Search

Electric fields can be effectively used to sense, manipulate, and move particles in lab-on-a-chip devices. Nevertheless, the throughput of such devices is a critical issue, which can be effectively improved by increasing the height of the microchannels. For this purpose, vertical electrodes are needed in order to apply electrical stimuli homogeneously over the full height of the channel. In this paper, we propose different fabrication processes based on a conformal coating of 3-D SU-8 structures with metal layers, defining vertical electrodes in microfluidic channels with high aspect ratio and uniform coating of the vertical sidewalls. We describe two different strategies to achieve the patterning of connection lines inside the gaps of the pillar electrodes—one based on liftoff and the other based on dry film resist. We show how the liftoff approach allows for high connection densities and high resolution of the patterning inside the 3-D electrode arrays. Moreover, we highlight how the dry film process provides an efficient and low-cost alternative when neither high-density patterning nor high resolution is needed. Standard resistive and impedance measurements show high conductivity of the structures whose fabrication process grants standard photolithographic resolution in the definition of the electrode features. [2016-0002]

This paper reports a method for label‐free single‐cell biophysical analysis of multiple cells trapped in suspension by electrokinetic forces. Tri‐dimensional pillar electrodes arranged along the width of a microfluidic chamber define actuators for single cell trapping and selective release by electrokinetic force. Moreover, a rotation can be induced on the cell in combination with a negative DEP force to retain the cell against the flow. The measurement of the rotation speed of the cell as a function of the electric field frequency define an electrorotation spectrum that allows to study the dielectric properties of the cell. The system presented here shows for the first time the simultaneous electrorotation analysis of multiple single cells in separate micro cages that can be selectively addressed to trap and/or release the cells. Chips with 39 micro‐actuators of different interelectrode distance were fabricated to study cells with different sizes. The extracted dielectric properties of Henrietta Lacks, human embryonic kidney 293, and human immortalized T lymphocytes cells were found in agreements with previous findings. Moreover, the membrane capacitance of M17 neuroblastoma cells was investigated and found to fall in in the range of 7.49 ± 0.39 mF/m2.

This paper presents a fabrication process for arrays of high-aspect-ratio micropillar electrodes, which are freestanding 3D structures that feature metal sidewalls connected to passivated planar wires. Facing vertical electrodes are considered to be a key solution in microdevice technologies, as they are able to improve the efficiency and accuracy of electrical methods by generating homogeneous electric fields along the height of microfluidic channels. Despite the acknowledged advantages of using vertical micro-electrodes, current microfabrication technologies do not allow the manufacture of such structures with the same resolution and versatility as planar electrodes. The present study focused on the fabrication of round and square-shaped silicon pillar arrays exposing metal on their sidewalls, which is decoupled from the substrate by means of a passivation layer. The pillars range in width from 10 mu m to 70 mu m, with gaps down to 10 mu m and a maximum aspect ratio of 5:1. Metal deposition and patterning were revealed to be the critical steps of the process. Deposition was achieved by sputtering, while patterning was performed by photolithography, and the photoresist was applied by spray-coating. The pattern was then transferred into the metal layer by means of dry etching. This new process can be adapted to any metal that is suitable for depositing by sputtering and patterning by dry etching. The presence of the metal layer on the vertical sidewalls was confirmed by SEM imaging combined with EDX analysis. The arrays were then characterized by electrical conductivity measurements and impedance spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.

A review is presented of advances and challenges in fully integrated systems for personalised medicine applications. One key issue for the commercialisation of such systems is the disposability of the assay-substrate at a low cost. This work adds a new dimension to the integrated circuits technology for lab-on-a-chip systems by employing 3D integration for improved performance and functionality. It is proposed that a disposable biosensing layer can be aligned and temporarily attached to the 3D CMOS stack by the vertical interconnections, and can be replaced after each measurement.