Dielectrophoretic Characterization of Dynamic Microcapsules and Their Magnetophoretic Manipulation.

In this work, we present dielectrophoresis (DEP) and in situ electrorotation (ROT) characterization of reversibly stimuli-responsive "dynamic" microcapsules that change the physicochemical properties of their shells under varying pH conditions and can encapsulate and release (macro)molecular cargo on demand. Specifically, these capsules are engineered to open (close) their shell under high (low) pH conditions and thus to release (retain) their encapsulated load or to capture and trap (macro)molecular samples from their environment. We show that the steady-state DEP and ROT spectra of these capsules can be modeled using a single-shell model and that the conductivity of their shells is influenced most by the pH. Furthermore, we measured the transient response of the angular velocity of the capsules under rotating electric field conditions, which allows us to directly determine the characteristic time scales of the underlying physical processes. In addition, we demonstrate the magnetic manipulation of microcapsules with embedded magnetic nanoparticles for lab-on-chip tasks such as encapsulation and release at designated locations and the in situ determination of their physicochemical state using on-chip ROT. The insight gained will enable the advanced design and operation of these dynamic drug delivery and smart lab-on-chip transport systems.