| Transistor-coupled bilayer electrochemical impedance spectroscopy | Without valinomycin, nominal membrane resistance was greater than 10 GΩ; increasing the valinomycin concentration to 65 µM progressively decreased membrane resistance by as much as 215 fold; area-normalized specific membrane resistance also decreased; specific membrane capacitance remained nearly unchanged, indicating that enhanced ionic permeability occurred without substantial alteration of the bilayer’s dielectric structure or effective thickness |
|---|---|
| Free-standing bilayer electrochemical impedance spectroscopy | For free-standing droplet interface bilayers containing varying concentrations of valinomycin, extracted membrane resistance decreased markedly with increasing valinomycin loading |
| Transistor-coupled bilayer electrical properties | Columns: Valinomycin Conc. (µM); Area (10⁻⁴ cm²); Specific Resistance (kΩ-cm²); Specific Capacitance (µF/cm²). Rows: 0; 3.94 ± 0.26; 5.63 × 10³; 0.5 — 20; 2.47 ± 0.44; 54.1; 0.511 — 35; 2.3866 ± 0.47; 23.866; 0.540 — 65; 2.66 ± 0.5; 7.714; 0.511 |
| Free-standing bilayer electrical properties | Columns: Valinomycin Conc. (µM); Area (10⁻⁴ cm²); Specific Resistance (kΩ-cm²); Specific Capacitance (µF/cm²). Rows: 0; 2.54 ± 0.549; 2230; 0.586 — 20; 1.82 ± 0.305; 23.98; 0.557 — 35; 1.98 ± 0.417; 11.07; 0.543 — 65; 1.22 ± 0.255; 6.51; 0.521 |
| Zero-charge crossover and intrinsic transmembrane potential | For pristine free-standing DIBs under symmetric electrolyte conditions, the zero-charge crossover was approximately 0 V. Coupling one lipid-coated droplet directly to the PEDOT:PSS channel shifted the pristine TCDB crossover to approximately −50 mV, indicating an intrinsic transmembrane potential of +50 mV. For the 35 µM valinomycin-doped TCDB, crossover points of approximately −50 to −70 mV indicated an intrinsic transmembrane potential of approximately +25 to +35 mV relative to the lipid-only TCDB. Lipid-coated droplets contained 100 mM KCl, 10 mM MOPS, and 2.6 mg/mL DPhPC in 3:1 decane/hexadecane oil; quasi-static charge–voltage hysteresis used a 100 mVpp, 0.0017 Hz sinusoidal voltage with a 500 mVpp, 10 Hz triangular voltage, reduced to 100 mVpp for the valinomycin-doped TCDB |
| Electrochemical impedance spectroscopy acquisition | Biologic SP200 potentiostat; standalone droplet interface bilayers and transistor-coupled bilayers were measured in a two-terminal configuration between the Ag/AgCl gate electrode and grounded source contact over 0.1 Hz to 100 kHz with a 10 mV root-mean-square sinusoidal perturbation at open-circuit potential; spectra were fitted to the equivalent-circuit model using ZFit/OriginLab to extract solution resistance, membrane resistance, membrane capacitance, and PEDOT:PSS gate capacitance for each device configuration and valinomycin concentration; all electrical measurements were performed at 22 ± 1 °C, with instrument control and data acquisition using custom MATLAB and LabVIEW scripts unless otherwise stated |
Nawara Tanzee Minim, Essraa A. Hussein, Beliz Utebay, Jonathan Rivnay, Neha Kamat, and Stephen A. Sarles. “Ion-selective transistor coupled droplet interface bilayer with short term memory and synaptic plasticity.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15008047/v1
Bare-transistor impedance parameters, direct-current leakage validation, and bilayer-formation verification were not retained