Folic acid-functionalized mesoporous silica nanospheres hybridized with AIE luminogens for targeted cancer cell imaging

The analytical and biomedical potential of cytosine-rich oligonucleotides: A review

Polycytosine DNA strands are often found among natural sequences, including the ends of telomeres, centromeres, and introns or in the regulatory regions of genes. A characteristic feature of oligonucleotides that are rich in cytosine (C-rich) is their ability to associate under acidic conditions to form a tetraplex i-motif consisting of two parallel stranded cytosine-hemiprotonated cytosine (C·C+) base-paired duplexes that are mutually intercalated in an antiparallel orientation. Nanotechnology has been exploiting the advantages of i-motif pH-dependent formation to fabricate nanomachines, nanoswitches, electrodes and intelligent nanosurfaces or nanomaterials. Although a few reviews regarding the structure, properties and applications of i-motifs have been published, this review focuses on recently developed biosensors (e.g., to detect pH, glucose or silver ions) and drug-delivery biomaterials. Furthermore, we have included examples of sensors based on parallel C-rich triplexes and silver nanoclusters (AgNCs) fabricated on cytosine-rich DNA strands. The potential diagnostic and therapeutic applications of this type of material are discussed.

Cetuximab-modified mesoporous silica nano-medicine specifically targets EGFR-mutant lung cancer and overcomes drug resistance

Drug resistance to tyrosine kinase inhibitor (TKI) is the main obstacle for efficient treatment of epidermal growth factor receptor (EGFR)-mutant lung cancer patients. Here we design a cetuximab-capped mesoporous silica nanoparticle (MP-SiO₂ NP) as the drug carrier to specifically target EGFR-mutant lung cancer cells and efficiently release loaded drugs including doxorubicin and gefitinib. This innovative nano-medicine can specifically target lung cancer cells with high EGFR expression rather than those with low EGFR level. Treatment of a gefitinib-resistant cell line derived from PC9 cell (PC9-DR) with the gefitinib-loaded cetuximab-capped MP-SiO₂ NP showed a significant inhibition of cell growth. Moreover, this nano-medicine successfully suppressed the progression of PC9-DR xenograft tumors. This tumor suppression was due to the endocytosis of large amount of nano-medicine and the effective gefitinib release induced by high glutathione (GSH) level in PC9-DR cells. Collectively, our study provides a novel approach to overcome EGFR-TKI resistance using cetuximab modified MP-SiO₂ NP, which holds strong potential for effective management of EGFR-mutant lung cancer.

Imaging Cancer Cells Expressing the Folate Receptor with Carbon Dots Produced from Folic Acid

Development of new imaging tools for cancer cells in vitro and in vitro is important for advancing cancer research, elucidating drug effects upon cancer cells, and studying cellular processes. We showed that fluorescent carbon dots (C-dots) synthesized from folic acid can serve as an effective vehicle for imaging cancer cells expressing the folate receptor on their surface. The C-dots, synthesized through a simple one-step process from folic acid as the carbon source, exhibited selectivity towards cancer cells displaying the folate receptor, making such cells easily distinguishable in fluorescence microscopy imaging. Biophysical measurements and competition experiments both confirmed the specific targeting and enhanced uptake of C-dots by the folate receptor-expressing cells. The folic acid-derived C-dots were not cytotoxic, and their use in bioimaging applications could aid biological studies of cancer cells, identification of agonists/antagonists, and cancer diagnostics.

Fluorescent nanoparticles based on AIE fluorogens for bioimaging

Fluorescent nanoparticles (FNPs) have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance in imaging. Compared with conventional molecular probes including small organic dyes and fluorescent proteins, FNPs based on aggregation-induced emission (AIE) fluorogens have shown significant advantages in tunable emission and brightness, good biocompatibility, superb photo- and physical stability, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of fluorescent nanoparticles based on AIE fluorogens including polymer nanoparticles and silica nanoparticles over the past few years, and the various biomedical applications based on these fluorescent nanoparticles are also elaborated.

Aggregation-Induced Emission Luminogen-Embedded Silica Nanoparticles Containing DNA Aptamers for Targeted Cell Imaging

Conventional fluorophores usually undergo aggregation-caused quenching (ACQ), which limits the loading amount of these fluorophores in nanoparticles for bright fluorescence imaging. On the contrary, fluorophores with aggregation-induced emission (AIE) characteristics are strongly fluorescent in their aggregate states and have been an ideal platform for developing highly fluorescent nanomaterials, such as fluorescent silica nanoparticles (FSNPs). In this work, AIE luminogens based on salicylaldehyde hydrazones were embedded in silica nanoparticles through a facile noncovalent approach, which afforded AIE-FSNPs emitting much brighter fluorescence than that of some commercial fluorescein-doped silica and polystyrene nanoparticles. These AIE-FSNPs displaying multiple fluorescence colors were fabricated by a general method, and they underwent much less fluorescence variation due to environmental pH changes compared with fluorescein-hybridized FSNPs. In addition, a DNA aptamer specific to nucleolin was functionalized on the surface of AIE-FSNPs for targeted cell imaging. Fluorescent microscopy and flow cytometry studies both revealed highly selective fluorescence staining of MCF-7 (a cancer cell line with nucleolin overexpression) over MCF-10A (normal) cells by the aptamer-functionalized AIE-FSNPs. The fluorescence imaging in different color channels was achieved using AIE-FSNPs containing each of the AIE luminogens, as well as photoactivatable fluorescent imaging of target cells by the caged AIE fluorophore.

Facile fabrication of amphiphilic AIE active glucan via formation of dynamic bonds: self assembly, stimuli responsiveness and biological imaging

A one-pot strategy has been developed for the preparation of stimuli responsive AIE active glucan through formation of a dynamic Schiff base and a phenyl borate.

Synthesis and biomedical applications of fluorescent nanogels

Fluorescent nanogel is an innovative biomedical material with hydroscopicity, degradability, and responsiveness.

Fabrication of amphiphilic fluorescent nanoparticles with an AIE feature via a one-pot clickable mercaptoacetic acid locking imine reaction: synthesis, self-assembly and bioimaging

Water dispersible and non-toxic AIE active fluorescent organic nanoparticles were fabricatedviaa one-pot clickable mercaptoacetic acid locking imine reaction.

Acid–base-controlled and dibenzylammonium-assisted aggregation induced emission enhancement of poly(tetraphenylethene) with an impressive blue shift

The non-covalent interaction between dibenzylammonium chloride and DB24C8 groups in poly(tetraphenylethene)-based conjugated polymers not only leads to an AIEE feature but also a significant blue shift from 515 to 483 nm.

Selective Modification of Halloysite Nanotubes with 1-Pyrenylboronic Acid: A Novel Fluorescence Probe with Highly Selective and Sensitive Response to Hyperoxide

A novel fluorescence probe based on modified halloysite nanotubes (HNTs) by using 1-pyrenylboronic acid selectively grafted onto the inner surface of lumen was successfully achieved. The solid-state nuclear magnetic resonance ((13)C and (11)B), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) confirmed that the boronic acid group only binds to alumina at the tube lumen and does not bind the tube's outer siloxane surface. The modified HNTs (HNTs-PY) inherit the spectroscopic properties relating to the pyrene units. Interestingly, the established Al-O-B linkage gives the H2O2-sensitivity to pyrene grafted tubes. HNTs-PY exhibits a highly specific "turn-off" response for hyperoxide over other reactive oxygen species (ROS) and oxidative ions owing to their chemoselective boronate-to-phenol switch. The "turn-off" response can even be tracked when the additional amount of H2O2 was limited to 1 × 10(-6) mol. Thus, the selective modification method under mild conditions for the design of novel organic-inorganic hybrid fluorescence probe may open up a broader application as well as for identification and diagnosis.

Selective functionalization of mesoporous silica nanoparticles with ibuprofen and Gd(III) chelates: a new probe for potential theranostic applications

Organo-modified mesoporous silica nanoparticles, loaded with ibuprofen into the pores and functionalized on the external surface with a stable Gd(iii)-DOTA-monoamide chelate, were prepared and explored as potential theranostic probes.

Polymeric AIE-based nanoprobes for biomedical applications: recent advances and perspectives

The development of polymeric luminescent nanomaterials for biomedical applications has recently attracted a large amount of attention due to the remarkable advantages of these materials compared with small organic dyes and fluorescent inorganic nanomaterials. Among these polymeric luminescent nanomaterials, polymeric luminescent nanomaterials based on dyes with aggregation-induced emission (AIE) properties should be of great research interest due to their unique AIE properties, the designability of polymers and their multifunctional potential. In this review, the recent advances in the design and biomedical applications of polymeric luminescent nanomaterials based on AIE dyes is summarized. Various design strategies for incorporation of these AIE dyes into polymeric systems are included. The potential biomedical applications such as biological imaging, and use in biological sensors and theranostic systems of these polymeric AIE-based nanomaterials have also been highlighted. We trust this review will attract significant interest from scientists from different research fields in chemistry, materials, biology and interdisciplinary areas.

Photoluminescent carbon dots synthesized by microwave treatment for selective image of cancer cells

In this work, a simple, low-cost and one-step microwave approach has been demonstrated for the synthesis of water-soluble carbon dots (C-dots). The average size of the resulting C-dots is about 4 nm. From the photoluminescence (PL) measurements, the C-dots exhibit excellent biocompatibility and intense PL with the high quantum yield (QY) at Ca. 25%. Significantly, the C-dots have excellent biocompatibility and the capacity to specifically target the cells overexpressing the folate receptor (FR). These exciting results indicate the as-prepared C-dots are promising biocompatible probe for cancer diagnosis and treatment.

Self-polymerization of dopamine and polyethyleneimine: novel fluorescent organic nanoprobes for biological imaging applications

The development of novel fluorescent nanoprobes has attracted great current research interest over the past few decades due to their superior optical properties and multifunctional capability as compared with small organic dyes. Although great advance has been made in the utilization of fluorescent nanoprobes for biomedical applications, development of novel fluorescent nanoprobes that possess good fluorescent properties, biocompatibility, biodegradability and water dispersibility through a convenient and effective route is still highly desirable. In this work, we reported for the first time that novel fluorescent organic nanoparticles (FONs) can be conveniently fabricated via self-polymerization of dopamine and polyethyleneimine at room temperature and in an air atmosphere within 2 h. These FONs exhibited strong green fluorescence, high water stability and excellent biocompatibility, making them highly potential for biological imaging applications. More importantly, due to the high reactivity of polydopamine, these FONs might also be further functionalized with other functional components through Michael addition or Schiff base reaction. Therefore the method described in this work would open new avenues for the fabrication of fluorescent nanoprobes for various biomedical applications.

Turn-on sensing for Ag+ based on AIE-active fluorescent probe and cytosine-rich DNA

An aggregation-induced-emission (AIE)-active molecule, 4,4'-(1E,1'E)-2,2'-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N,N-trimethylbenzenaminium iodide) (DSAI), used as a label-free and turn-on fluorescent probe, was developed for Ag(+) sensing. The cytosine-rich DNA (oligo-C) chosen as a base could be induced to form a hairpin structure in the presence of Ag(+). To improve the sensitivity of Ag(+) detection, we selected nuclease S1 to reduce the fluorescence intensity of DSAI via its strong ability to hydrolyze oligo-C. In the solution containing oligo-C, DSAI, and nuclease S1, in the absence of Ag(+), oligo-C was broken into fragments by nuclease S1; this meant DSAI could not aggregate, leading to non-emission of the solution. In the presence of Ag(+), oligo-C was induced to form a hairpin structure via the C-Ag(+)-C base pair and DSAI could aggregate on the surface of the hairpin structure to produce a strong emission. On increasing the amount of Ag(+) in the solution containing oligo-C, DSAI, and nuclease S1, the fluorescence intensity of DSAI gradually increased, and the highest intensity was nearly 16-fold higher than the original intensity. The detection limit at a signal-to-noise ratio (S/N) of 3 was estimated to be 155 nmol L(-1). The new sensing method provides simplicity, easy operation, and good sensitivity and selectivity for Ag(+) detection.

Photophysical properties, aggregation-induced fluorescence in nanoaggregates and cell imaging of 2,5-bisaryl 1,3,4-oxadiazoles

Conjugated fluorescence dyes of 2,5-bisaryl 1,3,4-oxadiazoles with carbazole-triphenylamine moieties encapsulated into different nanoparticles are successfully applied to cell imaging.

Supramolecular assembly-induced yellow emission of 9,10-distyrylanthracene bridged bis(pillar[5]arene)s

Newly synthesized DSA-bridged bis(pillar[5]arene)s with AIE properties form linear supramolecular polymers upon binding to a neutral guest linker, exhibiting supramolecular assembly-induced yellow fluorescence emission.

A highly bioactive and biodegradable poly(glycerol sebacate)–silica glass hybrid elastomer with tailored mechanical properties for bone tissue regeneration

A highly bioactive and biodegradable PGS–Silica bioactive glass hybrid elastomer with tailored mechanical properties was developed for bone tissue regeneration application.

Multi-stable fluorescent silica nanoparticles obtained from in situ doping with aggregation-induced emission molecules

Rigid structures provided by silica matrix restrict the intramolecular rotations of AIE molecules, and fluorescence of CWQ-11@SiO₂ nanoparticles maintains excellent pH-, viscosity- and photo-stability, especially stable in simulated gastric fluid.

Stimulus responsive cross-linked AIE-active polymeric nanoprobes: fabrication and biological imaging application

Stimuli responsive AIE-active polymeric luminescent nanoprobes have been fabricated through formation of dynamic bonds using AIE dye as the linker.

Fluorescence responsive conjugated poly(tetraphenylethene) and its morphological transition from micelle to vesicle

A crown ether-functionalized poly(tetraphenylethene) (AP-TPE) is synthesized and the rotation of the TPE group is successfully restricted, leading to a stepwise enhanced fluorescence accompanied by a morphological transition from micellar to vesicular.

Stable cross-linked fluorescent polymeric nanoparticles for cell imaging

Aggregation-induced emission (AIE) dye-based cross-linked fluorescent polymeric nanoparticles (FPNs) are facilely prepared via a two-step polymerization process including emulsion polymerization and subsequent anhydride cross-linking. Then, a variety of characterization methods are carried out to determine the performance of the FPNs, which show high dispersibility and strong fluorescence in an aqueous solution due to the hydrophilic carboxyl groups on the surfaces and the AIE components as the cores. Biocompatibility evaluation and cell imaging results suggest that these FPNs are biocompatible for cell imaging. More importantly, this cross-linking strategy is proven to overcome the issue of critical micelle concentration and opens the opportunity to develop more robust fluorescent bioprobes.

Aggregation-induced emission: the whole is more brilliant than the parts

"United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

Polylysine crosslinked AIE dye based fluorescent organic nanoparticles for biological imaging applications

Fluorescent organic nanoparticles based on aggregation induced emission dyes are fabricated through a ring-opening reaction using polylysine as the linker. The fluorescent organic nanoparticles obtained are characterized by a series of techniques including UV-vis absorption spectroscopy, fluorescence spectroscopy, Fourier Transform infrared spectroscopy, and transmission electron microscopy. A biocompatibility evaluation and the cell uptake behavior of the fluorescent organic nanoparticles are further investigated to evaluate their potential biomedical applications. It is demonstrated that these fluorescent organic nanoparticles can be obtained at room temperature in an air atmosphere without the need for catalyst or initiator. Furthermore, these crosslinked aggregation induced emission dye based fluorescent organic nanoparticles show uniform morphology, strong red fluorescence, high water dispersability, and excellent biocompatibility, making them promising candidates for various biomedical applications.

Self-assembled pH-responsive hyaluronic acid-g-poly((L)-histidine) copolymer micelles for targeted intracellular delivery of doxorubicin

Hyaluronic acid (HA) was conjugated with hydrophobic poly(l-histidine) (PHis) to prepare a pH-responsive and tumor-targeted copolymer, hyaluronic acid-g-poly(l-histidine) (HA-PHis), for use as a carrier for anti-cancer drugs. The effect of the degree of substitution (DS) on the pH-responsive behaviour of HA-PHis copolymer micelles was confirmed by studies of particles of different sizes. In vitro drug release studies demonstrated that doxorubicin (DOX) was released from HA-PHis micelles in a pH-dependent manner. In vitro cytotoxicity assays showed that all the blank micelles were nontoxic. However, MTT assay against Michigan Cancer Foundation-7 (MCF-7) cells (overexpressed CD44 receptors) showed that DOX-loaded micelles with a low PHis DS were highly cytotoxic. Cellular uptake experiments revealed that these pH-responsive HA-PHis micelles taken up in great amounts by receptor-mediated endocytosis and DOX were efficiently delivered into cytosol. Moreover, micelles with the lowest DS exhibited the highest degree of cellular uptake, which indicated that the micelles were internalized into cells via CD44 receptor-mediated endocytosis and the carboxylic groups of HA are the active binding sites for CD44 receptors. Endocytosis inhibition experiments and confocal images demonstrated that HA-PHis micelles were internalized into cells mainly via clathrin-mediated endocytosis and delivered to lysosomes, triggering release of DOX into the cytoplasm. These results confirm that the biocompatible pH-responsive HA-PHis micelles are a promising nanosystem for the intracellular targeted delivery of DOX.

"Fastening" porphyrin in highly cross-linked polyphosphazene hybrid nanoparticles: powerful red fluorescent probe for detecting mercury ion

It is a significant issue to overcome the concentration-quenching effect of the small fluorescent probes and maintain the high fluorescent efficiency at high concentration for sensitive and selective fluorescent mark or detection. We developed a new strategy to "isolate" and "fasten" porphyrin moieties in a highly cross-linked poly(tetraphenylporphyrin-co-cyclotriphosphazene) (TPP-PZS) by the polycondensation of hexachlorocyclotriphosphazene (HCCP) and 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (TPP-(OH)4) in a suitable solvent. The resulting TPP-PZS particles were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), (31)P nuclear magnetic resonance (NMR), and ultraviolet and visible (UV-vis) absorption spectra. Remarkably, TPP-PZS particles obtained in acetone emitted a bright red fluorescence both in powder state and in solution because the aggregation of porphyrin moieties in "H-type" (face-to-face) and "J-type" (edge-to-edge) was effectively blocked. The fluorescent TPP-PZS particles also showed superior resistance to photobleaching, and had a high sensitivity and selectivity for the detection of Hg(2+) ions. The TPP-PZS particles were therefore used as an ideal material for preparing test strips to quickly detect/monitor the Hg(2+) ions in a facile way.

Folic acid-functionalized AIE Pdots based on amphiphilic PCL-b-PEG for targeted cell imaging

Folic acid-functionalized polymer dots with aggregation induced emission features (AIE Pdots), which show high fluorescence efficiency and little toxicity to living cells, which possess a good capability for targeted HeLa intracellular imaging.