Gravure printing for mesoporous film preparation

Mesoporous ordered films via self-assembly: trends and perspectives

The synthesis of ordered mesoporous films via self-assembly represents one of the main accomplishments in nanoscience. In fact, controlling the complex chemical-physical phenomena that govern the process triggered by the solvent's fast evaporation during film deposition has represented a challenging task. Several years after the first articles on the subject, the research in the field entered a new stage. New advanced applications based on the peculiar properties of mesoporous films are envisaged while basic research is still going on, especially to clarify the mechanism behind self-organization in a spatially defined environment and the physics and chemistry in mesoscale porosity. This review has been dedicated to analysing the main trends in the fields and the perspective for future developments.

Three-Dimensional Printing and Its Potential to Develop Sensors for Cancer with Improved Performance

Cancer is the second leading cause of death globally and early diagnosis is the best strategy to reduce mortality risk. Biosensors to detect cancer biomarkers are based on various principles of detection, including electrochemical, optical, electrical, and mechanical measurements. Despite the advances in the identification of biomarkers and the conventional 2D manufacturing processes, detection methods for cancers still require improvements in terms of selectivity and sensitivity, especially for point-of-care diagnosis. Three-dimensional printing may offer the features to produce complex geometries in the design of high-precision, low-cost sensors. Three-dimensional printing, also known as additive manufacturing, allows for the production of sensitive, user-friendly, and semi-automated sensors, whose composition, geometry, and functionality can be controlled. This paper reviews the recent use of 3D printing in biosensors for cancer diagnosis, highlighting the main advantages and advances achieved with this technology. Additionally, the challenges in 3D printing technology for the mass production of high-performance biosensors for cancer diagnosis are addressed.

Effects of Hydrophobic Modification of Linear- and Branch-Structured Fluorinated and Nonfluorinated Silanes on Mesoporous Silica Particles

This work reports a comparison of hydrophobic surface modification on mesoporous silica particles (MSPs) obtained by large-scale production using a batch reactor with linear and branched fluorinated and nonfluorinated silanes. Fluorinated silanes were used with TDF-TMOS and TFP-TMOS as a linear and branched structure, respectively. Nonfluorinated silanes were used with OD-TEOS and HMDS as a linear and branched structure, respectively. These four silanes were grafted on the surface of the MSPs as the function of the concentrations, and then, the water contact angles (WCAs) were measured. The WCA of the four silane-grafted MSPs was higher in the branch-structured silanes, namely, TFP-TMOS@MSPs and HMDS@MSPs than in linear-structured silanes, namely, TDF-TMOS and OD-TEOS due to the higher hydrophobicity by a lot of -F and -CH₃ groups. Furthermore, the relationship between the WCA and BET parameters was demonstrated using the surface areas, pore volumes, and grafted amounts of the four silane-grafted MSPs. The structural characterization was demonstrated by solid-state ²⁹Si MAS NMR to determine the bonding environment of Si atoms between the grafted silane and the surfaces of MSPs using the T ³/T ² and Q ³/Q ⁴ ratios of the fluorinated and nonfluorinated silane-grafted MSPs. Among the four silanes, nonfluorinated HMDS@MSPs had a high contact angle of 135° as fluorinated TFP-TMOS@MSPs. When 5 wt % of HMDS@MSPs mixed with gravure ink was coated on a biodegradable polylactic acid (PLA) film, the contact angle was improved to 131.8 from 83.3° of the natural PLA film.

Printing Technologies as an Emerging Approach in Gas Sensors: Survey of Literature

Herein, we review printing technologies which are commonly approbated at recent time in the course of fabricating gas sensors and multisensor arrays, mainly of chemiresistive type. The most important characteristics of the receptor materials, which need to be addressed in order to achieve a high efficiency of chemisensor devices, are considered. The printing technologies are comparatively analyzed with regard to, (i) the rheological properties of the employed inks representing both reagent solutions or organometallic precursors and disperse systems, (ii) the printing speed and resolution, and (iii) the thickness of the formed coatings to highlight benefits and drawbacks of the methods. Particular attention is given to protocols suitable for manufacturing single miniature devices with unique characteristics under a large-scale production of gas sensors where the receptor materials could be rather quickly tuned to modify their geometry and morphology. We address the most convenient approaches to the rapid printing single-crystal multisensor arrays at lab-on-chip paradigm with sufficiently high resolution, employing receptor layers with various chemical composition which could replace in nearest future the single-sensor units for advancing a selectivity.

Pushing the limits of nanopore transport performance by polymer functionalization

Inspired by the design and performance of biological pores, polymer functionalization of nanopores has emerged as an evolving field to advance transport performance within the last few years. This feature article outlines developments in nanopore functionalization and the resulting transport performance including gating based on electrostatic interaction, wettability and ligand binding, gradual transport controlled by polymerization as well as functionalization-based asymmetric nanopore and nanoporous material design going towards the transport direction. Pushing the limits of nanopore transport performance and thus reducing the performance gap between biological and technological pores is strongly related to advances in polymerization chemistry and their translation into nanopore functionalization. Thereby, the effect of the spatial confinement has to be considered for polymer functionalization as well as for transport regulation, and mechanistic understanding is strongly increased by combining experiment and theory. A full mechanistic understanding together with highly precise nanopore structure design and polymer functionalization is not only expected to improve existing application of nanoporous materials but also opens the door to new technologies. The latter might include out of equilibrium devices, ionic circuits, or machine learning based sensors.

Simultaneous Nanolocal Polymer and In Situ Readout Unit Placement in Mesoporous Separation Layers

Bioinspired solid-state nanopores and nanochannels have attracted interest in the last two decades, as they are envisioned to advance future sensing, energy conversion, and separation concepts. Although much effort has been made regarding functionalization of these materials, multifunctionality and accurate positioning of functionalities with nanoscale precision still remain challenging. However, this precision is necessary to meet transport performance and complexity of natural pores in living systems, which are often based on nonequilibrium states and compartmentalization. In this work, a nanolocal functionalization and simultaneous localized sensing strategy inside a filtering mesoporous film using precisely placed plasmonic metal nanoparticles inside mesoporous films with pore accessibility control is demonstrated. A single layer of gold nanoparticles is incorporated into mesoporous thin films with precise spatial control along the nanoscale layer thickness. The local surface plasmon resonance is applied to induce a photopolymerization leading to a nanoscopic polymer shell around the particles and thus nanolocal polymer placement inside the mesoporous material. As near-field modes are sensitive to the dielectric properties of their surrounding, the in situ sensing capability is demonstrated using UV-vis spectroscopy. It is demonstrated that the sensing sensitivity only slightly decreases upon functionalization. The presented nanolocal placement of responsive functional polymers into nanopores offers a simultaneous filtering and nanoscopic readout function. Such a nanoscale local control is envisioned to have a strong impact onto the development of new transport and sensor concepts, especially as the system can be developed into higher complexity using different metal nanoparticles and additional design of mesoporous film filtering properties.

Wettability-defined droplet imbibition in ceramic mesopores

Wettability-defined liquid infiltration into porous materials in nature and several industrial applications is of fundamental interest. Direct observation of wetting-controlled imbibition in mesopores is anticipated to deliver important insights into the interplay between nanoconfined liquid movement and nanoscale wettability. We present a systematic study of water imbibition into mesoporous silica thin films with wetting properties precisely adjusted through chemical functionalization. We observe the liquid infiltration, resulting in an imbibition ring around the water droplet, by top-view imaging using a camera with collimated coaxial illumination. With decreasing hydrophilicity, the maximum imbibition area around the droplet decreases, accompanied by a simultaneous change in the imbibition kinetics and imbibition mechanism. Initially, the imbibition kinetics follow a modified Lucas-Washburn law that considers a strong influence of evaporation. However, with increasing imbibition time after reaching constant imbibition ring dimensions, the imbibition area starts to increase again, causing a deviation from the applied model. This observation is ascribed to water-mediated surface activation at the imbibition front, leading to a slightly increased wettability, which is also confirmed by water adsorption measurements. Furthermore, recently described spontaneous condensation-evaporation imbalances that cause oscillations of the imbibition front could be verified and were studied with regard to changing wetting properties. By increasing the contact angle of the material and therefore the partial pressure needed for capillary condensation, the amplitude of the imbibition front oscillations decreases. These results provide insights into the wettability-defined complex movement of water in mesoporous structures, which has practical implications, e.g., for nano/microfluidic devices and water purification or harvesting.

Syntheses of Silver Nanowires Ink and Printable Flexible Transparent Conductive Film: A Review

Nowadays, flexible transparent conductive film (FTCF) is one of the important components of many flexible electronic devices. Due to comprehensive performances on optoelectronics, FTCF based on silver nanowires (AgNWs) networks have received great attention and are expected to be a new generation of transparent conductive film materials. Due to its simple process, printed electronic technology is now an important technology for the rapid production of low-cost and high-quality flexible electronic devices. AgNWs-based FTCF fabricated by using printed electronic technology is considered to be the most promising process. Here, the preparation and performance of AgNW ink are introduced. The current printing technologies are described, including gravure printing, screen printing and inkjet printing. In addition, the latest methods to improve the conductivity, adhesion, and stability of AgNWs-based FTCF are introduced. Finally, the applications of AgNWs-based FTCF in solar cells, transparent film heaters, optoelectronic devices, touch panel, and sensors are introduced in detail. Therefore, combining various printing technologies with AgNWs ink may provide more opportunities for the development of flexible electronic devices in the future.

Recent trends in nanopore polymer functionalization

Functional nanopores play an essential role in many biotechnological applications such as sensing, or drug delivery. Prominent examples are polymer functionalized ceramic or solid state nanopores. Intensive research efforts led to a discovery of a plethora of polymer functionalized nanopores demonstrating gated molecular transport upon basically all common stimuli. Nevertheless, nature's biological pore transport precision is unreached. This can be, among others, ascribed to limits in design precision especially with respect to functionalization. Recent trends in polymer functionalized nanopores address the role of confinement and polymerization control, strategies toward more sustainable reaction conditions, such as visible light initiation and strategies toward nanoscale local placement of polymer functionalization. The resulting multi-stimuli responsive nanopore performance enables concerted release or transport, side selective separation and selective detection.

Surface-Plasmon- and Green-Light-Induced Polymerization in Mesoporous Thin Silica Films

The near-field of surface plasmon resonances at planar metal surfaces is confined to the nanoscale, but its resonance wavelength is located in the visible light range, making it interesting for confining polymer functionalization of surfaces but incompatible with the majority of polymerization reactions. Here, fluorescein as a polymerization initiator allowing dye-sensitized polymerization with green light (438-540 nm) is demonstrated to allow polymer functionalization of mesoporous films deposited onto planar silver metal layers. The fluorescein-induced polymer functionalization of mesoporous silica films is investigated with respect to the influence of irradiation power and irradiation time and its potential to generate polymer gradients. Finally, the polymer functionalization of mesoporous films upon surface-plasmon-initiated polymerization is demonstrated. Polymer functionalization thereby determines pH-responsive ionic mesopore accessibility. Consequently, these results present a sound basis for further nanoscale near-field-induced polymer functionalization of porous films.