Direct Acquisition of the Gap Height of Biological Tissue-Electronic Chemical Sensor Interfaces

Abstract

Interfacing biological tissues with electronic sensors offers the exciting opportunity to accurately investigate multiple biological processes. Accurate signal collection and application are the foundation of these measurements, but a long-term issue is the signal distortion resulting from the interface gap. The height of the gap is the key characteristic needed to evaluate or model the distortion, but it is difficult to measure. By integrating a pair of nanopores at the electronic sensor plane and measuring the ion conductance between them, we developed a versatile and straightforward strategy to realize the direct cooperative evaluation of the gap height during exocytotic release from adrenal gland tissues. The signaling distortion of this gap has been theoretically evaluated and shows almost no influence on the amperometric recording of exocytosis in a classic "semi-artificial synapse" configuration. This strategy should benefit research concerning various bio/chemical/machine interfaces.

Keywords: Biological Tissues; Diffusional Filtering; Exocytosis; Interfaces; Ion Conductance.

Figure 1

A) Schematic of the ion conductance‐amperometric (IC‐Amp) measurement. For the amperometric (Amp) recording, a constant potential (E _Amp=+700 mV vs. Ag/AgCl) was applied to the CFME to record the exocytotic catecholamines. For the ion conductance (IC) measurement, a triangle wave potential (E _IC, amplitude: 100 mV, scan rate: 1 V/s) was applied to the two nanopores neighboring the CFME. The resistance of the IC measurement circuit mainly includes the resistance of the solution within the cell to electrode gap (R _sol(H)) and inside the two nanopores (R _pore). The IC‐Amp sensor was placed on a cell and a gap (its height is indicated as H) was formed because of the macro‐molecules on the cell membrane. B) Schematic of an amperometric spike at a small H (i) vs. large H (ii). C) Schematic of the ion current through the nanopores at a small H (i) vs. large H (ii).

Figure 2

Schematic of the fabrication of the IC‐Amp sensor. A) A 7‐barrel glass capillary with a carbon fiber (d: 5 μm) in the center barrel was heated and pulled to a small tip; B) the carbon fiber was wrapped by the glass wall, whereas the 6 surrounding barrels were crescent shaped; C) after beveling, the probe tip was planar with the center elliptical CFME and 6 surrounding nanopores. (i) the view of the beveled plane, (ii) cross‐sectional view and (iii) a scanning electron microscopy image of the IC‐Amp sensor. The two nanopores used for IC measurement are labeled by asterisks.

Figure 3

A) Schematic of the IC measurement on PDMS sheets. E _IC: triangle wave, amplitude: 100 mV, scan rate: 1 V s⁻¹. B) Scanning electron microscopy images of the PDMS sheets. Scale bar: 1 μm. C) Ion current (I(H)) and calculated ion conductance of the IC circuit (G _total(H)=I(H)/E _IC). The variation of ion current amplitude and G_total(H) reflects the IC change when the sensor is moved from far (H→∞) to contacting the sheets (H=520 nm (i) or 90 nm (ii)) and then moved back (H→∞). D) Experimental and simulated relative G _sol(H)−H curves for this calibration experiment. The error bars present the standard deviations of relative G _sol(H) at respective H (n=5).

Figure 4

Representative IC measurement trace (A) and amperometric trace (B) for experiments on bovine adrenal gland slices. Three spikes were amplified as the inset in (B).