Intrinsically fluorescent PAMAM dendrimer as gene carrier and nanoprobe for nucleic acids delivery: bioimaging and transfection study

Clustering-Triggered Emission Mechanism of Sulfur Ester-Polyacrylamide Aqueous Solution

Most nonconventional luminogens enjoy good water solubility and biocompatibility, showing unique application prospects in fields like biological imaging. Although clustering-triggered emission (CTE) mechanisms have been proposed to explain such emissions, it has not been thoroughly elucidated, which limits their development and application. Herein, the photoluminescence properties of polyacrylamide prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization aqueous solution are utilized to further investigate the effects of changes in concentration, in order to elucidate the emission mechanism through transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and theoretical calculation. The results showed that the size distribution, morphology, and distance between the polymer clusters formed in the water solution are successfully correlated with the cluster emission centers. The emission mechanism of nonconventional luminogens solutions is more clearly and intuitively elucidated, which has a promoting effect on the emission and application of this field. It provides a strategy a strategy to clarify the CTE mechanism of nonconventional luminogens solution more clearly.

Exploring the Mechanisms behind Non-aromatic Fluorescence with the Density Functional Tight Binding Method

Recent experimental findings reveal nonconventional fluorescence emission in biological systems devoid of conjugated bonds or aromatic compounds, termed non-aromatic fluorescence (NAF). This phenomenon is exclusive to aggregated or solid states and remains absent in monomeric solutions. Previous studies focused on small model systems in vacuum show that the carbonyl stretching mode along with strong interaction of short hydrogen bonds (SHBs) remains the primary vibrational mode explaining NAF in these systems. In order to simulate larger model systems taking into account the effects of the surrounding environment, in this work we propose using the density functional tight-binding (DFTB) method in combination with non-adiabatic molecular dynamics (NAMD) and the mixed quantum/molecular mechanics (QM/MM) approach. We investigate the mechanism behind NAF in the crystal structure of l-pyroglutamine-ammonium, comparing it with the related nonfluorescent amino acid l-glutamine. Our results extend our previous findings to more realistic systems, demonstrating the efficiency and robustness of the proposed DFTB method in the context of NAMD in biological systems. Furthermore, due to its inherent low computational cost, this method allows for a better sampling of the nonradiative events at the conical intersection which is crucial for a complete understanding of this phenomenon. Beyond contributing to the ongoing exploration of NAF, this work paves the way for future application of this method in more complex biological systems such as amyloid aggregates, biomaterials, and non-aromatic proteins.

Controllable Blue Shift and Enhancement Emission during the Gradually Increasing Molecular Weight of Polyacrylamide

Nonconventional luminescent polymers have become research hotspots due to their advantages such as persistent room temperature phosphorescence (p-RTP) emission and strong film-forming properties. It is proven that the molecular weight (MW) of such luminescent polymers has a significant impact on their emission over a large range, generally with a red shift as the MW increases. Herein, four controllable MW polyacrylamides are prepared via reversible addition-fragmentation chain transfer polymerization (RAFT), and their photoluminescence quantum yield and p-RTP lifetimes gradually increase with the increasing MW. The emission of p-RTP gradually shifts blue with increasing MW, which is likely due to the gradually changing interactions between the electron-rich portion in RAFT reagent and the increasing acrylamide (AM) units in the molecular chain. These can be reasonably explained through small angle X-ray scattering, the clustering-triggered emission (CTE) mechanism, and supported by theoretical calculations. Powder with controllable p-RTP capability has the potential for strategic anti-counterfeiting encryption. The above results not only promote the development of the CTE mechanism toward more precise explanations but also provide new ideas for the preparation of nonconventional luminescent polymers with controllable p-RTP emission performance.

DNA Condensation by Peptide-Conjugated PAMAM Dendrimers. Influence of Peptide Charge

Nucleic acid delivery to cells is an important therapeutic strategy that requires the transport of nucleic acids to intracellular compartments and their protection from enzymatic degradation. This can be achieved through the complexation of the nucleic acids with polycations. Poly(amidoamine) (PAMAM) dendrimers and peptide-conjugated dendrimers have been investigated as delivery vectors. Inspired by these studies and the role of flexible peptide domains in protein-DNA interactions, we studied the impact of conjugating two peptides (tails) to generation 2 (G2) PAMAM dendrimers on DNA condensation and polyplex formation. Using gel electrophoresis, dye exclusion assays, atomic force microscopy, and Monte Carlo simulations, it is shown that the steric impact of neutral peptide tails is to hinder the formation of DNA-G2 polyplexes composed of multiple DNA chains. If the tails are negatively charged, which results in overall neutral G2 conjugates, then the interaction of G2 with DNA is hindered. Increasing the net positive charge of the tails resulted in the complexation capacity of G2 with the DNA being restored. While DNA complexation is obtained for a similar net charge balance for G2 and G2 conjugates with positive tails, fewer of the latter are required to achieve a comparable condensation degree. Furthermore, it is shown that about 40% of the DNA remains accessible to binding by small molecules. Overall, this shows that tuning the net charge of peptide tails conjugated to PAMAM dendrimers offers a handle to control the complexation capacity of DNA, which can be explored as a novel route for optimization as gene delivery vehicles.

Stimuli-Responsive Aggregation-Induced Emission (AIE)-Active Polymers for Biomedical Applications

At high concentration or in the aggregated state, most of the traditional luminophores suffer from the general aggregation-caused quenching (ACQ) effect, which significantly limits their biomedical applications. On the contrary, a few fluorophores exhibit an aggregation-induced emission (AIE) feature which is just the opposite of ACQ. The luminophores with aggregation-induced emission (AIEgens) have exhibited noteworthy advantages to get tunable emission, excellent photostability, and biocompatibility. Incorporating AIEgens into polymer design has yielded diversified polymer systems with fascinating photophysical characteristics. Again, stimuli-responsive polymers are capable of undergoing chemical and/or physical property changes on receiving signals from single or multiple stimuli. The combination of the AIE property and stimuli responses in a single polymer platform provides a feasible and effective strategy for the development of smart polymers with promising biomedical applications. Herein, the advancements in stimuli-responsive polymers with AIE characteristics for biomedical applications are summarized. AIE-active polymers are first categorized into conventional π-π conjugated and nonconventional fluorophore systems and then subdivided based on various stimuli, such as pH, redox, enzyme, reactive oxygen species (ROS), and temperature. In each section, the design strategies of the smart polymers and their biomedical applications, including bioimaging, cancer theranostics, gene delivery, and antimicrobial examples, are introduced. The current challenges and future perspectives of this field are also stated at the end of this review article.

Surface Engineered Dendrimers: A Potential Nanocarrier for the Effective Management of Glioblastoma Multiforme

Gliomas are the most prevailing intracranial tumors, which account for approximately 36% of the primary brain tumors of glial cells. Glioblastoma multiforme (GBM) possesses a higher degree of malignancy among different gliomas. The blood-brain barrier (BBB) protects the brain against infections and toxic substances by preventing foreign molecules or unwanted cells from entering the brain parenchyma. Nano-carriers such as liposomes, nanoparticles, dendrimers, etc. boost the brain permeability of various anticancer drugs or other drugs. The favorable properties like small size, better solubility, and the modifiable surface of dendrimers have proven their broad applicability in the better management of GBM. However, in vitro and in vivo toxicities caused by dendrimers have been a significant concern. The presence of multiple functionalities on the surface of dendrimers enables the grafting of target ligand and/or therapeutic moieties. Surface engineering improves certain properties like targeting efficiency, pharmacokinetic profile, therapeutic effect, and toxicity reduction. This review will be focused on the role of different surface-modified dendrimers in the effective management of GBM.

Cationic nanoparticles enhance T cell tumor infiltration and antitumor immune responses to a melanoma vaccine

In clinical settings, cancer vaccines as monotherapies have displayed limited success compared to other cancer immunotherapeutic treatments. Nanoscale formulations have the ability to increase the efficacy of cancer vaccines by combatting the immunosuppressive nature of the tumor microenvironment. Here, we have synthesized a previously unexplored cationic polymeric nanoparticle formulation using polyamidoamine dendrimers and poly(d,l-lactic-co-glycolic acid) that demonstrate adjuvant properties in vivo. Tumor-challenged mice vaccinated with an adenovirus-based cancer vaccine [encoding tumor-associated antigen (TAA)] and subsequently treated with this nanoparticulate formulation showed significant increases in TAA-specific T cells in the peripheral blood, reduced tumor burden, protection against tumor rechallenge, and a significant increase in median survival. An investigation into cell-based pathways suggests that administration of the nanoformulation at the site of the developing tumor may have created an inflammatory environment that attracted activated TAA-specific CD8⁺ T cells to the vicinity of the tumor, thus enhancing the efficacy of the vaccine.

Nonconventional luminophores: characteristics, advancements and perspectives

Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (-O-), hydroxyl (-OH), halogens, carbonyl (CO), carboxyl (-COOH), cyano (CN), thioether (-S-), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Modified Desolvation Method Enables Simple One-Step Synthesis of Gelatin Nanoparticles from Different Gelatin Types with Any Bloom Values

Gelatin nanoparticles found numerous applications in drug delivery, bioimaging, immunotherapy, and vaccine development as well as in biotechnology and food science. Synthesis of gelatin nanoparticles is usually made by a two-step desolvation method, which, despite providing stable and homogeneous nanoparticles, has many limitations, namely complex procedure, low yields, and poor reproducibility of the first desolvation step. Herein, we present a modified one-step desolvation method, which enables the quick, simple, and reproducible synthesis of gelatin nanoparticles. Using the proposed method one can prepare gelatin nanoparticles from any type of gelatin with any bloom number, even with the lowest ones, which remains unattainable for the traditional two-step technique. The method relies on quick one-time addition of poor solvent (preferably isopropyl alcohol) to gelatin solution in the absence of stirring. We applied the modified desolvation method to synthesize nanoparticles from porcine, bovine, and fish gelatin with bloom values from 62 to 225 on the hundreds-of-milligram scale. Synthesized nanoparticles had average diameters between 130 and 190 nm and narrow size distribution. Yields of synthesis were 62-82% and can be further increased. Gelatin nanoparticles have good colloidal stability and withstand autoclaving. Moreover, they were non-toxic to human immune cells.

A dendrimer-functionalized turn-on fluorescence probe based on enzyme-activated debonding feature of azobenzene linkage

The hypoxic feature of tumors has led to researchers developing hypoxia-activated prodrugs and probes that leverage oxidoreductases overexpressed in tumor tissues.

Fluorescence in "Nonfluorescent" Polymers

Recently, a great deal of research has been started on generating fairly strong photoluminescence from organic molecules without having any conjugated π-system or fluorophore. Discrete chromophores or auxochromophores termed as "subfluorophores" may undergo "space conjugation" via co-operative intramolecular conformation followed by intermolecular aggregation to generate fluorescence or sometimes phosphorescence emission. Polymeric materials are important in this regard as nonconjugated polymers self-assemble/aggregate in a moderately concentrated solution and also in the solid state, producing membranes, films, and so forth with good physical and mechanical properties. Therefore, promoting fluorescence in these commodity polymers is very much useful for sensing, organic light emitting diodes (OLED), and biological applications. In this perspective, we have discussed the aggregation-induced emission from four different types of architectures, for example, (i) dendrimers or hyperbranched polymers, (ii) entrapped polymeric micellar self-assembly, (iii) cluster formation, and (iv) stretching-induced aggregation, begining with the genesis of fluorescence from aggregation of propeller-shaped small organic molecules. The mechanism of induced fluorescence of polymers with subfluorophoric groups is also discussed from the theoretical calculations of the energy bands in the aggregated state. Also, an attempt has been made to highlight some useful applications in the sensing of surfactants, bacteria, cell imaging, drug delivery, gene delivery, OLED, and so forth.

New insights into the blue intrinsic fluorescence of oxidized PAMAM dendrimers considering their use as bionanomaterials

Like other bionanomaterials, dendrimers are usually labelled with fluorescent compounds in order to be optically detected within cells. However, this process can interfere with their biological properties, so it is crucial to find other solutions for their traceability. Here, the blue intrinsic fluorescence of amine-terminated poly(amidoamine) (PAMAM) dendrimers was enhanced using oxidative treatment with ammonium persulfate (APS). The effects of dendrimer generation (G3, G4, and G5) and pH on the spectroscopic behavior of both pristine and APS-treated PAMAM dendrimers were studied in aqueous solution. Overall, the results pointed out that there are at least two types of emitting electron-rich hetero-atomic sub-luminophores (HASLs) confined within the dendrimer scaffold that have very close maximum emission wavelengths and whose emission properties strongly depend on pH. The APS treatment significantly enhanced the fluorescence intensity by leading to the protonation of the interior of the dendrimer. However, fluorescence intensity was not only dependent on the number of HASLs in the dendrimer scaffold (i.e., on dendrimer generation), but also on the rigidification suffered by the dendrimer due to the acidic environment (at low pH values, APS-treated G4 was indeed the most emissive species). Moreover, photoluminescence studies with lyophilized samples were also conducted, which confirmed the coexistence of more than one type of HASLs emitting in the dendrimer structure. The APS treatment affected these HASLs to a different extent. Time-resolved fluorescence experiments always showed higher average lifetimes of HASLs for APS-treated dendrimers than for pristine ones, in accordance with the fluorescence intensity results. On the other hand, the fraction and lifetimes of HASLs in APS-treated dendrimers were similar in solution and the lyophilized form. This behaviour was different for the pristine dendrimers that presented increased luminescence upon aggregation. Finally, the highly emissive oxidized dendrimers were shown not only to be much less cytotoxic and hemotoxic than pristine dendrimers but also to be detectable inside cells upon excitation with UV light.

A Robust Intrinsically Green Fluorescent Poly(Amidoamine) Dendrimer for Imaging and Traceable Central Nervous System Delivery in Zebrafish

Intrinsically fluorescent poly(amidoamine) dendrimers (IF-PAMAM) are an emerging class of versatile nanoplatforms for in vitro tracking and bio-imaging. However, limited tissue penetration of their fluorescence and interference due to auto-fluorescence arising from biological tissues limit its application in vivo. Herein, a green IF-PAMAM (FGP) dendrimer is reported and its biocompatibility, circulation, biodistribution and potential role for traceable central nervous system (CNS)-targeted delivery in zebrafish is evaluated, exploring various routes of administration. Key features of FGP include visible light excitation (488 nm), high fluorescence signal intensity, superior photostability and low interference from tissue auto-fluorescence. After intravenous injection, FGP shows excellent imaging and tracking performance in zebrafish. Further conjugating FGP with transferrin (FGP-Tf) significantly increases its penetration through the blood-brain barrier (BBB) and prolongs its circulation in the blood stream. When administering through local intratissue microinjection, including intracranial and intrathecal injection in zebrafish, both FGP and FGP-Tf exhibit excellent tissue diffusion and effective cellular uptake in the brain and spinal cord, respectively. This makes FGP/FGP-Tf attractive for in vivo tracing when transporting to the CNS is desired. The work addresses some of the major shortcomings in IF-PAMAM and provides a promising application of these probes in the development of drug delivery in the CNS.

New insights into the blue intrinsic fluorescence of oxidized PAMAM dendrimers considering their use as bionanomaterials

The fluorescence intensity of oxidized PAMAM dendrimers is not only dependent on the number of HASLs in the dendrimer scaffold (i.e., on dendrimer generation), but also on the rigidification suffered by the dendrimer due to the acidic environment.

New insights into the blue intrinsic fluorescence of oxidized PAMAM dendrimers considering their use as bionanomaterials

The fluorescence intensity of oxidized PAMAM dendrimers is not only dependent on the number of HASLs in the dendrimer scaffold (i.e., on dendrimer generation), but also on the rigidification suffered by the dendrimer due to the acidic environment.

Three-dimensional DNA nanostructures for dual-color microRNA imaging in living cells via hybridization chain reaction

A well-defined 3D DNA nanostructure was developed by combination of DNA tetrahedron and Y-shaped DNA, which allowed multiplexed, signal amplified fluorescent imaging of miRNAs in living cells via hybridization chain reaction.

Recent advances in the development and applications of nonconventional luminescent polymers

Recently, nonconventional luminescent polymers (NLPs) have emerged as the most sought-after alternative luminescent materials. This review provides a thorough description of the importance and applications of each class of state-of-the-art NLPs.

Label-Free Fluorescent Poly(amidoamine) Dendrimer for Traceable and Controlled Drug Delivery

Poly(amidoamine) dendrimer (PAMAM) is well-known for its high efficiency as a drug delivery vehicle. However, the intrinsic cytotoxicity and lack of a detectable signal to facilitate tracking have impeded its practical applications. Herein, we have developed a novel label-free fluorescent and biocompatible PAMAM derivative by simple surface modification of PAMAM using acetaldehyde. The modified PAMAM possessed a strong green fluorescence, which was generated by the C=N bonds of the resulting Schiff Bases via n-π* transition, while the intrinsic cytotoxicity of PAMAM was simultaneously ameliorated. Through further PEGylation, the fluorescent PAMAM demonstrated excellent intracellular tracking in human melanoma SKMEL28 cells. In addition, our PEGylated fluorescent PAMAM derivative achieved enhanced loading and delivery efficiency of the anticancer drug doxorubicin (DOX) compared to the original PAMAM. Importantly, the accelerated kinetics of DOX-encapsulated fluorescent PAMAM nanocomposites in an acidic environment facilitated intracellular drug release, which demonstrated comparable cytotoxicity to that of the free-form doxorubicin hydrochloride (DOX·HCl) against melanoma cells. Overall, our label free fluorescent PAMAM derivative offers a new opportunity of traceable and controlled delivery for DOX and other drugs of potential clinical importance.

Sulphur-containing nonaromatic polymers: clustering-triggered emission and luminescence regulation by oxidation

Sulphur-containing nonconventional luminophores with clustering-triggered emission characteristics are developed, whose emission is readily modulated through oxidation.

Preparation and evaluation of PAMAM dendrimer-based polymer gels physically cross-linked by hydrogen bonding

Dendrimer-based polymer gels with good antibacterial properties and anti-inflammatory properties were prepared without any covalent bonding cross-linking agents.

Autofluorescent Polymers: 1 H,1 H,2 H,2 H-Perfluoro-1-decanol Grafted Poly(styrene- b-acrylic acid) Block Copolymers without Conventional Fluorophore

Recently, although several unconventional luminescent polymers have been synthesized, it still remains a significant challenge to prepare various new fluorescent polymers by functionalization of nonfluorescent polymers. A nonfluorescent 1 H,1 H,2 H,2 H-perfluoro-1-decanol grafted to nonfluorescent polystyrene- b-poly(acrylic acid) block copolymers through simply esterification reaction can exhibit strong blue emission. On the basis of control experiments and theoretical simulation, we have proposed that the luminescence stems from interchain n → π* interaction between the lone pair (n) of hydroxyl O atoms of carboxyl units and empty π* orbital of ester carbonyl unit. In addition, the fluorescent polymers are successfully employed for fluorescence imaging in living HeLa cell.

Fluorescent Dendritic Micro-Hydrogels: Synthesis, Analysis and Use in Single-Cell Detection

Hydrogels are of keen interest for a wide range of medical and biotechnological applications including as 3D substrate structures for the detection of proteins, nucleic acids, and cells. Hydrogel parameters such as polymer wt % and crosslink density are typically altered for a specific application; now, fluorescence can be incorporated into such criteria by specific macromonomer selection. Intrinsic fluorescence was observed at λmax 445 nm from hydrogels polymerized from lysine and aldehyde- terminated poly(ethylene glycol) macromonomers upon excitation with visible light. The hydrogel’s photochemical properties are consistent with formation of a nitrone functionality. Printed hydrogels of 150 μm were used to detect individual cell adherence via a decreased in fluorescence. The use of such intrinsically fluorescent hydrogels as a platform for cell sorting and detection expands the current repertoire of tools available.

Near-Infrared-Triggered Photodynamic Therapy toward Breast Cancer Cells Using Dendrimer-Functionalized Upconversion Nanoparticles

Water-soluble upconversion nanoparticles (UCNPs) that exhibit significant ultraviolet, blue, and red emissions under 980-nm laser excitation were successfully synthesized for performing near infrared (NIR)-triggered photodynamic therapy (PDT). The lanthanide-doped UCNPs bearing oleate ligands were first exchanged by citrates to generate polyanionic surfaces and then sequentially encapsulated with NH₂-terminated poly(amido amine) (PAMAM) dendrimers (G4) and chlorine6 (Ce6) using a layer-by-layer (LBL) absorption strategy. Transmission electron microscopy and X-ray diffraction analysis confirm that the hybrid UCNPs possess a polygonal morphology with an average dimension of 16.0 ± 2.1 nm and α-phase crystallinity. A simple calculation derived through thermogravimetric analysis revealed that one polycationic G4 dendrimer could be firmly accommodated by approximately 150 polyanionic citrates through multivalent interactions. Moreover, zeta potential measurements indicated that the LBL fabrication results in the hybrid nanoparticles with positively charged surfaces originated from these dendrimers, which assist the cellular uptake in biological specimens. The cytotoxic singlet oxygen based on the photosensitization of the adsorbed Ce6 through the upconversion emissions can be readily accumulated by increasing the irradiation time of the incident lasers. Compared with that of 660-nm lasers, NIR-laser excitation exhibits optimized in vitro PDT effects toward human breast cancer MCF-7 cells cultured in the tumorspheres, and less than 40% of cells survived under a low Ce6 dosage of 2.5 × 10-7 M. Fluorescence microscopy analysis indicated that the NIR-driven PDT causes more effective destruction of the cells located inside spheres that exhibit significant cancer stem cell or progenitor cell properties. Moreover, an in vivo assessment based on immunohistochemical analysis for a 4T1 tumor-bearing mouse model confirmed the effective inhibition of cancer cell proliferation through cellular DNA damage by the expression of Ki67 and γH2AXser139 protein markers. Thus, the hybrid UCNPs are a promising NIR-triggered PDT module for cancer treatment.

Modified PAMAM dendrimer with 4-carbomethoxypyrrolidone surface groups-its uptake, efflux, and location in a cell

Traditional amine terminated PAMAM dendrimers may be readily surface engineered by a facile one-pot conversion with dialkyl itaconate esters into 4-carbomethoxypyrrolidone terminated PAMAM (G=0-4) dendrimers. These terminated dendrimers are uniquely characterized by exhibiting blue fluorescence emissions (λ_exc=370nm, λ_maxem=440nm). Thanks to this property they can be directly analyzed by confocal microscopy and flow cytometry without additional fluorescence labeling, treatment of dendrimers with chemicals or adjusting pH. These intrinsically fluorescent dendrimers were shown to be very effective for assessing important biological cell features such as cellular entry, intracellular trafficking/localization and efflux properties. For example, all tested cell lines (e.g., B14, BRL-3A, and mHippoE-18) rapidly accumulated PAMAM-pyrrolidone dendrimer. The BRL-3A cell line exhibited both cytoplasmic and nuclear localization patterns; whereas in B14 cells and mHippoE-18 cells, the blue dendrimer fluorescence could only be detected in intracellular endosome-like structures. The dendrimer was observed to be released from all three cell lines during the first 24h; however, efflux was substantially slower from the B-14 cell line. The highest efflux rate was observed for the mHippoE-18 cells. This first successful biological experiment opens a broad spectrum of using these dendrimers as new bioimaging agents for extensive biological cell characterizations.

Clustering-Triggered Emission of Nonconjugated Polyacrylonitrile

Intrinsic emission from nonconjugated polymers has attracted considerable attention owing to its fundamental importance and intensive applications in diverse fields. The emission mechanism, however, is still in debate. Herein, nonconjugated polyacrylonitrile (PAN) molecules are found to be virtually nonluminescent in dilute solutions, while being highly emissive when concentrated or aggregated as nanosuspensions, solid powders, and films, exhibiting distinct aggregation-induced emission (AIE) characteristics. Moreover, triplet emissions of delayed fluorescence and room temperature phosphorescence are detected from the solid powders. Such unique emission of nonconjugated PAN is ascribed to the formation of cyano clusters, which act as the exact chromophores. In these clusters, through space electronic interactions, namely overlap of π and lone pair (n) electrons among cyano groups extend the conjugation and meanwhile rigidify the molecular conformations, thus offering remarkable emission upon irradiation. The AIE phenomenon can also be well rationalized by the formation of cyano clusters together with conformation rigidification. And the triplet emissions shall be originated from the n-π* transition owing to the presence of lone pairs. It is believed that such clustering-triggered emission mechanism is instructive for further development of unorthodox luminogens.

Dendrimer nanoarchitectures for cancer diagnosis and anticancer drug delivery

Dendrimers are novel nanoarchitectures with unique properties including a globular 3D shape, a monodispersed unimicellar nature and a nanometric size range. The availability of multiple peripheral functional groups and tunable surface engineering enable the facile modification of the dendrimer surface with different therapeutic drugs, diagnostic agents and targeting ligands. Drug encapsulation, and solubilizing and passive targeting also equally contribute to the therapeutic use of dendrimers. In this review, we highlight recent advances in the delivery of anticancer drugs using dendrimers, as well as other biomedical and diagnostic applications. Taken together, the immense potential and utility of dendrimers are envisaged to have a significant positive impact on the growing arena of drug delivery and targeting.

B, Wang SH. Dendrimer antibody conjugate to target and image HER-2 overexpressing cancer cells

Although many breast and lung cancers overexpress human epidermal growth factor receptor-2 (HER-2), no methods currently exist for effective and early detection of HER-2-positive cancers. To address this issue, we designed and synthesized dendrimer-based novel nano-imaging agents that contain gold nanoparticles (AuNPs) and gadolinium (Gd), conjugated with the humanized anti-HER-2 antibody (Herceptin). Generation 5 (G5) polyamidoamine (PAMAM) dendrimers were selected as the backbone for the nano-imaging agents due to their unique size, high ratio of surface functional groups and bio-functionality. We modified G5 PAMAM dendrimer surface with PEG and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelators to encapsulate AuNPs and complex Gd. These dendrimer entrapped AuNPs were further conjugated with Herceptin through copper-catalyzed azide- alkyne click reaction to construct the nano-imaging agent Au-G5-Gd-Herceptin. The targeted nano-imaging agent bound selectively to HER-2 overexpressing cell lines, with subsequent internalization into the cells. More importantly, non-targeted nano-imaging agent neither bound nor internalized into cells overexpressing HER-2. These results suggest that our approach could provide a platform to develop nano-diagnostic agents or nano-therapeutic agents for early detection and treatment of HER-2-positive cancers.

pH-Mediated Fluorescent Polymer Particles and Gel from Hyperbranched Polyethylenimine and the Mechanism of Intrinsic Fluorescence

We report that fluorescence properties and morphology of hyperbranched polyethylenimine (hPEI) cross-linked with formaldehyde are highly dependent on the pH values of the cross-linking reaction. Under acidic and neutral conditions, water-soluble fluorescent copolymer particles (CPs) were produced. However, under basic conditions, white gels with weak fluorescence emission would be obtained. The water-soluble hPEI-formaldehyde (hPEI-F) CPs show strong intrinsic fluorescence without the conjugation to any classical fluorescent agents. By the combination of spectroscopy and microscopy techniques, the mechanism of fluorescence emission was discussed. We propose that the intrinsic fluorescence originates from the formation of a Schiff base in the cross-linking process between hPEI and formaldehyde. Schiff base bonds are the fluorescence-emitting moieties, and the compact structure of hPEI-F CPs plays an important role in their strong fluorescence emission. The exploration on fluorescence mechanism may provide a new strategy to prepare fluorescent polymer particles. In addition, the investigation shows that the hPEI-F CPs hold potential as a fluorescent probe for the detection of copper ions in aqueous media.

PAMAM dendrimer based targeted nano-carrier for bio-imaging and therapeutic agents

In the last several decades, researchers have focused on developing suitable drug carriers to deliver pharmaceutical agents to treat cancer diseases.

Tough and strong nacre-like composites from hyperbranched poly(amido amine) and clay nanosheets cross-linked by genipin

Tough and strong nacre-like composite films were fabricated from hyperbranched poly(amido amine) (HPAMAM) and clay nanosheets with the aid of genipin crosslinking.

Self-Assembled Hybrids of Fluorescent Carbon Dots and PAMAM Dendrimers for Epirubicin Delivery and Intracellular Imaging

Advanced nanomaterials integrating imaging and therapeutic modalities on a single platform offers a new horizon in current cancer treatment strategies. Recently, carbon dots (CQDs) have been successfully employed for bioimaging of cancer cells. In the present study, luminescent CQDs with anionic terminus and cationic acetylated G5 poly(amido amine) (G5-Ac85) dendrimers were combined via noncovalent interactions to form self-assembled fluorescent hybrids. The fluorescence of CQDs in hybrids is enhanced in the vicinity of primary amine groups of dendrimers, making them suitable as cellular imaging probes. Encapsulation of chemo-drug epirubicin (EPI) in the dendrimer interiors endowed the fluorescent hybrids with therapeutic potential. The in vitro release of an entrapped EPI drug from CQDs@EPI⊂G5-Ac85 hybrids was faster in an acidic environment than under physiological conditions. Herein, multifunctional CQDs@EPI⊂G5-Ac85 hybrids serve as a dual-emission delivery system, to track the intracellular distribution and cytotoxic effects of EPI drugs. Green emission properties of CQDs were used for fluorescence microscopic imaging and cellular uptake by flow cytometry. Cell cycle analysis, field-emission scanning electron microscopy (FE-SEM), reactive oxygen species (ROS) generation, and up-regulation of apoptotic signaling genes unanimously demonstrated the apoptosis inducing ability of CQDs@EPI⊂G5-Ac85 hybrids in breast cancer (MCF-7) cells. Therefore, we have evaluated CQDs@EPI⊂G5-Ac85 hybrids as prospective candidates to achieve simultaneous imaging and drug delivery in cancer cells.

Cell penetrating peptide-based polyplexes shelled with polysaccharide to improve stability and gene transfection

Cell-penetrating peptides (CPP) have been widely developed as a strategy to enhance cell penetrating ability and transfection. In this work, octa-arginine modified dextran gene vector with pH-sensitivity was developed via host-guest interactions. α-Cyclodextrin was modified with octa-arginine (CDR), which had excellent cell penetrating ability. Dextran was selected as a backbone and modified with azobenzene as guest units by acid-labile imine bonds (Az-I-Dex). The supramolecular polymer CDR/Az-I-Dex with high a C/A molar ratio (molar ratio of CD on CDR to Az on Az-I-Dex) was unfavorable for DNA condensation. The dextran shell of CDR/Az-I-Dex/DNA polyplexes improved the stability under physiological conditions. However, once treated with acetate buffer (pH 5.4) for 3 h, large aggregates formed rapidly due to the cleavage of the dextran shell. As expected, the vector had cell viability of 80% even when the CDR concentration increased to 100 μg mL(-1). Moreover, due to the effective cellular uptake efficiency, CDR/Az-I-Dex/DNA polyplexes had 6-300 times higher transfection efficiency than CDR/DNA polyplexes. It was even higher than high molecular weight PLL-based polyplexes of HEK293 T cells. Importantly, chloroquine as an endosomal escape agent could not improve the transfection of CDR/Az-I-Dex/DNA polyplexes, which indicated that the CDR/Az-I-Dex supramolecular polymer had its own ability for endosomal escape. These results suggested that the CPP-based polyplexes shelled with polysaccharide can be promising non-viral gene delivery carriers.

Dendrimer-Inspired Nanomaterials for the in Vivo Delivery of siRNA to Lung Vasculature

Targeted RNA delivery to lung endothelial cells has the potential to treat conditions that involve inflammation, such as chronic asthma and obstructive pulmonary disease. To this end, chemically modified dendrimer nanomaterials were synthesized and optimized for targeted small interfering RNA (siRNA) delivery to lung vasculature. Using a combinatorial approach, the free amines on multigenerational poly(amido amine) and poly(propylenimine) dendrimers were substituted with alkyl chains of increasing length. The top performing materials from in vivo screens were found to primarily target Tie2-expressing lung endothelial cells. At high doses, the dendrimer-lipid derivatives did not cause chronic increases in proinflammatory cytokines, and animals did not suffer weight loss due to toxicity. We believe these materials have potential as agents for the pulmonary delivery of RNA therapeutics.

Robust, antibacterial, and fluorescent hybrid films mimicking nacre

The preparation of multifunctional nacre-like hybrid films is reported in this article.

A multi-functional fluorescent scaffold as a multi-colour probe: design and application in targeted cell imaging

A new scaffold material based on a novel targeting strategy has been developed, benefiting from recent progress in the development of tailor-made fluorescent bioprobes for cellular imaging and opening a new viewpoint for further improvements in in vitro and in vivo imaging.