Breaking the Interface: Efficient Extraction of Magnetic Beads from Nanoliter Droplets for Automated Sequential Immunoassays.

Droplet-based microfluidic systems offer a high potential for miniaturization and automation. Therefore, they are becoming an increasingly important tool in analytical chemistry, biosciences, and medicine. Heterogeneous assays commonly utilize magnetic beads as a solid phase. However, the sensitivity of state of the art microfluidic systems is limited by the high bead concentrations required for efficient extraction across the water-oil interface. Furthermore, current systems suffer from a lack of technical solutions for sequential measurements of multiple samples, limiting their throughput and capacity for automation. Taking advantage of the different wetting properties of hydrophilic and hydrophobic areas in the channels, we improve the extraction efficiency of magnetic beads from aqueous nanoliter-sized droplets by 2 orders of magnitude to the low µg/mL range. Furthermore, the introduction of a switchable magnetic trap enables repetitive capture and release of magnetic particles for sequential analysis of multiple samples, enhancing the throughput. In comparison to conventional ELISA-based sandwich immunoassays on microtiter plates, our microfluidic setup offers a 25-50-fold reduction of sample and reagent consumption with up to 50 technical replicates per sample. The enhanced sensitivity and throughput of this system open avenues for the development of automated detection of biomolecules at the nanoliter scale.

One-Step Photochemical Generation of Biofunctionalized Hydrogel Particles via Two-Phase Flow.

Biofunctional hydrogel particles have become increasingly popular in medical diagnostics; however, their generation is time-consuming and typically requires several process steps. We report on a new method for the simple, fast, and reproducible one-step generation of monodisperse hydrogel particles equipped with biofunctional molecules such as proteins or DNA. Key to the approach is the simultaneous photo cross-linking of the polymer chains and covalent binding of proteins or DNA through a C,H insertion reaction inside aqueous plug compartments that are produced via microfluidics. The strong performance in biological binding assays of the functionalized particles is demonstrated.

Functional Cryogel Microstructures Prepared by Light-Induced Cross-Linking of a Photoreactive Copolymer.

A novel, highly efficient method for the preparation of functional, microstructured and surface-attached cryogels is described. Photoinduced C,H-insertion reactions are used to generate cryogels in a single, rapid photo-cross-linking process. To this end, solutions containing both a photoreactive copolymer and the (bio)molecules to be immobilized are placed on a polymeric substrate followed by freezing and a short UV exposure. This strategy combines photolithography and cryogel formation allowing for a simultaneous generation and (bio)functionalization of cryogels in a single reaction step. To demonstrate the potential of the generated materials for bioanalytical applications, we successfully prepared DNA and protein cryogel microarrays.