A Cell-Semiconductor Synapse: Transistor Recording of Vesicle Release in Chromaffin Cells  Janosch Lichtenberger, Peter Fromherz  Biophysical Journal  Volume 92, Issue 6, Pages 2262-2268 (March 2007) DOI: 10.1529/biophysj.106.096446 Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 1 Chromaffin cell on a transistor. (A) Schematic cross section (not to scale, cell diameter ∼15μm, cell-chip distance ∼50nm). Vesicles are released into the narrow extracellular space between cell and transistor. A carbon fiber is used for amperometry. Exocytosis is elicited by BaCl2 applied with a pipette (θ-tube). (B) Micrograph of silicon chip with linear transistor array. Source, drain, and gate (black frame) are marked on the upper transistor. A chromaffin cell covers about one-half of the open gate area (2μm×20μm). The cell is touched by a carbon fiber from the right. Biophysical Journal 2007 92, 2262-2268DOI: (10.1529/biophysj.106.096446) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 2 Simultaneous detection of vesicle release by transistor recording and amperometry. (A) Distribution of events in time for the transistor signal (top) and amperometry (bottom). The stimulation by a pulse of 5mM BaCl2 is marked by an arrow. The band of vertical bars between the two records marks the events that are detected by the transistor and the carbon fiber within a time window of 5ms. (B) Transistor record (top) and amperometry (bottom) of a coincident event with a foot structure and a main signal. Biophysical Journal 2007 92, 2262-2268DOI: (10.1529/biophysj.106.096446) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 3 Effect of equilibrated pH across the vesicle membrane. BaCl2 is added together with nigericin and valinomycin at a raised potassium concentration (arrow). After an initial burst and a phase of suppressed release, the amplitudes of the events in the transistor signal (top) are low, whereas the events of the amperometric current (bottom) have normal amplitudes. Biophysical Journal 2007 92, 2262-2268DOI: (10.1529/biophysj.106.096446) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 4 Effect of acid-base buffer on transistor recording and amperometry. (A) Average of the five highest signals in an experiment, where 5mM HEPES is replaced by 20mM HEPES. (B) Integral distribution functions of rise time, duration, and amplitude of transistor recording (top) and of amperometry (bottom) for 5mM HEPES (drawn), 10mM (dashed), and 20mM (dotted). An enhanced concentration of acid-base buffer affects the time course and the amplitude of the transistor events, but not of amperometry. Biophysical Journal 2007 92, 2262-2268DOI: (10.1529/biophysj.106.096446) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 5 Extrusion model of transistor recording. (A) Profiles of pH along cell-transistor junction at 3 (open circles), 7 (solid circles), and 20ms (bars) after the start of matrix extrusion for 5mM HEPES. The parameters (optimal) are 3ms extrusion time, a factor 1/100 for the reduction of diffusion coefficients, and a density of 0.5×1014cm−2 of silanol groups. (B) Profiles of the electrical surface potential φS along the gate oxide. At 3ms, the changes of pH and surface potential are well localized in the area of the extruded matrix. Later, the local responses decay, and transient signals appear in the surrounding. (C) Average change of surface potential ΔφS versus time for 5, 10, and 20mM HEPES (from top to bottom) with optimal parameters (drawn line) and with a high density 5×1014cm−2 of silanol groups (dashed line). (D) Average surface potential for 5mM HEPES with optimal parameters (drawn line), with 10ms extrusion time (dotted line), and with a factor 1/10 for the reduction of diffusion coefficients (dashed line). The extrusion model with optimal parameters accounts for amplitude and shape of the transistor records and for lowered amplitude and duration with enhanced buffer concentration. Biophysical Journal 2007 92, 2262-2268DOI: (10.1529/biophysj.106.096446) Copyright © 2007 The Biophysical Society Terms and Conditions