Stable and Size-Tunable Aggregation-Induced Emission Nanoparticles Encapsulated with Nanographene Oxide and Applications in Three-Photon Fluorescence Bioimaging

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Chitosan- and hyaluronic acid-based nanoarchitectures in phototherapy: Combination cancer chemotherapy, immunotherapy and gene therapy

Cancer phototherapy has been introduced as a new potential modality for tumor suppression. However, the efficacy of phototherapy has been limited due to a lack of targeted delivery of photosensitizers. Therefore, the application of biocompatible and multifunctional nanoparticles in phototherapy is appreciated. Chitosan (CS) as a cationic polymer and hyaluronic acid (HA) as a CD44-targeting agent are two widely utilized polymers in nanoparticle synthesis and functionalization. The current review focuses on the application of HA and CS nanostructures in cancer phototherapy. These nanocarriers can be used in phototherapy to induce hyperthermia and singlet oxygen generation for tumor ablation. CS and HA can be used for the synthesis of nanostructures, or they can functionalize other kinds of nanostructures used for phototherapy, such as gold nanorods. The HA and CS nanostructures can combine chemotherapy or immunotherapy with phototherapy to augment tumor suppression. Moreover, the CS nanostructures can be functionalized with HA for specific cancer phototherapy. The CS and HA nanostructures promote the cellular uptake of genes and photosensitizers to facilitate gene therapy and phototherapy. Such nanostructures specifically stimulate phototherapy at the tumor site, with particle toxic impacts on normal cells. Moreover, CS and HA nanostructures demonstrate high biocompatibility for further clinical applications.

Multi-Stimuli-Responsive and Cell Membrane Camouflaged Aggregation-Induced Emission Nanogels for Precise Chemo-photothermal Synergistic Therapy of Tumors

Targeted and controllable drug release at lesion sites with the aid of visual navigation in real-time is of great significance for precise theranostics of cancers. Benefiting from the marvelous features (e.g., bright emission and phototheranostic effects in aggregates) of aggregation-induced emission (AIE) materials, constructing AIE-based multifunctional nanocarriers that act as all-arounders to integrate multimodalities for precise theranostics is highly desirable. Here, an intelligent nanoplatform (P-TN-Dox@CM) with homologous targeting, controllable drug release, and in vivo dual-modal imaging for precise chemo-photothermal synergistic therapy is proposed. AIE photothermic agent (TN) and anticancer drug (Dox) are encapsulated in thermo-/pH-responsive nanogels (PNA), and the tumor cell membranes are camouflaged onto the surface of nanogels. Active targeting can be realized through homologous effects derived from source tumor cell membranes, which advantageously elevates the specific drug delivery to tumor sites. After being engulfed into tumor cells, the nanogels exhibit a burst drug release at low pH. The near-infrared (NIR) photoinduced local hyperthermia can activate severe cytotoxicity and further accelerate drug release, thus generating enhanced synergistic chemo-photothermal therapy to thoroughly eradicate tumors. Moreover, P-TN-Dox@CM nanogels could achieve NIR-fluorescence/photothermal dual-modal imaging to monitor the dynamic distribution of therapeutics in real-time. This work highlights the great potential of smart P-TN-Dox@CM nanogels as a versatile nanoplatform to integrate multimodalities for precise chemo-photothermal synergistic therapy in combating cancers.

Fluorescent-Based Neurotransmitter Sensors: Present and Future Perspectives

Neurotransmitters (NTs) are endogenous low-molecular-weight chemical compounds that transmit synaptic signals in the central nervous system. These NTs play a crucial role in facilitating signal communication, motor control, and processes related to memory and learning. Abnormalities in the levels of NTs lead to chronic mental health disorders and heart diseases. Therefore, detecting imbalances in the levels of NTs is important for diagnosing early stages of diseases associated with NTs. Sensing technologies detect NTs rapidly, specifically, and selectively, overcoming the limitations of conventional diagnostic methods. In this review, we focus on the fluorescence-based biosensors that use nanomaterials such as metal clusters, carbon dots, and quantum dots. Additionally, we review biomaterial-based, including aptamer- and enzyme-based, and genetically encoded biosensors. Furthermore, we elaborate on the fluorescence mechanisms, including fluorescence resonance energy transfer, photon-induced electron transfer, intramolecular charge transfer, and excited-state intramolecular proton transfer, in the context of their applications for the detection of NTs. We also discuss the significance of NTs in human physiological functions, address the current challenges in designing fluorescence-based biosensors for the detection of NTs, and explore their future development.

GSH-Responsive Prodrug Nanoassembly as a Carrier-Free Nanoplatform for Tumor-Targeting Delivery and Chemo-Photothermal Therapy

Photothermal therapy, combined with chemotherapy, holds promising prospects for the therapeutic outcome of malignant tumors. However, the synergistic therapeutic effect suffers from low coloading capacity and inefficient synchronous tumor-targeting delivery of chemodrug and photothermal photosensitizers. Herein, we designed a versatile carrier-free nanoplatform to seek improvement for chemo-photothermal therapy. An NIR photosensitizer IR-808 was used for noninvasive cancer imaging, diagnosis, and imaging-guided photothermal therapy. A reduction-sensitive paclitaxel prodrug (PTX-SS-PEG2k) was rationally synthesized by covalently linking paclitaxel with polyethylene glycol 2000 via a disulfide bond. Then, the carrier-free nanoassemblies were constructed with an inner core of IR-808 and an amphiphilic paclitaxel prodrug shell. PTX-SS-PEG2k served as a stabilizer and chemodrug and could facilitate the self-assembly of IR-808 nanoparticles with high coloading efficiency and reduction-sensitive drug release. The versatile nanoplatform exhibited multiple advantages, including high drug payload, reduction-sensitive drug release, tumor-targeting drug delivery, and potent synergistic antitumor effect. We provide a versatile theranostic nanoplatform, which improves the effectiveness of synergetic chemo-photothermal therapy and reduces the off-target toxicity.

Multiphoton excited singlet/triplet mixed self-trapped exciton emission

Multiphoton excited luminescence is of paramount importance in the field of optical detection and biological photonics. Self-trapped exciton (STE) emission with self-absorption-free advantages provide a choice for multiphoton excited luminescence. Herein, multiphoton excited singlet/triplet mixed STE emission with a large full width at half-maximum (617 meV) and Stokes shift (1.29 eV) has been demonstrated in single-crystalline ZnO nanocrystals. Temperature dependent steady state, transient state and time-resolved electron spin resonance spectra demonstrate a mixture of singlet (63%) and triplet (37%) mixed STE emission, which contributes to a high photoluminescence quantum yield (60.5%). First-principles calculations suggest 48.34 meV energy per exciton stored by phonons in the distorted lattice of excited states, and 58 meV singlet-triplet splitting energy for the nanocrystals being consistent with the experimental measurements. The model clarifies long and controversial debates on ZnO emission in visible region, and the multiphoton excited singlet/triplet mixed STE emission is also observed.

The impact of co-treatment with graphene oxide and metal mixture on Salmo trutta at early development stages: The sorption capacity and potential toxicity

Graphene oxide (GO) are novel nanomaterials with a wide range of applications due to their high absorption capacity. This study was undertaken with a view to assess the bioaccumulation and acute toxicity of GO used in combination with the heavy metal mixture (Cr, Cu, Ni and Zn) to fish embryos and larvae. For this purpose, Salmo trutta embryos and larvae were subjected to the 4-day long treatment with three different concentrations of GO, the metal mixture, which was prepared of four metals at the concentrations corresponding to the maximum-permissible-concentrations for EU inland waters (Cr-0.01, Cu-0.01, Ni-0.034, and Zn-0.1 mg/L), and with GO in combination with MIX (GO+MIX). When used in combination with the metal mixture, GO exhibited a high metal sorption capacity. The obtained confocal fluorescence microscopy results showed that GO located in the embryo chorion causing its damage; in larvae, however, GO were found only in the gill region. Results of these experiments confirmed the hypothesis that GO affects the accumulation of metals and mitigates their toxic effects on organism. In embryos, the acute toxicity of exposure to GO and co-exposure to MIX+GO was found to manifest itself through the decreased heart rate (HR) and malondialdehyde (MDA) level and through the increased metallothionein (MT) concentration. Meanwhile, in larvae, GO and MIX+GO were found to induce genotoxicity effects. However, changes in HR, MDA, MT, gill ventilation frequency, yolk sack absorption and cytotoxicity compared with those of the control group were not recorded in larvae. The obtained results confirmed our hypothesis: the combined effect of MIX and GO was less toxic to larvae (especially survival) than individual effects of MIX components. However, our results emphasize that fish exposure to GO alone and in combination with heavy metal contaminants (MIX+GO) even at environmentally relevant concentrations causes health risks that cannot be ignored.

Coordination-Regulated Terpyridine-Mn(II) Complexes for Photodynamic Therapy Guided by Multiphoton Fluorescence/Magnetic Resonance Imaging

The synergy of multiphoton fluorescence imaging (MP-FI) and magnetic resonance imaging (MRI) provides an imaging platform with high resolution and unlimited penetration depth for early disease detection. Herein, two kinds of terpyridine-Mn(II) complexes (FD-Mn-O₂NO and FD-Mn-FD) possessing seven and six coordination modes, respectively, were designed rationally for photodynamic therapy (PDT) guided by MP-FI/MRI. The complexes obtain different multiphoton fluorescence/magnetic resonance properties by adjusting the number of terpyridine ligands. Among them, FD-Mn-FD exhibits the following superiorities: (1) The optimal three-photon excitation wavelength of FD-Mn-FD falls at 1450 nm (NIR-II), which brings high sensitivity and deep tissue penetration in MP-FI. (2) FD-Mn-FD has effective longitudinal relaxation efficiency (r₁ = 2.6 m M^-1 s^-1), which can be used for T₁-weighted MRI, overcoming the problems of limited tissue penetration depth and low spatial resolution. (3) FD-Mn-FD generates endogenous ¹O₂ under irradiation by 808 nm light, thereby enhancing the PDT effect in vitro and in vivo. To the best of our knowledge, the complex FD-Mn-FD is the first complex to guide PDT through MP-FI/MRI, providing a blueprint for accurate and effective early detection and timely treatment of the complex in the early stages of cancer.

A potent luminogen with NIR-IIb excitable AIE features for ultradeep brain vascular and hemodynamic three-photon imaging

Three-photon excited fluorescence microscopy (3PEFM) has emerged as a promising protocol for visualizing deep-brain vasculature and hemodynamics. However, the current situation is still far from satisfactory, due to small excitation action cross-section and short excitation wavelength of those previously reported 3PEFM luminogens. Herein, we manipulated molecular engineering by subtly regulating structural planarization/twisting to achieve ingenious integration of large three-photon absorption cross-section, high fluorescence quantum yield, ultralong near-infrared IIb excitation, and aggregation-induced emission features. The resulting molecule, namely DPCZ-BT, exhibited as high as 50.6% of fluorescence quantum yield and as large as 2.0 × 10-81 cm6s2/photon2 of three-photon absorption cross-section, which can be excited by 1665 nm fs laser and presents a recorded penetration depth of 1860 μm for deep-brain vascular structural imaging with high spatiotemporal resolution and signal-to-background ratio. Moreover, DPCZ-BT having good photostability and excellent biocompatibility is capable of impressively approaching 1600 μm depth in monitoring red blood cells flow velocity with extraordinary clarity for hemodynamics.

Design, synthesis and imaging of a novel mitochondrial fluorescent nanoprobe based on distyreneanthracene-substituted triphenylphosphonium salt

Targeting and monitoring the dynamics of mitochondria are of great significance because mitochondria are involved in a variety of physiological and pathological processes. For achieving this purpose, highly sensitive, photostable, tolerance and specific fluorescent probe is necessary. To obtain a superior mitochondrial fluorescent probe, (4-distyreneanthracenoxybutyl) bis(triphenylphosphonium) bromide (DSA-TPP) with aggregation-induced emission (AIE) characteristic was designed and synthesized for mitochondrial targeting. DSA-TPP dots with high fluorescence quantum yield (Φ = 17.9) and small particle size (8 nm) can be easily prepared by self-assembly formation. DSA-TPP dots had the ability of lightning mitochondria in living cells with high brightness, superior photostability and strong tolerance to cell environment change.

Enhanced photostability of aggregation induced emission by hydrophobic groups

Since the aggregation induced emission (AIE) phenomenon was reported, many research groups have used this unique AIE effect to develop chemo- or bio-sensors for detecting ions, gases, explosives, proteins, and enzymes. Most of these sensors work in their aggregate state, therefore, fluorescence stability has become one of the important problem, and unfortunately, as far as we know, there is no paper to discuss what factors can improve the fluorescence stability of AIE compounds in the aggregate state, if the fluorescence stability of the sensors are poor, there will seriously affect the detection result. In this article, we found that compounds with hydrophobic long alkyl substituents can maintain stable fluorescence intensity for a long time in the aggregate state. In addition, cyclohexane is introduced as a hydrophobic substituent. Therefore, the fluorescence stability of the aggregates also increased by 90% within 1800s. The aggregation solutions of CB-3 and CSB-2 were left for two weeks, and no significant changes were found in the fluorescence intensity. Molecular dynamics simulation (MDS) shows that the presence of hydrophobic substituents in compounds cause the molecules to be closely interspersed with each other, hence, making it difficult to change the optical properties, microstructure and stacking mode of the AIE aggregates by external stimulations. The introduction of hydrophobic substituents improves the fluorescence stability of AIE compounds, and makes the AIE phenomenon more valuable in the fields of biological/chemical sensing and imaging.

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1-3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

An AIE triggered fluorescence probe with three-photon absorption and its biological applications

Three-photon absorption (3 PA) in the near IR region is among the most prominent nonlinear optical (NLO) effects and has attractive applications in chemical/biological sensing and imaging. Yet, rationally constructed molecules with small molecular weight and reasonable 3 PA cross-section has been rarely reported. Herein, we designed a novel three-photon absorption photostable luminogen (namely X1) with enhanced aggregation induced emission (AIE) and the ability to achieve multi-photon imaging with femtosecond laser excitation. X1 was constructed from diaminobenzene and diethylamino salicylaldehyde forming a novel di-Schiff base. It possesses a large conjugated delocalization which exhibits large three-photon absorption (3 PA) cross-section values. We also showed that by using a suitable delivery vector, X1 compound could applied as a live cell imaging probe thus providing a valuable tool to study lipid droplets/lysosome interaction in depth tissues.

Photodynamic Therapy Directed by Three-Photon Active Rigid Plane Organic Photosensitizer

Multi-photon photosensitizers (PSs) could significantly improve the efficacy of photodynamic therapy due to the long-wavelength favorability for deeper tissue penetration and lower biological damage. However, most studies are limited to single-photon or two-photon PSs at a relatively short-wave excitation window. To overcome this barrier, we rationally design a series of rigid plane compounds with efficient reactive oxygen species (ROS) production in vitro under laser irradiation. Furthermore, the studies show that one of the compounds (U-TsO) could induce rapid multi-types of cell death under three-photon exposure, suggesting a promising clinical outcome in ex vivo 3D multicellular tumor spheroid. This work offers a novel strategy to construct functional materials with competitive multi-photon photodynamic therapy (PDT) outcome.

Emerging photothermal-derived multimodal synergistic therapy in combating bacterial infections

Due to the emerging bacterial resistance and the protection of tenacious biofilms, it is hard for the single antibacterial modality to achieve satisfactory therapeutic effects nowadays. In recent years, photothermal therapy (PTT)-derived multimodal synergistic treatments have received wide attention and exhibited cooperatively enhanced bactericidal activity. PTT features spatiotemporally controllable generation of hyperthermia that could eradicate bacteria without inducing resistance. The synergy of it with other treatments, such as chemotherapy, photo-dynamic/catalytic therapy (PDT/PCT), immunotherapy, and sonodynamic therapy (SDT), could lower the introduced laser density in PTT and avoid undesired overheating injury of normal tissues. Simultaneously, by heat-induced improvement of the bacterial membrane permeability, PTT is conducive for accelerated intracellular permeation of chemotherapeutic drugs as well as reactive oxygen species (ROS) generated by photosensitizers/sonosensitizers, and could promote infiltration of immune cells. Thereby, it could solve the currently existing sterilization deficiencies of other combined therapeutic modes, for example, bacterial resistance for chemotherapy, low drug permeability for PDT/PCT/SDT, adverse immunoreactions for immunotherapy, etc. Admittedly, PTT-derived synergistic treatments are becoming essential in fighting bacterial infection, especially those caused by antibiotic-resistant strains. This review firstly presents the classical and newly reported photothermal agents (PTAs) in brief. Profoundly, through the introduction of delicately designed nanocomposite platforms, we systematically discuss the versatile photothermal-derived multimodal synergistic therapy with the purpose of sterilization application. At the end, challenges to PTT-derived combinational therapy are presented and promising synergistic bactericidal prospects are anticipated.

A conformational tweak for enhanced cellular internalization, photobleaching resistance and prolonged imaging efficacy

A strategy of conformational tweaking regulates the condensed state behavior of naphthalimide skeletal isomers (NSIs) and enhances their photophysical properties, cellular uptake and prolonged imaging capability. This salient approach results in a large Stokes shift (>120 nm), rapid cellular internalization, photobleaching resistance, and efficient bioimaging of the ribbon-like nano-assembly superior to that of its electronically similar micro-flower isomer.

Toxicity Studies on Graphene-Based Nanomaterials in Aquatic Organisms: Current Understanding

Graphene and its oxide are nanomaterials considered currently to be very promising because of their great potential applications in various industries. The exceptional physiochemical properties of graphene, particularly thermal conductivity, electron mobility, high surface area, and mechanical strength, promise development of novel or enhanced technologies in industries. The diverse applications of graphene and graphene oxide (GO) include energy storage, sensors, generators, light processing, electronics, and targeted drug delivery. However, the extensive use and exposure to graphene and GO might pose a great threat to living organisms and ultimately to human health. The toxicity data of graphene and GO is still insufficient to point out its side effects to different living organisms. Their accumulation in the aquatic environment might create complex problems in aquatic food chains and aquatic habitats leading to debilitating health effects in humans. The potential toxic effects of graphene and GO are not fully understood. However, they have been reported to cause agglomeration, long-term persistence, and toxic effects penetrating cell membrane and interacting with cellular components. In this review paper, we have primarily focused on the toxic effects of graphene and GO caused on aquatic invertebrates and fish (cell line and organisms). Here, we aim to point out the current understanding and knowledge gaps of graphene and GO toxicity.

New barbituric acid derivatives for data encryption and decryption based on the mechanochromic fluorescence effect

Two barbituric acid derivatives CB-Ph and CB-Me were synthesized, both of which show a strong aggregation induced emission (AIE) effect. It was found that these two compounds show almost the same absorption and emission spectra. As a result, they show the same yellow color in daylight and the same yellow-green color under UV at 365 nm. Upon grinding, CB-Ph exhibits superior mechanochromic fluorescence (MCF) properties, with its fluorescence color from yellow-green (555 nm) to brown (580 nm) and its emission intensity decreases by 93%. However, neither the fluorescence peak wavelength nor the intensity of CB-Me shows observable changes after being ground, indicating no MCF effect. The X-ray diffraction (XRD) data indicate that the CB-Ph powder changes from the crystalline to amorphous state after being ground, whereas CB-Me remains in its crystalline state. Molecular dynamics simulation (MDS) shows that CB-Ph takes a 3D conformation due to three phenyl groups on the periphery of the molecule, which hinders the molecules from aggregating closely and results in the change of the microstructure by external force stimuli. However, CB-Me aggregated more closely due to its better planarity and hydrophobic n-hexane group, which make it difficult to change the microstructure upon being ground. Based on the unique optical properties of CB-Ph and CB-Me, a new data encryption-decryption technology is developed. CB-Ph is used as cryptographic ink due to its excellent MCF effect upon grinding. CB-Me is used as a camouflage material as it shows the same color as CB-Ph in the daylight and under UV-365 nm; furthermore, its colors remain unchanged after being ground.

Emission Control from Transition Metal Dichalcogenide Monolayers by Aggregation-Induced Molecular Rotors

Organic-inorganic (O-I) heterostructures, consisting of atomically thin inorganic semiconductors and organic molecules, present synergistic and enhanced optoelectronic properties with a high tunability. Here, we develop a class of air-stable vertical O-I heterostructures comprising a monolayer of transition-metal dichalcogenides (TMDs), including WS₂, WSe₂, and MoSe₂, on top of tetraphenylethylene (TPE) core-based aggregation-induced emission (AIE) molecular rotors. The created O-I heterostructures yields a photoluminescence (PL) enhancement of up to ∼950%, ∼500%, and ∼330% in the top monolayer WS₂, MoSe₂, and WSe₂ as compared to PL in their pristine monolayers, respectively. The strong PL enhancement is mainly attributed to the efficient photogenerated carrier process in the AIE luminogens (courtesy of their restricted intermolecular motions in the solid state) and the charge-transfer process in the created type I O-I heterostructures. Moreover, we observe an improvement in photovoltaic properties of the TMDs in the heterostructures including the quasi-Fermi level splitting, minority carrier lifetime, and light absorption. This work presents an inspiring example of combining stable, highly luminescent AIE-based molecules, with rich photochemistry and versatile applications, with atomically thin inorganic semiconductors for multifunctional and efficient optoelectronic devices.

Space Size-Dependent Transformation of Tetraphenylethylene Carboxylate Aggregates by Ice Confinement

Tetraphenylethylene carboxylate (TPEC) aggregates are transformed by ice confinement, which is controlled by the initial concentration of sucrose employed as a cryoprotectant and temperature. The freezing of aqueous sucrose leads to the formation of micro- or nanoliquid phase confined in ice. Aggregation-induced emission (AIE) of tetraphenylethylene carboxylate (TPEC) in the ice-confined space is explored using fluorescence spectroscopy and lifetime measurements. The characteristics of AIE in the ice-confined space strongly depend on the initial sucrose concentration and temperature, which determine the size of the liquid phase. The AIE of TPEC in the ice-confined space can be classified into three regimes in terms of spectroscopic features. Loosely packed J aggregates of TPEC are formed in the microliquid phase (>2 μm). The fluorescence intensity increases, and the wavelength is hypsochromically shifted with a decrease in the size of the space, indicating that the molecular arrangement in the aggregate depends on the space size. The fluorescence lifetimes indicate polydisperse, loosely packed aggregation. No further change in aggregate structure is observed once the liquid phase size is decreased to ∼2 μm, and a spectroscopically identical structure is maintained upon further reduction of the space size to ∼0.5 μm. The molecular arrangement in the aggregate is independent of the space size in this regime. However, when the size of the space becomes smaller than ∼0.5 μm, the aggregate structure again starts to change into a more tightly packed aggregate and a hypsochromic shift of the fluorescence wavelength occurs again. The fluorescence lifetime indicates monodispersed aggregation in this submicrospace.

A novel water-soluble quinoline–indole derivative as a three-photon fluorescent probe for identifying nucleolus RNA and mitochondrial DNA

We present the design and synthesis of water-soluble quinoline–indole-based derivatives (IM-1, IM-2, and IM-3) with three-photon absorption activity.

Aggregation-Induced Nonlinear Optical Effects of AIEgen Nanocrystals for Ultradeep In Vivo Bioimaging

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high-spatial-resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission is successfully demonstrated. Aggregation-induced nonlinear optical effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

Construction of biocompatible bovine serum albumin nanoparticles composed of nano graphene oxide and AIEgen for dual-mode phototherapy bacteriostatic and bacterial tracking

BACKGROUND

Efficient and highly controllable antibacterial effect, as well as good biocompatibility are required for antibacterial materials to overcome multi-drug resistance in bacteria. Herein, nano graphene oxide (NGO)-based near-infrared (NIR) photothermal antibacterial materials was schemed to complex with biocompatible bovine serum albumin (BSA) and aggregation-induced emission fluorogen (AIEgen) with daylight-stimulated ROS-producing property for dual-mode phototherapy in the treatment of antibiotic resistance bacteria.

RESULTS

Upon co-irradiation of daylight and NIR laser, NGO-BSA-AIE nanoparticles (NPs) showed superiorly antibacterial effect (more than 99%) both against amoxicillin (AMO)-resistant Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by comparison with sing-model phototherapy. Meanwhile, the NGO-BSA-AIE NPs displayed prominent stability and excellently controllable biocompatibility. More importantly, under daylight irradiation, the AIEgen not only produced plentiful ROS for killing bacteria, but also presented fluorescence image for tracking bacteria.

CONCLUSIONS

Hence, the designed system provided tempting strategy of employing light as impetus for tracking bacterial distribution and photothermal/photodynamic synergistic treatment of antibiotic resistance antibacterial.

Enhanced three-photon activity triggered by the AIE behaviour of a novel terpyridine-based Zn(ii) complex bearing a thiophene bridge

Multiphoton bioimaging benefits from good penetration of tissue, low phototoxicity and high resolution. Hence, development of efficient multiphoton imaging agents is highly desirable but remains challenging. Herein, a novel terpyridine-based Zn(ii) complex bearing a thiophene bridge was designed rationally and fabricated. Thanks to its aggregation-induced emission (AIE), DZ1 emitted bright yellow-green fluorescence (λ em = 575 nm) under physiological conditions. The three-photon spectral changes of DZ1 when binding with RNA unambiguously reflected its RNA-specific targeting behaviour, resulting in twofold enhancement in three-photon action cross-sections located at the second near-infrared window (1700 nm).

Carbon Dots-Stimulated Amplification of Aggregation-Induced Emission of Size-Tunable Organic Nanoparticles

Carbon dots (CDs)-induced microstructural modulation and amplification of emission intensity of self-aggregated fluorescent organic nanoparticles (FONPs) is a challenging task since CD is a well-known fluorescence quencher. In the present study, we have designed l-tyrosine-tagged hydrophobically (C-10) tailored naphthalene diimide derivative (NDI-i), which formed FONPs in tetrahydrofuran (THF)-water binary solvent mixture. NDI-i exhibited aggregation-induced emission (AIE) at 580 nm (orange) up to f_w = 70 vol % of water in THF via excimer formation in combination with intramolecular charge transfer (ICT) upon excitation at 350 nm. Beyond f_w = 70 vol %, the emission intensity gradually reduced up to f_w = 99 vol % due to poor water dispersibility of NDI-i FONPs. Doping of hydrophobically (C-2 to C-11 alkyl chain) surface-functionalized CDs (CD-i-iii) within self-aggregates of NDI-i FONPs at f_w = 99 vol % resulted in the modulation of both morphology and emission intensity of resulting self-assembled nanoconjugate. In the presence of C-2 alkyl chain tethered CD, the emission intensity of FONP-CD nanohybrid got quenched compared to that of native NDI-i FONPs. The emission intensity of NDI-i FONPs markedly enhanced by 3.6- to 5.0-fold upon inclusion of C-6 and C-11 alkyl chain containing CDs, respectively. Increasing the alkyl chain length on CD surface facilitated the interchain hydrophobic interaction between the organic nanoparticles and surface-functionalized CDs to form larger CD-doped fused FONPs. The extent of ICT between π-donor and π-acceptor residues became more efficient to exhibit enhanced AIE due to the accumulation of more NDI-i around CD surface through interchain hydrophobic interaction. The C-11 alkyl chain containing CD-integrated FONPs showed the brightest orange emission with superior aqueous stability. These water-dispersible, orange-emitting, cytocompatible NDI-i-CD-iii FONPs were explored for long-term bioimaging of mammalian cells.

Graphene Oxide: From Tunable Structures to Diverse Luminescence Behaviors

Since the first discovery of luminescent graphene oxide (GO), exponentially increasing investigations on the tunable structures and surfaces for modulating its optical properties have struggled to expand applications in imaging, sensing, biomedical diagnostics, and so on. Here, the latest works on reconstructing or modifying the structures and surfaces of GO to achieve diverse luminescence are systematically reviewed, including fluorescence, electroluminescence, and chemiluminescence. Moreover, the fundamental difficulties of the investigations and applications of luminescent GO nanomaterials are clarified to inspire more constructive thoughts for expanding their application boundaries.

Aggregation-induced emission (AIE) fluorophores as imaging tools to trace the biological fate of nano-based drug delivery systems

The vigorous development of nanotechnology has been accompanied by an equally strong interest and research efforts in nano-based drug delivery systems (NDDSs). However, only a few NDDSs have been translated into clinic thus far. One of the important hurdles is the lack of tools to comprehensively and directly trace the biological fate of NDDSs. Recently, aggregation-induced emission (AIE) fluorophores have emerged as attractive bioimaging tools due to flexible controllability, negligible toxicity and superior photostability. Herein, we recapitulate the current advances in the application of AIE fluorophores to monitor NDDSs both in vitro and in vivo. Particularly, we discuss the cellular fates of self-indicating and stimuli-responsive NDDSs with AIE fluorophores. Moreover, we highlight the in vivo application of AIE agents on the long-term tracking of therapeutics and the multi-modal monitoring of diagnostics in NDDSs. Challenges and opportunities in AIE-guided exploration of NDDSs are also discussed in detail.

Biomarkers-based Biosensing and Bioimaging with Graphene for Cancer Diagnosis

At the onset of cancer, specific biomarkers get elevated or modified in body fluids or tissues. Early diagnosis of these biomarkers can greatly improve the survival rate or facilitate effective treatment with different modalities. Potential nanomaterial-based biosensing and bioimaging are the main techniques in nanodiagnostics because of their ultra-high selectivity and sensitivity. Emerging graphene, including two dimensional (2D) graphene films, three dimensional (3D) graphene architectures and graphene hybrids (GHs) nanostructures, are attracting increasing interests in the field of biosensing and bioimaging. Due to their remarkable optical, electronic, and thermal properties; chemical and mechanical stability; large surface area; and good biocompatibility, graphene-based nanomaterials are applicable alternatives as versatile platforms to detect biomarkers at the early stage of cancer. Moreover, currently, extensive applications of graphene-based biosensing and bioimaging has resulted in promising prospects in cancer diagnosis. We also hope this review will provide critical insights to inspire more exciting researches to address the current remaining problems in this field.

Graphene-Based Nanomaterials Toxicity in Fish

Due to their unique physicochemical properties, graphene-based nanoparticles (GPNs) constitute one of the most promising types of nanomaterials used in biomedical research. GPNs have been used as polymeric conduits for nerve regeneration and carriers for targeted drug delivery and in the treatment of cancer via photothermal therapy. Moreover, they have been used as tracers to study the distribution of bioactive compounds used in healthcare. Due to their extensive use, GPN released into the environment would probably pose a threat to living organisms and ultimately to human health. Their accumulation in the aquatic environment creates problems to aquatic habitats as well as to food chains. Until now the potential toxic effects of GPN are not properly understood. Despite agglomeration and long persistence in the environment, GPNs are able to cross the cellular barriers successfully, entered into the cells, and are able to interact with almost all the cellular sites including the plasma membrane, cytoplasmic organelles, and nucleus. Their interaction with DNA creates more potential threats to both the genome and epigenome. In this brief review, we focused on fish, mainly zebrafish (Danio rerio), as a potential target animal of GPN toxicity in the aquatic ecosystem.

Cell-penetrating peptide modified AIE polymeric nanoparticles by miniemulsion polymerization and application for cell fluorescence imaging

AIE polymeric nanoparticles surface-modified with HIV Tat peptides for cell fluorescence imaging are efficiently prepared through miniemulsion polymerization, carbodiimide reaction, and thiol-maleimide click reaction in sequence.

A facile surface modification strategy for fabrication of fluorescent silica nanoparticles with the aggregation-induced emission dye through surface-initiated cationic ring opening polymerization

Fluorescent silica nanoparticles (FSNPs) have attracted great interest for potential applications in biological and biomedical fields because they possess higher fluorescence quantum yield and better fluorescence stability as comparison with small organic fluorescent molecules. The encapsulation of covalent linkage with fluorescent organic dyes or fluorescent metal complexes has demonstrated to be the commonly adopted strategies for fabrication of FSNPs previously. However, it is still challengeable to obtain FSNPs based polymer composites with intensive fluorescence and good water dispersibility through a one-pot surface modification strategy. In this paper, we developed a facile method to fabricate novel FSNPs based polymer composites (PhE@MSNs-PEtOx) through introducing the aggregation-induced emission (AIE) dye (PhE-OH) and poly(2-ethyl-2-oxazoline) (PEtOx) onto mesoporous silica nanoparticles (MSNs) based on cationic ring opening polymerization (CROP). The resulting PhE@MSNs-PEtOx composites possess strong fluorescence emission, excellent hydrophilicity and biocompatibility. These features make the final FSNPs based polymer composites great potential for biomedical applications. Taken together, we have developed for the first time that FSNPs based polymer composites can be facilely prepared through the one-pot introduction of AIE dyes and hydrophilic PEtOx on MSNs. Moreover, the novel FSNPs based composites could also be utilized for other biomedical applications considered their properties.

Nonlamellar liquid crystals: a new paradigm for the delivery of small molecules and bio-macromolecules

The aim of this article is to collate the recent developments in the field of drug delivery, medical therapeutics and diagnostics specifically involving the nonlamellar liquid crystalline (NLC) systems. This review highlights different NLC phases having cubic, hexagonal and sponge internal structures, and their application in the field of drug delivery, such as dose reduction, toxicity reduction and therapeutic efficacy enhancement either in the form of nanoparticles, colloidal dispersion or gels. In addition, application of NLC systems as vehicles for peptides, proteins and as a theranostic system in cancer and other disease conditions is also elaborated, which is a growing platform of interest. Overall, the present review gives us a complete outlook on applications of NLC systems in the field of medicine.

Aggregation-Induced Emission Nanoparticles Encapsulated with PEGylated Nano Graphene Oxide and Their Applications in Two-Photon Fluorescence Bioimaging and Photodynamic Therapy in Vitro and in Vivo

Aggregation-induced emission (AIE) nanoparticles have been shown promise for fluorescence bioimaging and photodynamic therapy due to the good combination of nanoparticles and organic dyes or photosensitizers. Among several kinds of AIE nanoparticles, those that are capsulated with nanographene oxides (NGO) are easy to make, size-tunable, and have proven to be very stable in deionized water. However, the stability in saline solution still needs improvement for further applications in chemical or biomedical fields, and the efficacy of photodynamic therapy using NGO-capsulate AIE photosensitizers has not been evaluated yet. Herein, we modified NGO with polyethylene glycol (PEG) to improve the stability of NGO-capsulated AIE nanoparticles in phosphate buffer saline. Furthermore, by combining this modification method with a dual-functional molecule which has both typical AIE property and photosensitizing ability, we performed both two-photon fluorescence bioimaging and photodynamic therapy in vitro and in vivo. Our work shows that AIE nanoparticles capsulated with PEGylated nanographene oxide can be a powerful tool for future bioimaging and photodynamic therapy applications.

Morphology Tuning of Aggregation-Induced Emission Probes by Flash Nanoprecipitation: Shape and Size Effects on in Vivo Imaging

Aggregation-induced emission (AIE) imaging probes have recently received considerable attention because of their unique property of high performance in the aggregated state and their imaging capability. However, the tendency of AIE molecules to aggregate into micron long irregular shapes, which significantly limits their application in vivo, is becoming a serious issue that needs to be addressed. Here, we introduce a novel engineering strategy to tune the morphology and size of AIE nanoaggregates, based on flash nanoprecipitation (FNP). Quinolinemalononitrile (ED) is encapsulated inside properly selected amphiphilic block copolymers of varying concentration. This leads to a variety of ED particle morphologies with different sizes. The shape and size are found to have strong influences on tumor targeting both in vitro and in vivo. The current results therefore indicate that the FNP method together with optimal choice of an amphiphilic copolymer is a universal method to systematically control the aggregation state of AIE materials and hence tune the morphology and size of AIE nanoaggregates, which is potentially useful for precise imaging at specific tumor sites.

A Facile Approach towards Fluorescent Nanogels with AIE-Active Spacers

A facile and efficient approach for design and synthesis of organic fluorescent nanogels has been developed by using a pre-synthesized polymeric precursor. This strategy is achieved by two key steps: (i) precise synthesis of core⁻shell star-shaped block copolymers with crosslinkable AIEgen-precursor (AIEgen: aggregation induced emission luminogen) as pending groups on the inner blocks; (ii) gelation of the inner blocks by coupling the AIEgen-precursor moieties to generate AIE-active spacers, and thus, fluorescent nanogel. By using this strategy, a series of star-shaped block copolymers with benzophenone groups pending on the inner blocks were synthesized by grafting from a hexafunctional initiator through atom transfer radical copolymerization (ATRP) of 4-benzoylphenyl methacrylate (BPMA) or 2-(4-benzoylphenoxy)ethyl methacrylate (BPOEMA) with methyl methacrylate (MMA) and tert-butyldimethylsilyl-protected 2-hydroxyethyl methacrylate (ProHEMA) followed by a sequential ATRP to grow PMMA or PProHEMA. The pendent benzophenone groups were coupled by McMurry reaction to generate tetraphenylethylene (TPE) groups which served as AIE-active spacers, affording a fluorescent nanogel. The nanogel showed strong emission not only at aggregated state but also in dilute solution due to the strongly restricted inter- and intramolecular movement of TPE moiety in the crosslinked polymeric network. The nanogel has been used as a fluorescent macromolecular additive to fabricate fluorescent film.

Fluorescence resonance energy transfer (FRET) based nanoparticles composed of AIE luminogens and NIR dyes with enhanced three-photon near-infrared emission for in vivo brain angiography

Near-infrared (NIR) fluorescence is very important for high-contrast biological imaging of high-scattering tissues such as brain tissue. Unfortunately, commercial NIR dyes are excited usually by visible light, and their multi-photon absorption (MPA) cross-sections are small. Here, we design new co-encapsulated NIR nanoparticles (NPs) with a large three-photon (3PA) absorption cross-section. A form of aggregation-induced emission (AIE) luminogen (AIEgen), 2,3-bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl) fumaronitrile (TPATCN), is introduced as the donor, and a form of NIR dye, silicon 2,3-naphthalocyanine bis-(trihexylsilyloxide) (NIR775), is adopted as the acceptor. Under the excitation of a 1550 nm fs laser, TPATCN-NIR775 NPs demonstrated a bright three-photon fluorescence centered at 785 nm. The energy transfer efficiency of the TPATCN-NIR775 NPs was calculated to be as high as 90%, which could be attributed to the good spectral overlap between the emission of TPATCN and the absorption of NIR775. By injection with TPATCN-NIR775 NPs, a vivid 3D reconstruction of mouse brain vasculature was obtained with even small blood vessels clearly visualized. The design strategy used for the co-encapsulated AIE-NIR NPs would be helpful in synthesizing more NIR probes for deep-tissue biological imaging in the future.

AIEE Active Donor-Acceptor-Donor-Based Hexaphenylbenzene Probe for Recognition of Aliphatic and Aromatic Amines

In the present investigation, an intramolecular charge transfer (ICT) and aggregation induced emission enhancement (AIEE) active donor-acceptor-donor (D-A-D) system 5 having fumaronitrile as the acceptor and hexaphenylbenzene (HPB) as the donor moieties joined through rotatable phenyl rings has been designed and synthesized that is highly emissive in the solid state and exhibits stimuli-responsive reversible piezochromic behavior upon grinding and heating. Because of its AIEE characteristics, HPB derivative 5 undergoes aggregation to form fluorescent aggregates in mixed aqueous media that exhibit ratiometric fluorescence response toward aliphatic amines (primary/secondary/tertiary) and turn-off response toward aromatic amines and hence differentiates between them. Further, the solution-coated portable paper strips of derivative 5 showed pronounced and sensitive response toward aromatic and aliphatic amines with a detection limit in the range of picogram and nanogram level, respectively.

Progress and Trends in AIE-Based Bioprobes: A Brief Overview

Luminescent bioprobes are powerful analytical means for biosensing and optical imaging. Luminogens featured with aggregation-induced emission (AIE) attributes have emerged as ideal building blocks for high-performance bioprobes. Bioprobes constructed with AIE luminogens have been identified to be a novel class of FL light-up probing tools. In contrast to conventional bioprobes based on the luminophores with aggregation-caused quenching (ACQ) effect, the AIE-based bioprobes enjoy diverse superiorities, such as lower background, higher signal-to-noise ratio and sensitivity, better accuracy, and more outstanding resistance to photobleaching. AIE-based bioprobes have been tailored for a vast variety of purposes ranging from biospecies sensing to bioimaging to theranostics (i.e., image-guided therapies). In this review, recent five years' advances in AIE-based bioprobes are briefly overviewed in a perspective distinct from other reviews, focusing on the most appealing trends and progresses in this flourishing research field. There are altogether 11 trends outlined, which have been classified into four aspects: the probe composition and form (bioconjugtes, nanoprobes), the output signal of probe (far-red/near-infrared luminescence, two/three-photon excited fluorescence, phosphorescence), the modality and functionality of probing system (dual-modality, dual/multifunctionality), the probing object and application outlet (specific organelles, cancer cells, bacteria, real samples). Typical examples of each trend are presented and specifically demonstrated. Some important prospects and challenges are pointed out as well in the hope of intriguing more interests from researchers working in diverse areas into this exciting research field.

Anisamide-Anchored Lyotropic Nano-Liquid Crystalline Particles with AIE Effect: A Smart Optical Beacon for Tumor Imaging and Therapy

The prospective design of nanocarriers for personalized oncotherapy should be an ensemble of targeting, imaging, and noninvasive therapeutic capabilities. Herein, we report the development of the inverse hexagonal nano-liquid crystalline (NLC) particles that are able to host formononetin (FMN), a phytoestrogen with known anticancer activity, and tetraphenylethene (TPE), an iconic optical beacon with aggregation-induced emission (AIE) signature, simultaneously. Ordered three-dimensional mesoporous internal structure and high-lipid-volume fraction of NLC nanoparticles (NLC NPs) frame the outer compartment for the better settlement of payloads. Embellishment of these nanoparticles by anisamide (AA), a novel sigma receptor targeting ligand using carbodiimide coupling chemistry ensured NLC's as an outstanding vehicle for possible utility in surveillance of tumor location as well as the FMN delivery through active AIE imaging. The size and structural integrity of nanoparticles were evaluated by quasi-elastic light scattering, cryo field emission scanning electron microscopy small-angle X-ray scattering. The existence of AIE effect in the nanoparticles was evidenced through the photophysical studies that advocate the application of NLC NPs in fluorescence-based bioimaging. Moreover, confocal microscopy illustrated the single living cell imaging ability endowed by the NLC NPs. In vitro and in vivo studies supported the enhanced efficacy of targeted nanoparticles (AA-NLC-TF) in comparison to nontargeted nanoparticles (NLC-TF) and free drug. Apparently, this critically designed multimodal NLC NPs may establish a promising platform for targeted and image-guided chemotherapy for breast cancer.

Fluorogen-free aggregation induced NIR emission from gold nanoparticles

Controlled diluted aqua regia addition leads to NIR (near infrared) luminescence from aggregated gold nanoparticles at 916 nm. This turn-on luminescence has been observed for gold nanoparticles, regardless of reductants used in their preparation. These aggregated nanoparticles are nontoxic and have been used for bioimaging in human liver carcinoma cells.