A novel side electrode configuration integrated in fused silica microsystems for synchronous optical and electrical spectroscopy

Abstract

We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and impedance measurements for both cell counting and characterization.

Vertical sidewall electrodes monolithically integrated into 3D glass microfluidic chips using water-assisted femtosecond-laser fabrication for in situ control of electrotaxis

“…The introduction of water into the laser ablation process greatly improves the removal of debris, leading to a higher quality of ablated micropatterns and enhancing the exibility and precision of the metal patterning for electroless plating as a result. 34 Although this method has an ability to place the side electrodes at any position on the glass microchip without blocking the optical visibility, multiple photolithographic processes are still required. Monolithic integration of sidewall electrodes into microuidic components provides a simple means of creating electrouidic glass chips, with which electrotaxis experiments on C. elegans were performed.…”

“…24 For example, electrical sorting of nematode Caenorhabditis elegans (C. elegans) from a mixed culture has been achieved by using local electric-eld traps in a microuidic device. [26][27][28][29][30][31][32][33][34][35] However, the fabrication of exible electrodes on sidewalls using the aforementioned techniques is in principle very challenging due to the difficulties to control the features of the electrode such as the electrode prole along the vertical/height direction in microuidic channels and the aspect ratio of sidewall electrode. Initially, conductive wires such as metal wires were inserted into the ends of microuidic channels.…”

“…25 For more efficient, exible, and sophisticated electro-tactic control which expands the potential of electrouidics and makes possible more in-depth biological investigation, the spatially-selective integration of microelectric components with designable structures into microuidic chips is necessary. [26][27][28][29]32,34 For those methods, precise alignment and nondestructive bonding of patterned electrodes in the microuidic devices is also not easy. However, this approach suffers from poor stability and low exibility in terms of the positioning of external electrodes and makes it difficult to spatially control the electric-eld distribution in closed microchannels, in particular, with complicated geometries.…”

Controllable alignment of elongated microorganisms in 3D microspace using electrofluidic devices manufactured by hybrid femtosecond laser microfabrication

“…Compared with conventional electrode fabrication methods, this technique provides a simpler scheme to reliably install electrodes with flexible configurations at any position in 3D microfluidic structures. In addition to the development of the 3D continuous control of the electro-orientation of cells and particles, we expect that this technique can be extended to the fabrication of different types of electrofluidic devices for 3D dielectrophoretic manipulation of biological samples [51][52][53] , 3D electrorotation in microscale spaces 54,55 , and electrical impedance sensors 56,57 . The incorporation of photonic components, such as optical waveguides, fibers, and microlenses 38 , into the fabricated electrofluidic devices using the same fs laser would significantly enhance the performance of biochips, paving the way to 3D 'all-in-one' lab-on-a-chip devices.…”

Electroporation in Microfluidic Devices

“…3. (continued) fused silica microchannel equipped with integrated electrodes placed at half height of the channel to provide an homogeneous electric field across the channel while allowing optical inspection of the cells during their exposure to the electric field (Reproduced from (Sukas et al 2014) with permission of The Royal Society of Chemistry). (c) Schematic drawing of the electroporation chip including hydrogel plugs that function as salt bridges to form an integrated electrode junction in the channel.…”