Microfluidic Biosensor for the In Vitro Electrophysiological Characterization of Actin Bundles

The essential cytoskeletal protein actin and its functions are paramount for motility, communication, and locomotive processes in eukaryotic cells. Detection and quantification of actin protein is of great interest for in vitro studies potentially elucidating unknown cellular mechanisms affecting drug responses with an extension to the study of disease states (e.g., study of neurodegenerative disorders). To this end, development of biomedical platforms and biosensors plays an important role in providing reliable and sensitive devices to study such intracellular constructs. Here, we present for the first time the microfabrication, characterization, testing, and electrical/interfacial modeling of a microfluidic biosensor for actin protein characterization. The device allows for the interaction and characterization of actin bundles using electrochemical impedance spectroscopy (EIS). The device was tested with $1 \mu \text{M}$ and $8 \mu \text{M}$ actin bundles concentrations producing shifts in impedance response in the significant biological frequency of 1 kHz from 17 to 30 kOhm ( $\text{k}\Omega $ ). Interfacial capacitance and electrical modeling showed that at increasing actin bundles concentrations, the distance from the electrode to the diffusion region (Debye length) was reduced from 386 to 136, and from 1526 to 539 Å. Interfacial capacitance was evaluated for $1 \mu \text{M}$ concentration at two dielectric constants ( $\boldsymbol {\varepsilon }_{\mathbf {r}}$ = 5 and 78) resulting in 3.8 and 15.6 mF/m2 respectively. Similarly, for $8 \mu \text{M}$ concentration, interfacial capacitance resulted in 10.1 and 43.3 mF/m2 for the same values of $\boldsymbol {\varepsilon }_{\mathbf {r}}$ . Based on these theoretical calculations, the interface model could accurately predict the quantification of the actin bundles previously elucidated by the experimental EIS method. [2023-0180]