A CMOS Image Sensor Integrated with Plasmonic Colour Filters

Multi-pixel, 4.5?×?9???m, plasmonic colour filters, consisting of periodic subwavelength holes in an aluminium film, were directly integrated on the top surface of a complementary metal oxide semiconductor (CMOS) image sensor (CIS) using electron beam lithography and dry etch. The 100?×?100-pixel plasmonic CIS showed full colour sensitivities across the visible range determined by a photocurrent measurement. The filters were fabricated in a simple process utilising a single lithography step. This is to be compared with the traditional multi-step processing when using dye-doped polymers. The intrinsic compatibility of these plasmonic components with a standard CMOS process allows them to be manufactured in a metal layer close to the photodiodes. The incorporation of such plasmonic components may in the future enable the development of advanced CIS with low cost, low cross-talk and increased functionality.     

Uniform aligned bioconjugation of biomolecule motifs for integration within microfabricated microfluidic devices

Full details and a step-by-step guide suitable for printing proteins aligned to micron-sized sensors and subsequent integration and alignment of microfluidic structures are presented. The precise alignment and grafting of micron-sized biomolecule patterns with an underlying substrate at predefined locations is achieved using a novel semi-automated microcontact printer. Through integration of optical alignment methods in the x, y, and z directions, uniform contact of micron-sized stamps is achieved. Feature compression of the stamp is avoided by fine control of the stamp during contact. This printing method has been developed in combination with robust, compatible bioconjugate chemistry for patterning of a dextran-functionalized silicon oxide substrate with a NeutrAvidin-"inked" stamp and subsequent incubation with a biotin-functionalized protein. The bioconjugate chemistry is such that uniform coverage of the protein (without denaturation) over the printed motif is obtained and reproduction of the initial mask shape and dimensions is achieved. Later integration with a microfluidic structure aligned with the printed motif on the substrate is also described.     

Microcontact Peeling as a New Method for Cell Micropatterning

Micropatterning is becoming a powerful tool for studying morphogenetic and differentiation processes of cells. Here we describe a new micropatterning technique, which we refer to as microcontact peeling. Polydimethylsiloxane (PDMS) substrates were treated with oxygen plasma, and the resulting hydrophilic layer of the surface was locally peeled off through direct contact with a peeling stamp made of aluminum, copper, or silicon. A hydrophobic layer of PDMS could be selectively exposed only at the places of the physical contact as revealed by water contact angle measurements and angle-resolved X-ray photoelectron spectroscopy, which thus enabled successful micropatterning of cells with micro-featured peeling stamps. This new micropatterning technique needs no procedure for directly adsorbing proteins to bare PDMS in contrast to conventional techniques using a microcontact printing stamp. Given the several unique characteristics, the present technique based on the peel-off of inorganic materials may become a useful option for performing cell micropatterning.     

Atomic Layer Deposition as a General Method Turns any 3D‐Printed Electrode into a Desired Catalyst: Case Study in Photoelectrochemisty

3D‐printing technologies have begun to revolutionize many manufacturing processes, however, there are still significant limitations that are yet to be overcome. In particular, the material from which the products are fabricated is limited by the 3D‐printing material precursor. Particularly, for photoelectrochemical (PEC) energy applications, the as‐printed electrodes can be used as is, or modified by postfabrication processes, e.g., electrochemical deposition or anodization, to create active layers on the 3D‐printed electrodes. However, the as‐printed electrodes are relatively inert for various PEC energy applications, and the aforementioned postfabrication processing techniques do not offer layer conformity or control at the Ångström/nano level. Herein, for the first time, atomic layer deposition (ALD) is utilized in conjunction with metal 3D‐printing to create active electrodes. To illustrate the proof‐of‐concept, TiO₂ is deposited by ALD onto stainless steel 3D‐printed electrodes and subsequently investigated as a photoanode for PEC water oxidation. Furthermore, by tuning the TiO₂ thickness by ALD, the activity can be optimized. By combining 3D‐printing and ALD, instead of other metal deposition techniques, i.e., sputtering, rapid prototyping of electrodes with controllable thickness of the desired material onto an as‐printed electrodes with any porosity can be achieved that can benefit a multitude of energy applications.     

All‐Inkjet‐Printed,All‐Air‐Processed Solar Cells

The prospective of using direct‐write printing techniques for the manufacture of organic photovoltaics (OPVs) has made these techniques highly attractive. OPVs have the potential to revolutionize small‐scale portable electronic applications by directly providing electric power to the systems. However, no route is available for monolithically integrating the energy‐harvesting units into a system in which other components, such as transistors, sensors, or displays, are already fabricated. Here, the fabrication and the measurement of inkjet‐printed, air‐processed organic solar cells is reported for the first time. Highly controlled conducting and semiconducting films using engineered inks for inkjet printing enable good efficiencies for printed OPVs between ≈2 and 5% power conversion efficiency. The results show that inkjet printing is an attractive digital printing technology for cost‐effective, environmentally friendly integration of photovoltaic cells onto plastic substrates.     

Printing of polymer microcapsules for enzyme immobilization on paper substrate

Poly(ethyleneimine) (PEI) microcapsules containing laccase from Trametes hirsuta (ThL) and Trametes versicolor (TvL) were printed onto paper substrate by three different methods: screen printing, rod coating, and flexo printing. Microcapsules were fabricated via interfacial polycondensation of PEI with the cross-linker sebacoyl chloride, incorporated into an ink, and printed or coated on the paper substrate. The same ink components were used for three printing methods, and it was found that laccase microcapsules were compatible with the ink. Enzymatic activity of microencapsulated TvL was maintained constant in polymer-based ink for at least eight weeks. Thick layers with high enzymatic activity were obtained when laccase-containing microcapsules were screen printed on paper substrate. Flexo printed bioactive paper showed very low activity, since by using this printing method the paper surface was not fully covered by enzyme microcapsules. Finally, screen printing provided a bioactive paper with high water-resistance and the highest enzyme lifetime.     

Effect of Layer Thickness and Printing Orientation on Mechanical Properties and Dimensional Accuracy of 3D Printed Porous Samples for Bone Tissue Engineering

Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products'' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young''s modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity.     

Microcontact printing of axon guidance molecules for generation of graded patterns

Microcontact printing (microCP) of proteins has been successfully used for patterning surfaces in various contexts. Here we describe a simple 'lift-off' method to print precise patterns of axon guidance molecules, which are used as substrate for growing chick retinal ganglion cell (RGC) axons. Briefly, the etched pattern of a silicon master is transferred to a protein-coated silicone cuboid (made from polydimethylsiloxane, PDMS), which is then used as a stamp on a glass coverslip. RGC explants are placed adjacent to the pattern and cultured overnight. Fluorescent labeling of the printed proteins allows the quantitative analysis of the interaction of axons and growth cones with single protein dots and of the overall outgrowth and guidance rate in variously designed patterns. Patterned substrates can be produced in 3-4 h and are stable for up to one week at 4 degrees C; the entire protocol can be completed in 3 d.     

Plasmonic Ladder-Like Structure for NIR Polarizer

Polarization-dependent light transmission property is investigated in two-dimensional plasmonic ladder-like structure in the Near-infrared (NIR) regime of 900 to 1600 nm. The plasmonic ladder-like structures are fabricated using cost-effective laser interference lithography. Optical transmission studies reveal that in the stated NIR regime, the structure has nearly 30 % absolute transmission with respect to air when the long axis is aligned parallel to the polarization axis of the incident excitation and has negligible transmission at the crossed polarization state. The findings have potential implications in designing large area flat NIR polarizers.     

Effect of Different Gums on Features of 3D Printed Object Based on Vitamin-D Enriched Orange Concentrate

This study examined the effects of different gums viz. gum arabic (GA), guar gum (GG), k-carrageenan gum (KG), and xanthan gum (XG) on rheological and 3D printing characteristics of vitamin D (Vit D) enriched orange concentrate (OC) wheat starch (WS) blends. The textural and microstructural properties of printed objects from above mixture were evaluated and compared. The addition of gums induced an increase in apparent viscosity, storage modulus (G′), and loss modulus (G″) of the OC-WS mixtures, while GA decreased the apparent viscosity and G′. Nuclear magnetic resonance (NMR) analysis of 3D printed samples revealed that the movement of transverse time (T₂) toward closer to 0 ms indicated an increase in immobilized and bound water populations suggesting the gel formation. The slight shift toward shorter wavelength in FT-IR results for the broadband centered around 3400 cm^?1 after addition of gums possibly caused an increase of G′ and load bearing capacity of the blends. 3D printing characteristics revealed that the objects printed using KG containing blend possessed maximum fidelity to the target geometry and good loading bearing capacity, preventing collapsing over time due to the proper G′ value. At tanδ of 0.238, OC-WS-KG mixture achieved the best printing condition. Higher tanδ of GA (0.038) containing samples led to an unwanted collapse of the printed constructs. The objects printed using KG also exhibited the smoothest visible surface as well as microstructure and best mastication properties. Considering the studied features, vitamin D enriched OC with WS-KG was found to be the best match for orange fruit concentrate-based 3D food printing. This work demonstrates the novel ways to develop fortified 3D printed foods.     

Application of inkjet printing technique for biological material delivery and antimicrobial assays

A modified commercial inkjet printer was developed to deliver biological samples. The active Escherichia coli cells were directly printed at precisely targeted positions on agar-coated substrates via this technique to generate complex bacterial colony patterns. Viable cell arrays with a high density of 400 dots/cm² were obtained without the addition of any surfactants or other chemicals. Moreover, an applicable example of multiple-layer inkjet printing technique was adapted to deposit bacteria and antibiotics for antimicrobial potential assays. After fluorescent E. coli cells were printed, gradient concentrations of water-soluble antibiotics were ejected onto them to determine its minimum inhibitory concentration (MIC) to test the antimicrobial activities. This approach simplifies the experimental manipulation by replacing laborious manual loading processes with automatically controlled printing procedures, which makes it a versatile tool for high-throughput applications.     

Scaffold‐free inkjet printing of three‐dimensional zigzag cellular tubes

The capability to print three‐dimensional (3D) cellular tubes is not only a logical first step towards successful organ printing but also a critical indicator of the feasibility of the envisioned organ printing technology. A platform‐assisted 3D inkjet bioprinting system has been proposed to fabricate 3D complex constructs such as zigzag tubes. Fibroblast (3T3 cell)‐based tubes with an overhang structure have been successfully fabricated using the proposed bioprinting system. The post‐printing 3T3 cell viability of printed cellular tubes has been found above 82% (or 93% with the control effect considered) even after a 72‐h incubation period using the identified printing conditions for good droplet formation, indicating the promising application of the proposed bioprinting system. Particularly, it is proved that the tubular overhang structure can be scaffold‐free fabricated using inkjetting, and the maximum achievable height depends on the inclination angle of the overhang structure. As a proof‐of‐concept study, the resulting fabrication knowledge helps print tissue‐engineered blood vessels with complex geometry. Biotechnol. Bioeng. 2012; 109: 3152–3160. © 2012 Wiley Periodicals, Inc.     

Colorimetry as Quality Control Tool for Individual Inkjet-Printed Pediatric Formulations

Printing technologies were recently introduced to the pharmaceutical field for manufacturing of drug delivery systems. Printing allows on demand manufacturing of flexible pharmaceutical doses in a personalized manner, which is critical for a successful and safe treatment of patient populations with specific needs, such as children and the elderly, and patients facing multimorbidity. Printing of pharmaceuticals as technique generates new demands on the quality control procedures. For example, rapid quality control is needed as the printing can be done on demand and at the point of care. This study evaluated the potential use of a handheld colorimetry device for quality control of printed doses of vitamin Bs on edible rice and sugar substrates. The structural features of the substrates with and without ink were also compared. A multicomponent ink formulation with vitamin B₁, B₂, B₃, and B₆ was developed. Doses (4 cm²) were prepared by applying 1–10 layers of yellow ink onto the white substrates using thermal inkjet technology. The colorimetric method was seen to be viable in detecting doses up to the 5th and 6th printed layers until color saturation of the yellow color parameter (b*) was observed on the substrates. Liquid chromatography mass spectrometry was used as a reference method for the colorimetry measurements plotted against the number of printed layers. It was concluded that colorimetry could be used as a quality control tool for detection of different doses. However, optimization of the color addition needs to be done to avoid color saturation within the planned dose interval.     

Diagonally Aligned Squared Metal Nano-pillar with Increased Hotspot Density as a Highly Reproducible SERS Substrate

Metal nanostructure on dielectric substrate with increased hotspot density has drawn considerable research interest in recent years toward the study of surface-enhanced Raman spectroscopy (SERS). In this paper, we report the fabrication of a diagonally aligned squared metal nano-pillar (SMNP) on a dielectric substrate and revealed it as an efficient SERS substrate with increased hotspot density for sensing of Raman active materials. Due to dipolar coupling and lightening rod effect between the neighboring nano-pillars, the localized surface plasmon resonance (LSPR) field intensity increased significantly in the space between two neighboring SMNP which would lead to the enhancement of SERS signal. The SMNP has been fabricated using electron beam lithographic (EBL) technique with hotspot density of 2.45 × 10⁷/mm². With the designed SERS substrate an average enhancement factor (EF) of 3.27 × 10⁸ has been observed with relative standard deviation of ～13 %.     

Enzyme-etching technique to fabricate micropatterns of aligned collagen fibrils

A technique to tailor-make pre-coated, pre-aligned bovine collagen fibrils, derived from neonatal cardiomyocytes, on the surface of a glass slide into a designated pattern is reported. The unwanted collagen-coated area was erased by a collagenase solution and the tailored area was retained by attaching a microfabricated polydimethylsiloxane stamp directly to the collagen-coated surface. Using this technique, collagen patterns with designated orientations and with clear pattern boundaries and defined shapes were fabricated.     

Soft Lithographic Functionalization and Patterning Oxide-free Silicon and Germanium

The development of hybrid electronic devices relies in large part on the integration of (bio)organic materials and inorganic semiconductors through a stable interface that permits efficient electron transport and protects underlying substrates from oxidative degradation. Group IV semiconductors can be effectively protected with highly-ordered self-assembled monolayers (SAMs) composed of simple alkyl chains that act as impervious barriers to both organic and aqueous solutions. Simple alkyl SAMs, however, are inert and not amenable to traditional patterning techniques. The motivation for immobilizing organic molecular systems on semiconductors is to impart new functionality to the surface that can provide optical, electronic, and mechanical function, as well as chemical and biological activity. Microcontact printing (μCP) is a soft-lithographic technique for patterning SAMs on myriad surfaces.^1-9 Despite its simplicity and versatility, the approach has been largely limited to noble metal surfaces and has not been well developed for pattern transfer to technologically important substrates such as oxide-free silicon and germanium. Furthermore, because this technique relies on the ink diffusion to transfer pattern from the elastomer to substrate, the resolution of such traditional printing is essentially limited to near 1 μm.^10-16In contrast to traditional printing, inkless μCP patterning relies on a specific reaction between a surface-immobilized substrate and a stamp-bound catalyst. Because the technique does not rely on diffusive SAM formation, it significantly expands the diversity of patternable surfaces. In addition, the inkless technique obviates the feature size limitations imposed by molecular diffusion, facilitating replication of very small (<200 nm) features.^17-23 However, up till now, inkless μCP has been mainly used for patterning relatively disordered molecular systems, which do not protect underlying surfaces from degradation.Here, we report a simple, reliable high-throughput method for patterning passivated silicon and germanium with reactive organic monolayers and demonstrate selective functionalization of the patterned substrates with both small molecules and proteins. The technique utilizes a preformed NHS-reactive bilayered system on oxide-free silicon and germanium. The NHS moiety is hydrolyzed in a pattern-specific manner with a sulfonic acid-modified acrylate stamp to produce chemically distinct patterns of NHS-activated and free carboxylic acids. A significant limitation to the resolution of many μCP techniques is the use of PDMS material which lacks the mechanical rigidity necessary for high fidelity transfer. To alleviate this limitation we utilized a polyurethane acrylate polymer, a relatively rigid material that can be easily functionalized with different organic moieties. Our patterning approach completely protects both silicon and germanium from chemical oxidation, provides precise control over the shape and size of the patterned features, and gives ready access to chemically discriminated patterns that can be further functionalized with both organic and biological molecules. The approach is general and applicable to other technologically-relevant surfaces.     

3D‐Printed Conical Arrays of TiO2 Electrodes for Enhanced Photoelectrochemical Water Splitting

Control over the topography of semiconducting materials can lead to enhanced performances in photoelectrochemical related applications. One means of implementing this is through direct patterning of metal‐based substrates, though this is inadequately developed. Conventional techniques for patterned fabrication commonly involve technologically demanding and tedious processes. 3D printing, a form of additive fabrication, enables creation of a 3D object by deposition of successive layers of material via computer control. In this work, the feasibility of fabricating metal‐based 3D printed photoelectrodes is explored. Electrodes comprised of conical arrays are fabricated and the performance for photoelectrochemical water splitting is further enhanced by the direct growth of TiO2 nanotubes on this platform. 3D metal printing provides a flexible and versatile approach for the design and fabrication of novel electrode structures.     

Synthesis of a Nano-Silver Metal Ink for Use in Thick Conductive Film Fabrication Applied on a Semiconductor Package

The success of printing technology in the electronics industry primarily depends on the availability of metal printing ink. Various types of commercially available metal ink are widely used in different industries such as the solar cell, radio frequency identification (RFID) and light emitting diode (LED) industries, with limited usage in semiconductor packaging. The use of printed ink in semiconductor IC packaging is limited by several factors such as poor electrical performance and mechanical strength. Poor adhesion of the printed metal track to the epoxy molding compound is another critical factor that has caused a decline in interest in the application of printing technology to the semiconductor industry. In this study, two different groups of adhesion promoters, based on metal and polymer groups, were used to promote adhesion between the printed ink and the epoxy molding substrate. The experimental data show that silver ink with a metal oxide adhesion promoter adheres better than silver ink with a polymer adhesion promoter. This result can be explained by the hydroxyl bonding between the metal oxide promoter and the silane grouping agent on the epoxy substrate, which contributes a greater adhesion strength compared to the polymer adhesion promoter. Hypotheses of the physical and chemical functions of both adhesion promoters are described in detail.     

Creating Transient Cell Membrane Pores Using a Standard Inkjet Printer

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication.^1-10 Recently, thermal inkjet printing has also been used for gene transfection.^8,9 The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm.^8,9,11The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells.^{8, 12} Cell viability after printing has been shown to be similar to standard cell plating methods^1,8. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. ^8,9,11A standard HP DeskJet 500 printer was modified to allow for cell printing.^{3, 5, 8} The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The cell suspension was pipetted into the ink cartridge and lines of cells were printed onto glass microscope cover slips. The live cells were imaged using fluorescence microscopy and actin was found throughout the cytoplasm. Incorporation of fluorescent actin into the cell allows for imaging of short-time cytoskeletal dynamics and is useful for a wide range of applications.^13-15     

A disposable polymer sensor chip combined with micro-fluidics and surface plasmon read-out

This paper describes a new type of disposable polymeric sensor chip based on the grating coupling of surface plasmon modes combined with a micro-fluidic channel system. A specifically designed silicon stamp with nano-structure (grating) on the micro-structures (micro-channel) was fabricated by combining a holographic method and photolithography. By using such a stamp the micro-channels, the grating coupler and the gold which was first thermally evaporated onto the stamp were transferred to the polymeric substrate successfully in one step. It is demonstrated that the grating profile in the micro-channels allowed a very efficient coupling of the laser light to the surface plasmons propagating at the bottom of the micro-channels. The transferred gold exhibits properties of a freshly cleaned surface, and the self-assembly of a functional thiol derivative (mercapto-PEG) onto the sensor chip can be monitored by surface plasmon spectroscopy. The results obtained in this sensor chip show no difference from those obtained on a regular grating-coupled SPR sensor chip.