Magnetically Encoded Luminescent Composite Nanoparticles through Layer‐by‐Layer Self‐Assembly

Sensitive and rapid detection of multiple analytes and the collection of components from complex samples are important in fields ranging from bioassays/chemical assays, clinical diagnosis, to environmental monitoring. A convenient strategy for creating magnetically encoded luminescent CdTe@SiO₂@n Fe₃O₄ composite nanoparticles, by using a layer‐by‐layer self‐assembly approach based on electrostatic interactions, is described. Silica‐coated CdTe quantum dots (CdTe@SiO₂) serve as core templates for the deposition of alternating layers of Fe₃O₄ magnetic nanoparticles and poly(dimethyldiallyl ammonium chloride), to construct CdTe@SiO₂@n Fe₃O₄ (n=1, 2, 3, …?) composite nanoparticles with a defined number (n) of Fe₃O₄ layers. Composite nanoparticles were characterized by zeta‐potential analysis, fluorescence spectroscopy, vibrating sample magnetometry, and transmission electron microscopy, which showed that the CdTe@SiO₂@n Fe₃O₄ composite nanoparticles exhibited excellent luminescence properties coupled with well‐defined magnetic responses. To demonstrate the utility of these magnetically encoded nanoparticles for near‐simultaneous detection and separation of multiple components from complex samples, three different fluorescently labeled IgG proteins, as model targets, were identified and collected from a mixture by using the CdTe@SiO₂@n Fe₃O₄ nanoparticles.     

Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Construction of Polycation‐Based Non‐Viral DNA Nanoparticles and Polyanion Multilayers via Layer‐by‐Layer Self‐Assembly

Summary: The multilayers of polycation‐based non‐viral DNA nanoparticles and biodegradable poly(L ‐glutamic acid) (PGA) were constructed by a layer‐by‐layer (LbL) technique. Poly(ethyleneimine) (PEI) was used to condense DNA to develop non‐viral DNA nanoparticles. AFM, UV‐visible spectrometry, and TEM measurements revealed that the PEI‐DNA nanoparticles were successfully incorporated into the multilayers. The well‐structured, easily processed multilayers with the non‐viral DNA nanoparticles may provide a novel approach to precisely control the delivery of DNA, which may have great potential for gene therapy applications in tissue engineering, medical implants, etc.

A TEM image of the cross section of a (PGA/PEI‐DNA nanoparticle)₂₀ multilayer.     

Self‐Assembly of Carboxylic Acid Appended Naphthalene Diimide Derivatives with Tunable Luminescent Color and Electrical Conductivity

Self‐assembly of a series of carboxylic acid‐functionalized naphthalene diimide (NDI) chromophores with a varying number (n=1–4) of methylene spacers between the NDI ring and the carboxylic acid group has been studied. The derivatives show pronounced aggregation due to the synergistic effects of H‐bonding between the carboxylic acid groups in a syn–syn catemer motif and π stacking between the NDI chromophores. Solvent‐dependent UV/Vis studies reveal the existence of monomeric dye molecules in a “good” solvent such as chloroform and self‐assembly in “bad” solvents such as methylcyclohexane. The propensity of self‐assembly is comparable for all samples. Temperature‐dependent spectroscopic studies show high thermal stability of the H‐bonding‐mediated self‐assembled structures. In the presence of a protic solvent such as MeOH, self‐assembly can be suppressed, suggesting a decisive role of H‐bonding, whereas π stacking is more a consequence of than a cause for self‐assembly. Syn–syn catemer‐type H‐bonding is supported by powder XRD studies and the results corroborate well with DFT calculations. The morphology as determined by AFM is found to be dependent on the value of n; with increasing n, the morphology gradually shifts from 2D nanosheets to 1D nanofibers. Emission spectra show sharp emission bands with relatively small Stokes shifts. In addition, a rather broad emission band is observed at longer wavelengths because of the in situ formation of excimer‐type species. Due to such a heterogeneous nature, the emission spectrum spans almost the entire red–green–blue region. Depending on the value of n, the ratio of intensities of the two emission bands is changed, which results in a tunable luminescent color. Furthermore, in the case of n=1 and 3, almost pure white light emission is observed. Time‐resolved photoluminescence spectra show a very short lifetime (a few picoseconds) of monomeric dye molecules and biexponential decays with longer lifetimes (on the order of nanoseconds) for aggregated species. Current–voltage measurements show electrical conductivity in the range of 10^?4 S cm^?1 for the aggregated chromophores, which is four orders of magnitude higher than the value for a structurally similar NDI control molecule lacking the H‐bonding functionality.     

Self‐Assembly of a Trinuclear Luminescent Europium Complex

Triangular luminescent box : Self‐assembly of a new multidentate receptor with europium cations results in the formation of trinuclear discrete complexes. X‐ray crystallography shows that nine‐coordinate cations are linked by ligands to provide a triangular complex in the solid state and in solution. Despite the coordinated solvent molecules, this topologically unusual complex exhibits remarkable luminescent properties.

     

Thermally Reversible Self‐Assembly of Nanoparticles via Polymer Crystallization

The directed self‐assembly of gold nanoparticles through the crystallization of surface‐grafted polyethylene oxide (PEO) in ethanol–water mixtures is described. This process is fully reversible and tunable through either the size of the core or the polymeric coating. Characterization by X‐ray scattering and electron microscopy of the self‐assembled structures reveals order at the nanoscale, typically not the case for thermoresponsive gold nanoparticles coated with lower or upper critical solution temperature polymers. A further novelty is the result of selective binding of calcium ions to the PEO in the fluid state: a reversible thermoresponsive transition become irreversible.

     

Carbon Dioxide‐Controlled Assembly of Water‐Soluble Conjugated Polymers Catalyzed by Carbonic Anhydrase

The CO₂‐responsive and biocatalytic assembly based on conjugated polymers has been demonstrated by combining the signal amplification property of the polythiophene derivative (PTP) and the catalytic actions of carbonic anhydrase (CA). CO₂ is applied as a new trigger mode to construct the smart assembly by controlling the electrostatic and hydrophobic interactions between the PTP molecules in aqueous solution, leading to the visible fluorescence changes. Importantly, the assembly transformation of PTP can be specifically and highly accelerated by CA based on the efficient catalytic activity of CA for the inter‐conversion between CO₂ and HCO₃⁻, mimicking the CO₂‐associated biological processes that occurred naturally in living organisms. Moreover, the PTP‐based assembly can be applied for biomimetic CO₂ sequestration with fluorescence monitoring in the presence of CA and calcium.

     

Water‐Soluble Molecular Capsules: Self‐Assembly and Binding Properties

The self‐assembly and characterization of water‐soluble calix[4]arene‐based molecular capsules ( 1?2 ) is reported. The assemblies are the result of ionic interactions between negatively charged calix[4]arenes 1 a and 1 b , functionalized at the upper rim with amino acid moieties, and a positively charged tetraamidiniumcalix[4]arene 2 . The formation of the molecular capsules is studied by ¹H NMR spectroscopy, ESI mass spectrometry (ESI‐MS), and isothermal titration calorimetry (ITC). A molecular docking protocol was used to identify potential guest molecules for the self‐assembled capsule 1 a?2 . Experimental guest encapsulation studies indicate that capsule 1 a?2 is an effective host for both charged (N‐methylquinuclidinium cation) and neutral molecules (6‐amino‐2‐methylquinoline) in water.     

Intracellular Self‐Assembly of Taxol Nanoparticles for Overcoming Multidrug Resistance

Multidrug resistance (MDR) remains the biggest challenge in treating cancers. Herein we propose the intracellular self‐assembly of nanodrugs as a new strategy for overcoming MDR. By employing a biocompatible condensation reaction, we rationally designed a taxol derivative Ac‐Arg‐Val‐Arg‐Arg‐Cys(StBu)‐Lys(taxol)‐2‐cyanobenzothiazole (CBT‐Taxol) which could be subjected to furin‐controlled condensation and self‐assembly of taxol nanoparticles (Taxol‐NPs). In vitro and in vivo studies indicated that, compared with taxol, CBT‐Taxol showed a 4.5‐fold or 1.5‐fold increase in anti‐MDR effects, respectively, on taxol‐resistant HCT 116 cancer cells or tumors without being toxic to the cells or the mice. Our results demonstrate that structuring protease‐susceptible agents and assembling them intracellularly into nanodrugs could be a new optimal strategy for overcoming MDR.     

Stimuli‐Responsive Water‐Soluble Fullerene (C60) Polymeric Systems

This review documents the advances in stimuli‐responsive water‐soluble fullerene (C₆₀) polymeric systems. Stimuli‐responsive polymers, when grafted onto C₆₀ impart “smart” and “responsive” characteristics, and these novel materials adopt various morphologies when subjected to external stimuli, such as pH, temperature, and salt. Various synthetic approaches for producing C₆₀‐polymers are outlined and discussed. The responsive behavior, water solubility, and self‐assembly characteristics of these C₆₀‐polymers make them attractive for applications such as drug delivery, temperature sensors, and personal care.     

Hierarchical Self‐Assembly of PDMA‐b‐PS Chains into Granular Nanoparticles: Genesis and Fate

The hierarchical self‐assembly of an amphiphilic block copolymer, poly(N,N‐dimethylacrylamide)‐block‐polystyrene with a very short hydrophilic block (PDMA₁₀‐b‐PS₆₂), in large granular nanoparticles is reported. While these nanoparticles are stable in water, their disaggregation can be induced either mechanically (i.e., by applying a force via the tip of the cantilever of an atomic force microscope (AFM)) or by partial hydrolysis of the acrylamide groups. AFM force spectroscopy images show the rupture of the particle as a combination of collapse and flow, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of partly hydrolyzed nanoparticles provide a clear picture of the granular structure.

     

Non‐covalent Versus Covalent Control of Self‐Assembly and Chirality of Nile Red‐modified Nucleoside and DNA

A DNA‐based covalent versus a non‐covalent approach is demonstrated to control the optical, chirooptical and higher order structures of Nile red ( Nr ) aggregation. Dynamic light scattering and TEM studies revealed that in aqueous media Nr ‐modified 2′‐deoxyuridine aggregates through the co‐operative effect of various non‐covalent interactions including the hydrogen bonding ability of the nucleoside and sugar moieties and the π‐stacking tendency of the highly hydrophobic dye. This results in the formation of optically active nanovesicles. A left‐handed helically twisted H‐type packing of the dye is observed in the bilayer of the vesicle as evidenced from the optical and chirooptical studies. On the other hand, a left‐handed helically twisted J‐type packing in vesicles was obtained from a non‐polar solvent (toluene). Even though the primary stacking interaction of the dye aggregates transformed from H→J while going from aqueous to non‐polar media, the induced supramolecular chirality of the aggregates remained the same (left‐handed). Circular dichroism studies of DNA that contained several synthetically incorporated and covalently attached Nr ‐modified nucleosides revealed the formation of helically stacked H‐aggregates of Nr but—in comparison to the noncovalent aggregates—an inversed chirality (right‐handed). This self‐assembly propensity difference can, in principle, be applied to other hydrophobic dyes and chromophores and thus open a DNA‐based approach to modulate the primary stacking interactions and supramolecular chirality of dye aggregates.     

Solvatochromism,Reversible Chromism and Self‐Assembly Effects of Heteroatom‐Assisted Aggregation‐Induced Enhanced Emission (AIEE) Compounds

Two compounds, 9,10‐bis[2‐(quinolyl)vinyl]anthracene (BQVA) and 9,10‐bis[2‐(naphthalen‐2‐yl)vinyl]anthracene (BNVA), have been synthesised and investigated. Both of them have aggregation‐induced enhanced emission (AIEE) properties. Heteroatom‐assisted BQVA shows solvatochromism, reversible chromism properties and self‐assembly effects. When increasing the solvent polarities, the green solution of BQVA turns to orange with a redshift of the fluorescence emission wavelengths from λ=527 to 565 nm. Notably, BQVA exhibits reversible chromism properties, including mechano‐ and thermochromism. The as‐prepared BQVA powders show green fluorescence (λ_em=525 nm) and the colour can turn into orange (λ_em=573 nm) after grinding. Interestingly, the orange colour can return at high temperature. Based on these reversible chromism properties, a simple and convenient erasable board has been designed. Different from BQVA, non‐heteroatom‐assisted BNVA has no clear chromic processes. The results obtained from XRD, differential scanning calorimetry, single‐crystal analysis and theoretical calculations indicate that the chromic processes depend on the heteroatoms in BQVA. Additionally, BQVA also exhibits excellent self‐assembly effects in different solvents. Homogeneous nanospheres are formed in mixtures of tetrahydrofuran and water, which are then doped into silica nanoparticles and treated with 3‐aminopropyltriethoxysilane to give amino‐functionalised nanoparticles (BQVA?AFNPs). The BQVA?AFNPs could be used to stain protein markers in polyacrylamide gel electrophoresis.     

Self‐Assembly of Amphiphilic Block Copolymer‐Tethered Nanoparticles: a New Approach to Nanoscale Design of Functional Materials

Colloidal molecules constructed from polymers and nanoparticles (NPs) have recently emerged as a novel class of building blocks for assembling functional hybrid materials. Particularly, self‐assembly of amphiphilic block copolymer (BCP)‐tethered NPs (BNPs) has shown great promise in the nanoscale design of functional hybrid materials. On the one hand, structurally the BNPs can be considered as molecular equivalents that are capable of self‐assembly at multiple hierarchical levels. On the other hand, the assembly of BNPs shows significant differences from molecular assembly due to their large dimension, complex geometry, and multi‐scale interactions involved in the assembly process. The manipulation of BCPs localized near the surface of the NPs offers an effective tool for engineering the interactions between NPs and hence the complexity of NP assembly. In this Feature Article, recent progresses on the self‐assembly of BNPs into functional materials are summarized. First, major strategies for assembling amphiphilic BNPs are highlighted. Secondly, the application of hybrid nanostructures (e.g., vesicles) assembled from BNPs in the field of biomedical imaging and delivery is discussed. Finally, current challenges and perspectives at this frontier are outlined.