Single-cell Electrophysiology

TIn recent years, an introduction of CMOS bioelectronics system to biotechnology gave unprecedented opportunities in extremely high-throughput (1k – 10M parallel recordings) and improved noise performance. However, recent developments of CMOS bioelectronics devices mostly focused on Application Specific Integrated Circuits (ASIC) in which the mode of operation is fixed from the design phase. Thus, ASIC devices offer little flexibility and a new design is mandatory to support alternative modes. We developed a reconfigurable design that can switch between different operational modes to suit the type of demanded analysis. The benefit of this approach is the full customizability, conceptually similar to field-programmable gate array (FPGA). The presented semiconductor device contains a reconfigurable array of 32 × 32 electrodes and amplifiers. Memory cells are embedded in each amplifier unit to store the configuration and allows for rapid re-programming. Each amplifier supports amperometry, cyclic voltammetry, and patch-clamp. With the demonstrated multifunctionality of the CMOS-based biosensor design, various type of single-cell analysis using electrophysiology can be conducted from a low cost, high-throughput device.

Fig. 1. Array of electrode-amplifiers for single-cell analysis. Each golden-color square represents on-chip electrode. The amplifier circuit is embedded underneath the electrode. The high density array of 320 electrode-amplifier pairs.

The high-throughput of the biosensor array will accelerate the data collection needed to determine statistical significance of changes produced under varying conditions, from several weeks to a few hours. The biosensor is designed and fabricated using a combination of CMOS integrated circuit (IC) technology and a photolithography process to incorporate platinum working electrodes on-chip. We demonstrate the operation of an electrode array with integrated high-gain potentiostats and output time-division multiplexing with minimum dead time for readout. The on-chip working electrodes are patterned by conformal deposition of Pt and lift-off photolithography. The conformal deposition method protects the underlying electronic circuits from contact with the electrolyte that covers the electrode array during measurement. The biosensor was validated by simultaneous measurement of amperometric currents from 100 electrodes in response to dopamine injection, which revealed the time course of dopamine diffusion along the surface of the biosensor array. The biosensor simultaneously recorded neurotransmitter release successfully from multiple individual living chromaffin cells. The biosensor was capable of resolving small and fast amperometric spikes reporting release from individual vesicle secretions. We anticipate that this device will accelerate the characterization of the modulation of neurotransmitter secretion from neuronal and endocrine cells by pharmacological and molecular manipulations of the cells.

Fig. 2. The parallel recordings of amperometric spike (exocytosis of vesicles) on the semiconductor device. Each peak represents a release of single vesicle. A 10-minute recording on the semiconductor device revealed sufficient statistical information about the vesicle release. The drug testing using L-dopa revealing the enlargement of quantal size.