Multilayer Nanofilms Research Articles

Robust High-κ Response in Molecularly Thin Perovskite Nanosheets

Size-induced suppression of permittivity in perovskite thin films is a fundamental problem that has remained unresolved for decades. This size-effect issue becomes increasingly important due to the integration of perovskite nanofilms into high-κ capacitors, as well as concerns that intrinsic size effects may limit their device performance. Here, we report a new approach to produce robust high-κ nanodielectrics using perovskite nanosheet (Ca2Nb3O10), a new class of nanomaterials that is derived from layered compounds by exfoliation. By a solution-based bottom-up approach using perovskite nanosheets, we have successfully fabricated multilayer nanofilms directly on SrRuO3 or Pt substrates without any interfacial dead layers. These nanofilms exhibit high dielectric constant (>200), the largest value seen so far in perovskite films with a thickness down to 10 nm. Furthermore, the superior high-κ properties are a size-effect-free characteristic with low leakage current density (<10(-7) A cm(-2)). Our work provides a key for understanding the size effect and also represents a step toward a bottom-up paradigm for future high-κ devices.

Combustion of heterogeneous nanostructural systems (Review)

The current status of research in the field of combustion of heterogeneous nanostructural systems is reviewed. Four classes of reactive media are considered: nanothermites, sol-gels, mechanically activated nanocomposites, and multilayer nanofilms. Based on the summary of publications, possible mechanisms of combustion in such systems and prospects of their further applications are discussed.

Cefazolin embedded biodegradable polypeptide nanofilms promising for infection prevention: a preliminary study on cell responses.

Implant-associated infection is a serious complication in orthopedic surgery, and endowing implant surfaces with antibacterial properties could be one of the most promising approaches for preventing such infection. In this study, we developed cefazolin loaded biodegradable polypeptide multilayer nanofilms on orthopedic implants. We found that the amount of cefazolin released could be tuned. A high local concentration of cefazolin was achieved within the first a few hours and therefore may inhibit bacterial colonization in the critical postimplantation period. The developed cefazolin loaded nanofilms showed their in vitro efficacy against Staphylococcus aureus; the more antibiotics loaded, the longer the nanocoated implant had antibacterial properties. More interestingly, antibiotic-loaded polypeptide multilayer nanofilms also improved osteoblast bioactivity including cell viability and proliferation. These findings suggested that biodegradable polypeptide multilayer nanofilms as antibiotic carriers at the implant/tissue interface are compatible with human cells such as osteoblasts and bactericidal to bacteria such as S. aureus. These characteristics could be promising for preventing implant-associated infection and potentially improving bone healing.

Solution-Based Fabrication of High-k Dielectrics Using Oxide Nanosheets

We report a novel procedure for fabricating high-k dielectric nanofilms by using titania nanosheet as a building block. Langmuir-Blodgett deposition using atomically flat SrRuO3 or Pt substrates is advantageous as a means of fabricating atomically uniform multilayer high-k nanofilms. High-resolution transmission electron microscopy revealed that these multilayer nanofilms are composed of a well-ordered lamellar structure without an interfacial dead layer. These nanofilms exhibited both high dielectric constant (~125) and low leakage current density (J < 10-7 A/cm2) even for thicknesses as low as 10 nm. These results indicate that titania nanosheet is a very promising candidate as a high-k nanoblock, and its bottom-up fabrication provides new opportunities for the development of high-k devices.

Advances in polyelectrolyte multilayer nanofilms as tunable drug delivery systems

There has been considerable interest in polyelectrolyte multilayer nanofilms, which have a variety of applications ranging from optical and electrochemical materials to biomedical devices. Polyelectrolyte multilayer nanofilms are constructed from aqueous solutions using electrostatic layer-by-layer self-assembly of oppositely-charged polyelectrolytes on a solid substrate. Multifunctional polyelectrolyte multilayer nanofilms have been studied using charged dyes, metal and inorganic nanoparticles, DNA, proteins, and viruses. In the past few years, there has been increasing attention to developing polyelectrolyte multilayer nanofilms as drug delivery vehicles. In this mini-review, we present recent developments in polyelectrolyte multilayer nanofilms with tunable drug delivery properties, with particular emphasis on the strategies in tuning the loading and release of drugs in polyelectrolyte multilayer nanofilms as well as their applications.

Present and Future Prospects for Polypeptide Multilayer Nanofilms in Biotechnology and Medicine

Polypeptide multilayer nanofilms are a promising nanotechnology for commercial product development because the processes used to prepare them are simple, flexible, reliable, automatable, and scalable. Moreover, these materials can display a remarkable diversity of physical, chemical, and biological properties. Furthermore, the constituents of these nanofilms, in most cases the nanofilms themselves, and the fabrication process are environmentally benign. Nanofilm structure and function can be tailored to address two Grand Challenges of the US National Nanotechnology Initiative.

Analysis of 2-Benzo[c]cinnoline Nanofilm at the Gold Surface

A polycrystalline gold surface was modified with 2-benzo[c]cinnoline (BCC) in nonaqueous media using cyclic voltammetry. A multilayer BCC nanofilm at the gold surface was formed by the electrochemical reduction of 2-benzo[c]cinnoline diazonium salt (BCC-DAS). Grafting of BCC molecules onto the gold surface was verified by cyclic voltammetry using various redox probes, electrochemical impedance spectroscopy, and Raman spectroscopy. The BCC film thickness was measured by ellipsometry and calculated as 46 nm indicating a multilayer film formation. The stability and the potential range of the novel Au-BCC modified electrode were also studied in open atmosphere and pure water. The working potential range of Au-BCC electrode was found to be between −1.8 and +1.6 V.

Tunable drug loading and release from polypeptide multilayer nanofilms.

Polypeptide multilayer nanofilms were prepared using electrostatic layer-by-layer self-assembly nanotechnology. Small charged drug molecules (eg, cefazolin, gentamicin, and methylene blue) were loaded in polypeptide multilayer nanofilms. Their loading and release were found to be pH-dependent and could also be controlled by changing the number of film layers and drug incubation time, and applying heat-treatment after film formation. Antibioticloaded polypeptide multilayer nanofilms showed controllable antibacterial properties against Staphylococcus aureus. The developed biodegradable polypeptide multilayer nanofilms are capable of loading both positively- and negatively-charged drug molecules and promise to serve as drug delivery systems on biomedical devices for preventing biomedical device-associated infection, which is a significant clinical complication for both civilian and military patients.

Multilayer nanofilms as substrates for hepatocellular applications

Multilayer nanofilms, formed by the layer-by-layer (LbL) adsorption of positively and negatively charged polyelectrolytes, are promising substrates for tissue engineering. We investigate here the attachment and function of hepatic cells on multilayer films in terms of film composition, terminal layer, rigidity, charge, and presence of biofunctional species. Human hepatocellular carcinoma (HepG2) cells, adult rat hepatocytes (ARH), and human fetal hepatoblasts (HFHb) are studied on films composed of the polysaccharides chitosan (CHI) and alginate (ALG), the polypeptides poly( l-lysine) (PLL) and poly( l-glutamic acid) (PGA), and the synthetic polymers poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS). The influence of chemical cross-linking following LbL assembly is also investigated. We find HepG2 to reach confluence after 7 days of culture on only 2 of 18 candidate multilayer systems: (PAH–PSS) n (i.e. nPAH–PSS bilayers) and cross-linked (PLL–ALG) n –PLL. Cross-linked PLL–ALG and PLL–PGA films support attachment and function of ARH, independently of the terminal layer, provided collagen is adsorbed to the top of the film. (PAH–PSS) n , cross-linked (PLL–ALG) n , and cross-linked (PLL–PGA) n –PLL films all support attachment, layer confluence, and function of HFHb, with the latter film promoting the greatest level of function at 8 days. Overall, film composition, terminal layer, and rigidity are key variables in promoting attachment and function of hepatic cells, while film charge and biofunctionality are somewhat less important. These studies reveal optimal candidate multilayer biomaterials for human liver tissue engineering applications.

Protein-Mediated Assembly of Nanodiamond Hydrogels into a Biocompatible and Biofunctional Multilayer Nanofilm

Aqueous dispersible detonation nanodiamonds (NDs) with a diameter of 2-8 nm were assembled into a closely packed ND multilayer nanofilm with positively charged poly-L-lysine via the layer-by-layer deposition technique. The innate biocompatibility of the NDs in both free-floating and thin-film forms was confirmed via cellular gene expression examination by real-time polymerase chain reaction as well as MTT and DNA fragmentation assays. The highly biologically amenable ND nanofilm was successfully integrated with therapeutic molecules, and the functionality of the composite drug-ND material was assessed via interrogation of the suppression of inflammatory cytokine release. Knockdown of lipopolysaccharide-mediated inflammation was observed through the potent attenuation of tumor necrosis factor-alpha, interleukin-6, and inducible nitric oxide synthase levels following ND nanofilm interfacing with RAW 264.7 murine macrophages. Furthermore, basal cytokine secretion levels were assessed to examine innate material biocompability, revealing unchanged cellular inflammatory responses which strongly supported the relevance of the NDs as effective treatment platforms for nanoscale medicine. In addition to the easy preparation, robustness, and fine controllability of the film structures, these hybrid materials possess enormous potential for biomedical applications such as localized drug delivery and anti-inflammatory implant coatings and devices, as demonstrated in vitro in this work.

Reversibility of Structural Changes of Polypeptides in Multilayer Nanofilms

Structural properties of different polypeptide multilayer nanofilms fabricated at neutral pH have been analyzed by UV spectroscopy, circular dichroism spectroscopy (CD), and Fourier-transform infrared spectroscopy (FTIR). The various peptides studied exhibit a strong tendency to adopt a beta sheet conformation in the films. Changes in film structure on dehydration are completely reversed on rewetting. The time scale of reversibility is, however, substantially shorter for the polymer backbone than the side chains, as in protein folding.

Context Dependence of the Assembly, Structure, and Stability of Polypeptide Multilayer Nanofilms

Polyelectrolyte multilayer nanofilms and nanocomposites have shown considerable promise for the rational development of multifunctional materials with wide-ranging properties. Polypeptides are a distinctive and largely unexplored class of polyelectrolytes in this context. Methods now exist for the synthesis of peptides with control at the level of the amino acid sequence, and for the preparation of these polymers in massive quantities. Here, we analyze the roles of six designed 32mer peptides in the fabrication, structure, and stability of multilayer nanofilms prepared by layer-by-layer self-assembly. The data show that amino acid sequence and the specific combination of anionic and cationic peptides together have a marked impact on nanofilm growth behavior, secondary structure content, and density in experimental studies. The same factors determine physical properties of the corresponding interpolypeptide complexes in molecular dynamics simulations.

Corrosion properties of 316L stainless steel coated with polyelectrolyte multilayers of varying anionic acidity

Polyelectrolytes have been proposed as promising systems for the potection of stainless steels and for biomedical and drug release applications. Multilayer nanofilms with varying anion acidity were deposited on AISI316L stainless steel. The cationic polyelectrolyte was polyallylamine hydrochloride (PAH) whereas the anionic polyelectrolytes with increasing acidity were polyacrylic acid (PAA), polystyrene sulphonate-co-maleic acid and polystyrene sulphonate (PSS). Potentiodynamic polarisation showed an increase in corrosion potential Ecorr upon coating with multilayer nanofilms and a corresponding decrease in corrosion current. Transient currents were observed upon application of PSS due to its high acidic strength although it showed better pit recovery characteristics as shown in cyclic polarisation experiments. Constant potential experiments at 700 mV v. Ag/AgCl for 12 h showed a suppressed current by 50% for the PAH/PSS coated steel compared to the uncoated specimen. The SEM images showed the existence of agglomerates, uncovered areas and corrosion products underneath channels on the coating.

Applications of polypeptide multilayer nanofilms in vitro and in vivo

Applications of polypeptide multilayer nanofilms in vitro and in vivo

Solution-Based Fabrication of High-κ Dielectric Nanofilms Using Titania Nanosheets as a Building Block

We have demonstrated a novel procedure for fabricating high-κ dielectric nanofilms by using a titania nanosheet as a building block. The layer-by-layer assembly of titania nanosheets using an atomically flat SrRuO3 substrate is advantageous as a means of fabricating atomically uniform multilayer high-κ nanofilms. High-resolution transmission electron microscopy revealed that these multilayer nanofilms are composed of a well-ordered lamellar structure without an interfacial dead layer. These nanofilms exhibited both high dielectric constant (εr∼125) and low leakage current density (J<10-7 A/cm2) even for thicknesses as low as 10 nm. These results indicate that the titania nanosheet is a very promising candidate as a high-κ nanoblock, and its bottom-up fabrication provides new opportunities for the development of high-κ devices.

Controlled loading and release of a model drug from polypeptide multilayer nanofilms

A major concern of medicine today is the sustained release of therapeutic compounds. Delivery vehicles for such compounds must be biocompatible. Ideally, loading a drug into the delivery vehicle will be a simple process, and vehicle properties will allow control over the drug release profile under desired conditions. Here, polypeptide multilayer nanofilms have been prepared by electrostatic layer-by-layer self-assembly to study the post-fabrication loading and release of a model therapeutic, methylene blue (MB). Drug loading and release have been characterized by optical spectroscopy for different peptide designs at different pH values, and film surface morphology has been characterized by atomic force microscopy (AFM). Differences in peptide structure have been found to influence MB loading and release under otherwise fixed conditions. Release is also influenced by pH, salt concentration, and number of “capping” layers. Although more research will be needed to exhaust the potential of polypeptide multilayer films, present results would suggest that the technology holds considerable promise for applications in medicine.

Internal Structure of Wet and Dry Polypeptide Multilayer Nanofilms

Internal Structure of Wet and Dry Polypeptide Multilayer Nanofilms

Dynamics of phase formation in multilayer Ti-Al nanofilms upon heating

Structural transformations in multilayer Ti-Al films (layer thickness from 4 to 500 nm, number of layers up to 4440, total foil thickness ∼18 µm) upon slow heating have been studied by time-resolved synchrotron radiation diffraction. Some specific features of heterogeneous reactions and the sequence of phase formation in multilayer samples during the interaction of interaction between layer components have been determined as functions of the single layer thickness.

Microscale enzymatic optical biosensors using mass transport limiting nanofilms. 1. Fabrication and characterization using glucose as a model analyte.

"Smart tattoo" sensors-fluorescent microspheres that can be implanted intradermally and interrogated noninvasively using light-are being developed as potential tools for in vivo biochemical monitoring. In this work, a platform for enzymatic tattoo-type sensors is described and prototype devices evaluated using glucose as a model analyte. Sensor particles were prepared by immobilizing Pt(II) octaethylporphine (PtOEP), a phosphorescent dye readily quenched by molecular oxygen, into hybrid silicate microspheres, followed by loading and subsequent covalent immobilization of glucose oxidase. Rhodamine B-doped multilayer nanofilms were subsequently assembled on the surfaces of the particles to provide a reference signal and provide critical control of glucose transport into the particle. The enzymatic oxidation of glucose within the sensor results in the glucose concentration-dependent depletion of local oxygen levels, enabling indirect monitoring of glucose by measuring relative changes in PtOEP emission. A custom testing apparatus was used to monitor the dynamic sensor response to varying bulk oxygen and glucose levels, respectively. For the prototypes tested, dynamic test results indicate that the sensors respond rapidly (t(95) = 84 s) and reversibly to changes in bulk glucose levels, while demonstrating high baseline stability. The sensitivity (change in intensity ratio) of these devices was determined to be 4.16 +/- 0.57%/mg dL(-1). The analytical range for the prototypes was determined to be 2-120 mg/dl, though this can be extended to cover the physiologically relevant range by tailoring the nanofilm coatings. These findings confirm the potential for enzymatic microscale optical and pave the way for extension of this initial demonstration with glucose to target other biochemical species relevant to metabolic monitoring.

Photon pressure and its effect on the magnetic properties of multilayer films

The effect of nanosecond laser pulses on the optical and magnetic properties of Bi-SiC-TbFe-SiC, SiC-TbFe-SiC, SiC-Tb-Au-Fe-SiC, and phthalocyanine dye-bismuth-phthalocyanine dye multilayer nanofilms is experimentally studied. The photon pressure of a laser beam is shown to cause electrons to drift in the direction of beam propagation. As a result of the injection of spin-polarized electrons from the magnetic layer, a nonequilibrium magnetization arises in the nonmagnetic Bi or Au layer, which changes the magnetooptic properties of the films. In three-layer dye-bismuth-dye films, the photon pressure of the laser radiation induces a space electron charge in the exit dye layer, which causes a drift of ionized bismuth atoms.