Cocatalyst‐Free Photocatalysts for Efficient Visible‐Light‐Induced H2 Production: Porous Assemblies of CdS Quantum Dots and Layered Titanate Nanosheets

Highly efficient, visible‐light‐induced H₂ generation can be achieved without the help of a Pt cocatalyst by new hybrid photocatalysts, in which CdS quantum dots (QDs) (particle size ≈2.5 nm) are incorporated in the porous assembly of sub‐nanometer‐thick layered titanate nanosheets. Due to the very‐limited crystal dimension of component semiconductors, the electronic structure of CdS QDs is strongly coupled with that of the layered titanate nanosheets, leading to an efficient electron transfer between them and the enhancement of the CdS photostability. As a consequence of the promoted electron transfer, the photoluminescence of CdS QDs is nearly quenched after hybridization, indicating the almost‐suppression of electron‐hole recombination. These Pt‐cocatalyst‐free, CdS‐layered titanate nanohybrids show much‐higher photocatalytic activity for H₂ production than the precursor CdS QDs and layered titanate, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization. The observed photocatalytic efficiency of these Pt‐free hybrids (≈1.0 mmol g^?1 h^?1) is much greater than reported values of other Pt‐free CdS‐TiO₂ systems. This finding highlights the validity of 2D semiconductor nanosheets as effective building blocks for exploring efficient visible‐light‐active photocatalysts for H₂ production.     

Quantum Dot–Carbon Nanotube Hybrid Phototransistor with an Enhanced Optical Stark Effect

Enhanced carrier–carrier interactions in hybrid nanostructures exhibit exceptional electronic and optoelectronic properties. Carbon nanotubes demonstrate excellent switching behavior with high on/off ratio and high mobility but do not show photoresponse in the visible range, whereas quantum dots (QDs) shows excellent optical response in various optical ranges which can be tuned with diameter. Here, a simple and effective way to develop hybrid phototransistors with extraordinary optoelectronic properties is presented by decorating semiconducting QDs on the surface of a single‐walled carbon nanotube (SWCNT). This hybrid structure demonstrates clear negative photoresponse and optical switching behavior, which could be further tuned by applying external gate bias in the future. A clear type conversion of SWCNT transistor from p‐type to n‐type caused by a charge transfer from attached QDs to CNT is demonstrated. Moreover, this hybrid structure also demonstrates an enhancement in ‘optical Stark effect’ without applying any external electric field. Charged SWCNT surface plays a key role behind the enhancement of optical Stark effect in QDs. The carrier dynamics of the QD and CNT heterostructures system highlights the potential application opportunity of the quantum dot systems, which can be adaptable to the current technologies.     

PbS and CdS Quantum Dot‐Sensitized Solid‐State Solar Cells: “Old Concepts,New Results”

Lead sulfide (PbS) and cadmium sulfide (CdS) quantum dots (QDs) are prepared over mesoporous TiO₂ films by a successive ionic layer adsorption and reaction (SILAR) process. These QDs are exploited as a sensitizer in solid‐state solar cells with 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as a hole conductor. High‐resolution transmission electron microscopy (TEM) images reveal that PbS QDs of around 3 nm in size are distributed homogeneously over the TiO₂ surface and are well separated from each other if prepared under common SILAR deposition conditions. The pore size of the TiO₂ films and the deposition medium are found to be very critical in determining the overall performance of the solid‐state QD cells. By incorporating promising inorganic QDs (PbS) and an organic hole conductor spiro‐OMeTAD into the solid‐state cells, it is possible to attain an efficiency of over 1% for PbS‐sensitized solid‐state cells after some optimizations. The optimized deposition cycle of the SILAR process for PbS QDs has also been confirmed by transient spectroscopic studies on the hole generation of spiro‐OMeTAD. In addition, it is established that the PbS QD layer plays a role in mediating the interfacial recombination between the spiro‐OMeTAD⁺ cation and the TiO₂ conduction band electron, and that the lifetime of these species can change by around 2 orders of magnitude by varying the number of SILAR cycles used. When a near infrared (NIR)‐absorbing zinc carboxyphthalocyanine dye (TT1) is added on top of the PbS‐sensitized electrode to obtain a panchromatic response, two signals from each component are observed, which results in an improved efficiency. In particular, when a CdS‐sensitized electrode is first prepared, and then co‐sensitized with a squarine dye (SQ1), the resulting color change is clearly an addition of each component and the overall efficiencies are also added in a more synergistic way than those in PbS/TT1‐modified cells because of favorable charge‐transfer energetics.     

Multiluminescent Hybrid Organic/Inorganic Nanotubular Structures: One‐Pot Fabrication of Tricolor (Blue–Red–Purple) Luminescent Parallepipedic Organic Superstructure Grafted with Europium Complexes

This article focuses on an innovative one‐pot fabrication of organic/inorganic hybrid parallepipedic tubes with rectangular cavities displaying multicolor luminescence. Firstly, using a novel back‐to‐back coupled 2,6‐di‐pyrazol‐1‐ylpyridine ligand, blue‐emitting several‐micrometer‐long (ca. 50 μm) parallepipedic organic nanotubes with rectangular cavities were fabricated in THF/water via supramolecular (H‐bonding and π–π stacking) and solvent‐assisted self‐assembly. Secondly, in the same pot, the ligand molecules available on the surface of the ligand nanotubes were reacted with Eu(tta)₃ molecules at the solid/liquid interface to form a layer of red‐emitting Eu(III) complex coating on the inner and outer surface of the tubes. The resultant organic/inorganic hybrid parallepipedic nanotubes fabricated using this novel bottom‐up one‐pot technique display tricolor (blue–red–purple) luminescence, i.e., blue and red dual emission from the organic ligand and the Eu(III) complex, respectively, and a purple color due to the mixing of the two colors. This simple technique signifies an innovative and important method in the development of bottom‐up nanotechnology of multiluminescent organic/inorganic hybrid nanotubes.     

Integrative Self‐Assembly of Graphene Quantum Dots and Biopolymers into a Versatile Biosensing Toolkit

Hybrid self‐assembly has become a reliable approach to synthesize soft materials with multiple levels of structural complexity and synergistic functionality. In this work, photoluminescent graphene quantum dots (GQDs, 2–5 nm) are used for the first time as molecule‐like building blocks to construct self‐assembled hybrid materials for label‐free biosensors. Ionic self‐assembly of disc‐shaped GQDs and charged biopolymers is found to generate a series of hierarchical structures that exhibit aggregation‐induced fluorescence quenching of the GQDs and change the protein/polypeptide secondary structure. The integration of GQDs and biopolymers via self‐assembly offers a flexible toolkit for the design of label‐free biosensors in which the GQDs serve as a fluorescent probe and the biopolymers provide biological function. The versatility of this approach is demonstrated in the detection of glycosaminoglycans (GAGs), pH, and proteases using three strategies: 1) competitive binding of GAGs to biopolymers, 2) pH‐responsive structural changes of polypeptides, and 3) enzymatic hydrolysis of the protein backbone, respectively. It is anticipated that the integrative self‐assembly of biomolecules and GQDs will open up new avenues for the design of multifunctional biomaterials with combined optoelectronic properties and biological applications.     

Selective Formation of Bi‐Component Arrays Through H‐Bonding of Multivalent Molecular Modules

Here, the formation of discrete supramolecular mono‐ and bi‐component architectures from novel and multivalent molecular modules bearing complementary recognition moieties that are prone to undergo multiple H‐bonds, such as 2,6‐di(acetylamino)pyridine and uracil residues, is described. These nanostructured H‐bonded arrays, including dimeric and pentameric species, are thoroughly characterized in solution by NMR, in the solid state by FT‐IR, and at the solid–liquid interface by means of scanning tunneling microscopy. The employed strategy is extremely versatile as it relies on the tuning of the valency, size, and geometry of the molecular modules; thus, it may be of interest for the bottom‐up fabrication of nanostructured functional materials with sub‐nanometer precision.     

Efficiency Enhanced Hybrid Solar Cells Using a Blend of Quantum Dots and Nanorods

The cell performance of organic‐inorganic hybrid photovoltaic devices based on CdSe nanocrystals and the semiconducting polymer poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (PCPDTBT) is strongly dependent on the applied polymer‐to‐nanocrystal loading ratio and the annealing temperature. It is shown here that higher temperatures for the thermal annealing step have a beneficial impact on the nanocrystal phase by forming extended agglomerates necessary for electron percolation to enhance the short‐circuit current. However, there is a concomitant reduction of the open‐circuit voltage, which arises from energy‐level alterations of the organic and the inorganic component. Based on quantum dots and PCPDTBT, we present an optimized organic–inorganic hybrid system utilizing an annealing temperature of 210 °C, which provides a maximum power conversion efficiency of 2.8%. Further improvement is obtained by blending nanocrystals of two different shapes to compose a favorable n‐type network. The blend of spherical quantum dots and elongated nanorods results in a well‐interconnected pathway for electrons within the p‐type polmer matrix, yielding maximum efficiencies of 3.6% under simulated AM 1.5 illumination.     

NIR/ROS‐Responsive Black Phosphorus QD Vesicles as Immunoadjuvant Carrier for Specific Cancer Photodynamic Immunotherapy

2D black phosphorus (BP) nanosheets and BP quantum dots (BPQD), as two main material styles of BP, are widely used in the biomedical filed. However, few stimuli‐responsive BP nanocarriers are reported to meet the need of nanomedicine. Herein, near‐infrared region/reactive oxygen species (NIR/ROS) sensitive BPQD vesicles (BPNVs) are prepared by self‐assembly of amphiphilic BPQDs grafted with polyethylene glycol and ROS sensitive poly(propylene sulfide) (PPS). BPNVs exhibit enhanced photo‐absorption in the NIR region, and have high loading efficiency of immunoadjuvant CpG oligodeoxynucleotides (CpG ODNs) in the cavity of the BPNVs. Upon NIR laser irradiation, high levels of ROS are generated from BPNVs to trigger the change of hydrophobic PPS to hydrophilic polymers, leading to disassembly of the vesicles to BPQDs. In this manner, the BPNVs show synergistic photodynamic therapy combined with immunotherapy, due to simultaneous release of small BPQDs with deep tumor penetration and CpG with enhanced immunotherapy. The BPNVs‐CpG achieves potent photodynamic immunotherapy in vivo, in addition to block distant tumor growth and metastasis.     

Construction of White‐Light‐Emitting Silk Protein Hybrid Films by Molecular Recognized Assembly among Hierarchical Structures

The fabrication of bio‐hybrid functional films is demonstrated by applying a materials assembly technique. Based on the hierarchical structures of silk fibroin materials, functional molecular/materials, i.e., quantum dots (QDs), can be fixed to amino acid groups in silk fibroin films. It follows that white‐light‐emitting QD silk hybrid films are obtained by hydrogen bond molecular recognition to the –COO^– groups functionalized to blue luminescent ZnSe (5.2 nm) and yellow luminescent CdTe (4.1 nm) QDs in a molar ratio of 30:1 of ZnSe to CdTe QDs. Simultaneously, a systematic blue shift in the emission peak is observed from the QD solution to QDs silk fibroin films. The significant blue shift hints the appearance of the strong interaction between QDs and silk fibroins, which causes strong white‐light‐emitting uniform silk films. The molecular recognized interactions are confirmed by high resolution transmission electron microscopy, field scanning electron microscope, and attenuated total internal reflectance Fourier transform infrared spectroscopy. The QD silk films show unique advantages, including simple preparation, tunable white‐light emission, easy manipulation, and low fabrication costs, which make it a promising candidate for multicomponent optodevices.     

Distinct Optoelectronic Signatures for Charge Transfer and Energy Transfer in Quantum Dot–MoS2 Hybrid Photodetectors Revealed by Photocurrent Imaging Microscopy

Atomically thin transition metal dichalcogenides (TMDCs) have intriguing nanoscale properties like high charge mobility, photosensitivity, layer‐thickness‐dependent bandgap, and mechanical flexibility, which are all appealing for the development of next generation optoelectronic, catalytic, and sensory devices. Their atomically thin thickness, however, renders TMDCs poor absorptivity. Here, bilayer MoS₂ is combined with core‐only CdSe QDs and core/shell CdSe/ZnS QDs to obtain hybrids with increased light harvesting and exhibiting interfacial charge transfer (CT) and nonradiative energy transfer (NET), respectively. Field‐effect transistors based on these hybrids and their responses to varying laser power and applied gate voltage are investigated with scanning photocurrent microscopy (SPCM) in view of their potential utilization in light harvesting and photodetector applications. CdSe–MoS₂ hybrids are found to exhibit encouraging properties for photodetectors, like high responsivity and fast on/off response under low light exposure while CdSe/ZnS–MoS₂ hybrids show enhanced charge carrier generation with increased light exposure, thus suitable for photovoltaics. While distinguishing optically between CT and NET in QD–TMDCs is nontrivial, it is found that they can be differentiated by SPCM as these two processes exhibit distinctive light‐intensity dependencies: CT causes a photogating effect, decreasing the photocurrent response with increasing light power while NET increases the photocurrent response with increasing light power, opposite to CT case.     

Nanostructures from Single Amino Acid‐Based Molecules: Stability,Fibrillation, Encapsulation,and Fabrication of Silver Nanoparticles

The small‐sized molecules that have been developed from single hydrophobic amino acids (Phe, Trp, Tyr and Leu) by suitably protecting the –NH₂ and –CO₂H groups generate diverse nanoscopic structures – such as nanorods, nanofibrils, nanotubes, and nanovesicles – depending upon the protection parameters and solvent polarity. The vesicular structures get disrupted in the presence of various salts, such as KCl, CaCl₂, (NH₄)₂SO₄ and N(n‐Bu)₄Br. Insertion of unnatural (o/m/p)‐aminobenzoic acids as a protecting group and the lack of conventional peptide bonds in the molecules give the nanostructures proteolytic stability. The nanostructures also show significant thermal stability along with a morphological transformation upon heat treatment. Our in vitro studies reveal that the addition of micromolar concentration “curcumin” significantly reduces the formation of amyloid‐like fibrils. These diverse nanostructures are used as a template for fabricating silver nanoparticles on their outer surfaces as well as in the inner part, followed by calcination in air which helps to obtain a 1D silver nanostructure. Furthermore, the nanovesicles are observed to encapsulate a potent drug (curcumin) and other biologically important molecules, which could be released through salt‐triggered disruption of vesicles.     

Mussel Inspired Dynamic Cross‐Linking of Self‐Healing Peptide Nanofiber Network

A general drawback of supramolecular peptide networks is their weak mechanical properties. In order to overcome a similar challenge, mussels have adapted to a pH‐dependent iron complexation strategy for adhesion and curing. This strategy also provides successful stiffening and self‐healing properties. The present study is inspired by the mussel curing strategy to establish iron cross‐link points in self‐assembled peptide networks. The impact of peptide‐iron complexation on the morphology and secondary structure of the supramolecular nanofibers is characterized by scanning electron microscopy, circular dichroism and Fourier transform infrared spectroscopy. Mechanical properties of the cross‐linked network are probed by small angle oscillatory rheology and nanoindentation by atomic force microscopy. It is shown that iron complexation has no influence on self‐assembly and β‐sheet‐driven elongation of the nanofibers. On the other hand, the organic‐inorganic hybrid network of iron cross‐linked nanofibers demonstrates strong mechanical properties comparable to that of covalently cross‐linked network. Strikingly, iron cross‐linking does not inhibit intrinsic reversibility of supramolecular peptide polymers into disassembled building blocks and the self‐healing ability upon high shear load. The strategy described here could be extended to improve mechanical properties of a wide range of supramolecular polymer networks.     

A New Type of Efficient CO2 Adsorbent with Improved Thermal Stability: Self‐Assembled Nanohybrids with Optimized Microporosity and Gas Adsorption Functions

A new type of efficient CO₂ absorbent with improved thermal stability is synthesized via self‐assembly between 2D inorganic nanosheets and two kinds of 0D inorganic nanoclusters. In these self‐assembled nanohybrids, the nanoclusters of CdO and Cr₂O₃ are commonly interstratified with layered titanate nanosheets, leading to the formation of highly microporous pillared structure with increased basicity of pore wall. The co‐pillaring of basic CdO with Cr₂O₃ is fairly effective at increasing a proportion of micropores and reactivity for CO₂ molecules and at improving the thermal stability of the resulting porous structure. Of prime importance is that the present inorganic‐pillared nanohybrids show highly efficient CO₂ adsorption capacity, which is much superior to those of many other absorbents and compatible to those of CO₂ adsorbing metal?organic framework (MOF) compounds. Taking into account an excellent thermal stability of the present nanohybrids, these materials are very promising CO₂ adsorbents usable at elevated temperature. This is the first example of efficient CO₂ adsorbent from pillared materials. The co‐pillaring of basic metal oxide nanoclusters employed in this study can provide a very powerful way of developing thermally stable CO₂ adsorbents from many known pillared systems.     

Dendrimer‐Functionalized Iron Oxide Nanoparticles for Specific Targeting and Imaging of Cancer Cells

We demonstrated a unique approach that combines a layer‐by‐layer (LbL) self‐assembly method with dendrimer chemistry to functionalize Fe₃O₄ nanoparticles (NPs) for specific targeting and imaging of cancer cells. In this approach, positively charged Fe₃O₄ NPs (8.4 nm in diameter) synthesized by controlled co‐precipitation of Fe^II and Fe^III ions were modified with a bilayer composed of polystyrene sulfonate sodium salt and folic acid (FA)‐ and fluorescein isothiocyanate (FI)‐functionalized poly(amidoamine) dendrimers of generation 5 (G5.NH₂‐FI‐FA) through electrostatic LbL assembly, followed by an acetylation reaction to neutralize the remaining surface amine groups of G5 dendrimers. Combined flow cytometry, confocal microscopy, transmission electron microscopy, and magnetic resonance imaging studies show that Fe₃O₄/PSS/G5.NHAc‐FI‐FA NPs can specifically target cancer cells overexpressing FA receptors. The present approach to functionalizing Fe₃O₄ NPs opens a new avenue to fabricating various NPs for numerous biological sensing and therapeutic applications.     

Motif‐Designed Peptide Nanofibers Decorated with Graphene Quantum Dots for Simultaneous Targeting and Imaging of Tumor Cells

Nanohybrids based on biomolecular nanostructures and graphene quantum dots (GQDs) have found wide application in the biological and biomedical fields. Herein, the design of a peptide with trifunctional motifs is reported as the precursor building block for constructing a novel multifunctional protein nanofiber (PNF), and further conjugated with highly fluorescent GQDs by noncovalent interactions. The physicochemical properties of these PNF–GQD nanohybrids are thoroughly characterized by a variety of spectroscopic and microscopic techniques, revealing that the GQDs essentially maintain their favorable optical properties in the nanohybrids. A good biocompatibility of the PNF–GQD nanohybrids is found with cell viability assays. With both, a recognition moiety (RGD) and an imaging probe (GQD), these PNF–GQD nanohybrids possess the capability of targeting and imaging tumor cells simultaneously. A potential application of these novel nanohybrids, i.e., fluorescence imaging of HeLa tumor cells, has been investigated by confocal fluorescence microscopy, which shows much enhanced labeling efficiency compared with GQDs only. Moreover, cellular internalization by nontumorous COS‐7 cells was much weaker than by HeLa cells. Our results show that GQD‐decorated PNF nanohybrids have great potential as multifunctional platforms for biomedical applications, particularly, where the capability of sensitive tracking and efficient labeling is appreciated.     

Macroscopic Properties of Biomimetic Ceramics Are Governed by the Molecular Recognition at the Bioorganic–Inorganic Interface

Bioinspired materials design aims for high‐performing composite materials based on natural biomineralization processes and biomineral architectures. A key component to the research is the bioorganic–inorganic interface, one of the most crucial parameters for controlling the material properties. In this study, genetically engineered phages expressing an inorganic‐binding peptide for the molecular recognition of a ceramic material is exploited to generate thin film multilayer assemblies, with the phage template as minority component. The bioorganic–inorganic interface in the ceramic (zinc oxide, ZnO) multilayer systems is strengthened by the ZnO‐binding motif HSSHH of a peptide to increase Young's modulus and hardness. Applying a point‐mutated version of the peptide, DSSHH, which modulates the interface forces, shows an increased fracture toughness without deteriorating the Young's modulus and the hardness. Molecular matching of the organic phase and its modulation in order to form a specific interface is shown to be important in controlling material properties like in natural biominerals. With this tool in hand, it is not only possible to imitate the structure of biominerals but also to genetically control the molecular recognition of bioorganic molecules to induce macroscopic effects in synthetic composite materials.     

Nanoengineering Hybrid Supramolecular Multilayered Biomaterials Using Polysaccharides and Self‐Assembling Peptide Amphiphiles

Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high‐molecular‐weight biopolymers and oppositely charged low‐molecular‐weight peptide amphiphiles (PAs), through combination of self‐assembly and electrostatically driven layer‐by‐layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self‐assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications.