Development of a Microfluidic Impedance Flow Cytometer

Leukocyte differentiation and counting are critical for clinical diagnostics but are hindered by the low throughput and labor-intensive nature of traditional microscopy and the limitations of physical constriction microchannels in flow cytometry. A recent study in the journal of Microsystems and Nanoengineering introduces a microfluidic chip serving as an impedance flow cytometer with a virtual constriction microchannel. This system uses a novel approach by creating a virtual constriction through the controlled crossflow of conductive and insulated fluids, allowing for cell focusing without physical channel constriction, thereby avoiding the common issues of clogging and wear.

“In this study, a microfluidic impedance flow cytometer based on a virtual constriction microchannel was reported, in which the virtual constriction microchannel was constructed by crossflow of conductive sample and insulated sheath fluids with underneath micro-electrodes for impedance measurements. Compared to conventional mechanical constriction microchannels, this virtual counterpart could effectively avoid direct physical contact between cells and the microchannel walls to maintain high throughputs, and significantly reduce the volume of the impedance detection region for sensitivity improvements.“, the authors explained.

The chip was fabricated using conventional standard soft lithography techniques for microfluidics fabrication. It features a layer of PDMS molded from a photolithographically patterned SU-8 master and an electrode layer made by depositing chromium/gold onto a glass substrate. The layers were bonded together after a plasma treatment. This design creates a virtual constriction by manipulating the crossflow of conductive sample and insulated sheath fluids, focusing the cells and electric fields without physical contact between the cells and microchannel walls.

Experiments were conducted on the microfluidic device using leukemia cell lines and leukocytes from healthy donors, which were encapsulated in a conductive PBS solution. The sheath fluid was an insulating sucrose solution, ensuring the cells remained viable and well-focused in the detection zone. Cells passed through the virtual constriction microchannel where impedance measurements were taken by electrodes positioned underneath the microchannel. These measurements captured detailed electrical properties of the cells influenced by their biophysical characteristics.

The virtual constriction microchannel significantly enhanced detection sensitivities and throughputs. Leukemia cell lines (K562, Jurkat, HL-60) and leukocyte subpopulations (neutrophils, eosinophils, monocytes, lymphocytes) were analyzed with high accuracy. The study achieved differentiation accuracies exceeding 99%, utilizing a deep learning model to classify the impedance profiles. This model was robust across various white blood cell types, showing minimal variance and high reliability in cell classification.

The development of a microfluidic impedance flow cytometer with a virtual constriction microchannel represents a significant advancement in the field of leukocyte analysis. This technology eliminates the drawbacks associated with physical constrictions, offering a high-throughput, highly accurate method for clinical diagnostics. The enhanced sensitivity and specificity facilitated by the virtual constriction design allow for more detailed and reliable blood analysis, potentially transforming routine clinical practices by providing rapid and accurate results with reduced sample preparation and maintenance requirements.

Figures are reproduced from Wang, M., Zhang, J., Chen, X. et al. Microfluidic impedance flow cytometer leveraging virtual constriction microchannel and its application in leukocyte differential. Microsyst Nanoeng 10, 192 (2024). https://doi.org/10.1038/s41378-024-00833-y under a CC BY 4.0 Attribution 4.0 International license.

Read the original article: Microfluidic impedance flow cytometer leveraging virtual constriction microchannel and its application in leukocyte differential

For more insights into the world of microfluidics and its burgeoning applications in biomedical research, stay tuned to our blog and explore the limitless possibilities that this technology unfolds. If you need high quality microfluidics chip for your experiments, do not hesitate to contact us.