Fast Spray Deposition of Super Gas Barrier Polyelectrolyte Multilayer Thin Films

Fluorescence Signal Enhancement by a Spray-Assisted Layer-by-Layer Technique on Aluminum Tape Devices for Biosensing Applications

Layer-by-layer (LbL) self-assembled polyelectrolyte multilayer (PEM) films are a simple yet elegant bottom-up technology to create films at the nano-microscale. This low-cost technology has been widely used as a universal functionalization technique on a broad spectrum of substrates. Biomolecules under investigation can be incubated onto films based on complementary charge interactions between the films and biomolecules. There is a great demand for developing an ultralow-cost biosensing device, which can optimally enhance the fluorescence signal of the adsorbed biomolecules from the traditional labeled sensing platforms. In this work, we have incorporated a blend of the conventional metal enhanced fluorescence technology and the PEM as a dielectric spacer and functionalized film, coated on an aluminum paper (tape)-based substrate. These device has been found to be capable of holding biomolecules in three-dimensional PEM space. The devices fabricated by the proposed spray LbL technique provide significant fluorescence signal enhancement by holding a relatively higher mass per volume of the adsorbed biomolecules, when compared to traditional spin- and dip-coating techniques. Interestingly, our proposed device has expressed a fluorescence enhancement factor, which is 9 times higher than PEM-functionalized glass-based devices. To demonstrate the practical utility of our devices, we also compared our devices to Whatman FAST slides. Our experimental fluorescence results are almost comparable to Whatman FAST slides. Such PEM devices fabricated on top of low-cost aluminum tape using a spray LbL technique give new insights into the future development of ultralow-cost, high-throughput, and disposable lab-on-chip diagnostic applications.

UV-protection from chitosan derivatized lignin multilayer thin film

Lignin is one of the most abundant renewable materials on the earth. Despite possessing useful antioxidant and UV absorbing properties, its effective utilization in technology has been hampered by its relative insolubility and difficulty to process. In this work, a simple chemical derivatization process is utilized which yields water-soluble lignin possessing anionic carboxylate groups. These carboxylate groups give lignin polyanionic behavior and enable its utilization in the growth of a functional film via layer-by-layer (LbL) assembly with biologically sourced chitosan. The growth mechanism of this film is hypothesized to be a result of both hydrogen bonding and ionic interactions. The film demonstrates excellent UV-absorptive capability. A 100 nm thick chitosan/lignin coating was applied to a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and shown to reduce its degradation sixfold over the course of a 1 hour exposure to harsh UV light. This is the first demonstration of lignin being utilized in a fully biologically derived LbL film. Utilization of lignin in LbL assembly is an important step in the development of renewable nanotechnology.

An environmentally benign derivatization process enables the use of lignin in an entirely biosourced functional thin film.

Weak polyelectrolyte-based multilayers via layer-by-layer assembly: Approaches, properties, and applications

Layer-by-layer (LbL) assembly is a nanoscale technique with great versatility, simplicity and molecular-level processing of various nanoscopic materials. Weak polyelectrolytes have been used as major building blocks for LbL assembly providing a fundamental and versatile tool to study the underlying mechanisms and practical applications of LbL assembly due to its pH-responsive charge density and molecular conformation. Because of high-density uncompensated charges and high-chain mobility, weak polyelectrolyte exponential multilayer growth is considered one of the fastest developing areas for organized molecular films. In this article, we systematically review the current status and developments of weak polyelectrolyte-based multilayers including all-weak-polyelectrolyte multilayers, weak polyelectrolytes/other components (e.g. strong polyelectrolytes, neutral polymers, and nanoparticles) multilayers, and exponentially grown weak polyelectrolyte multilayers. Several key aspects of weak polyelectrolytes are highlighted including the pH-controllable properties, the responsiveness to environmental pH, and synergetic functions obtained from weak polyelectrolyte/other component multilayers. Throughout this review, useful applications of weak polyelectrolyte-based multilayers in drug delivery, tunable biointerfaces, nanoreactors for synthesis of nanostructures, solid state electrolytes, membrane separation, and sensors are highlighted, and promising future directions in the area of weak polyelectrolyte-based multilayer assembly such as fabrication of multi-responsive materials, adoption of unique building blocks, investigation of internal molecular-level structure and mechanism of exponentially grown multilayers, and exploration of novel biomedical and energy applications are proposed.

Crab-on-a-Tree: All Biorenewable, Optical and Radio Frequency Transparent Barrier Nanocoating for Food Packaging

Plastic packaging effectively protects foods from mechanical, microbial, and chemical damage, but oxygen can still permeate these plastics, degrading foods. Improving the gas barrier usually requires metallic or halogenated polymeric coatings; however, both cause environmental concerns and metallic coatings block visible light and electromagnetic signals. This paper reports a design of a highly flexible, visible light and radio frequency transparent coating on commercial poly(ethylene terephthalate) (PET) film. Nanoscale blending was achieved between negatively charged cellulose nanofibers and positively charged chitin nanowhiskers by employing spray-assisted layer-by-layer assembly. Synergetic interplay between these highly crystalline nanomaterials results in a flexible film with superior barrier characteristics. The oxygen transmission rate was below 0.5 mL m^-2 day^-1. Moreover, this coating maintains its performance even when exposed to common hazards such as bending stress and hydration. The coating also notably reduces the haziness of PET with a negligible loss of transparency and provides effective inhibition of antibacterial growth. This "crab-on-a-tree" nanocoating holds high potential for biorenewable and optical and radio frequency transparent packaging applications.

A deep look into the spray coating process in real-time-the crucial role of x-rays

Tailoring functional thin films and coating by rapid solvent-based processes is the basis for the fabrication of large scale high-end applications in nanotechnology. Due to solvent loss of the solution or dispersion inherent in the installation of functional thin films and multilayers the spraying and drying processes are strongly governed by non-equilibrium kinetics, often passing through transient states, until the final structure is installed. Therefore, the challenge is to observe the structural build-up during these coating processes in a spatially and time-resolved manner on multiple time and length scales, from the nanostructure to macroscopic length scales. During installation, the interaction of solid-fluid interfaces and between the different layers, the flow and evaporation themselves determine the structure of the coating. Advanced x-ray scattering methods open a powerful pathway for observing the involved processes in situ, from the spray to the coating, and allow for gaining deep insight in the nanostructuring processes. This review first provides an overview over these rapidly evolving methods, with main focus on functional coatings, organic photovoltaics and organic electronics. Secondly the role and decisive advantage of x-rays is outlined. Thirdly, focusing on spray deposition as a rapidly emerging method, recent advances in investigations of spray deposition of functional materials and devices via advanced x-ray scattering methods are presented.