Chip-on-foil devices for DNA analysis based on inkjet-printed silver electrodes.

For a rapid on-site diagnosis of pathogens, low-cost chip-based devices are of great interest. Here, we report the successful fabrication of inkjet printed silver electrodes on polymer foils as disposable chips for molecular DNA analytics. In order to manufacture these electrode structures, silver nanoparticle inks were inkjet printed onto planar polypropylene substrates. Due to the low thermal stability of the foils, substrate preserving sintering techniques, including low temperature thermal sintering and low pressure argon plasma sintering, were implemented. Thus, sufficient electrical conductance of the printed structures at processing temperatures ≤100 °C was achieved. To test the applicability of the manufactured chips, specific capture DNA was immobilized within the gaps of the conductive electrode paths and hybridized in the next step with biotin-labeled target DNA. Subsequently, an enzymatically generated silver nanoparticle deposition was induced that bridges the electrode gap. This enabled both conductance measurement and gray value analysis as a fast, simple and robust electrical and optical read-out system. The proof-of-principle experiments successfully demonstrated the applicability of these convenient chip-on-foil devices for nucleic acid based pathogen detection.

Combinatorial screening of inkjet printed ternary blends for organic photovoltaics: absorption behavior and morphology.

Inkjet printing was used for the preparation of ternary polymer/polymer/fullerene layers for organic solar cell application, as part of a combinatorial setup for the preparation and characterization of thin-film libraries. Poly(phenylene-ethynylene)-alt-poly(phenylene-vinylene) (PPE-alt-PPV) and poly(diketopyrrolopyrrole-alt-fluorene) (P(DPP-alt-F)) were systematically blended with poly(3-octylthiophene) (P3OT) and investigated by UV-vis spectroscopy to improve the photon harvesting by extending the absorption range. The blends with the broadest absorption range (20 and 40 wt % of PPE-alt-PPV and P(DPP-alt-F), respectively) were mixed with mono(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C61 (PCBM). The blend with the low band gap polymer P(DPP-alt-F) revealed the most extended absorption, which ranges over the whole visible spectrum (350 to 750 nm). The mixing with PCBM (ratio 1/3) led to an optimal emission quenching and revealed a smooth film formation. In this contribution, we show that the combinatorial screening using inkjet printing represents an effective, time- and material-saving workflow for the investigation of polymer blend libraries, which is of high interest for the development of new materials for active layers in organic photovoltaics.

Plasma and microwave flash sintering of a tailored silver nanoparticle ink, yielding 60% bulk conductivity on cost-effective polymer foils.

A combination of plasma and microwave flash sintering is used to sinter an inkjet-printed and tailored silver nanoparticle formulation. By using two sintering techniques sequentially, the obtained conductivity is 60%, while keeping the processing temperature well below the glass transition temperature (T(g)) of the used polymer substrate. This approach leads to highly conductive features on cost-effective polymer substrates in relatively short times, which are compatible with roll-to-roll (R2R) production. An electroluminescence device is prepared as an example.

Inkjet Printing of zinc(II) bis-2,2':6',2"-terpyridine metallopolymers: printability and film-forming studies by a combinatorial thin-film library approach.

For the first time, thin-film libraries of zinc(II) bis-2,2':6',2"-terpyridine metallopolymers are prepared by inkjet printing to study structure-property relationships and their possible usage for organic photovoltaic (OPV) or polymer light-emitting diode (PLED) applications. By using a combinatorial approach, various important parameters, including solvent system, dot spacing, and substrate temperature, as well as UV-vis absorption and emission properties, are screened in a materials efficient and reproducible manner. Homogeneous films with a thickness of 150 -200 nm were obtained when printed at 40 -50 °C and from a solvent mixture of N,N-dimethylformamide and acetophenone in a ratio of 90/10. In applications such as OPV and PLEDs the control over film thickness and homogeneity are central to obtain good device properties.

Organ weaving: woven threads and sheets as a step towards a new strategy for artificial organ development.

The concept of "organ weaving" is presented, a fabrication technique that can be an attractive option for the development of artificial tissues and organs. "Living threads" are created by immersing threads that are soaked in a CaCl(2) solution into a sodium-alginate-loaded cell suspension bath, encapsulating the cells and creating a bio-friendly, easily manageable starting material for building up larger scaffold structures. Such living threads have the advantage of being a particularly mild culturing medium for mammalian cells, protecting the cells during subsequent processing steps from dehydration and other rapid changes in the chemistry of the surrounding environment. Connecting different types of threads into 3D objects gives unique opportunities to address tissue engineering challenges.

Combinatorial optimization of multiple MALDI matrices on a single tissue sample using inkjet printing.

Taking advantage of the drop-on-demand capabilities of inkjet printing, the first example of a single tissue being used as a substrate for preparing combinatorial arrays of different matrix-assisted laser desorption/ionization (MALDI) matrices in multiple concentrations on a single chip is reported. By varying the number of droplets per spot that were printed, a gradient array of different amounts of matrix material could be printed on a single chip, while the selection of matrices could be adjusted by switching different matrix materials. The result was a two-dimensional array of multiple matrices on a single tissue slice, which could be analyzed microscopically and by MALDI to elucidate which combination of matrix and printing conditions offered the best resolution in terms of spot-to-spot distance and signal-to-noise ratios for proteins in the recorded MS spectra. This combinatorial approach enables the efficient optimization of possible matrices in an organized, side-by-side array format, which can particularly be useful for the detection of specific protein markers.

A practical approach to the development of inkjet printable functional ionogels-bendable, foldable, transparent, and conductive electrode materials.

Ionic liquid gels, or ionogels, are semi-conductive, flexible materials, offering a host of tunable physical properties, gaining an increasing level of scientific interest. One of the challenges of this emerging category of materials is that the structure-process-property relationships are still empirically driven. In this study, a simple, practical approach is laid out to prepare standardized libraries of these materials, for the purpose of selecting transparent, flexible conductive formulations that can be dispensed using inkjet printing. The net result of this was the optimization of a PEG-DMA ionogel formulation exhibiting an optical transparency that was greater than 94% from near-UV to near-IR from a 150 µm thick films, and a resistivity of 12.4 Ω · m.

One-step inkjet printing of conductive silver tracks on polymer substrates.

A one-step process to fabricate conductive features on flexible polymer substrates by inkjet printing an organometallic silver ink directly onto a substrate that is heated to 130 degrees C is presented. This process led to the immediate sintering of the printed features. The samples were left for 5 min at elevated temperature, which resulted in conductive silver features with a resistivity of eight times the bulk silver value. The combination of this ink and the simultaneous printing/sintering process opens up routes for the direct fabrication of conductive features on common polymer substrates that could be applied, for example, in roll-to-roll production of flexible microelectronic systems.

The preferential deposition of micro-particles at the boundary of inkjet printed droplets.

The deposition behaviour of uniformly sized silica particles in drying aqueous droplets has been investigated for a range of particle sizes, 0.33, 1, 3 and 5 µm, in order to gain an improved understanding of the coffee drop effect. The droplets were produced by inkjet printing, which allowed multiple droplets of similar volume to be studied. Our observations show that particle size and the contact angle formed by the solvent droplet with the substrate determine how close to the boundary a particle is deposited. After drying, it was found that if the contact angle was less than 90°, smaller particles were located closer to the original droplet's periphery than larger particles in similar sized droplets. This deposition of particles can be explained by the wedge shape of the drying droplet's edge, which physically limits the movement of particles towards the droplet's periphery. In this paper we show that the size of a suspended particle influences the final dried morphology of a printed feature.

Inkjet printing of polyurethane colloidal suspensions.

An aqueous 40 wt% dispersion of polyurethane has been successfully printed at room temperature using a piezoelectric inkjet printer. Simple layered structures, as well as dots, were made and subsequently analyzed using white-light interferometry. A single layer was found to have a structure height of 10 µm; a value that suggests that this polyurethane dispersion may be suitable for use in rapid prototyping, since tall structures can be rapidly produced using only a few printing passes. Finally, by the simple addition of a water-soluble dye, colour gradients were produced using this printing technique.