Fig 1.
Impedance magnitude of uncoated gold and PEDOT/PSS modified microelectrodes in artificial cerebrospinal fluid (n = 3).
Fig 2.
Illustration of the set-up used to obtain simulatanous electrical and optical signals from primary hippocampal cells cultured onto MEA devices.
The MEA device sat on the microscope stage and shielded wires were connected to each of the electrodes through an interface board to enable electrical recording. The camera and mercury light source (highlighted in red) were mounted onto the microscope to enable optical recordings.
Fig 3.
Primary hippocampal cells cultured onto control cover slips or MEA devices at DIV 7, 14 and 21.
The images were taken using differential interference contrast microscopy through a light microscope equipped with a 20x water immersion objective lens. Scale bar represents 100 μm.
Fig 4.
An example of combined electrical and optical recordings from a single electrode (indicated by a red encircled dot).
A) Processed images of a typical action potential imaged through the high-speed camera, each frame is 1 ms long and the neuron is represented by the black dots which appear in the image. The correlating electrical signal to each of the frames is shown in B) where the numbers 1,2,3,4,5,6,7,8 correlate with the frame image at 1 ms, 2 ms, 3 ms, 4 ms, 5 ms, 6 ms, 7 ms and 8 ms in A. The measured change in fluorescence intensity from the acquired images is displayed in C) and this trace correlates in time with the electrical recording trace above it. The stars (⋆) highlight action potentials which were recorded electrically but not optically, possibly arising from another source within the culture.
Fig 5.
Electrical and optical signals were confirmed as neuronal action potentials due to antagonism following tetrodotoxin (TTX) addition.
A) Representative electrical waveforms before TTX addition and 1 min, 5 min and 20 min post TTX addition, a clear reduction in electrical activity is shown. B) Representative change in fluorescence intensity waveforms for a single neuronal action potential prior to TTX addition and 1 min, 5 min and 20 min post TTX addition where a clear reduction in the waveform shape is observed. The ROI used to calculate fluorescence waveforms is identical to that used in Fig 4A to ensure consistency as the same neuron is being analysed. C) Demonstrates the relationship between the maximum change in fluorescence intensity and time following TTX exposure.
Fig 6.
Optical image of gold (left) and PEDOT/PSS (right) microelectrode (displayed as red dot) with neuronal activity.
The corresponding electrical recording for the optical image is shown below each image and represented as a black trace. The portion of the electrical recording which correlates with neuronal firing in the optical image is highlighted in red.
Table 1.
Calculation of microelectrode performance utilising the volume conduction theory to calculate an expected potential.