In this study, the use of flexographic printing was investigated for low cost, high volume production of devices incorporating nanowires through the printing of zinc acetate precursors on a substrate used to form zinc oxide (ZnO) seeds for the growth of nanowires using a hydrothermal growth technique. The printing of precursors allows the selective area growth of ZnO nanowires, which has implications in high-yield production of devices incorporating ZnO nanowires. The work presented here achieved printed line widths of <60 μm with low edge distortion (<3 μm) using a printing plate with a line width of 50 μm. The hydrothermally grown ZnO nanowires show uniform density of growth over the printed area with nanowire diameters between 40 and 60 nm on both silicon and polyimide substrates. Energy-dispersive x-ray spectra showed contamination-free crystals with a 1:1 (zinc to oxygen) stoichiometry. Crystal orientation is along the c-axis with high quality crystalline structure shown using x-ray diffraction spectroscopy and high resolution transmission electron microscopy. A ZnO nanowire gas sensor, fabricated using the flexographic printing technique, is demonstrated. Such a printing-assisted fabrication offers low cost, high volume production of devices incorporating ZnO nanowires, ranging from gas sensors to field emission devices.

In this paper, we have presented the use of flexographic printing techniques in the selective patterning of gold nanoparticles (AuNPs) onto a substrate. Highly uniform coverage of AuNPs was selectively patterned on the substrate surface, which was subsequently used in the development of a glucose sensor. These AuNPs provide a biocompatible site for the attachment of enzymes and offer high sensitivity in the detection of glucose due to their large surface to volume ratio. The average size of the printed AuNPs is less than 60 nm. Glucose sensing tests were performed using printed carbon-AuNP electrodes functionalized with glucose oxidase (GOx). The results showed a high sensitivity of 5.52 μA mM−1 cm−2 with a detection limit of 26 μM. We have demonstrated the fabrication of AuNP-based biosensors using flexographic printing, which is ideal for low-cost, high-volume production of the devices.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0835-1) contains supplementary material, which is available to authorized users.

A three electrode electrochemical enzymatic biosensor consisting of ZnO nanowires was successfully fabricated using flexographic printing technique. The incorporation of ZnO nanowires at the working electrode provides advantages such as simple functionalization and high surface area for enhanced sensitivity. The flexographic printing technique allows ultra-high throughput and low cost mass production of devices due to the roll-to-roll nature of the technique. Therefore, the techniques developed here are prudent to the development of technologies capable of meeting the vast market demand for biosensing. Carbon electrodes, silver/silver chloride reference electrodes and ZnO seed layer precursors were directly printed onto a flexible plastic substrate through flexographic printing. The printing process was optimised to allow a suitable seed layer to be formed on the porous printed-carbon electrode to allow selective growth of ZnO nanowires using a hydrothermal growth method. The ZnO nanowires were subsequently functionalised with glucose oxidase, which was used in this work to form a glucose sensor as an exemplary use of the device. The fabricated nanowire electrochemical biosensing devices showed a typical sensitivity of 1.2 ± 0.2 µA mM-1 cm-2 with a linear response to the addition of glucose over a concentration range of 0.1 mM to 3.6 mM.

In this work, the formation of a nanotextured surface is reported on flexographic printed zinc oxide thin films which provide an excellent platform for low-cost, highly sensitive biosensing applications. The ability to produce nanotextured surfaces using a high-throughput, roll-to-roll production method directly from precursor ink without any complicated processes is commercially attractive for biosensors that are suitable for large-scale screening of diseases at low cost. The zinc oxide thin film was formed by printing a zinc acetate precursor ink solution and annealing at 300 °C. An intricate nanotexturing of the film surface was achieved through 150 °C drying process between multiple prints. These surface nanostructures were found to be in the range of 100 to 700 nm in length with a width of 58 ± 18 nm and a height of between 20 and 60 nm. Such structures significantly increase the surface area to volume ratio of the biosensing material, which is essential to high sensitivity detection of diseases. Nonfaradaic electrochemical impedance spectroscopy measurements were carried out to detect the pp65-antigen of the human cytomegalovirus using the printed device, which has a low limit of detection of 5 pg/mL.

In this study, a uniformly mixed sensing layer of typically immiscible compounds, such as tetrathiafulvalene (TTF) mediator and glucose oxidase (GOx) enzyme, was developed using a simultaneous spray deposition technique ideal for mass production of glucose sensors at low cost while exhibiting enhanced amperometric response. For comparison, the sensors were fabricated via three different methods: conventional drop-cast of TTF and GOx compounds in subsequent layers (DL), spray deposition of the compounds in subsequent layers (SL), and spray mixing of the compounds as one uniform layer (SM). Uniformity of the sensing layers was investigated via Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) techniques demonstrating an even distribution of the TTF and GOx throughout the sensing layer for the SM sensors. The amperometric studies showed a significantly larger maximum current response, I and sensitivity for the SM sensors as compared to the SL and DL sensors. The significantly better performance of the SM sensors correlated well with the even distribution of TTF and GOx throughout the sensing layer, resulting in enhanced electron transfer and redox reaction between GOx and TTF. The SM spray technique was then applied to deposit a uniformly mixed sensing layer on to 3D microneedle arrays to provide minimally invasive continuous glucose monitoring (CGM). In-vivo studies showed amperometric response from the microneedle CGM device was compatible to changes in blood glucose levels measured via the standard finger prick tests. Importantly, the deposition technique is suitable for mass production of the microneedle CGM at very low cost.