Applications of hollow nanostructures in water treatment considering organic, inorganic, and bacterial pollutants

One of the major issues of modern society is water contamination with different organic, inorganic, and contaminants bacteria. Finding cost-effective and efficient materials and methods for water treatment and environment remediation is among the scientists' most important considerations. Hollow-structured nanomaterials, including hollow fiber membranes, hollow spheres, hollow nanoboxes, etc., have shown an exciting capability for wastewater refinement approaches, including membrane technology, adsorption, and photocatalytic procedure due to their extremely high specific surface area, high porosity, unique morphology, and low density. Diverse hollow nanostructures could potentially eliminate organic contaminants, including dyes, antibiotics, oil/water emulsions, pesticides, and other phenolic compounds, inorganic pollutants, such as heavy metal ions, salts, phosphate, bromate, and other ions, and bacteria contaminations. Here, a comprehensive overview of hollow nanostructures' fabrication and modification, water contaminant classification, and recent studies in the water treatment field using hollow-structured nanomaterials with a comparative attitude have been provided, indicating the privilege abd detriments of this class of nanomaterials. Eventually, the future outlook of employing hollow nanomaterials in water refinery systems and the upcoming challenges arising in scaling up are also propounded.

Self-Assembled Polysaccharide-Diphenylalanine/Au Nanospheres for Photothermal Therapy and Photoacoustic Imaging

Gold-based nanomaterials have attracted extensive interest for potential application in photothermal therapy (PTT) owing to their distinctive properties including high photothermal transduction, biocompatibility, and low cytotoxicity. Herein, assembled gold nanoparticle architecture-based photothermal conversion agents were synthesized by using polysaccharides (alginate dialdehyde, ADA) as both the cross-linker to induce self-assembly of diphenylalanine (FF) and the reducer for in situ reduction of Au³⁺ ions into Au nanoparticles (Au NPs). The extinction spectrum of the obtained self-assembled ADA-FF/Au nanospheres was finely modulated into a near-infrared region by controlling the growth of Au NPs inside the assemblies. The strong plasmonic coupling effect of the assembled Au NPs also leads to high photothermal conversion (η = 40%) of the ADA-FF/Au nanospheres, hence presenting good performance in PTT and photoacoustic imaging. This synthesis technique is promising to construct nanomaterials with desired functions for potential biomedical application by self-assembly of various nanocrystals in situ.

The controlled synthesis of complex hollow nanostructures and prospective applications†

Functionality in nanoengineered materials has been usually explored on structural and chemical compositional aspects of matter that exist in such solid materials. It is well known that the absence of solid matter is also relevant and the existence of voids confined in the nanostructure of certain particles is no exception. Indeed, over the past decades, there has been great interest in exploring hollow nanostructured materials that besides the properties recognized in the dense particles also provide empty spaces, in the sense of condensed matter absence, as an additional functionality to be explored. As such, the chemical synthesis of hollow nanostructures has been driven not only for tailoring the size and shape of particles with well-defined chemical composition, but also to achieve control on the type of hollowness that characterize such materials. This review describes the state of the art on late developments concerning the chemical synthesis of hollow nanostructures, providing a number of examples of materials obtained by distinct strategies. It will be apparent by reading this progress report that the absence of solid matter determines the functionality of hollow nanomaterials for several technological applications.

Amyloid-Like Fibrillary Morphology Originated by Tyrosine-Containing Aromatic Hexapeptides

Phenylalanine-based nanostructures have attracted the attention of the material science community for their functional properties. These properties strongly depend on the hierarchic organization of the nanostructure that in turn can be finely tuned by punctual chemical modifications of the building blocks. Herein, we investigate how the partial or the complete replacement of the Phe residues in PEG₈ -(Phe)₆ (PEG₈ -F6) with tyrosines to generate PEG₈ -(Phe-Tyr)₃ (PEG₈ -(FY)3) or PEG₈ -(Tyr)₆ (PEG₈ -Y6) affects the structural/functional properties of the nanomaterial formed by the parental compound. Moreover, the effect of the PEG derivatization was evaluated through the characterization of the peptides without the PEG moiety (Tyr)₆ (Y6) and (Phe-Tyr)₃ ((FY)3). Both PEG₈ -Y6 and PEG₈ -(FY)3 can self-assemble in water at micromolar concentrations in β-sheet-rich nanostructures. However, WAXS diffraction patterns of these compounds present significant differences. PEG₈ -(FY)3 shows a 2D WAXS oriented fiber diffraction profile characterized by the concomitant presence of a 4.7 Å meridional and a 12.5 Å equatorial reflection that are generally associated with cross-β structure. On the other hand, the pattern of PEG₈ -Y6 is characterized by the presence of circles typically observed in the presence of PEG crystallization. Molecular modeling and dynamics provide an atomic structural model of the peptide spine of these compounds that is in good agreement with WAXS experimental data. Gelation phenomenon was only detected for PEG₈ -(FY)3 above a concentration of 1.0 wt % as confirmed by storage (G'≈100 Pa) and loss (G''≈28 Pa) moduli in rheological studies. The cell viability on CHO cells of this soft hydrogel was certified to be 90 % after 24 hours of incubation.

Peptide nanoparticles (PNPs) modified disposable platform for sensitive electrochemical cytosensing of DLD-1 cancer cells

A novel diphenylalaninamid (FFA) based peptide nanoparticles (PNPs) modified pencil graphite electrodes (PGEs) for construction of electrochemical cytosensor was demonstrated for the first time in this study. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed the spherical nanostructure of the synthesized FFA based PNPs while attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectra provided information about the structure and conformation of proteins in their structure. Self-assembly of PNPs on PGE surface and adhesion of DLD-1 cancer cells on this surface was also characterized by electrochemical measurements. PNP/PGEs acted as a sensitive platform for simple and rapid quantification of low concentration of DLD-1 cancer cells in early diagnosis using the electrochemical impedance method (EIS). The offered cytosensor demonstrated outstanding performance for the detection of DLD-1 cells by the EIS method. The impedance of electronic transduction was associated with the amount of the immobilized cells ranging from 2 × 10² to 2.0 × 10⁵ cellsmL^-1 with a limit of detection of 100 cellsmL^-1. The efficient performance of the cytosensor was attributed to the well-defined nanostructure and biocompability of PNPs on the substrate.

Targeted Soft Biodegradable Glycine/PEG/RGD-Modified Poly(methacrylic acid) Nanobubbles as Intelligent Theranostic Vehicles for Drug Delivery

The development of multifunctional ultrasound contrast agents has inspired considerable interest in the application of biomedical imaging and anticancer therapeutics. However, combining multiple components that can preferentially accumulate in tumors in a nanometer scale poses one of the major challenges in targeting drug delivery for theranostic application. Herein, reflux-precipitation polymerization, and N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide-meditated amidation reaction were introduced to effectively generate a new type of soft glycine/poly(ethylene glycol) (PEG)/RGD-modified poly(methacrylic acid) nanobubbles with a uniform morphology and desired particle size (less than 100 nm). Because of the enhanced biocompatibility resulting from the glycine modification, over 80% of the cells survived, even though the dosage of glycine-modified polymeric nanobubbles was up to 5 mg/mL. By loading doxorubicin as an anticancer drug and perfluorohexane as an ultrasound probe, the resulting glycine/PEG/RGD-modified nanobubbles showed remarkable cancer therapeutic efficacy and a high quality of ultrasonic imaging; thus, the ultrasonic signal exhibited a 1.47-fold enhancement at the tumor site after intravenous injection. By integrating diagnostic and therapeutic functions into a single nanobubble, the new type of theranostic nanobubbles offers a promising strategy to monitor the therapeutic effects, giving important insights into the ultrasound-traced and enhanced targeting drug delivery in biomedical applications.

Diversity and Hierarchy in Supramolecular Assemblies of Triphenylalanine: From Laminated Helical Ribbons to Toroids

Microstructures from small phenylalanine-based peptides have attracted great attention lately because these compounds are considered to be a new class of tunable materials. In spite of the extensive studies on uncapped diphenylalanine and tetraphenylalanine peptides, studies on the self-assembly of uncapped triphenylananine (FFF) are very scarce and nonsystematic. In this work, we demonstrate that FFF assemblies can organize in a wide number of well-defined supramolecular structures, which include laminated helical-ribbons, leaflike dendrimers, doughnut-, needle-, and flower-shapes. These organizations are produced by the attractive or repulsive interactions between already formed assemblies and therefore can be controlled through the choice of solvents used as the incubation medium. Thus, the formation of the desired supramolecular structures is regulated through the protonation/deprotonation of the terminal groups, the polarity of the incubation medium, which affects both peptide···solvent interactions and the cavity solvation energy (i.e., solvent···solvent interactions), and the steric interactions between own assemblies that act as building blocks. Finally, the β-sheet disposition in the latter structural motifs has been examined using both theoretical calculations and Fourier transform infrared spectroscopy. Results indicate that FFF molecules can adopt both parallel and antiparallel β-sheets. However, the former one is the most energetically favored because of the formation of π-π stacking interactions between the aromatic rings of hydrogen-bonded strands.

Facile fabrication of pH-sensitive peptide–inorganic hollow spheres using a template-free method

The self-assembly of a heptapeptide and phosphotungstic acid into hollow spheres with pH-responsive properties was achieved using a template-free method.

Novel layer-by-layer self-assembled peptide nanocarriers for siRNA delivery

Novel stable diphenylalaninamide peptide based nanocarriers were designed by layer-by-layer polyelectrolyte deposition to load siRNA for gene silencing.

Peptide-Modulated Self-Assembly of Chromophores toward Biomimetic Light-Harvesting Nanoarchitectonics

Elegant self-assembling complexes by the combination of proteins/peptides with functional chromophores are decisively responsible for highly efficient light-harvesting and energy transfer in natural photosynthetic systems. Mimicking natural light-harvesting complexes through synthetic peptides is attractive due to their advantanges of programmable primary structure, tunable self-assembly architecture and easy availability in comparison to naturally occuring proteins. Here, an overview of recent progresses in the area of biomimetic light-harvesting nanoarchitectonics based on peptide-modulated self-assembly of chromophores is provided. Adjusting the organization of chromophores, either by creating peptide-chromophore conjugates or by the non-covalent assembly of peptides and chromophores are highlighted. The light-harvesting properties, especially the energy transfer of the biomimetic complexes are critically discussed. The applications of such complexes in the mineralization of inorganic nanoparticles, generation of molecular hydrogen and oxygen, and photosynthesis of bioactive molecules are also included.

Facile preparation of bridged silsesquioxane microspheres with interconnected multi-cavities and open holes

Bridged silsesquioxane (BSQ) microspheres featured with interconnected multi-cavities and open holes are facilely prepared from water-in-oil-in-water emulsion.

Dipeptide concave nanospheres based on interfacially controlled self-assembly: from crescent to solid

Concave nanospheres based on the self-assembly of simple dipeptides not only provide alternatives for modeling the interactions between biomacromolecules, but also present a range of applications for purification and separation, and delivery of active species.

Solvent Controlled Structural Transition of KI4K Self-Assemblies: from Nanotubes to Nanofibrils

The structural modulation of peptide and protein assemblies under well-controlled conditions is of both fundamental and practical significance. In spite of extensive studies, it remains hugely challenging to tune the self-assembled nanostructures in a controllable manner because the self-assembly processes are dictated by various noncovalent interactions and their interplay. We report here how to manipulate the self-assembly of a designed, symmetric amphiphilic peptide (KI4K) via the solvent-controlled structural transition. Structural transition processes were carefully followed by the combination of transmission electronic microscopy (TEM), atomic force microscopy (AFM), circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and small angle neutron scattering (SANS). The results show that the introduction of acetonitrile into water significantly affected the hydrophobic interactions among hydrophobic side chains while imposing little impact on the β-sheet hydrogen bonding between peptide backbones. A structural transition occurred from nanotubes to helical/twisted ribbons and then to thin fibrils with the addition of acetonitrile due to the reduced hydrophobic interactions and the consequent weakening of the lateral stacking between KI4K β-sheets. The increased intermolecular electrostatic repulsions among lysine side chain amino groups had little effect on the lateral stacking of KI4K β-sheets due to the molecular symmetry. Complementary molecular dynamic (MD) simulations also indicated the solvation of acetonitrile molecules into the hydrophobic domains weakening the coherence between the neighboring sheets.

Functional architectures based on self-assembly of bio-inspired dipeptides: Structure modulation and its photoelectronic applications

Getting inspiration from nature and further developing functional architectures provides an effective way to design innovative materials and systems. Among bio-inspired materials, dipeptides and its self-assembled architectures with functionalities have recently been the subject of intensive studies. However, there is still a great challenge to explore its applications likely due to the lack of effective adaptation of their self-assembled structures as well as a lack of understanding of the self-assembly mechanisms. In this context, taking diphenylalanine (FF, a core recognition motif for molecular self-assembly of the Alzheimer's β-amyloid polypeptides) as a model of bio-inspired dipeptides, recent strategies on modulation of dipeptide-based architectures were introduced with regard to both covalent (architectures modulation by coupling functional groups) and non-covalent ways (controlled architectures by different assembly pathways). Then, applications are highlighted in some newly emerging fields of innovative photoelectronic devices and materials, such as artificial photosynthetic systems for renewable solar energy storage and renewable optical waveguiding materials for optoelectronic devices. At last, the challenges and future perspectives of these bio-inspired dipeptides are also addressed.