Microfluidics has found numerous applications ranging from the life sciences industries for pharmaceuticals and biomedicine (drug design, delivery and detection, diagnostic devices) to industrial applications of combinational synthesis (such as rapid analysis and high throughput screening). Among all these, one of the intriguing exploitation of microfluidics or micro total analysis systems (µTAS) is the separation of circulating tumor cells (CTCs) from body fluids. Cancer cells spread from the initial site of a tumor by first invading the surrounding tissue, then by entering the blood or lymph vessels, and finally by crossing the vessel wall to exit the vasculature into distal organs. The September 2006 issue of the Journal of the National Cancer Institute (NCI) states: "The war on cancer was declared 40 years ago and cancer is still here," and "Technologies that capture enemy CTCs for further interrogation might prove useful in the war on cancer." CTCs cannot only become a new marker for cancer prognosis, but their detection can also be a valid new parameter for diagnosing cancer early, for monitoring disease progression and relapse, and for optimizing therapy.

This research established a new method to manipulate rare cell types based on their electrical signatures using dielectrophoresis (DEP) without having direct contact between the electrodes and the sample, known as contactless dielectrophoresis (cDEP). DEP is the motion of a particle in a suspending medium due to its polarization in the presence of a non-uniform electric field. cDEP relies upon reservoirs filled with highly conductive fluid to act as electrodes and provide the necessary electric field. These reservoirs are placed adjacent to the main microfluidic channel and are separated from the sample by a thin barrier of a dielectric material as is shown in Figure 1h. The application of a high-frequency electric field to the electrode reservoirs causes their capacitive coupling to the main channel and an electric field is induced across the sample fluid. Similar to traditional DEP, cDEP exploits the varying geometry of the electrodes to create spatial non-uniformities in the electric field. However, by utilizing reservoirs filled with a highly conductive solution, rather than a separate thin film array, the electrode structures employed by cDEP can be fabricated in the same step as the rest of the device; hence the process is conducive to mass production.

We demonstrated the ability to isolate human leukemia cancer cells (THP-1) cells from a heterogeneous mixture of live and dead cells using cDEP with more than 99% selectivity and 95% removal efficiency. Through numerical and experimental investigations, new generation of cDEP devices have been designed and tested to detect and isolate THP-1 cells from spiked blood samples with high selectivity and cell capture efficiency. Our experimental observations, using prototype devices, indicate that breast cancer cell lines at their different stages (MCF-7, MCF-10, and MDA-MB231) have unique electrical. Furthermore, through collaborations at the Wake Forest Comprehensive Center, we demonstrated that prostate tumor initiating cells (TICs) exhibit unique electrical signatures and DEP responses and cDEP technology can be exploited to isolate and enrich TICs for further genetic pathways investigations.