Functional Magnetic Microdroplets for Antibody Extraction

Antibodies play an essential role in modern medicine for diagnostic and therapeutic applications. Even though the production of antibodies is the fastest growing pharmaceutical industry area, the cost of antibodies remains high, which limits access to antibody‐based medicine both in developing and developed countries. The bottleneck and major cost factor in the production is purification of the antibody. Here, a proof‐of‐concept is presented for antibody extraction using ferrofluid microdroplets. An external magnetic field splits oil‐based ferrofluid droplets into an array of daughter microdroplets, which serve as a magnetically tunable, hydrophobic, liquid substrate with a relatively large surface area. A fusion protein (HFBI‐Protein A), added to the solution surrounding the magnetic droplets, adsorbs strongly at the liquid‐liquid interface by the hydrophobin HFBI moiety, creating a bifunctional monolayer that can catch antibody molecules. After adsorption at the liquid‐liquid interface, these antibody molecules can be released by decreasing the pH of the solution. The antibody extraction process is investigated using confocal microscopy and gel electrophoresis. In addition, the effect of HFBI on the field‐induced ferrofluid droplet splitting is examined. This study provides a proof of concept for utilizing liquid‐liquid instead of a solid‐liquid system in antibody handling. A multifunctional interface consisting of two advanced materials (oil‐based ferrofluid and HFBI‐protein A fusion protein) for antibody extraction is presented. This magnetically controllable liquid‐liquid substrate with a tunable surface area offers a versatile, pH dependent catching and releasing of antibodies.