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Circulating tumor cell (CTC) clusters play a more critical role in cancer metastasis than single CTCs. The study of CTC clusters might therefore provide more biologically meaningful information for a clear understanding of cancer metastasis. To achieve this goal, the isolation of high-purity, and integral CTC clusters from the blood samples of cancer patients is required. We herein propose to integrate optically-induced-dielectrophoresis (ODEP)-based cell manipulation with a microfluidic system for isolating cancer cell clusters based on their size characteristics. In this work, a two-step ODEP-based cell manipulation was designed. A dynamic square light image array was designed for the preliminary isolation of cancer cell clusters, followed by the utilization of another ODEP-based cell manipulation to refine the purity of the cancer cell clusters harvested in the first step. In this study, the optimal ODEP operating conditions for cell isolation process were experimentally determined. Moreover, the performance of cell isolation was experimentally evaluated for the isolation of CTC clusters with a cell purity and recovery rate of 91.5 ± 5.6%, and 70.5 ± 5.2%, respectively, without compromising the integrity of cancer cell clusters. Overall, this study presents a method and device capable of isolating high-purity and integral cancer cell clusters.

High purity isolation of circulating tumor cells (CTCs) is important for their subsequent gene-related analysis. Nevertheless, the conventional CTC isolation schemes might not be able to avoid the contamination of leukocytes in a treated sample. To address this issue, we proposed to integrate the technique of optically induced dielectrophoresis (ODEP)-based cell manipulation, and flow velocity control in a microfluidic system for further isolating CTCs after a conventional CTC isolation process. The working principle was based on the cell size difference between the CTCs and leukocytes. In the ODEP microfluidic system, a four-cascade cell isolation using four optical light-based virtual cell filters was designed. Based on this, four different selection conditions were simultaneously implemented for a higher-resolution cell separation, and thus higher-purity cell isolation. In this work, the ODEP microfluidic system was designed and fabricated. Moreover, the optimal ODEP operating conditions such as light bar width (40 μm), gap (80 μm), and number (4), as well as the sample flow rate (0.4 μl min −1 ) were experimentally determined. Results revealed the presented method was able to isolate cancer cells with cell purity as high as 94.9 ± 0.3% (cancer cell recovery rate: 54 ± 7%). Overall, this study has presented an ODEP microfluidic system capable of refining CTC purity after a conventional CTC isolation process.

Isolation of high-purity, label-free, and viable circulating tumour cells (CTCs) from cancer patients is crucial for subsequent analyses. To address this issue, a two-step CTC isolation scheme was proposed, wherein a spheroid cell culture was used to further purify viable CTCs after conventional negative selection-based CTC isolation methods. Our results from a cancer cell line model revealed that the survival of leukocytes in spheroid cell cultures was significantly decreased with time, whereas OECM-1 cells maintained viability and proliferated. Therefore, such a cell culture operation was expected to increase cancer cell purity in the cell spheroids. This assumption was confirmed by our results, which showed that cancer cell purities were 10.6 to 80.3-fold increased after spheroid cell culture for 8 days. In the following clinical tests, CTC-related cells were observed in 6 of 13 blood samples. Furthermore, the average purity of CTC-related cells was 34.8 ± 14.0%. By utilizing a second-step spheroid cell culture operation, the purity of CTC-related cells was greatly improved when compared with that (less than 10%) achievable by conventional negative selection-based CTC isolation. Overall, this study proposed a two-step process for the isolation of high-purity, label-free, and viable CTCs.