Design and fabrication of a Ti/Al thin-film electrode in the meander-shaped microchannel and its application for promoting capillary-driven dielectrophoresis blood separation

In this article, a Ti/Al thin film with Ti as an adhesive layer that merits high conductivity, excellent adhesion and low cost is used as the electrode in a biomedical blood separation chip instead of the conventional biomedical electrode mostly made of expensive Au and/or Pt. The design and fabrication of the meander-shaped Ti/Al thin-film electrode are studied for the application to promote the capillary-driven dielectrophoresis (DEP) blood separation chip. The meandered electrode with a castellated profile of 0.6 and 0.2 mm spacing instead of the flat one is designed on the glass substrate to produce an asymmetric electric field for the DEP force to separate the blood. The meander-with-castellated electrode shape and gap affects the electric field gradient on the separation performance. The patterning of the electrode was performed by the low-cost CO₂ laser-ablated polymer tape rather than an expensive-complex photolithography process and then followed by sputtering together with lift-off process. The Ti/Al thin film is coated on the channel backside rather than inside for contactless DEP to avoid the contact pollution of the sample as well to reduce the operation voltage. The COMSOL Multiphysics^® simulation of the electric field and the blood separation test were done for verifying the design and experiment. In the simulation, the 0.2 mm castellated electrode can greatly enhance the asymmetric electric field peak of 24000 V m^-1 compared to the flat electrode of about 12000 V m^-1. Also, the 0.2 mm gap castellated electrode with three-time electric-field-gradient-pulse frequency can enhance the DEP force compared to the 0.6 mm gap electrode. In the experiment, the blood chip of 0.2 mm castellated electrode with the highly increased electric field and DEP force can shorten the starting separation time from 533 s to 253 s and enhance the separation efficiency from 20.0% to 51.7% at the applied voltage of 5 V and 1 MHz.