Hongcheng Sun

Micelle-Induced Self-Assembling Protein Nanowires: Versatile Supramolecular Scaffolds for Designing the Light-Harvesting System

Organic nanoparticle induced self-assembly of proteins with periodic nanostructures is a promising and burgeoning strategy to develop functional biomimetic nanomaterials. Cricoid proteins afford monodispersed and well-defined hollow centers, and can be used to multivalently interact with geometrically symmetric nanoparticles to form one-dimensional protein nanoarrays. Herein, we report that core-cross-linked micelles can direct cricoid stable protein one (SP1) to self-assembling nanowires through multiple electrostatic interactions. One micelle can act as an organic nanoparticle to interact with two central concaves of SP1 in an opposite orientation to form a sandwich structure, further controlling the assembly direction to supramolecular protein nanowires. The reported versatile supramolecular scaffolds can be optionally manipulated to develop multifunctional integrated or synergistic biomimetic nanomaterials. Artificial light-harvesting nanowires are further developed to mimic the energy transfer process of photosynthetic bacteria for their structural similarity, by means of labeling donor and acceptor chromophores to SP1 rings and spherical micelles, respectively. The absorbing energy can be transferred within the adjacent donors around the ring and shuttling the collected energy to the nearby acceptor chromophore. The artificial light-harvesting nanowires are designed by mimicking the structural characteristic of natural LH-2 complex, which are meaningful in exploring the photosynthesis process in vitro.

Structural, optical and electrical characterization of gadolinium and indium doped cadmium oxide/p-silicon heterojunctions for solar cell applications

Gadolinium and indium co-doped CdO thin films were prepared by a pulsed laser deposition method. The XRD and XPS results indicated that Gd3+ and In3+ ions occupied locations in the interstitial positions and/or Cd2+-ion vacancies in the CdO lattice. The FESEM images showed that the films were homogeneous and consisted of nanograins with a size range of 23–40 nm. The optical band gap of the CdO thin films can be engineered over a wide range of 2.72–3.56 eV by introducing Gd and In dopants. Such transparent semiconducting Gd and In co-doped CdO films were then grown on p-type Si substrates to fabricate n-CdO/p-Si heterojunction devices. The important junction parameters such as the series resistance (Rs), ideality factor (n) and Schottky barrier height (Φb) were determined by analysing different plots from the current density–voltage (J–V) characteristics. The obtained results indicated that the electrical properties of the heterojunction diodes were controlled by the dopant concentration. The p-Si/n-Cd1−x−yGdxInyO heterojunction diode showed the best values of open circuit voltage, Voc = 1.04 V and short circuit current density, Jsc = 11.4 mA cm−2 under an illumination intensity of 100 mW cm−2, which was suitable for solar cell applications.

Enzyme-Triggered Defined Protein Nanoarrays: Efficient Light-Harvesting Systems to Mimic Chloroplasts

The elegance and efficiency by which chloroplasts harvest solar energy and conduct energy transfer have been a source of inspiration for chemists to mimic such process. However, precise manipulation to obtain orderly arranged antenna chromophores in constructing artificial chloroplast mimics was a great challenge, especially from the structural similarity and bioaffinity standpoints. Here we reported a design strategy that combined covalent and noncovalent interactions to prepare a protein-based light-harvesting system to mimic chloroplasts. Cricoid stable protein one (SP1) was utilized as a building block model. Under enzyme-triggered covalent protein assembly, mutant SP1 with tyrosine (Tyr) residues at the designated sites can couple together to form nanostructures. Through controlling the Tyr sites on the protein surface, we can manipulate the assembly orientation to respectively generate 1D nanotubes and 2D nanosheets. The excellent stability endowed the self-assembled protein architectures with promising applications. We further integrated quantum dots (QDs) possessing optical and electronic properties with the 2D nanosheets to fabricate chloroplast mimics. By attaching different sized QDs as donor and acceptor chromophores to the negatively charged surface of SP1-based protein nanosheets via electrostatic interactions, we successfully developed an artificial light-harvesting system. The assembled protein nanosheets structurally resembled the natural thylakoids, and the QDs can achieve pronounced FRET phenomenon just like the chlorophylls. Therefore, the coassembled system was meaningful to explore the photosynthetic process in vitro, as it was designed to mimic the natural chloroplast.

Light-controlled switching of the self-assembly of ill-defined amphiphilic SP-PAMAM

Light-responsive amphiphilic spiropyrans-decorated polyamidoamine (SP-P3) with ill-defined structure was prepared by using 3.0G-PAMAM as the scaffold and introducing the spiropyrans to the periphery of it randomly. Under visible light illumination, the ill-defined structure SP-P3 could form an adaptive amphiphilic macromolecule by rearranging dynamically the peripheral amino and SP groups on the surface of PAMAM. The resultant adaptive amphiphilic SP-P3 could hierarchically self-assemble into uniform macrorods about 800–1100 nm in width and 50–80 μm in length. When irradiated with UV light (365 nm), hydrophobic SP-P3 would isomerise into hydrophilic MC-P3, and induced the disassembly of rod-like aggregates. Irradiation with visible light transformed the MC-P3 back to the SP-P3 and then it could re-self-assemble into the rod-like aggregates. These results demonstrated that these macrorods could reversibly disassemble and re-self-assemble in aqueous solution under alternative UV and visible light irradiation. Our experiments not only provide a novel strategy for preparing responsive dynamic materials, but also support the concept that ill-defined amphiphilic macromolecules could also self-assemble to form well-shaped supramolecular structures.