging Lipid Droplet-Mitochondrion Interactions in Live Cells and In Vivo

Inter-organelle interactions play a vital role in diverse biological processes. Thus, chemical tools are highly desirable for understanding the spatiotemporal dynamic interplay among organelles in live cells and in vivo. However, designing such tools is still a great challenge due to the lack of universal design strategies. To break this bottleneck, herein, a novel unimolecular platform integrating the twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) dual mechanisms was proposed. As a proof of concept, two organelles, lipid droplets (LDs) and mitochondria, were selected as models. Also, the first TICT-AIE integration molecule, BETA-1, was designed for simultaneous and dual-color imaging of LDs and mitochondria. BETA-1 can simultaneously target LDs and mitochondria due to its lipophilicity and cationic structure and emit cyan fluorescence in LDs and red fluorescence in mitochondria. Using BETA-1, for the first time, we obtained long-term tracking of dynamic LD-mitochondrion interactions and identified several impressive types of dynamic interactions between these two organelles. More importantly, the increase in LD-mitochondrion interactions during ferroptosis was revealed with BETA-1, suggesting that intervening in the LD-mitochondrion interactions may modulate this cell death. BETA-1 was also successfully applied for in vivo imaging of LD-mitochondrion interactions in C. elegans. This study not only provides an effective tool for uncovering LD-mitochondrion interactions and deciphering related biological processes but also sheds light on the design of new probes with an integrated TICT-AIE mechanism for imaging of inter-organelle interactions.

Construction of Multi-color fluorescent carbon dots by Aggregation-Induced emission

Aggregation-induced emission luminogens (AIEgens) have garnered significant attention because of their outstanding photophysical characteristics. AIEgens are used in fluorescence imaging, sensors, tumor treatment, and other related fields. However, the synthese of these AIEgens are relatively complicated and requires expensive raw materials. These drawbacks limit their applications and development to a certain extent. In this study, using cheap and convenient materials, we developed a new type of carbon dots (O-CDs) using a one-step solvothermal method, which has the potential to become a new AIEgen. O-CDs exhibit different fluorescence colors in different solvents, and they exist as monomers in ethylic acid and, ethanol alcohol, etc., exhibiting blue fluorescence. After adding water, the fluorescence of O-CDs gradually turns orange red, because the internal rotation of the disulfide bond molecules is restricted and the AIE effect occurs. Using the unique AIE performance of O-CDs, we fabricated an anti-counterfeiting luminous ink, that can be used for encryption in the reversible double switch mode.

Substituent Effect on AIE mechanism of two coumarin derivatives: uncommon TICT fluorescence in aggregation state

Two coumarin derivatives, 7-diethylamino-3-(4-nitrophenyl)coumarin (DNC) and 7-hydroxy-3-(4-nitrophenyl)coumarin (HNC), were synthesized via Knoevenagel condensation of salicylaldehyde derivatives with 4-nitrophenylacetonitrile and then cyclization reaction. Both of them were characterized by single-crystal X-ray diffraction. The molecules of DNC are stacked via π-π interaction, while the hydrogen bond interactions instead of π-π interaction were observed in the crystal packing of HNC. Both of DNC and HNC showed solvatochromic properties and aggregation-induced emission (AIE) activities, but the AIE characteristics of them were entirely different. HNC exhibited an AIE phenomenon as the result of the restriction of twisted intramolecular charge transfer (TICT), while DNC emitted peculiar dual fluorescence which was assigned to the emission based on the inhibition of TICT state formation and the emission from the TICT state respectively.

Mechanochemical synthesis of an AIE-TICT-ESIPT active orange-emissive chemodosimeter for selective detection of hydrogen peroxide in aqueous media and living cells, and solid-phase quantitation using a smartphone

We report herein the design and mechanochemical synthesis of a chemodosimeter, benzothiazole-derived unsymmetrical azine protected by 4-bromomethylphenylboronic acid (BTPAB), an orange aggregation-induced emission (AIE), for the selective detection of H2O2 in a turn-on manner.

The screening of drug-induced nephrotoxicity using gold nanocluster-based ratiometric fluorescent probes

Herbal medicines are potential candidates for the treatment of various diseases, but their medication safety remains poorly regulated. Current screening methods for the herbal medicine-induced nephrotoxic effects include histological and serological assessments, which often fail to reflect the kidney dysfunction instantly. Here we report a ratiometric fluorescence approach for the rapid and facile screening of drug-induced acute kidney injury using chromophore-modified gold nanoclusters. These gold nanoclusters are highly sensitive to reactive oxygen species (ROS), with a detection limit of 14 nM for ˙OH. After passing through the glomerular filtration barrier, the gold nanocluster-based probes can quantify the fluctuation of the ROS level in the kidneys and evaluate the risk of drug-induced nephrotoxicity. We further employed nephrotoxic triptolide as the model drug and the screening of drug-induced early renal injury was demonstrated using the nanoprobes, which is unattainable by conventional diagnostic approaches. Our fluorescent probes also allow the identification of other nephrotoxic components from herbal medicine such as aristolochine, providing a high-throughput strategy for the screening of herbal supplement-induced nephrotoxicity.

Fabrication of Double Emission Enhancement Fluorescent Nanoparticles with Combined PET and AIEE Effects

The major challenge in the fabrication of fluorescent silica nanoparticles (FSNs) based on dye-doped silica nanoparticles (DDSNs) is aggregation-caused fluorescence quenching. Here, we constructed an FSN based on a double emission enhancement (DEE) platform. A thio-reactive fluorescence turn-on molecule, N-butyl-4-(4-maleimidostyryl)-1,8-naphthalimide (CS), was bound to a silane coupling agent, (3-mercaptopropyl)-trimethoxysilane (MPTMS), and the product N-butyl-4-(3-(trimethoxysilyl-propylthio)styryl)-1,8-naphthalimide (CSP) was further used to fabricate a core–shell nanoparticle through the Stöber method. We concluded that the turn-on emission by CSP originated from the photoinduced electron transfer (PET) between the maleimide moiety and the CSP core scaffold, and the second emission enhancement was attributed to the aggregation-induced emission enhancement (AIEE) in CSP when encapsulated inside a core–shell nanoparticle. Thus, FSNs could be obtained through DEE based on a combination of PET and AIEE effects. Systematic investigations verified that the resulting FSNs showed the traditional solvent-independent and photostable optical properties. The results implied that the novel FSNs are suitable as biomarkers in living cells and function as fluorescent visualizing agents for intracellular imaging and drug carriers.

Dual-acting antibacterial porous chitosan film embedded with a photosensitizer

This study proposes to develop a dual-acting antibacterial film of porous chitosan (Cs) embedded with small molecular compound, which possesses photosensitive characteristics with bactericidal efficacy, to promote the accelerated recovery of infectious wounds. The Cs/small molecular compound (Cs-cpd.2) dressing was prepared using the freeze-drying method. Characterization of the synthesized Cs-cpd.2 indicated that it has high porosity and moisture absorption effect, hence enhancing the absorption of wound exudate. Experimental results showed that Cs-cpd.2 dressing has good bactericidal and bacteriostatic effects on Staphylococcus aureus under visible-light irradiation and has antibacterial effect in the dark. It was also found that the small molecular compound does not have cytotoxicity at a dose of 0-5 μM. Furthermore, Cs-cpd.2 that contained small molecular compound with a concentration of 0.3-1 μM has positive effect on both the cell viability rate and cell proliferation rate of human fibroblast CG1639. Cs-cpd.2 can significantly promote cell proliferation when the small molecular compound and the basic fibroblast growth factor bFGF were added together. Therefore, the proposed Cs-cpd.2 dressing is feasible for photodynamic therapy (PDT) and clinical wound dressing applications.

Red fluorescent pyrazoline-BODIPY nanoparticles for ultrafast and long-term bioimaging

Fluorescence bioimaging is very significant in studying biological processes. Fluorescent nanoparticles (NPs) manufactured from aggregation-induced emission (AIE) materials, as promising candidates, have attracted more attention. However, it is still a challenge to explore suitable AIE NPs for bioimaging. Herein, we synthesized pyrazoline-BODIPY (PZL-BDP) with a donor and acceptor (D-A) structure by a condensation reaction, cultured its single crystal, and studied its twisted intramolecular charge transfer (TICT) and AIE effects. PZL-BDP could self-assemble to form red fluorescent nanoparticles (PZL-BDP NPs) which showed a good fluorescence quantum yield of 15.8% in water. PZL-BDP NPs with excellent stability and biocompatibility exhibited a large Stokes shift (Δλ = 111 nm) which resulted in the reduction of external interference and enhancement of the fluorescence contrast. Furthermore, these nanoparticles could be readily internalized by HeLa cells and they stain the cells in just five seconds, indicating an ultrafast bioimaging protocol. Moreover, long-term tracking fluorescence signals in vivo for about 12 days were obtained. The bright red fluorescence, ultrafast cell staining ability, and long-term in vivo tracking competence outline the great potential of rational design nanomaterials with AIE characteristics for monitoring biological processes.