Signal-to-Noise Ratio Enhancement Using Graphene-Based Passive Microelectrode Arrays

This work is aimed toward the goal of investigating the influence of different materials on the signal-to-noise ratio (SNR) of passive neural microelectrode arrays (MEAs). Noise reduction is one factor that can substantially improve neural interface performance. The MEAs are fabricated using gold, indium tin oxide (ITO), and chemical vapor deposited (CVD) graphene. 3D-printed Nylon reservoirs are then adhered to the glass substrates with identical MEA patterns. Reservoirs are filled equally with a fluid that is commonly used for neuronal cell culture. Signal is applied to glass micropipettes immersed in the solution, and response is measured on an oscilloscope from a microprobe placed on the contact pad external to the reservoir. The time domain response signal is transformed into a frequency spectrum, and SNR is calculated from the ratio of power spectral density of the signal to the power spectral density of baseline noise at the frequency of the applied signal. We observed as the magnitude or the frequency of the input voltage signal gets larger, graphene-based MEAs increase the signal-to-noise ratio significantly compared to MEAs made of ITO and gold. This result indicates that graphene provides a better interface with the electrolyte solution and could lead to better performance in neural hybrid systems for in vitro investigations of neural processes

Electrically Controlling the Environmental Interactions of Neurons Cultured on Graphene

In neural interfaces, a major challenge is finding an electronic material that will be accepted by the human body. Currently, electrode arrays are often made from silicon, but graphene seems to be a better material for humans due to its biocompatibility and flexibility. However, it is unknown how neural cells react to being electrically stimulated on graphene. For this work, we will observe the interactions between graphene electrodes and cultured neural stem cells using a probe station specially designed for electrophysiology. The cells are kept in a salt solution contained in a 3D printed reservoir. This is mounted on top of a graphene sample and is attached to a fluidic system consisting of two pump controllers that refresh the solution at a small rate, thus keeping the cells alive for several hours. This also allows us to introduce different salt concentrations and/or chemicals that modify the cellular environment, and thus the interactions with the graphene. The cells must be kept at a temperature of 37°C, which is achieved by using a heating pad attached to a chuck. Currently, we have the pump controllers working and have been able to control them using a computer

Measurement of Signal-to-Noise Ratio in Neural Microelectrodes

Signal noise has limited the performance and application of bioelectronics in areas such as neural interfaces and biosensors. Graphene, a two-dimensional hexagonal array of carbon atoms, shows promise as a material for bio-interface applications. This study explores the properties of graphene as a low-noise neural electrode material. Using glass-micropipette electrophysiology, signals are applied to solution-based microelectrode arrays and the response is precisely measured. Signal-to-noise ratio (SNR) is characterized and analyzed using concepts from signal theory on several material systems. These include indium-tin-oxide, various metals deposited by sputtering and inkjet printing, as well as large-area chemical vapor-deposited (CVD) graphene. Our hypothesis is that the unique chemical and electronic properties of graphene increases charge transfer and therefore lowers interfacial impedance at the biological/solid state interface. This effect is expected to be accompanied by increased SNR

Measurement of Signal‐to‐Noise Ratio In Graphene‐Based Passive Microelectrode Arrays

This work aims to investigate the influence of various electrode materials on the signal‐to‐noise ratio (SNR) of passive microelectrode arrays (MEAs) intended for use in neural interfaces. Noise reduction substantially improves the performance of systems which electrically interface with extracellular solutions. The MEAs are fabricated using gold, indium tin oxide (ITO), inkjet printed (IJP) graphene, and chemical vapor deposited (CVD) graphene. 3D‐printed Nylon reservoirs are adhered to glass substrates with identical MEA patterns and filled with neuronal cell culture media. To precisely control the electrode area and minimize the parasitic coupling of metal interconnects and solution, SU‐8 photoresist is patterned to expose only the area of the electrode to solution and cap the remainder of the sample. Voltage signals with varying amplitude and frequencies are applied to the solution using glass micropipettes, and the response is measured on an oscilloscope from a microprobe placed on the contact pad external to the reservoir. The time domain response signal is transformed into a frequency spectrum, and SNR is calculated. As the magnitude or the frequency of the input signal gets larger, a significantly increased signal‐to‐noise ratio was observed in CVD graphene MEAs compared to others. This result indicates that 2‐dimensional nanomaterials such as graphene can provide better signal integrity and potentially lead to improved performance in hybrid neural interface systems

Features of acute COVID-19 associated with post-acute sequelae of SARS-CoV-2 phenotypes: results from the IMPACC study

Post-acute sequelae of SARS-CoV-2 (PASC) is a significant public health concern. We describe Patient Reported Outcomes (PROs) on 590 participants prospectively assessed from hospital admission for COVID-19 through one year after discharge. Modeling identified 4 PRO clusters based on reported deficits (minimal, physical, mental/cognitive, and multidomain), supporting heterogenous clinical presentations in PASC, with sub-phenotypes associated with female sex and distinctive comorbidities. During the acute phase of disease, a higher respiratory SARS-CoV-2 viral burden and lower Receptor Binding Domain and Spike antibody titers were associated with both the physical predominant and the multidomain deficit clusters. A lower frequency of circulating B lymphocytes by mass cytometry (CyTOF) was observed in the multidomain deficit cluster. Circulating fibroblast growth factor 21 (FGF21) was significantly elevated in the mental/cognitive predominant and the multidomain clusters. Future efforts to link PASC to acute anti-viral host responses may help to better target treatment and prevention of PASC