Enhanced Response of ZnO Nanorod-Based Flexible MEAs for Recording Ischemia-Induced Neural Activity in Acute Brain Slices

Abstract

Brain ischemia is a severe condition caused by reduced cerebral blood flow, leading to the disruption of ion gradients in brain tissue. This imbalance triggers spreading depolarizations, which are waves of neuronal and glial depolarization propagating through the gray matter. Microelectrode arrays (MEAs) are essential for real-time monitoring of these electrophysiological processes both in vivo and in vitro, but their sensitivity and signal quality are critical for accurate detection of extracellular brain activity. In this study, we evaluate the performance of a flexible microelectrode array based on gold-coated zinc oxide nanorods (ZnO NRs), referred to as nano-fMEA, specifically for high-fidelity electrophysiological recording under pathological conditions. Acute mouse brain slices were tested under two ischemic models: oxygen-glucose deprivation (OGD) and hyperkalemia. The nano-fMEA demonstrated significant improvements in event detection rates and in capturing subtle fluctuations in neural signals compared to flat fMEAs. This enhanced performance is primarily attributed to an optimized electrode-tissue interface that reduces impedance and improves charge transfer. These features enabled the nano-fMEA to detect weak or transient electrophysiological events more effectively, making it a valuable platform for investigating neural dynamics during metabolic stress. Overall, the results underscore the promise of ZnO NRs in advancing electrophysiological tools for neuroscience research.

Keywords: acute brain slices; cerebral ischemia; micro/nano electrode array; spreading depolarization; zinc oxide nanorods.

Figure 1

(a) Recording setup; (b) size comparison of flexible MEA.

Figure 2

SEM images of zinc oxide nanorods (ZnO NRs) at two different magnifications. The hexagonal structure is notable in the inset of the picture.

Figure 3

DMA characterization of nano-fMEA: (a) frequency sweep, performed at 40 °C; (b) temperature sweep, performed at 1 Hz.

Figure 4

TGA analysis of nano-fMEA under a nitrogen atmosphere. The black curve shows the weight loss as a function of temperature, while the blue curve represents the derivative of the weight loss, indicating the rate of decomposition with respect to temperature.

Figure 5

EIS of nanostructured and flat flexible electrodes.

Figure 6

Nano-fMEA and its components. (a) Custom-made system developed at CNR-IMM with: (a1) acquisition board, (a2) connection to computer and energy source, (a3) grounding, and (a4) fMEA. (b) fMEA with: (b1) pins to interface with the system, (b2) custom-made PCB adaptor, and (b3) polyimide-based grid. (c) fMEA highlighting its asymmetric design, which is tailored for recordings on the slice or wrapped around it. (d) Zoom-in of the nano-fMEA, which highlights: (d1) the open holes that allow oxygenation and (d2) the nanostructured recording pads, with a size of 20 µm.

Figure 7

Example of a qualitative acquisition of NS/PC-derived astrocytes grown on control, poly-L-lysine-coated surfaces (left) and on ZnO surfaces (right) for 7 days in in vitro conditions; astrocytes are visualized in green (GFAP) and cell nuclei are in blue (DAPI). GFAP, glial fibrillary acidic protein; DAPI, 4′,6-diamidino-2-phenylindole.

Figure 8

(a) Comparison of activity detection between a traditional flat flexible grid (flat fMEA) and the nanostructured flexible MEA (nano-fMEA) compared to the background noise in OGD conditions. Recording of hyperkalemic stimulation using (b) flat fMEA and (c) nano-fMEA. Recording of OGD model using (d) flat fMEA and (e) nano-fMEA.

Figure 9

Power spectral density (PSD) obtained with nano-fMEAs during the OGD protocol. As expected, brain activity from the starting levels (red traces) increases due to oxygen and glucose deprivation (green trace), and then it returns to the starting levels (blue trace).