Fabrication of Multilayered Two-Dimensional Micelles and Fibers by Controlled Self-Assembly of Rod-Coil Block Copolymers

Fabricating hierarchical nanomaterials by self-assembly of rod-coil block copolymers attracts great interest. However, the key factors that affect the formation of the hierarchical nanomaterials have not been thoroughly researched. Herein, we have synthesized two diblock copolymers composed of poly(3-hexylthiophene) (P3HT) and polyethylene glycol (PEG). Through a heating, cooling, and aging process, a series of multilayered hierarchical micelles and fibers were prepared in alcoholic solutions. The transition from fibers to hierarchical micelles are strictly influenced by the strength of the π-π stacking interaction, the PEG chain length, and solvent. In isopropanol, the P3HT₂₂-b-PEG₄₃ could self-assemble into hierarchical micelles composed of several two-dimensional (2D) laminar layers, driven by the π-π stacking interaction and van der Waals force. The P3HT₂₂-b-PEG₄₃ could not self-assemble into well-defined nanostructures in methanol and ethanol, but could self-assemble into fibers in isobutanol. However, the P3HT₂₂-b-PEG₁₁₃ with a longer corona block only self-assembled into fibers in four alcoholic solutions, due to the increase in dissolving capacity and steric hindrance. The sizes and the size distributions of the nanostructures both increased with the increase in polymer concentration and the decrease in solvent polarity. This study shows a method to fabricate the hierarchical micelles.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Highly Sensitive Polydiacetylene Ensembles for Biosensing and Bioimaging

Polydiacetylenes are prepared from amphiphilic diacetylenes first through self-assembly and then polymerization. Different from common supramolecular assemblies, polydiacetylenes have stable structure and very special optical properties such as absorption, fluorescence, and Raman. The hydrophilic head of PDAs is easy to be chemically modified with functional groups for detection and imaging applications. PDAs will undergo a specific color change from blue to red, fluorescence enhancement and Raman spectrum changes in the presence of receptor ligands. These properties allow PDA-based sensors to have high sensitivity and specificity during analysis. Therefore, the PDAs have been widely used for detection of viruses, bacteria, proteins, antibiotics, hormones, sialic acid, metal ions and as probes for bioimaging in recent years. In this review, the preparation, polymerization, and detection mechanisms of PDAs are discussed, and some representative research advances in the field of bio-detection and bioimaging are highlighted.

Cation-Directed Self-Assembly of Macrocyclic Diacetylene for Developing Chromogenic Polydiacetylene

The cation-directed self-assembly process has emerged as a fascinating approach for constructing supramolecular architectures and manifested a diverse range of assembly related applications. Herein, we synthesized a macrocyclic structure containing bis-amidopyridine and photopolymerizable diacetylene template, PyMCDA. Owing to the metal coordination affinity of bis-amidopyridine and the π-π stacking characteristic of diacetylene template and complementary to the cyclic molecular framework, Cs⁺-directed organic nanotubes are generated via unidirectional self-assembly of PyMCDA. The monomeric PyMCDA nanotubes are transformed into the covalently cross-linked chromogenic polydiacetylene nanotubes (PyMCPDA-Cs⁺) by UV-promoted topochemical polymerization. The result of a metal-ligand coordination characteristic, geometric parameters in solid-state assemblies, and topochemical polymerization behavior reveals a generation of Cs⁺ ion inserted nanotubes. Interestingly, PyMCDA-Cs⁺ nanotubes display thermochromic property with a brilliant blue-to-red color transition.

Selective Labeling and Growth Inhibition of Pseudomonas aeruginosa by Aminoguanidine Carbon Dots

Pseudomonas aeruginosa is a highly virulent bacterium, particularly associated with the spread of multidrug resistance. Here we show that carbon dots (C-dots), synthesized from aminoguanidine and citric acid precursors, can selectively stain and inhibit the growth of P. aeruginosa strains. The aminoguanidine-C-dots were shown both to target P. aeruginosa bacterial cells and also to inhibit biofilm formation by the bacteria. Mechanistic analysis points to interactions between aminoguanidine residues on the C-dots' surface and P. aeruginosa lipopolysaccharide moieties as the likely determinants for both antibacterial and labeling activities. Indeed, the application of biomimetic membrane assays reveals that LPS-promoted insertion and bilayer permeation constitute the primary factors in the anti- P. aeruginosa effect of the aminoguanidine-C-dots. The aminoguanidine C-dots are easy to prepare in large quantities and are inexpensive and biocompatible and thus may be employed as a useful vehicle for selective staining and antibacterial activity against P. aeruginosa.

Polydiacetylene Capacitive Artificial Nose

Polydiacetylenes are a class of conjugated polymers exhibiting unique color and fluorescence properties and employed as useful sensing vehicles. Here we demonstrate for the first time that the dielectric properties of polydiacetylenes can be exploited for vapor sensing. Specifically, electrodes coated with polydiacetylenes, embedded within a porous polyvinylpyrrolidone (PVP) matrix, exhibit significant capacitance transformations upon exposure to different vapors. The capacitive response of the polydiacetylene/PVP films depended upon both the structures of the diacetylene monomer and the extent of ultraviolet irradiation (i.e., polymerization), underscoring a unique sensing mechanism affected by conjugation, structure, and dielectric properties of the polydiacetylene/polymer matrix. Importantly, the variability of polydiacetylene structures allows vapor identification through an array-based pattern recognition (i.e., artificial nose). This study opens new avenues for applications of polydiacetylene systems, particularly pointing to their dielectric properties as powerful sensing determinants.

Reversibly Thermochromic Cyclic Dipeptide Nanotubes

Owing to their capability of forming extensive hydrogen bondings and the facile introduction of chirality, cyclic dipeptides (CDPs) have gained great attention as scaffolds for functional supramolecules. Surprisingly, introduction of a photopolymerizable diacetylene (DA) moiety to the CDP afforded nanotubular structures with enhanced stability and reversible thermochromism. A series of CDP-containing DAs (CDP-DAs) are prepared by coupling 10,12-pentacosadiynoic acid with CDPs, cyclo(-Gly-Ser) and cis/trans cyclo(-Ser-Ser). Fabrication of CDP-DA self-assemblies in a polar chloroform and methanol solvent mixture affords nanotubes comprising single-wall and multiwall structures. The self-assembly behavior and morphology characteristic are examined by scanning electron microscopy and transmission electron microscopy. Next, X-ray diffraction analysis confirms well-ordered lamellar structures with a perfect agreement with the bilayer formation leading to the tubular structure via lamellar scrolling behavior. Upon UV irradiation, monomeric CDP-DA tubular assemblies result in the blue-colored CDP/polydiacetylene (PDA) nanotubes. Interestingly, CDP/PDA nanotubes exhibit a reversible blue-to-red color change for over 10 consecutive thermal cycles. The CDP-DA/PDA supramolecular system demonstrates potential applications in developing stimulus-responsive functional materials.

Self-Assembled Polydiacetylene Vesicle and Helix with Chiral Interface for Visualized Enantioselective Recognition of Sulfinamide

An l-glutamic acid terminated amphiphilic diacetylene was designed and found to self-assemble into vesicles in water and supramolecular gel with helical structures in mixed methanol/water solvent. Both the vesicles and the helices underwent topochemical photopolymerization under UV irradiation and changed to a blue color. During the self-assembly and photopolymerization, the chirality of localized l-glutamic acid was successfully transferred to polydiacetylene (PDA), which resulted in obvious CD signals in the PDA blue phase. Interestingly, the CD signals for PDA vesicles and helices were opposite due to the different packing modes in the PDA skeleton. However, although these two assembly systems own opposite supramolecular chirality, both of them showed the same enantioselective recognition of sulfinamide enantiomers, in which the assemblies with S-enantiomer turned red while the other remained blue in the presence of the R-enantiomer. It is suggested that the chiral interface composed of l-glutamic acid played an important role in the enantioselective recognition. This work revealed the function of molecular and supramolecular chirality in the supramolecular self-assembly system.

Light-Induced Conductivity in a Solution-Processed Film of Polydiacetylene and Perylene Diimide

We prepared a solution-processed film comprising a drop-casted mixture of melamine-diacetylene and perylene bis(dicarboximide) (PDI). We show that the diacetylene monomers adopt distinct crystalline organization in the presence of the PDI residues. Importantly, the drop-casted diacetylene/PDI film exhibits ultraviolet light-induced conductivity, ascribed to effective transport of charge carriers in the conjugated polymerized network.