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1.  Self-Assembly of Natural and Synthetic Drug Amphiphiles into Discrete Supramolecular Nanostructures 
Faraday discussions  2013;166:285-301.
Molecular assembly provides an effective approach to construct discrete supramolecular nanostructures of various sizes and shapes in a simple manner. One important technological application of the resulting nanostructures is their potential use as anticancer drug carriers to facilitate targeted delivery to tumour sites and consequently to improve clinical outcomes. In this carrier-assisted delivery strategy, anticancer drugs have been almost exclusively considered as the cargo to be carried and delivered, and their potential as molecular building blocks has been largely ignored. In this discussion, we report the use of anticancer drugs as molecular building units to create discrete supramolecular nanostructures that contain a high and quantitative drug loading and also have the potential for self-delivery. We first show the direct assembly of two amphiphilic drug molecules (methotrexate and folic acid) into discrete nanostructures. Our results reveal that folic acid exhibits rich self-assembly behaviours via Hoogsteen hydrogen bonding in various solvent conditions, whereas methotrexate was unable to assemble into any well-defined nanostructures under the same conditions, despite its similar chemical structures. Considering the low water solubility of most anticancer drugs, hydrophilic segments must be conjugated to the drug in order to bestow the necessary amphiphilicity. We have demonstrated this for camptothecin through the attachment of β-sheet-forming peptides with overall hydrophilicity. We found that the intermolecular interactions among camptothecin segments and those among β-sheet peptides act together to define the formation of stable one-dimensional nanostructures in dilute solutions, giving rise to nanotubes or nanofibers depending upon the processing conditions used. These results lead us to believe that self-assembly of drugs into discrete nanostructures not only offers an innovative way to craft self-delivering anticancer drugs, but also extends the paradigm of using molecular assembly as a toolbox to achieve functional nanostructures, to a new area which is specifically focused on the direct assembly of functional molecules (e.g. drugs, or imaging agents) into nanostructures of their own.
PMCID: PMC3955011  PMID: 24611283
2.  Aluminum Nanostructured Films as Substrates for Enhanced Fluorescence in the Ultraviolet-Blue Spectral Region 
Analytical chemistry  2007;79(17):6480-6487.
Particulate aluminum films of varied thicknesses were deposited on quartz substrates by thermal evaporation. These nanostructured substrates were characterized by scanning electron microscopy (SEM). With the increase of aluminum thickness, the films progress from particulate toward smooth surfaces as observed by SEM images. To date, metal-enhanced fluorescence (MEF) has primarily been observed in the visible–NIR wavelength region using silver or gold island films or roughened surfaces. We now show that fluorescence could also be enhanced in the ultraviolet-blue region of the spectrum using nanostructured aluminum films. Two probes, one in the ultraviolet and another one in the blue spectral region, have been chosen for the present study. We observed increased emission, decrease in fluorescence lifetime, and increase in photostability of a DNA base analogue 2-aminopurine and a coumarin derivative (7-HC) in 10-nm spin-casted poly(vinyl alcohol) film on Al nanostructured surfaces. The fluorescence enhancement factor depends on the thickness of the Al films as the size of the nanostructures formed varies with Al thickness. Both probes showed increased photostability near aluminum nanostructured substrates, which is consistent with the shorter lifetime. Our preliminary studies indicate that Al nanostructured substrates can potentially find widespread use in MEF applications particularly in the UV-blue spectral regime. Furthermore, these Al nanostructured substrates are very stable in buffers that contain chloride salts compared to usual silver colloid-based substrates for MEF, thus furthering the usefulness of these Al-based substrates in many biological assays where high concentration of salts are required. Finite-Difference Time-Domain calculations were also employed to study the enhanced near-fields induced around aluminum nanoparticles by a radiating fluorophore, and the effect of such enhanced fields on the fluorescence enhancement observed was discussed.
doi:10.1021/ac071363l
PMCID: PMC2737393  PMID: 17685553
3.  Simulation of electron transport during electron-beam-induced deposition of nanostructures 
Summary
We present a numerical investigation of energy and charge distributions during electron-beam-induced growth of tungsten nanostructures on SiO2 substrates by using a Monte Carlo simulation of the electron transport. This study gives a quantitative insight into the deposition of energy and charge in the substrate and in the already existing metallic nanostructures in the presence of the electron beam. We analyze electron trajectories, inelastic mean free paths, and the distribution of backscattered electrons in different compositions and at different depths of the deposit. We find that, while in the early stages of the nanostructure growth a significant fraction of electron trajectories still interacts with the substrate, when the nanostructure becomes thicker the transport takes place almost exclusively in the nanostructure. In particular, a larger deposit density leads to enhanced electron backscattering. This work shows how mesoscopic radiation-transport techniques can contribute to a model that addresses the multi-scale nature of the electron-beam-induced deposition (EBID) process. Furthermore, similar simulations can help to understand the role that is played by backscattered electrons and emitted secondary electrons in the change of structural properties of nanostructured materials during post-growth electron-beam treatments.
doi:10.3762/bjnano.4.89
PMCID: PMC3869256  PMID: 24367747
electron backscattering; electron transport; (F)EBID; Monte Carlo simulation; PENELOPE
4.  Multifunctional hierarchically-assembled nanostructures as complex stage-wise dual-delivery systems for coincidental yet differential trafficking of siRNA and paclitaxel 
Nano letters  2013;13(5):2172-2181.
Development of multifunctional nanostructures that can be tuned to co-deliver multiple drugs and diagnostic agents to diseased tissues is of great importance. Hierarchically-assembled theranostic (HAT) nanostructures based on anionic cylindrical shell crosslinked nanoparticles and cationic shell crosslinked knedel-like nanoparticles (cSCKs) have recently been developed by our group to deliver siRNA intracellularly, and to undergo radiolabeling. In the current study, paclitaxel, a hydrophobic anticancer drug, and siRNA have been successfully loaded into the cylindrical and spherical components of the hierarchical assemblies, respectively. Cytotoxicity, immunotoxicity and intracellular delivery mechanism of the HAT nanostructures and their individual components have been investigated. Decoration of nanoparticles with F3-tumor homing peptide was shown to enhance the selective cellular uptake of the spherical particles, whereas the HAT nanoassemblies underwent an interesting disassembly process in contact with either OVCAR-3 or RAW 264.7 cell lines. The HAT nanostructures were found to “stick” to the cell membrane and “trigger” the release of spherical cSCKs templated onto their surfaces intracellularly, while retaining the cylindrical part on the cell surface. Combination of paclitaxel and cell-death siRNA (siRNA that induces cell death) into the HAT nanostructures resulted in greater reduction in cell viability than siRNA complexed with Lipofectamine and the assemblies loaded with the individual drugs. In addition, a shape-dependent immunotoxicity was observed for both spherical and cylindrical nanoparticles, with the latter being highly immunotoxic. Supramolecular assembly of the two nanoparticles into the HAT nanostructures significantly reduced the immunotoxicity of both cSCKs and cylinders. HAT nanostructures decorated with targeting moieties, loaded with nucleic acids, hydrophobic drugs, radiolabels, fluorophores, with control over their toxicity, immunotoxicity and intracellular delivery might have great potential for biomedical delivery applications.
doi:10.1021/nl4006645
PMCID: PMC3681414  PMID: 23574430
Multifunctional shell crosslinked nanoparticles; siRNA; paclitaxel; combinational therapy; theranostics; intracellular delivery mechanisms; immunotoxicity; nanoparticle shape; cylindrical nanoparticles
5.  Enzymatic Self-Assembly of Nanostructures for Theranostics 
Theranostics  2012;2(2):139-147.
Self-assembly of small molecules or macromolecules through non-covalent or covalent bonds to build up supramolecular nanostructures is a prevalent and important process in nature. While most chemists use small molecules to assemble nanostructures with physical or chemical perturbations, nature adopts enzymes to catalyze the reaction to assemble biological, functional nanostructures with high efficiency and specificity. Although enzymatic self-assembly of nanostructures has been remained challenging for chemists, there are still a few examples of using important enzymes to initiate the self-assembly of nanostructures for diagnosis or therapy of certain diseases because down-regulation or overexpression of certain enzymes always associates with abnormalities of tissues/organs or diseases in living body. Herein, we introduce the concept of enzymatic self-assembly and illustrate the design and application of enzyme-catalyzed or -regulated formation of nanostructures for theranostics.
doi:10.7150/thno.3696
PMCID: PMC3287425  PMID: 22375155
Enzyme; Self-assembly; Nanostructures; Diagnosis; Therapy; Theranostics.
6.  Synthesis of magnetic nanofibers using femtosecond laser material processing in air 
Nanoscale Research Letters  2011;6(1):375.
In this study, we report formation of weblike fibrous nanostructure and nanoparticles of magnetic neodymium-iron-boron (NdFeB) via femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Scanning electron microscopy (SEM) analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanofibers diameter varies between 30 and 70 nm and they are mixed with nanoparticles. The effect of pulse to pulse separation rate on the size of the magnetic fibrous structure and the magnetic strength was reported. X-ray diffraction (XRD) analysis revealed metallic and oxide phases in the nanostructure. The growth of magnetic nanostructure is highly recommended for the applications of magnetic devices like biosensors and the results suggest that the pulsed-laser method is a promising technique for growing nanocrystalline magnetic nanofibers and nanoparticles for biomedical applications.
doi:10.1186/1556-276X-6-375
PMCID: PMC3211468  PMID: 21711890
7.  Fabrication and spectroscopic investigation of branched silver nanowires and nanomeshworks 
Nanoscale Research Letters  2012;7(1):596.
Wide wavelength ranges of light localization and scattering characteristics can be attributed to shape-dependent longitude surface plasmon resonance in complicated nanostructures. We have studied this phenomenon by spectroscopic measurement and a three-dimensional numerical simulation, for the first time, on the high-density branched silver nanowires and nanomeshworks at room temperature. These nanostructures were fabricated with simple light-induced colloidal method. In the range from the visible to the near-infrared wavelengths, light has been found effectively trapped in those trapping sites which were randomly distributed at the corners, the branches, and the junctions of the nanostructures in those nanostructures in three dimensions. The broadened bandwidth electromagnetic field enhancement property makes these branched nanostructures useful in optical processing and photovoltaic applications.
doi:10.1186/1556-276X-7-596
PMCID: PMC3577568  PMID: 23101991
Silver Nanowires; Nanomeshworks; Branched nanostructures; Localized surface plasmon resonance; Hot spots; Bandwidth
8.  Hierarchically nanostructured hydroxyapatite: hydrothermal synthesis, morphology control, growth mechanism, and biological activity 
Hierarchically nanosized hydroxyapatite (HA) with flower-like structure assembled from nanosheets consisting of nanorod building blocks was successfully synthesized by using CaCl2, NaH2PO4, and potassium sodium tartrate via a hydrothermal method at 200°C for 24 hours. The effects of heating time and heating temperature on the products were investigated. As a chelating ligand and template molecule, the potassium sodium tartrate plays a key role in the formation of hierarchically nanostructured HA. On the basis of experimental results, a possible mechanism based on soft-template and self-assembly was proposed for the formation and growth of the hierarchically nanostructured HA. Cytotoxicity experiments indicated that the hierarchically nanostructured HA had good biocompatibility. It was shown by in-vitro experiments that mesenchymal stem cells could attach to the hierarchically nanostructured HA after being cultured for 48 hours.
Objective
The purpose of this study was to develop facile and effective methods for the synthesis of novel hydroxyapatite (HA) with hierarchical nanostructures assembled from independent and discrete nanobuilding blocks.
Methods
A simple hydrothermal approach was applied to synthesize HA by using CaCl2, NaH2PO4, and potassium sodium tartrate at 200°C for 24 hours. The cell cytotoxicity of the hierarchically nanostructured HA was tested by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.
Results
HA displayed the flower-like structure assembled from nanosheets consisting of nanorod building blocks. The potassium sodium tartrate was used as a chelating ligand, inducing the formation and self-assembly of HA nanorods. The heating time and heating temperature influenced the aggregation and morphology of HA. The cell viability did not decrease with the increasing concentration of hierarchically nanostructured HA added.
Conclusion
A novel, simple and reliable hydrothermal route had been developed for the synthesis of hierarchically nanosized HA with flower-like structure assembled from nanosheets consisting of nanorod building blocks. The HA with the hierarchical nanostructure was formed via a soft-template assisted self-assembly mechanism. The hierarchically nanostructured HA has a good biocompatibility and essentially no in-vitro cytotoxicity.
doi:10.2147/IJN.S29884
PMCID: PMC3356187  PMID: 22619527
hierarchical; biocompatibility; nanorods; nanosheets
9.  Seed/catalyst-free vertical growth of high-density electrodeposited zinc oxide nanostructures on a single-layer graphene 
We report the seed/catalyst-free vertical growth of high-density electrodeposited ZnO nanostructures on a single-layer graphene. The absence of hexamethylenetetramine (HMTA) and heat has resulted in the formation of nanoflake-like ZnO structure. The results show that HMTA and heat are needed to promote the formation of hexagonal ZnO nanostructures. The applied current density plays important role in inducing the growth of ZnO on graphene as well as in controlling the shape, size, and density of ZnO nanostructures. High density of vertically aligned ZnO nanorods comparable to other methods was obtained. The quality of the ZnO nanostructures also depended strongly on the applied current density. The growth mechanism was proposed. According to the growth timing chart, the growth seems to involve two stages which are the formation of ZnO nucleation and the enhancement of the vertical growth of nanorods. ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics such as photovoltaic devices, sensing devices, optical devices, and photodetectors.
doi:10.1186/1556-276X-9-95
PMCID: PMC3937434  PMID: 24568668
Electrochemical deposition; Graphene; Zinc oxide; One-dimensional nanostructure
10.  A 3D insight on the catalytic nanostructuration of few-layer graphene 
Nature Communications  2014;5:4109.
The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting.
The nanostructuration of graphene by catalytic cutting using iron oxide nanoparticles leads to the formation of well-defined trenches and tunnels. Here, the authors use electron microscopy to investigate this process in three dimensions and to gain insight into the formation and nature of these nanostructures.
doi:10.1038/ncomms5109
PMCID: PMC4082640  PMID: 24916201
11.  Gold Nanocages: From Synthesis to Theranostic Applications 
Accounts of chemical research  2011;44(10):914-924.
CONSPECTUS
Gold nanostructures have garnered considerable attention in recent years for their potential to enhance both the diagnosis and treatment of cancer through their advantageous chemical and physical properties. The key feature of Au nanostructures for enabling this diverse array of biomedical applications is their attractive optical properties, i.e. the scattering and absorption of light at resonant wavelengths due to the excitation of plasmon oscillations. This phenomenon is commonly known as localized surface plasmon resonance (LSPR) and is the source of the ruby red color of conventional Au colloids. The resonant wavelength is highly dependent on the size, shape, and geometry of the nanostructures, providing a set of knobs to maneuver the optical properties as needed. For in vivo applications, especially when optical excitation or transduction is involved, the LSPR peaks of the Au nanostructures have to be tuned to the transparent window of soft tissues in the near-infrared (NIR) region (from 700–900 nm) in order to maximize the penetration depth.
One class of nanostructures with tunable LSPR peaks in the NIR region is Au nanocages. These versatile nanostructures are characterized by hollow interiors, ultrathin and porous walls, and can be prepared in relatively large quantities using a remarkably simple procedure based on the galvanic replacement between Ag nanocubes and aqueous chloroauric acid. The LSPR peaks of Au nanocages can be readily and precisely tuned to any wavelength in the NIR region by controlling their size and/or wall thickness. Other significant features of Au nanocages that make them particularly intriguing materials for biomedical applications include their compact sizes, large absorption cross sections (almost five orders of magnitude greater than those of conventional organic dyes), bio-inertness, as well as a robust and straightforward procedure for surface modification based on the Au-thiolate chemistry. In this article, we present some of the most recent advances in the use of Au nanocages for a broad range of theranostic applications, including their use: i) as tracers for tracking by multi-photon luminescence; ii) as contrast agents for photoacoustic (PA) and mutimodal (PA/fluorescence) imaging; iii) as photothermal agents for the selective destruction of cancerous or diseased tissue; and iv) as drug delivery vehicles for controlled and localized release in response to external stimuli such as NIR radiation or high-intensity focused ultrasound (HIFU).
doi:10.1021/ar200061q
PMCID: PMC3168958  PMID: 21528889
12.  Nanostructured Biomaterials for Regeneration** 
Advanced functional materials  2008;18(22):3566-3582.
Biomaterials play a pivotal role in regenerative medicine, which aims to regenerate and replace lost/dysfunctional tissues or organs. Biomaterials (scaffolds) serve as temporary 3D substrates to guide neo tissue formation and organization. It is often beneficial for a scaffolding material to mimic the characteristics of extracellular matrix (ECM) at the nanometer scale and to induce certain natural developmental or/and wound healing processes for tissue regeneration applications. This article reviews the fabrication and modification technologies for nanofibrous, nanocomposite, and nanostructured drug-delivering scaffolds. ECM-mimicking nanostructured biomaterials have been shown to actively regulate cellular responses including attachment, proliferation, differentiation and matrix deposition. Nano-scaled drug delivery systems can be successfully incorporated into a porous 3D scaffold to enhance the tissue regeneration capacity. In conclusion, nano-structured biomateials are a very exciting and rapidly expanding research area, and are providing new enabling technologies for regenerative medicine.
doi:10.1002/adfm.200800662
PMCID: PMC2701700  PMID: 19946357
Biomaterials; Nanofiber; Drug Delivery; Tissue Engineering; Regenerative Medicine
13.  Cell-directed-assembly: Directing the formation of nano/bio interfaces and architectures with living cells 
Biochimica et biophysica acta  2010;1810(3):259-267.
Background
The desire to immobilize, encapsulate, or entrap viable cells for use in a variety of applications has been explored for decades. Traditionally, the approach is to immobilize cells to utilize a specific functionality of the cell in the system.
Scope of Review
This review describes our recent discovery that living cells can organize extended nanostructures and nano-objects to create a highly biocompatible nano//bio interface [1].
Major Conclusions
We find that short chain phospholipids direct the formation of thin film silica mesophases during evaporation-induced self-assembly (EISA) [2], and that the introduction of cells alter the self-assembly pathway. Cells organize an ordered lipid-membrane that forms a coherent interface with the silica mesophase that is unique in that it withstands drying - yet it maintains accessibility to molecules introduced into the 3D silica host. Cell viability is preserved in the absence of buffer, making these constructs useful as standalone cell-based sensors. In response to hyperosmotic stress, the cells release water, creating a pH gradient which is maintained within the nanostructured host and serves to localize lipids, proteins, plasmids, lipidized nanocrystals, and other components at the cellular surface. This active organization of the bio/nano interface can be accomplished during ink-jet printing or selective wetting - processes allowing patterning of cellular arrays - and even spatially-defined genetic modification.
General Significance
Recent advances in the understanding of nanotechnology and cell biology encourage the pursuit of more complex endeavors where the dynamic interactions of the cell and host material act symbiotically to obtain new, useful functions.
doi:10.1016/j.bbagen.2010.09.005
PMCID: PMC3090153  PMID: 20933574
14.  The Interaction of Bacteria with Engineered Nanostructured Polymeric Materials: A Review 
The Scientific World Journal  2014;2014:410423.
Bacterial infections are a leading cause of morbidity and mortality worldwide. In spite of great advances in biomaterials research and development, a significant proportion of medical devices undergo bacterial colonization and become the target of an implant-related infection. We present a review of the two major classes of antibacterial nanostructured materials: polymeric nanocomposites and surface-engineered materials. The paper describes antibacterial effects due to the induced material properties, along with the principles of bacterial adhesion and the biofilm formation process. Methods for antimicrobial modifications of polymers using a nanocomposite approach as well as surface modification procedures are surveyed and discussed, followed by a concise examination of techniques used in estimating bacteria/material interactions. Finally, we present an outline of future sceneries and perspectives on antibacterial applications of nanostructured materials to resist or counteract implant infections.
doi:10.1155/2014/410423
PMCID: PMC4084677  PMID: 25025086
15.  Investigating bioconjugation by atomic force microscopy 
Nanotechnological applications increasingly exploit the selectivity and processivity of biological molecules. Integration of biomolecules such as proteins or DNA into nano-systems typically requires their conjugation to surfaces, for example of carbon-nanotubes or fluorescent quantum dots. The bioconjugated nanostructures exploit the unique strengths of both their biological and nanoparticle components and are used in diverse, future oriented research areas ranging from nanoelectronics to biosensing and nanomedicine. Atomic force microscopy imaging provides valuable, direct insight for the evaluation of different conjugation approaches at the level of the individual molecules. Recent technical advances have enabled high speed imaging by AFM supporting time resolutions sufficient to follow conformational changes of intricately assembled nanostructures in solution. In addition, integration of AFM with different spectroscopic and imaging approaches provides an enhanced level of information on the investigated sample. Furthermore, the AFM itself can serve as an active tool for the assembly of nanostructures based on bioconjugation. AFM is hence a major workhorse in nanotechnology; it is a powerful tool for the structural investigation of bioconjugation and bioconjugation-induced effects as well as the simultaneous active assembly and analysis of bioconjugation-based nanostructures.
doi:10.1186/1477-3155-11-25
PMCID: PMC3723498  PMID: 23855448
Atomic force microscopy (AFM); Nanotechnology; Bioconjugation; Nanoelectronics; Nanolithography; Nanomedicine; Biosensors; Nanorobot; DNA origami; Single molecule
16.  Broadband antireflective silicon nanostructures produced by spin-coated Ag nanoparticles 
We report the fabrication of broadband antireflective silicon (Si) nanostructures fabricated using spin-coated silver (Ag) nanoparticles as an etch mask followed by inductively coupled plasma (ICP) etching process. This fabrication technique is a simple, fast, cost-effective, and high-throughput method, making it highly suitable for mass production. Prior to the fabrication of Si nanostructures, theoretical investigations were carried out using a rigorous coupled-wave analysis method in order to determine the effects of variations in the geometrical features of Si nanostructures to obtain antireflection over a broad wavelength range. The Ag ink ratio and ICP etching conditions, which can affect the distribution, distance between the adjacent nanostructures, and height of the resulting Si nanostructures, were carefully adjusted to determine the optimal experimental conditions for obtaining desirable Si nanostructures for practical applications. The Si nanostructures fabricated using the optimal experimental conditions showed a very low average reflectance of 8.3%, which is much lower than that of bulk Si (36.8%), as well as a very low reflectance for a wide range of incident angles and different polarizations over a broad wavelength range of 300 to 1,100 nm. These results indicate that the fabrication technique is highly beneficial to produce antireflective structures for Si-based device applications requiring low light reflection.
doi:10.1186/1556-276X-9-54
PMCID: PMC3917369  PMID: 24484636
Silicon nanostructures; Spin-coated Ag nanoparticles; Antireflection; Rigorous coupled-wave analysis
17.  Melanin-templated rapid synthesis of silver nanostructures 
Background
As a potent antimicrobial agent, silver nanostructures have been used in nanosensors and nanomaterial-based assays for the detection of food relevant analytes such as organic molecules, aroma, chemical contaminants, gases and food borne pathogens. In addition silver based nanocomposites act as an antimicrobial for food packaging materials. In this prospective, the food grade melanin pigment extracted from sponge associated actinobacterium Nocardiopsis alba MSA10 and melanin mediated synthesis of silver nanostructures were studied. Based on the present findings, antimicrobial nanostructures can be developed against food pathogens for food industrial applications.
Results
Briefly, the sponge associated actinobacterium N. alba MSA10 was screened and fermentation conditions were optimized for the production of melanin pigment. The Plackett-Burman design followed by a Box-Behnken design was developed to optimize the concentration of most significant factors for improved melanin yield. The antioxidant potential, reductive capabilities and physiochemical properties of Nocardiopsis melanin was characterized. The optimum production of melanin was attained with pH 7.5, temperature 35°C, salinity 2.5%, sucrose 25 g/L and tyrosine 12.5 g/L under submerged fermentation conditions. A highest melanin production of 3.4 mg/ml was reached with the optimization using Box-Behnken design. The purified melanin showed rapid reduction and stabilization of silver nanostructures. The melanin mediated process produced uniform and stable silver nanostructures with broad spectrum antimicrobial activity against food pathogens.
Conclusions
The melanin pigment produced by N. alba MSA10 can be used for environmentally benign synthesis of silver nanostructures and can be useful for food packaging materials. The characteristics of broad spectrum of activity against food pathogens of silver nanostructures gives an insight for their potential applicability in incorporation of food packaging materials and antimicrobials for stored fruits and foods.
doi:10.1186/1477-3155-12-18
PMCID: PMC4038705  PMID: 24885756
Marine Nocardiopsis; Melanin; Optimization; Silver nanostructures; Antimicrobial activity
18.  A Comprehensive Review of One-Dimensional Metal-Oxide Nanostructure Photodetectors 
Sensors (Basel, Switzerland)  2009;9(8):6504-6529.
One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years. Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates. Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities. This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field. It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO2, Cu2O, Ga2O3, Fe2O3, In2O3, CdO, CeO2, and their photoresponses. The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials. Finally, the review is concluded with some perspectives and outlook on the future developments in this area.
doi:10.3390/s90806504
PMCID: PMC3312456  PMID: 22454597
metal oxide semiconductor; one-dimensional nanostructures; sensor; photodetector; transistor
19.  Mesoporous Single-crystal CoSn(OH)6 Hollow Structures with Multilevel Interiors 
Scientific Reports  2013;3:1391.
Hollow nanostructures represent a unique class of functional nanomaterials with many applications. In this work, a one-pot and unusual “pumpkin-carving” protocol is demonstrated for engineering mesoporous single-crystal hollow structures with multilevel interiors. Single-crystal CoSn(OH)6 nanoboxes with uniform size and porous shell are synthesized by fast growth of CoSn(OH)6 nanocubes and kinetically-controlled etching in alkaline medium. Detailed investigation on reaction course suggests that the formation of a passivation layer of Co(III) species around the liquid-solid interface is critical for the unusual hollowing process. With reasonable understanding on the mechanism involved, this approach shows high versatility for the synthesis of CoSn(OH)6 hollow architectures with a higher order of interior complexity, such as yolk-shell particles and multishelled nanoboxes. The obtained CoSn(OH)6 hollow nanostructures can be easily converted to hollow nanostructures of tin-based ternary metal oxides with excellent photocatalytic and electrochemical properties.
doi:10.1038/srep01391
PMCID: PMC3589726  PMID: 23462692
20.  Self-Assembly of Cytotoxic Peptide Amphiphiles into Supramolecular Membranes for Cancer Therapy 
Advanced healthcare materials  2012;2(1):126-133.
Peptide amphiphiles (PAs) provide a versatile platform for the design of complex and functional material constructs for biomedical applications. The hierarchical self-assembly of PAs with biopolymers is used to create robust hybrid membranes with molecular order on the micron scale. Fabrication of membranes by assembling hyaluronic acid with positively charged PA nanostructures containing anti-cancer PAs bearing a (KLAKLAK)2 peptide sequence is reported here. Changes in nanoscale membrane morphology as the positively charged PA nanostructures vary from cylindrical nanofibers to spherical aggregates are characterized. Results indicate that formation of highly aligned fibrous membranes requires a threshold concentration of nanofibers in solution. Additionally, variation of PA nanostructure morphology from spherical aggregates to cylindrical nanofibers allows membranes to act either as reservoirs for sustained release of cytotoxicity upon enzymatic degradation or as membranes with surface-bound cytotoxicity, respectively. Thus, the self-assembly processes of these PA-biopolymer membranes can be potentially used to design delivery platforms for anti-cancer therapeutics.
doi:10.1002/adhm.201200118
PMCID: PMC3680364  PMID: 23184589
breast cancer; drug delivery; membranes; peptide amphiphiles; self-assembly
21.  Friction-induced nanofabrication method to produce protrusive nanostructures on quartz 
Nanoscale Research Letters  2011;6(1):310.
In this paper, a new friction-induced nanofabrication method is presented to fabricate protrusive nanostructures on quartz surfaces through scratching a diamond tip under given normal loads. The nanostructures, such as nanodots, nanolines, surface mesas and nanowords, can be produced on the target surface by programming the tip traces according to the demanded patterns. The height of these nanostructures increases with the increase of the number of scratching cycles or the normal load. Transmission electron microscope observations indicated that the lattice distortion and dislocations induced by the mechanical interaction may have played a dominating role in the formation of the protrusive nanostructures on quartz surfaces. Further analysis reveals that during scratching, a contact pressure ranged from 0.4Py to Py (Py is the critical yield pressure of quartz) is apt to produce protuberant nanostructures on quartz under the given experimental conditions. Finally, it is of great interest to find that the protrusive nanostructures can be selectively dissolved in 20% KOH solution. Since the nanowords can be easily 'written' by friction-induced fabrication and 'erased' through selective etching on a quartz surface, this friction-induced method opens up new opportunities for future nanofabrication.
doi:10.1186/1556-276X-6-310
PMCID: PMC3211397  PMID: 21711819
22.  Incorporation of DOPE into Lipoplexes formed from a Ferrocenyl Lipid leads to Inverse Hexagonal Nanostructures that allow Redox-Based Control of Transfection in High Serum 
Soft matter  2012;8(24):2608-2619.
We report small angle X-ray and neutron scattering measurements that reveal that mixtures of the redox-active lipid bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA) and dioleoylphosphatidylethanolamine (DOPE) spontaneously form lipoplexes with DNA that exhibit inverse hexagonal nanostructure (HIIc). In contrast to lipoplexes of DNA and BFDMA only, which exhibit a multilamellar nanostructure (Lαc) and limited ability to transfect cells in the presence of serum proteins, we measured lipoplexes of BFDMA and DOPE with the HIIc nanostructure to survive incubation in serum and to expand significantly the range of media compositions (e.g., up to 80% serum) over which BFDMA can be used to transfect cells with high efficiency. Importantly, we also measured the oxidation state of the ferrocene within the BFDMA/DNA lipoplexes to have a substantial influence on the transfection efficiency of the lipoplexes in media containing serum. Specifically, whereas lipoplexes of reduced BFDMA and DOPE transfect cells with high efficiency, lipoplexes of oxidized BFDMA and DNA lead to low levels of transfection. Complementary measurements using SAXS reveal that the low transfection efficiency of the lipoplexes of oxidized BFDMA and DOPE correlates with the presence of weak Bragg peaks and thus low levels of HIIc nanostructure in solution. Overall, these results provide support for our hypothesis that DOPE-induced formation of the HIIc nanostructure of the BFDMA-containing lipoplexes underlies the high cell transfection efficiency measured in the presence of serum, and that the oxidation state of BFDMA within lipoplexes with DOPE substantially regulates the formation of the HIIc nanostructure and thus the ability of the lipoplexes to transfect cells with DNA. More generally, the results presented in this paper suggest that lipoplexes formed from BFDMA and DOPE may offer the basis of approaches that permit active and external control of transfection of cells in the presence of high (physiologically relevant) levels of serum.
doi:10.1039/C2SM00047D
PMCID: PMC3374640  PMID: 22707977
23.  Morphology control and optical properties of SiGe nanostructures grown on glass substrate 
Nanoscale Research Letters  2012;7(1):155.
With the rapid progress of nanotechnology, nanostructures with different morphologies have been realized, which may be very promising to enhance the performance of semiconductor devices. In this study, SiGe nanostructures with several kinds of configurations have been synthesized through a chemical vapor deposition process. By controlling growth conditions, different SiGe nanostructures can be easily tuned. Structures and compositions of the nanostructures were determined by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The optical properties of various SiGe nanostructures revealed some dependence with their morphologies, which may be suitable for solar cell applications. The control of the SiGe morphology on nanoscale provides a convenient route to produce diverse SiGe nanostructures and creates new opportunities to realize the integration of future devices.
doi:10.1186/1556-276X-7-155
PMCID: PMC3298705  PMID: 22369313
SiGe; reflectance; nanowire; core-shell; transformation
24.  Quantitative prediction of 3D solution shape and flexibility of nucleic acid nanostructures 
Nucleic Acids Research  2011;40(7):2862-2868.
DNA nanotechnology enables the programmed synthesis of intricate nanometer-scale structures for diverse applications in materials and biological science. Precise control over the 3D solution shape and mechanical flexibility of target designs is important to achieve desired functionality. Because experimental validation of designed nanostructures is time-consuming and cost-intensive, predictive physical models of nanostructure shape and flexibility have the capacity to enhance dramatically the design process. Here, we significantly extend and experimentally validate a computational modeling framework for DNA origami previously presented as CanDo [Castro,C.E., Kilchherr,F., Kim,D.-N., Shiao,E.L., Wauer,T., Wortmann,P., Bathe,M., Dietz,H. (2011) A primer to scaffolded DNA origami. Nat. Meth., 8, 221–229.]. 3D solution shape and flexibility are predicted from basepair connectivity maps now accounting for nicks in the DNA double helix, entropic elasticity of single-stranded DNA, and distant crossovers required to model wireframe structures, in addition to previous modeling (Castro,C.E., et al.) that accounted only for the canonical twist, bend and stretch stiffness of double-helical DNA domains. Systematic experimental validation of nanostructure flexibility mediated by internal crossover density probed using a 32-helix DNA bundle demonstrates for the first time that our model not only predicts the 3D solution shape of complex DNA nanostructures but also their mechanical flexibility. Thus, our model represents an important advance in the quantitative understanding of DNA-based nanostructure shape and flexibility, and we anticipate that this model will increase significantly the number and variety of synthetic nanostructures designed using nucleic acids.
doi:10.1093/nar/gkr1173
PMCID: PMC3326316  PMID: 22156372
25.  Controlled synthesis and characterization of hollow flower-like silver nanostructures 
Background
The synthesis of anisotropic silver nanoparticles is a time-consuming process and involves the use of expensive toxic chemicals and specialized laboratory equipment. The presence of toxic chemicals in the prepared anisotropic silver nanostructures hindered their medical application. The authors have developed a fast and inexpensive method for the synthesis of three-dimensional hollow flower-like silver nanostructures without the use of toxic chemicals.
Methods
In this method, silver nitrate was reduced using dextrose in presence of trisodium citrate as a capping agent. Sodium hydroxide was added to enhance reduction efficacy of dextrose and reduce time of synthesis. The effects of all four agents on the shape and size of silver nanostructures were investigated.
Results
Robust hollow flower-like silver nanostructures were successfully synthesized and ranged in size from 0.2 μm to 5.0 μm with surface area between 25–240 m2/g. Changing the concentration of silver nitrate, dextrose, sodium hydroxide, and trisodium citrate affected the size and shape of the synthesized structures, while changing temperature had no effect.
Conclusion
The proposed method is simple, safe, and allows controlled synthesis of anisotropic silver nanostructures, which may represent promising tools as effective antimicrobial agents and for in vitro diagnostics. The synthesized hollow nanostructures may be used for enhanced drug encapsulation and sustained release.
doi:10.2147/IJN.S26524
PMCID: PMC3356183  PMID: 22619511
silver nanoparticles; 3D hollow; flower-like; green synthesis

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