High-throughput residual white blood cell counter enabled by microfluidic cell enrichment and reagent-containing patch integration

A residual white blood cell (rWBC) count is the remaining concentration of WBCs in leucodepleted blood products, and is an important quality-assurance parameter for blood transfusion. Current cell-counting methods rely on a small test volume that can result in the inherent statistical error involved in counting rWBCs present at low concentrations or manual sample preparation that increases experimental workload. To address these critical challenges, we present a microfluidic rWBC counter that (i) rapidly enriches rWBCs to reduce a sample volume to be examined and thus enable high-throughput cell counting, and (ii) integrates an on-chip cell staining module that contains reagent-containing hydrogel patches and allows the controlled release of a staining reagent. With these novel features, we demonstrated high-throughput rWBC counting by achieving reliable cell counting over a dynamic range of 0.1-26.8 rWBCs/mu L and processing a blood sample at a high throughput of 400 mu L per minute. In addition, we successfully performed sample preparation-free counting of rWBCs by integrating the on-chip staining module into the rWBC counter, offering sample-in-answer-out capability. On the basis of the results, the rWBC counter represents a promising tool for the quality control of WBC depletion and improvement in the safety of blood transfusion.