Portable platform for leukocyte extraction from blood using sheath-free microfluidic DLD.

Leukocyte count is routinely performed for diagnostic purposes and is rapidly emerging as a significant biomarker for a wide array of diseases. Additionally, leukocytes have demonstrated considerable promise in novel cell-based immunotherapies. However, the direct retrieval of leukocytes from whole blood is a significant challenge due to their low abundance compared to erythrocytes. Here, we introduce a microfluidic-based platform that isolates and recovers leukocytes from diluted whole blood in a single step. Our platform utilizes a novel, sheathless method to initially sediment and focus blood cells into a dense stream while flowing through a tubing before entering the microfluidic device. A hexagonal-shaped structure, patterned at the device's inlet, directs all the blood cells against the channel's outer walls. The focused cells are then separated based on their size using the deterministic lateral displacement (DLD) microfluidic technique. We evaluated various parameters that could influence leukocyte separation, including different focusing structures (assessed both computationally and experimentally), the orientation of the tubing-chip interface, the effects of blood sample hematocrit (dilution), and flow rate. Our device demonstrated the ability to isolate leukocytes from diluted blood with a separation efficiency of 100%, a recovery rate of 76%, and a purity of 80%, while maintaining a cell viability of 98%. The device operates for over 30 min at a flow rate of 2 µL min-1. Furthermore, we developed a handheld pressure controller to drive fluid flow, enhancing the operability of our platform outside of central laboratories and enabling near-patient testing. Our platform can be integrated with downstream cell-based assays and analytical methods that require high leukocyte purity (80%), ranging from cell counting to diagnostics and cell culture applications.

Secretion Function Analysis of Ex Vivo Immune Cells in an Integrated Microfluidic Device.

Immune cells play a major role in the development of cancer, from being able to inhibit it by secreting pro-inflammatory mediators, to assist in its development by secreting growth factors, immunosuppressive mediators, and ECM-modifying enzymes. Therefore, the ex vivo analysis of the secretion function of immune cells can be employed as a reliable prognostic biomarker in cancer. However, one limiting factor in current approaches to probe the ex vivo secretion function of cells is their low throughput and the consumption of large quantities of sample. Microfluidics provides a unique advantage, by being able to integrate different components, such as cell culture and biosensors in a monolithic microdevice; it can increase the analytical throughput and leverage it with its intrinsic low sample requirement. Furthermore, the integration of fluid control elements also allows this analysis to be highly automatable, leading to increases in consistency in the results. Here, we describe an approach to analyze the ex vivo secretion function of immune cells using a highly integrated microfluidic device.

On-Chip Analysis of Protein Secretion from Single Cells Using Microbead Biosensors.

The profiling of the effector functions of single immune cells─including cytokine secretion─can lead to a deeper understanding of how the immune system operates and to potential diagnostics and therapeutical applications. Here, we report a microfluidic device that pairs single cells and antibody-functionalized microbeads in hydrodynamic traps to quantitate cytokine secretion. The device contains 1008 microchambers, each with a volume of ∼500 pL, divided into six different sections individually addressed to deliver an equal number of chemical stimuli. Integrating microvalves allowed us to isolate cell/bead pairs, preventing cross-contamination with factors secreted by adjacent cells. We implemented a fluorescence sandwich immunoassay on the biosensing microbeads with a limit of detection of 9 pg/mL and were able to detect interleukin-8 (IL-8) secreted by single blood-derived human monocytes in response to different concentrations of LPS. Finally, our platform allowed us to observe a significant decrease in the number of IL-8-secreting monocytes when paracrine signaling becomes disrupted. Overall, our platform could have a variety of applications for which the analysis of cellular function heterogeneity is necessary, such as cancer research, antibody discovery, or rare cell screening.

Microfluidic systems for the analysis of blood-derived molecular biomarkers.

Biomarkers are relevant indicators of the physiological state of an individual. Although biomarkers can be found in diseased tissue and different biofluids, sampling from blood plasma is relatively easy and less invasive. Among the molecular biomarkers that can be found circulating in plasma are proteins, metabolites, nucleic acids, and exosomes. Some of these plasma-circulating biomarkers are now employed for patient stratification in a broad range of diseases with high sensitivity and specificity and are useful in early diagnosis, initial risk assessment, and therapy selection. However, there is a pressing need to develop novel approaches for biomarker analysis that can be translated into clinical or other settings without complex methodologies or instrumentation. Microfluidics has been touted as a promising technology to carry out this task because it offers high-throughput, automation, multiplexed detection, and portability, possibly overcoming the bottleneck that prevent the translation of novel biomarkers to the point-of-care (POC). Here, we provide a review of the microfluidic systems that have been engineered to detect circulating molecular biomarkers in blood plasma. We also review the different microfluidic approaches for plasma enrichment, which are now being integrated with microfluidic-based biomarker analyzers. Such integration should lead to cost-effective solutions in in vitro diagnostics, with special relevance to POC platforms.

A high-throughput multiplexed microfluidic device for COVID-19 serology assays.

The applications of serology tests to the virus SARS-CoV-2 are diverse, ranging from diagnosing COVID-19, understanding the humoral response to this disease, and estimating its prevalence in a population, to modeling the course of the pandemic. COVID-19 serology assays will significantly benefit from sensitive and reliable technologies that can process dozens of samples in parallel, thus reducing costs and time; however, they will also benefit from biosensors that can assess antibody reactivities to multiple SARS-CoV-2 antigens. Here, we report a high-throughput microfluidic device that can assess antibody reactivities against four SARS-CoV-2 antigens from up to 50 serum samples in parallel. This semi-automatic platform measures IgG and IgM levels against four SARS-CoV-2 proteins: the spike protein (S), the S1 subunit (S1), the receptor-binding domain (RBD), and the nucleocapsid (N). After assay optimization, we evaluated sera from infected individuals with COVID-19 and a cohort of archival samples from 2018. The assay achieved a sensitivity of 95% and a specificity of 91%. Nonetheless, both parameters increased to 100% when evaluating sera from individuals in the third week after symptom onset. To further assess our platform's utility, we monitored the antibody titers from 5 COVID-19 patients over a time course of several weeks. Our platform can aid in global efforts to control and understand COVID-19.

Integrated Microfluidic Device for Functional Secretory Immunophenotyping of Immune Cells.

Integrated platforms for automatic assessment of cellular functional secretory immunophenotyping could have a widespread use in the diagnosis, real-time monitoring, and therapy evaluation of several pathologies. We present a microfluidic platform with integrated biosensors and culture chambers to measure cytokine secretion from a consistent and uniform number of immune cells. The biosensor relies on a fluorescence sandwich immunoassay enabled by the mechanically induced trapping of molecular interactions method. The platform contains 32 cell culture chambers, each patterned with an array of 492 microwells, to capture and analyze both adherent and nonadherent immune cells. Multiple stimuli can be delivered to a set of culture chambers. Per chamber, we were able to capture consistently 1113 ± 191 of blood-derived monocytes and neutrophils and 348 ± 37 THP-1 monocytes. Good occupancy efficiencies of ∼70% with a uniformity of ∼90% across all of the culture chambers of the device were achieved. Furthermore, we demonstrate that up to 96% of cells remain viable for the first 48 h. The employment of epoxy-modified glass substrates and active mixing enhanced the biosensing performance compared to the use of bare glass and simple diffusion. Finally, we performed functional secretory analysis of interleukin-8 and tumor necrosis factor alpha from human neutrophils and monocytes, stimulated with various doses of lipopolysaccharide and phorbol 12-myristate 13-acetate-ionomycin, respectively. We foresee the employment of our microfluidic platform in the diagnosis of different pathologies where alterations in cytokine secretion patterns can be used as biomarkers.

Massive Parallel Analysis of Single Cells in an Integrated Microfluidic Platform.

New tools that facilitate the study of cell-to-cell variability could help uncover novel cellular regulation mechanisms. We present an integrated microfluidic platform to analyze a large number of single cells in parallel. To isolate and analyze thousands of individual cells in multiplexed conditions, our platform incorporates arrays of microwells (7 pL each) in a multilayered microfluidic device. The device allows the simultaneous loading of cells into 16 separate chambers, each containing 4640 microwells, for a total of 74 240 wells per device. We characterized different parameters important for the operation of the microfluidic device including flow rate, solution exchange rate in a microchamber, shear stress, and time to fill up a single microwell with molecules of different molecular weight. In general, after ∼7.5 min of cell loading our device has an 80% microwell occupancy with 1-4 cells, of which 36% of wells contained a single cell. To test the functionality of our device, we carried out a cell viability assay with adherent and nonadherent cells. We also studied the production of neutrophil extracellular traps (NETs) from single neutrophils isolated from peripheral blood, observing the existence of temporal heterogeneity in NETs production, perhaps having implications in the type of the neutrophil response to an infection or inflammation. We foresee our platform will have a variety of applications in drug discovery and cellular biology by facilitating the characterization of phenotypic differences in a monoclonal cell population.