The IBJT as an addressable delivery point for modulation of neuronal cell signaling. (A) Schematic illustration of the IBJT in a circuitry. SH-SY5Y cells were cultured on top of the collector electrode and ACh was placed on the emitter electrode. When switching on the device, ACh migrates through the E-C circuit and is released to the cells. (B) Intracellular Ca²⁺ recording of ACh stimulated SH-SY5Y cell. Switching V_EB on/off regulates ACh delivery, which then modulates the cellular Ca²⁺ response.

Schematic drawing of ion concentrations and electric potentials along emitter-collector in the active- and in the cutoff mode. The salt concentration of the electrolytes (c₀) is lower than the concentration of negative fixed charges in the membranes (X_N). In the emitter and the collector, the concentration of mobile cations (c_P) is high while the concentration of mobile anions (c_N) is low. In the cutoff mode, the salt concentration in the junction (c_J) is low and therefore the potential () drop primarily occurs across this region. In the active mode, c_J is higher and the potential drop is split over the emitter (ΔV_E), the collector and the junction.

Characteristics of the IBJT. (A) The transfer curve reveals a linear relationship between I_C and V_EB, with only minor hysteresis. I_B is higher in the forward scan due to injection of ions into the junction. (B) The output characteristics of the IBJT shows ion current saturation in the active mode. The saturation mode (gray region) is avoided in these scans. (C) The amount of anionic charge in the junction (Q_J) versus different V_EB. A linear fit to the data is displayed in red. (D) The switching transient for a voltage step in V_EB. The rise and fall of I_C correlates with positive and negative I_B, respectively. (E) Current versus voltage characteristics for the emitter-base diode circuit (V_EC disconnected). The expected rectification of the ionic current is observed.

Architecture of the IBJT. (A) The principal device structure of a BM, including a neutral intermediate membrane layer. In reverse and forward bias voltage, mobile ions are extracted from or accumulate within the intermediate layer, respectively. This results in ionic current rectification. (B) The IBJT biased according to the common-emitter configuration. PEDOT:PSS electrodes with aqueous electrolytes generate the ionic currents within the device. Emitter and collector (cation selective, L × W = 1.5 × 0.2 mm) meet the base (anion selective) defining the junction. (C) Vertical cross section along the emitter-collector configuration (not to scale). The emitter and collector (∼250 nm thick PSS) are patterned on top of a PET substrate. A crosslinked PEG gel (referred to as the junction) is employed into the opening of the 10 μm thick SU-8 insulating layer. The base (∼20 μm thick) contacts the gel and is covered by a PDMS seal layer. I_C is the flow of cations (M⁺) from the emitter to the collector while I_B, in steady state, primarily consists of anions (A^-) migrating from the base to the emitter. (D) Top-down view of the IBJT. Emitter and collector are horizontally separated by 100 μm and the base covers the whole junction area. (E) The proposed circuit symbol of the pnp-IBJT.