An open-source transparent microelectrode array

Abstract

Objective.The micro-electrode array (MEA) is a cell-culture surface with integrated electrodes used for assays of electrically excitable cells and tissues. MEAs have been a workhorse in the study of neurons and myocytes, owing to the scalability and millisecond temporal resolution of the technology. However, traditional MEAs are opaque, precluding inverted microscope access to modern genetically encoded optical sensors and effectors.Approach. To address this gap, transparent MEAs have been developed. However, for many labs, transparent MEAs remain out of reach due to the cost of commercially available products, and the complexity of custom fabrication. Here, we describe an open-source transparent MEA based on the OpenEphys platform (Siegleet al2017J. Neural Eng.14045003).Main results.We demonstrate the performance of this transparent MEA in a multiplexed electrical and optogenetic assay of primary rat hippocampal neurons.Significance.This open-source transparent MEA and recording platform is designed to be accessible, requiring minimal microelectrode fabrication or circuit design experience. We include low-noise connectors for seamless integration with the Intan Technologies headstage, and a mechanically stable adaptor conforming to the 24-well plate footprint for compatibility with most inverted microscopes.

Keywords: electrophysiology; glass indium tin oxide (ITO) electrodes; open source; optogenetics; photometry; printed circuit board pre-amplifier; transparent multi-electrode array.

Figure 1.

Illustration of fabrication steps: (A) cross section of base substrate (ITO coated glass wafer); (B) photoresist deposition; (C) photoresist patterning; (D) ITO patterning via wet etch; (E) photoresist stripped following wet etch; (F) SU-8 deposition; (G) SU-8 patterning and hard bake.

Figure 2.

Render of MEA interface: (A) PCB with assembled components; (B) PCB with clamshell incorporation into the inverted microscope stage attachment with MEA.

Figure 3.

Transparent MEA device and recording: (A) cross section of device showing material layers and conductive polymer coating (PEDOT:PSS); (B) photo of MEA (left), zoomed insert showing PEDOT:PSS coated electrode pads after deposition (middle). Fluorescence image (right) showing the same device weeks later with cultured neurons expressing GCaMP6s. Green intensity represents the delta-F in response to optogenetic illumination (maximum minus minimum of GCaMP6s signal). (C) Electrophysiological recordings showing millisecond-precision extracellular spike waveforms in response to optogenetic stimulation at various optical power intensities; (D) analysis of latency to first spike as a function of illumination intensity.