White Blood Cell Separation for On-Chip Detection of Myeloperoxidase Activity Using a Microfluidic Platform

White blood cells (WBCs) are crucial biomarkers for various chronic inflammatory diseases and need to be separated with a high purity for accurate disease diagnosis. WBC separation remains a challenging task due to abundant red blood cell (RBC) population affecting various bioassays. This letter emphasis on efficient WBC separation from diluted human blood using a microfluidic platform. Herein, we reported a simple spiral polydimethylsiloxane (PDMS)-based microfluidic device, comprises single inlet with multiple outlets to remove the highly abundant RBCs. The microdevice employs an inertial focusing technique for separating WBCs that can be subsequently utilized for on-chip myeloperoxidase (MPO) assay. The MPO enzyme is an inflammatory biomarker signifying oxidative stress and inflammatory status during disease progression. The microdevice can provide a WBC sample by eliminating 99.99% RBCs and subsequently decreasing the ratio of RBCs to WBCs from 850:1 to 3:1, which is sufficient for bioassays, such as MPO. Our simple spiral microfluidic device is easy to fabricate and simple to operate. The microdevice needs only a drop of unprocessed blood ($\sim\!5 \,\mu l$) acquired by the finger-prick technique for an MPO assay. This microfluidic system can potentially translate into numerous point-of-care applications that need a high-purity WBC sample.