Microfluidic Chip development for acoustophoresis assisted selective cell sorting

Abstract: Analysis of blood samples is one of the major steps in diagnosing pathological conditions like cancer. The upstream sample preparation for the pathological cell analysis from complex biological fluid like blood, involves selective cell sorting. It can be achieved using fluorescently activated or magnetically activated cell sorters. Another way is to sort them using acoustophoresis which is cheaper, gives better spatial control and is also rapid apart from the fact that, it does not affect the cellular viability.6,9 In acoustophoresis, particles depending upon their density and compressibility relative to the suspended medium migrate to either pressure anti-nodes or nodes, when subjected to acoustic field. Poly vinyl alcohol-based microbubbles have a strong negative acoustic contrast factor and hence migrate to the anti-nodes in a standing ultrasonic wave. Previously, this property was utilized for cell separation by conjugating the bubbles to cells and subjecting them to ultrasonic waves in a silicon glass based microfluidic channel.55 A protocol for coating the microbubbles with avidin, so that these can readily attach to the cells has been developed in this work. However, microfluidic channel is obtained from a master mold which is developed in a clean room facility using photolithography. A cost-effective way has been developed for the production of a mold using a Computerized Numerical Control system (where the positive master for the microfluidic channel is drilled onto a PMMA sheet) for continuous separation of cancer cells. Alternate methods like a cutting plotter (which uses a double sided adhesive tape as a positive master) and a 3-D printer have been investigated, in order to be used as a mold for the microfluidic channel. As a proof, microbubbles-cell complex was focused in a PDMS based microfluidic channel, by utilizing standing Bulk acoustic waves. At flow rate of 10µl/min, efficiency greater than 80% has been achieved. This technique is low cost and can be implemented in places without a clean room facility for size independent cell sorting.