This work explored hybrid films of silver nanowires (AgNWs) with indium zinc oxide (IZO) for developing high-performance and low-cost electrocorticography (ECoG) electrodes. The transparent hybrid films achieved a sheet resistance of 6 Ω/sq, enabling electrodes with a diameter of 500 μm to reach an impedance of 20 kΩ at 1 kHz and a charge storage capacity of 3.2 mC/cm2, an improvement in properties over IZO electrodes, whose performance is on par with classical tin-doped indium oxide (ITO). Characterization of light-induced artifacts was performed, showing that light intensities <14 mW/mm2 elicit minimum electrical potential variation, which falls within the magnitude of baseline noise. The validation of the electrodes in vivo was achieved by recording electrical neural activity from the surface of the rat cortex under anesthesia. Moreover, the presence of the hybrid films did not cause the distortion of light during fluorescence microscopy. This study highlighted the capabilities of transparent ECoG electrodes based on AgNWs with IZO. In the end, we leveraged available, yet affordable, techniques and materials to facilitate ease of production, creating a tool that is cost-effective and scalable for laboratories looking to record neural electrical activity on a large and fast scale with direct visualization of neurons.
This work explored hybrid films of silver nanowires (AgNWs) with indium-doped zinc oxide (IZO) for developing high-performance and low-cost electrocorticography (ECoG) electrodes.The hybrid films achieved a sheet resistance of 6 Ω/sq while maintaining a transparency of ≈60% at 550 nm. Electrodes with 500 μm diameter were fabricated with these films and reached an impedance of 20 kΩ at 1 kHz and a charge storage capacity of 3.2 mC/cm 2 , a 2× and 320× improvement over IZO electrodes, respectively. Characterization of light-induced artifacts was performed showing that small light intensities (<14 mW/mm 2 ) elicit electrical potential variation in the magnitude order of baseline noise. The validation of electrodes in vivo was achieved by recording electrical neural activity from the surface of rat cortex under anaesthesia. Moreover, the presence of the films did not cause obstruction of light during fluorescence microscopy.The presented film and electrode characterization studies highlighted the capabilities of this hybrid structure to fabricate transparent and flexible electrodes that are able to combine the superior temporal resolution of extracellular electrophysiology with the spatial resolution offered by optical imaging.
Minimally invasive medical devices can greatly benefit from Narrow Band Imaging (NBI) diagnostic capabilities, as different wavelengths allow penetration of distinct layers of the gastrointestinal tract mucosa, improving diagnostic accuracy and targeting different pathologies. An important performance parameter is the light intensity at a given power consumption of the medical device. A method to increase the illumination intensity in the NBI diagnostic technique was developed and applied to minimally invasive medical devices (e.g., endoscopic capsules), without increasing the size and power consumption of such instruments. Endoscopic capsules are generally equipped with light-emitting diodes (LEDs) operating in the RGB (red, green, and blue) visible light spectrum. A polydimethylsiloxane (PDMS) µ-lens was designed for a maximum light intensity at the target area of interest when placed on top of the LEDs. The PDMS µ-lens was fabricated using a low-cost hanging droplet method. Experiments reveal an increased illumination intensity by a factor of 1.21 for both the blue and green LEDs and 1.18 for the red LED. These promising results can increase the resolution of NBI in endoscopic capsules, which can contribute to early gastric lesions diagnosis.
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