Abstract
Inkjet technology as a maskless, direct-writing technology offers the potential for structured deposition of functional materials for the realization of electrodes for, e.g., sensing applications. In this work, electrodes were realized by inkjet-printing of commercial nanoparticle gold ink on planar substrates and, for the first time, onto the 2.5D surfaces of a 0.5 mm-deep microfluidic chamber produced in cyclic olefin copolymer (COC). The challenges of a poor wetting behavior and a low process temperature of the COC used were solved by a pretreatment with oxygen plasma and the combination of thermal (130 °C for 1 h) and photonic (955 mJ/cm²) steps for sintering. By performing the photonic curing, the resistance could be reduced by about 50% to 22.7 µΩ cm. The printed gold structures were mechanically stable (optimal cross-cut value) and porous (roughness factors between 8.6 and 24.4 for 3 and 9 inkjet-printed layers, respectively). Thiolated DNA probes were immobilized throughout the porous structure without the necessity of a surface activation step. Hybridization of labeled DNA probes resulted in specific signals comparable to signals on commercial screen-printed electrodes and could be reproduced after regeneration. The process described may facilitate the integration of electrodes in 2.5D lab-on-a-chip systems.
Highlights
The introduction of electrodes in lab-on-a-chip cartridges enables various important electrokinetic unit-operations [1] and allows the integration of important electrochemical biosensing methods, which in turn can benefit from the miniaturization, automation, and increased throughput possibilities of microfluidics [2]
We demonstrate for the first time the production of highly conductive, ready-to-use gold electrodes by inkjet-printing of a commercialized nanoparticle gold ink on cyclic olefin copolymer (COC), a typical substrate material for lab-on-a-chip applications thanks to its good chemical resistance, low water absorption and compatibility with biological samples [18]
The results of the cross cut tests have shown a strong influence of the plasma power of 40 W for 20 s and a sintering temperature of 130 ◦ C for 1 h with a subsequent photonic curing
Summary
The introduction of electrodes in lab-on-a-chip cartridges enables various important electrokinetic unit-operations [1] and allows the integration of important electrochemical biosensing methods, which in turn can benefit from the miniaturization, automation, and increased throughput possibilities of microfluidics [2]. The electrodes are commonly produced by screen-printing, etching of printed circuit boards (PCB) or by cleanroom processes like metal evaporation and sputtering [3], often on planar substrates that need to be bonded afterwards to the fluidic layer [2]. The digital technology of inkjet-printing is an interesting alternative, as it enables the deposition of functional materials like metal-based nanoparticle inks on a large variety of substrate materials with a high resolution of the printed structures [4,5]. By using nanoparticle gold inks, the melting point typically can be lowered to 150 ◦ C and below [14,15] This allows the fabrication of conductive gold structures on polymer substrates with a relatively low glass-transition temperature, but high resistances [16] or a required post-production activation step [17] demonstrate that challenges still remain
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