Tailored Current—Voltage Relationships of Droplet-Interface Bilayers Using Biomolecules and External Feedback Control

The development of a new class of active material based on the ion transport properties of functional biomolecules is introduced in this work. The new class of materials utilizes a recently developed technique known as the droplet-interface bilayer (DIB) to enable the reconstitution of biomolecules into a durable matrix. Methods to modify the current— voltage relationship across the bilayer, including the incorporation of proteins and the use of an external feedback loop, are explored. Electrical impedance spectroscopy and cyclic voltammetry measurements are used to characterize the bilayers and indicate that a single DIB can be modeled as a resistor in parallel with a capacitor. Alpha-hemolysin proteins from Staphyloccus aureus cause a reduction in the resistance of the bilayer and exhibit current-rectification at positive cis potentials. Alamethicin proteins from Trichoderma viride produce a voltage-dependent conductance allowing the specific resistance (MΩ cm ² ) of the bilayer to be varied reversibly by 2—3 orders of magnitude. Feedback integral current control is demonstrated on pure 1,2-diphytanoyl-sn-glycero-3-phosphocholine DIBs and provides accurate current tracking at a driving rate of 10 mHz and less. Proportional—integral voltage control applied to a DIB establishes a second-order frequency response where the natural frequency and damping ratio of the resonance can be selected.