Durability of the bubble-jet sorter enables high performance bio sample isolation.

Sorting cells while maintaining their viability for further processing or analysis is an essential step in a variety of biological processes ranging from early diagnostics to cell therapy. Sorting techniques such as fluorescence-activated cell sorting (FACS) have evolved considerably and provide standard ways of sorting. Nevertheless, the search for compact, integrated, efficient, and high throughput microfluidic sorting platforms continues due to challenges such as cost, cell viability, and biosafety. In our previous work, we introduced a technology with the potential to become such a platform: the bubble-jet sorter. It is a silicon-based sorter chip relying on cell deflection through micro vapor bubble formation. In this work, we present a new version of the sorter chip that emphasizes durability and continuous sorting operation. To characterize the sorter, we first focus on the technical performance and show a sorter lifetime that repeatedly exceeds 80 million actuation cycles. In addition, we show continuous operation at high firing rates, but also discuss limitations due to heat buildup. In a second step, we present continuous sorting runs of millions of beads and CD3 positive T cells at rates surpassing 1000 sorting events per second, while maintaining high purity (>90%) and recovery (>85%). Dedicated viability tests show that the gentle sorting process maintains cell viability in this closed, aerosol-free device. The remarkable combination of high lifetime, sorting rate, and sorting efficiency, along with the potential for on-chip parallelization show the promise of this technology to meet the growing demand for large-scale sample isolation in drug and immunotherapy development.

SUPERCELLS: a novel microfluidic reactor architecture for ultra-fast sequential delivery of chemical reagents.

Applications such as nucleic acid synthesis or next-generation sequencing involve repeated fluidic cycles with the same set of reagents. The large dead volumes present in external valves and pumps with relatively long supply lines mandate the inclusion of extensive rinsing steps in current protocols, resulting in the consumption of significant quantities of reagents. To allow for fast rinsing, to reduce reagent consumption, and to ensure high reagent purity, we propose a fluidic concept based on a hierarchical branching structure. The working principle comprises a 3D fluidic network of supply lines - one line per reagent - that ensures reagents to be provided up to the entrance of every single reaction cavity, called supercells. Because all reagents are always present inside or at the inlet of a supercell, the principle allows for very rapid reagent switching, while a continuous flow avoids cross contamination. Selection of a specific reagent to enter the supercells is controlled by adjusting the pressure over different supply lines. As the pressure is regulated by a single, external controller per reagent, no integrated valves are needed. The very small distances to the reaction cavities also results in the use of minimal reagent volumes and, hence, largely reduces operational costs. We demonstrated the working principle of this concept and show an average switching time of 0.23 ± 0.09 s for the current design at a flow rate of 10 nL s-1. We used a 10 × 10 matrix of supercells to validate the fluidic concept to be scalable towards a large number of reaction sites. In summary, we believe the presented fluidic 3D hierarchical concept allows designing flow cells that enable highly parallel, more cost-efficient, and faster work flows for applications requiring many reagent cycles.

On-chip flow cytometer using integrated photonics for the detection of human leukocytes.

Differentiation between leukocyte subtypes like monocytes and lymphocytes is essential for cell therapy and research applications. To guarantee the cost-effective delivery of functional cells in cell therapies, billions of cells must be processed in a limited time. Yet, the sorting rates of commercial cell sorters are not high enough to reach the required yield. Process parallelization by using multiple instruments increases variability and production cost. A compact solution with higher throughput can be provided by multichannel flow cytometers combining fluidics and optics on-chip. In this work, we present a micro-flow cytometer with monolithically integrated photonics and fluidics and demonstrate that both the illumination of cells, as well as the collection of scattered light, can be realized using photonic integrated circuits. Our device is the first with sufficient resolution for the discrimination of lymphocytes and monocytes. Innovations in microfabrication have enabled complete integration of miniaturized photonic components and fluidics in a CMOS-compatible wafer stack. In combination with external optics, the device is ready for the collection of fluorescence using the on-chip excitation.