Thermo-optics of gilded hollow-core fibers.

Hollow core fibers, supporting waveguiding in a void, open a room of opportunities for numerous applications owing to an extended light-matter interaction distance and relatively high optical confinement. Decorating an inner capillary with functional materials allows tailoring the fiber's optical properties further and turns the structure into a functional device. Here, we functionalize an anti-resonant hollow-core fiber with 18 nm-size gold nanoparticles, approaching a uniform 45% surface coverage along 10 s of centimeters along its inner capillary. Owing to a moderately low overlap between the fundamental mode and the gold layer, the fiber maintains its high transmission properties; nevertheless, the entire structure experiences considerable heating, which is observed and quantified with the aid of a thermal camera. The hollow core and the surrounding capillary are subsequently filled with ethanol and thermo-optical heating is demonstrated. We also show that at moderate laser intensities, the liquid inside the fiber begins to boil and, as a result, the optical guiding is destroyed. The gilded hollow core fiber and its high thermal-optical responsivity suggest considering the structure as an efficient optically driven catalytic reactor in applications where either small reaction volumes or remote control over a process are demanded.

Thin-film conformal fluorescent SU8-phenylenediamine.

The SU8 polymer is a negative photoresist widely used to produce high-quality coatings, with controllable thicknesses ranging from nanometers to millimeters, depending on fabrication protocols. Apart from conventional use cases in microelectronics and fluidics, SU8 is quite an attractive platform in nanophotonics. This material, being straightforwardly processed by ultraviolet lithography, is transparent to wavelengths longer than 500 nm. However, introducing fluorescent agents within the SU8 matrix remains a challenge owing to its high hydrophobicity. Here, we develop a process, where colorful quantum dots co-participate in the polymerization process by epoxide amination and become a part of a new fluorescent material - SU8-phenylenediamine. Through comprehensive characterization methods, including XPS and 1H-NMR analyses, we demonstrate that m-PD covalently binds to SU8 epoxy sites with its molecular amine, virtually forming a new material and not just a mixture of two compounds. After characterizing the new strongly fluorescent platform, thin 300 nm films were created on several surfaces, including a conformal coverage of a nanofluidic capillary. This new process provides opportunities to incorporate various functional molecules into optoelectronic devices without the need for multistep deposition and surface functionalization.

Inkjet Printing Humidity Sensing Pattern Based on Self-Organizing Polystyrene Spheres.

This study is devoted to the development of photonic patterns based on polystyrene spheres (PSS) incorporated in chitosan hydrogels by inkjet printing. Using this method, high-resolution encrypted images that became visible only in high humidity were obtained. Inks based on PSS with carboxylic groups on the surface were made, and their rheological parameters (viscosity, surface tension, and ζ-potential) were optimized according to the Ohnesorge theory. The obtained value of the ζ-potential indicated the stability of the synthesized colloidal inks. The dependences of the printing parameters on the concentration of ethylene glycol in PSS dispersion, the drop spacing, the shape of the printed pattern, waveform, the temperature of the printing process, and the degree of ordering of the PSS-based photonic crystal were investigated. The scanning electronic microscope (SEM) images confirmed that the optimal self-organization of PSS was achieved at the following values of 0.4% weight fraction (wt%) carboxylic groups, the drop spacing of 50 µm, and the temperature of the printing table of 25 °C. High-resolution microstructures were obtained by drop-on-demand printing with a deposited drophead diameter of 21 µm and an accuracy of ±2 µm on silicon and glass substrates. The deposition of chitosan-based hydrogels on the obtained polystyrene photonic crystals allowed reversibly changing the order of the diffraction lattice of the photonic crystal during the swelling of the hydrogel matrix, which led to a quick optical response in the daylight. The kinetics of the appearance of the optical response of the obtained coating were discussed. The simplicity of production, the speed of image appearance, and the ability to create high-resolution patterns determine the potential applications of the proposed systems as humidity sensors or anticounterfeiting coatings.

Printing of Colorful Cellulose Nanocrystalline Patterns Visible in Linearly Polarized Light.

This study addresses the inkjet printing approach for fabrication of cellulose nanocrystalline (CNC) patterns with tunable optical properties varied by the thickness of deposited layers. In particular, forming functional patterns visible only in linearly polarized light is of the primary interest. The possibility of controlling the bright iridescent color response associated with the birefringence in the chiral anisotropic structure of inkjet-printed layers of CNC with sulfo-groups (s-CNC) has been thoroughly investigated. In this connection, we have elaborated an appropriate synthesis sequence for deriving printable inks in the form of sedimentation-stable s-CNC colloids with various concentrations of solid phase and experimentally determined the optimal regimes of their inkjet printing. For this purpose, the rheological parameters and s-CNC particle concentration have also been optimized. The study is accomplished with a comprehensive optical characterization of the deposited s-CNC layers with variable thickness, drying conditions, and the polarization state. The experimental results demonstrate the feasibility of inkjet printing technology to perform the precise fabrication of optically active s-CNC patterns with variable optical properties. These results are particularly relevant for applications requiring special conditions of color demonstration in security printing for such as anticounterfeiting applications, polygraphy decoration printing, and color photo filters.

Test-System for Bacteria Sensing Based on Peroxidase-Like Activity of Inkjet-Printed Magnetite Nanoparticles.

Rapid detection of bacterial contamination is an essential task in numerous medical and technical processes and one of the most rapidly developing areas of nano-based analytics. Here, we present a simple-to-use and special-equipment-free test-system for bacteria detection based on magnetite nanoparticle arrays. The system is based on peroxide oxidation of chromogenic substrate catalyzed by magnetite nanoparticles, and the process undergoes computer-aided visual analysis. The nanoparticles used had a pristine surface free of adsorbed molecules and demonstrated high catalytic activities up to 6585 U/mg. The catalytic process showed the Michaelis-Menten kinetic with Km valued 1.22 mmol/L and Vmax of 4.39 µmol/s. The nanoparticles synthesized were used for the creation of inkjet printing inks and the design of sensor arrays by soft lithography. The printed sensors require no special equipment for data reading and showed a linear response for the detection of model bacteria in the range of 104-108 colony-forming units (CFU) per milliliter with the detection limit of 3.2 × 103 CFU/mL.

Correction: Inkjet assisted fabrication of planar biocompatible memristors.

[This corrects the article DOI: 10.1039/C9RA08114C.].

Optical interference-based sensors for the visual detection of nano-scale objects.

In this study, we present a new concept for the simple visual detection of nano-scale objects in solutions. To achieve this goal, we developed chromogen-free interference-based sensors that provided a color visible reaction directly after the interaction of the analyte with the substrate. The effect is based on the strong optical interference occurring at the interface between the inkjet printed sol-gel titania film (a layer with high refractive index) and the adsorbed nano-sized objects (layer with low refractive index), which can be detected even with the naked eye. Herein, we have developed a synthetic strategy for the inkjet printing of interference sensors with controllable color change through thickness adjustment.

Inkjet assisted fabrication of planar biocompatible memristors.

In this study we address a novel design of a planar memristor and investigate its biocompatibility. An experimental prototype of the proposed memristor assembly has been manufactured using a hybrid nanofabrication method, combining sputtering of electrodes, patterning the insulating trenches, and filling them with a memristive substance. To pattern the insulating trenches, we have examined two nanofabrication techniques employing either a focused ion beam or a cantilever tip of an atomic force microscope. Inkjet printing has been used to fill the trenches with the functional titania ink. The experimental prototypes have qualitatively demonstrated memristive current-voltage behavior, as well as high biocompatibility.