Inkjet-printed Electrodes Research Articles

Fabrication and characterization of inkjet-printed interdigitated electrodes for non-faradaic electrochemical detection of uromodulin in urine

Fabrication and characterization of inkjet-printed interdigitated electrodes for non-faradaic electrochemical detection of uromodulin in urine

Effect of high-boiling point solvents on inkjet printing of catalyst layers for proton exchange membrane fuel cells

Inkjet printing (IJP) is considered as a promising and flexible method for low cost and drop-on-demand pattern formation in proton exchange membrane (PEM) fuel cells. Although significant advancements have been made in inkjet-printed electrodes, identifying the optimal ink formulations remains challenging due to severe restrictions on the ink properties. Generally, the catalyst layer prepared by IJP using low boiling point solvents (water/alcohol) show reasonable electrochemical performance. However, low boiling point solvents lead to clogging of the printhead nozzle due to fast evaporation of the solvent in the inkjet print head. In this study, high boiling point solvents (propylene glycol (PG) or ethylene glycol (EG)) were used as additives to reduce nozzle clogging and improve printing efficiency. In this context, the relationship between catalyst ink properties, CL microstructure, and electrochemical performance of the MEA is investigated. Results show that printing time is significantly reduced with adding high boiling point solvents in the ink (66.67 % reduction of time with 30 wt% PG). However, an increased amount of additive is detrimental in terms of electrochemical performance due to formation of larger agglomerates, lower porosity of the catalyst layer, and reduced ECSA. The results of this work can be used to develop a strategy to adjust the trade-off between printing time and electrochemical performance of electrodes prepared using IJP.

Measurement of Human and Bovine Exhaled Breath Condensate pH Using Polyaniline-Modified Flexible Inkjet-Printed Nanocarbon Electrodes.

The collection, processing, and electrochemical analysis of exhaled breath condensate (EBC) from healthy human and animal subjects is reported on. EBC is a biospecimen potentially rich in biomarkers of respiratory disease. The EBC pH was analyzed potentiometrically using a disposable polyaniline (PANI)-modified inkjet-printed (IJP) carbon electrode. Comparison measurements were performed using a commercial screen-printed carbon (SPC) electrode. The PANI-modified electrodes exhibited reproducible and near-Nernstian responses for pH values between 2 and 9 with slopes from -50 to -60 mV/dec. The PANI-modified IJP carbon electrode exhibited a faster response time and superior reproducibility to the modified SPC electrode. In proof-of-concept studies, the healthy human EBC pH was found to be 6.57 ± 0.09 and the healthy bovine EBC pH was 5.9 ± 0.2. All pH determined using the PANI-modified electrodes were in good agreement with the pH determined using a micro glass pH electrode. An RTube device was used to collect EBC from humans while a modified device was used to collect EBC from calves in the field. EBC volumes of 0.5-2 mL for 5-6 min of tidal breathing were collected from healthy animals. The pH of EBC from healthy calves (17 animals) depends on their age from 1 to 9 weeks with values ranging from 5.3 to 7.2. A distinct alkaline shift was observed for many animals around 20 days of age. The bovine EBC pH also depends on the ambient temperature and humidity at the time of collection. The results indicate that the PANI-modified IJP carbon electrodes outperform commercial SPC and provide reproducible and accurate measurement of pH across various biospecimen types.

Inkjet-Printed LSM-YSZ Thin Films for Enhanced Oxygen Electrodes in Solid Oxide Fuel Cells.

In the present work, symmetrical oxide ion conducting solid oxide single cells with inkjet-printed composite LSM-YSZ electrodes, onto commercially available YSZ dense substrates using GDC as buffer interlayer, were fabricated and characterized. Stable inkjet-printable LSM-YSZ nanoparticle inks were developed based on water solvent, after processing with high intensity ball milling. The deposition of LSM-YSZ electrodes was performed by inkjet printing, as well as a conventional additive manufacturing technique, screen printing, in order to compare the electrochemical performance of the produced cells for the reversible charge transfer reaction (O2 + 4 e- ↔ 2 O2-). The physicochemical properties of the LSM-YSZ nanoparticle ink was investigated to determine ink printability. The electrochemical performance of fabricated inkjet-printed and screen printed symmetrical cells (LSM-YSZ | GDC | YSZ | GDC | LSM-YSZ) exposed under a synthetic air atmosphere was evaluated in a single chamber cell reactor, employing the AC impedance spectroscopy and linear scan voltammetry techniques, at the temperature range of 700-850 °C. The inkjet-printed electrodes exhibited highly homogeneous and porous morphologies with the corresponding cell achieving current densities almost five times higher, up to 1 A/cm2 at 2 V cell potential and 850 °C, than those of the equivalent screen-printed one. To the best of our knowledge, this is the first successful implementation of water-based inks of LSM-YSZ electrodes in the fabrication of inkjet-printed solid oxide cells.

Low-cost inkjet-printed nanostructured biosensor based on CRISPR/Cas12a system for pathogen detection

The escalating global incidence of infectious diseases caused by pathogenic bacteria, especially in developing countries, emphasises the urgent need for rapid and portable pathogen detection devices. This study introduces a sensitive and specific electrochemical biosensing platform utilising cost-effective electrodes fabricated by inkjet-printing gold and silver nanoparticles on a plastic substrate. The biosensor exploits the CRISPR/Cas12a system for detecting a specific DNA sequence selected from the genome of the target pathogen. Upon detection, the trans-activity of Cas12a/gRNA is triggered, leading to the cleavage of rationally designed single-strand DNA reporters (linear and hairpin) labelled with methylene blue (ssDNA-MB) and bound to the electrode surface. In principle, this sensing mechanism can be adapted to any bacterium by choosing a proper guide RNA to target a specific sequence of its DNA. The biosensor's performance was assessed for two representative pathogens (a Gram-negative, Escherichia coli, and a Gram-positive, Staphylococcus aureus), and results obtained with inkjet-printed gold electrodes were compared with those obtained by commercial screen-printed gold electrodes. Our results show that the use of inkjet-printed nanostructured gold electrodes, which provide a large surface area, in combination with the use of hairpin reporters containing a poly-T loop can increase the sensitivity of the assay corresponding to a signal variation of 86%. DNA targets amplified from various clinically isolated bacteria, have been tested and demonstrate the potential of the proposed platform for point-of-need applications.

Graphene derivative-based ink advances inkjet printing technology for fabrication of electrochemical sensors and biosensors

The field of biosensing would significantly benefit from a disruptive technology enabling flexible manufacturing of uniform electrodes. Inkjet printing holds promise for this, although realizing full electrode manufacturing with this technology remains challenging. We introduce a nitrogen-doped carboxylated graphene ink (NGA-ink) compatible with commercially available printing technologies. The water-based and additive-free NGA-ink was utilized to produce fully inkjet-printed electrodes (IPEs), which demonstrated successful electrochemical detection of the important neurotransmitter dopamine. The cost-effectiveness of NGA-ink combined with a total cost per electrode of $0.10 renders it a practical solution for customized electrode manufacturing. Furthermore, the high carboxyl group content of NGA-ink (13 wt%) presents opportunities for biomolecule immobilization, paving the way for the development of advanced state-of-the-art biosensors. This study highlights the potential of NGA inkjet-printed electrodes in revolutionizing sensor technology, offering an affordable, scalable alternative to conventional electrochemical systems.

Enzyme Immobilization by Inkjet Printing on Reagentless Biosensors for Electrochemical Phosphate Detection.

Enzyme-based biosensors commonly utilize the drop-casting method for their surface modification. However, the drawbacks of this technique, such as low reproducibility, coffee ring effects, and challenges in mass production, hinder its application. To overcome these limitations, we propose a novel surface functionalization strategy of enzyme crosslinking via inkjet printing for reagentless enzyme-based biosensors. This method includes printing three functional layers onto a screen-printed electrode: the enzyme layer, crosslinking layer, and protective layer. Nanomaterials and substrates are preloaded together during our inkjet printing. Inkjet-printed electrodes feature a uniform enzyme deposition, ensuring high reproducibility and superior electrochemical performance compared to traditional drop-casted ones. The resultant biosensors display high sensitivity, as well as a broad linear response in the physiological range of the serum phosphate. This enzyme crosslinking method has the potential to extend into various enzyme-based biosensors through altering functional layer components.

Electrical and mechanical performance of Inkjet-printed flexible electrodes based on reduced graphene oxide/silver nanoparticles

Electrical and mechanical performance of Inkjet-printed flexible electrodes based on reduced graphene oxide/silver nanoparticles

Pattern-dependent resistivity variations in inkjet-printed conductors due to non-uniform ink drying

When fabricating inkjet-printed electronic devices and circuits, inkjet-printed conductive materials require drying and sintering to improve electrical conductivity. Electrical conductivity should be the same irrespective of pattern design, size, location, or density of adjacent patterns. However, we demonstrate that spatial variations in the drying process for inkjet-printed patterns with proximity to others cause resistivity variations. These resistivity variations are studied here experimentally for different circuit patterns and in arrays of inkjet-printed square electrodes. This variation depends not only on the location of each electrode in an array but also on the number of electrodes. This means that for the same drying temperature and duration, the array with a larger number of electrodes exhibits a larger resistivity variation. The sooner an electrode dries, the lower resistivity it achieves. The resistivity variation between an individual electrode and the center electrode in a 7 × 7 electrode array can be a factor of seven. This variation decreases for lower numbers of electrodes to a factor of three for a 3 × 3 array. Furthermore, x-ray photoelectron spectroscopy analyses provide evidence for the residual presence of carbon-based materials within electrodes after the drying process. These results confirm that the location of electrodes within an array significantly influences the amount of residual carbon-based materials, thereby contributing to resistivity variations. Although intense pulsed light sintering can decrease this variation, its optimal parameters depend on the printed designs, and our simulation results show a non-uniform temperature profile over the electrode arrays. Temperature increases more at the center of patterns than the corners, which can be useful in this case to improve resistivity uniformity. In this study, for the first time, we show how different printed shapes and designs can result in non-uniform resistivity after drying and sintering.

Unleashing inkjet-printed nanostructured electrodes and battery-free potentiostat for the DNA-based multiplexed detection of SARS-CoV-2 genes

Following the global COVID-19 pandemic triggered by SARS-CoV-2, the need for rapid, specific and cost-effective point-of-care diagnostic solutions remains paramount. Even though COVID-19 is no longer a public health emergency, the disease still poses a global threat leading to deaths, and it continues to change with the risk of new variants emerging causing a new surge in cases and deaths. Here, we address the urgent need for rapid, cost-effective and point-of-care diagnostic solutions for SARS-CoV-2. We propose a multiplexed DNA-based sensing platform that utilizes inkjet-printed nanostructured gold electrodes and an inkjet-printed battery-free near-field communication (NFC) potentiostat for the simultaneous quantitative detection of two SARS-CoV-2 genes, the ORF1ab and the N gene. The detection strategy based on the formation of an RNA-DNA sandwich structure leads to a highly specific electrochemical output. The inkjet-printed nanostructured gold electrodes providing a large surface area enable efficient binding and increase the sensitivity. The inkjet-printed battery-free NFC potentiostat enables rapid measurements and real-time data analysis via a smartphone application, making the platform accessible and portable. With the advantages of speed (5 min), simplicity, sensitivity (low pM range, ∼450% signal gain) and cost-effectiveness, the proposed platform is a promising alternative for point-of-care diagnostics and high-throughput analysis that complements the COVID-19 diagnostic toolkit.

Easy-to-prepare graphene-based inkjet-printed electrodes for diclofenac electrochemical sensing

Inkjet-printed electrodes (IPEs) from flexible Kapton® as substrate and easy to prepare graphene oxide (GO)-based inks (K/GO) were prepared using a standard desktop printer. Subsequently, they were submitted to a post-processing thermal treatment (K/GO_TR400) and assessed as disposable working electrodes (WEs) for diclofenac (DCF) indirect electrochemical detection at pH 7.0 (close to physiological pH value). DCF monitoring is attracting much interest, due to its classification as contaminant of emerging concern in water sources. The performance of the printed active sensor material was compared to that of thermally reduced (at 400 °C) graphene oxide (TRGO-400, in a powder form), which has been successfully used as glassy carbon electrode (GCE) modifier for the detection of DCF. This electrode worked linearly within the concentration range between 5 and 25 μM with an LOD value of 2.25 μM. Moreover, the morphology and chemical composition of the obtained IPEs were characterized by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) and compared with GCE/TRGO-400. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements using a miniaturized 3-electrode cell of the post-processed IPEs showed a promising electrochemical performance for DCF sensing. Thus, this study demonstrated the effective partial recovery of the valuable properties of graphene on the IPEs after the thermal treatment and the successful production of flexible and disposable electrodes for target analyte detection. Therefore, this is a promising alternative to conventional modified GCEs, as it offers a facile approach for the fabrication of cutting edge graphene-based electrodes and widens the available portfolio of electrochemical sensors towards detection of water contaminants of emerging concern.

Characterizations and Inkjet Printing of Carbon Black Electrodes for Dielectric Elastomer Actuators.

Dielectric elastomer actuators (DEAs) have been proposed as a promising technology for developing soft robotics and stretchable electronics due to their large actuation. Among available fabrication techniques, inkjet printing is a digital, mask-free, material-saving, and fast technology, making it versatile and appealing for fabricating DEA electrodes. However, there is still a lack of suitable materials for inkjet-printed electrodes. In this study, multiple carbon black (CB) inks were developed and tested as DEA electrodes inkjet-printed on acrylic membranes (VHB). Triethylene glycol monomethyl ether (TGME) and chlorobenzene (CLB) were selected to disperse CB. The inks' stability, particle size, surface tension, viscosity, electrical resistance, and printability were characterized. The DEA with Ink-TGME/CLB (mixture solvent) electrodes obtained 80.63% area strain, a new benchmark for the DEA actuation with CB powder electrodes on VHB. The novelty of this work involves the disclosure of a new ink recipe (TGME/CLB/CB) for inkjet printing that can obtain stable drop formations with a small nozzle (17 × 17 μm), high resolution (∼25 μm, approaching the limit of drop-on-demand inkjet printing), and the largest area strain of DEAs under similar conditions, distinguishing this contribution from the previous works, which is important for the fabrication and miniaturization of DEA-based soft and stretchable electronics.

Electrochemical Determination of Epinephrine in Pharmaceutical Preparation Using Laponite Clay-Modified Graphene Inkjet-Printed Electrode.

Epinephrine (EP, also called adrenaline) is a compound belonging to the catecholamine neurotransmitter family. It can cause neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. This work describes an amperometric sensor for the electroanalytical detection of EP by using an inkjet-printed graphene electrode (IPGE) that has been chemically modified by a thin layer of a laponite (La) clay mineral. The ion exchange properties and permeability of the chemically modified electrode (denoted La/IPGE) were evaluated using multi-sweep cyclic voltammetry, while its charge transfer resistance was determined by electrochemical impedance spectroscopy. The results showed that La/IPGE exhibited higher sensitivity to EP compared to the bare IPGE. The developed sensor was directly applied for the determination of EP in aqueous solution using differential pulse voltammetry. Under optimized conditions, a linear calibration graph was obtained in the concentration range between 0.8 µM and 10 μM. The anodic peak current of EP was directly proportional to its concentration, leading to detection limits of 0.34 μM and 0.26 μM with bare IPGE and La/IPGE, respectively. The sensor was successfully applied for the determination of EP in pharmaceutical preparations. Recovery rates and the effects of interfering species on the detection of EP were evaluated to highlight the selectivity of the elaborated sensor.

Feasibility of a piezoelectric pressure sensor using metal-organic framework hafnium-based UiO-66 and inkjet-printed interdigitated electrodes

Metal-organic framework (MOF) hafnium-based UiO-66 is a promising material for piezoelectric pressure sensors. The synthetic material is advantageous due to its tunability, porosity, and capability for wearable technology. Additionally, MOF UiO-66 possesses superior stability and exhibits both piezoelectric and ferroelectric responses. The material is synthesized via a solvothermal approach and examined through XRD, FT-IR, and UV-Vis spectroscopy. This study aims to evaluate the piezoelectric and ferroelectric properties and investigate the preliminary steps of incorporating a UiO-66 formulated functional ink with interdigitated electrodes by drop casting a thin film onto printed silver interdigitated electrodes and observing compatible solvents for ink formulation.

Aqueous MXene inks for inkjet-printing microsupercapacitors with ultrahigh energy densities

Although inkjet-printing technology has achieved significant development in preparing scalable and adaptable energy storage devices for portable and micro devices, searching for additive-free and environmentally friendly aqueous inks is a significant challenge. Hence, an aqueous MXene/sodium alginate-Fe2+ hybrid ink (denoted as MXene/SA-Fe) with solution processability and suitable viscosity is prepared for direct inkjet printing microsupercapacitors (MSCs). The SA molecules are adsorbed on the surface of MXene nanosheets to construct three-dimensional (3D) structures, thus effectively alleviating the two notorious problems of oxidation and self-restacking of MXene. Concurrently, Fe2+ ions can compress the ineffective macropore volume and make the 3D structure more compact. Moreover, the hydrogen and covalent bonding formed between the MXene nanosheet, SA, and Fe2+ effectively protects the oxidation of MXene and thus increases its stability. Thus, the MXene/SA-Fe ink endows the inkjet-printed MSC electrode with abundant active sites for ion storage and a highly conductive network for electron transfer. As a demonstration, the MXene/SA-Fe ink is used to direct inkjet-printed MSCs with an electrode spacing of 310 μm, which exhibit remarkable capacitances of 123.8 mF cm−2 (@5 mV s−1), good rate capability, an extraordinary energy density of 8.44 μWh cm−2 at a power density of 33.70 μW cm−2, long-term cycling stability of 91.4 % capacitance retention after 10,000 cycles, and surprising mechanical durability with 90.0 % of its initial capacitance retained after 10,000 bending cycles. Therefore, MXene/SA-Fe inks are expected to create various opportunities for printable electronics.

Lamination of inkjet-printed Ag electrodes for highly patternable and customizable polymer light-emitting diodes

Inkjet printing that ensures superior patternability and customizability can be fully exploited as top electrodes in thin-film-based light-emitting devices. However, direct inkjet printing onto multi-layered thin films severely damages the underlying functional layers due to intermixing with the ink solvents, resulting in poor device efficiencies. Here, we report a lamination of inkjet-printed Ag electrodes as a top cathode for polymer light-emitting diodes (PLEDs). The organometallic Ag ink was printed on surface-modified elastomers with stable wettability, and drop spacing was further optimized for low surface roughness. The lamination of Ag cathodes establishes intimate contact between the electrodes and the functional layers, allowing light emission of PLEDs along the printed patterns. Furthermore, additional heat treatment improves the electron injection, resulting in a reduction of turn-on voltage and higher current/power efficiencies. To illustrate the practicability of our laminated PLEDs, we demonstrate passive-matrix driven PLEDs with all-inkjet-printed electrodes by laminating the top cathode arrays crossing the bottom inkjet-printed anodes.

Self-aligned bilayer inkjet printing process for reducing shadow area by auxiliary electrodes in OLED lighting

Auxiliary electrodes are a key component for uniform luminance of large area organic light emitting diode (OLED) lighting. A shadow area is created by the auxiliary electrodes covering the light emitting area of ​​the OLED, reducing the light emitting area. To minimize the shadow area of ​​ printed auxiliary electrodes, we developed a self-aligned bilayer inkjet printing (SABP) process. A silver-insulator bilayer was self-aligned by a hydrophobic bank where the ink did not spread. Through the SABP process, the insulator was covered with a width that was about 400 nm wider than the width of the Ag electrode. In addition, electro-optical characteristics such as luminance, current density, current efficiency, and external quantum efficiency of 40 × 40 mm 2 OLED lighting were measured to confirm the effect of the fabricated auxiliary electrodes. The luminance non-uniformity of the OLED lighting with the printed auxiliary electrode was 17%. For OLED lighting, inkjet-printed auxiliary electrodes provide potentials comparable to those of vacuum-deposited auxiliary electrodes. • Self-aligned bilayer printing patterns the silver-insulator of an auxiliary electrode for OLED lighting. • The auxiliary electrode is printed with a height of 1.09 μm and a width of 21.1 μm. • The insulator covers the width of the Ag electrode with a margin of 400 nm wide. • Self-aligned bilayer printing is effective in reducing a shadow area by auxiliary electrodes. • The luminance non-uniformity of OLED lighting with printed auxiliary electrodes is 17%.

(Invited, Digital Presentation) 3D Printing of Flexible and Wearable Supercapacitors

Flexible and wearable electronics have recently emerged as a potential solution for next-generation electronics for healthcare, sports, transport, military, soft robotics, artificial intelligence, the internet of things, and other applications. However, these devices are still at a fledgling stage due to the use of traditional manufacturing processes, lack of compatible power supply, poor commercialization capabilities, and integration problems. Here, we present 3D printing approaches for developing batteries and supercapacitors for flexible electronic applications. Such manufacturing techniques can revolutionize the rapidly growing field of flexible and wearable electronics due to their several attributes like; rapid production, simplicity, capability to produce size and shape versatile patterns, computer-aided design, user control, and environmental friendliness.(1-4) Different aspects of 3D printed supercapacitors (such as; device design, ink preparation of electrode/ electrolyte components, rheology control of inks, surface modification to get good print quality, electrochemical performance of printed devices, and flexibility analysis) will be discussed in detail with a focus on future requirements.References Sundriyal P, Bhattacharya S. Scalable micro-fabrication of flexible, solid-state, inexpensive, and high-performance planar micro-supercapacitors through inkjet printing. ACS Applied Energy Materials. 2019;2(3):1876-90.Sundriyal P, Bhattacharya S. Inkjet-printed electrodes on A4 paper substrates for low-cost, disposable, and flexible asymmetric supercapacitors. ACS Applied Materials & Interfaces. 2017;9(44):38507-21.Sundriyal P, Bhattacharya S, editors. 3-D Printed Electrode Materials for Low-Cost, Flexible, and Stretchable Energy Storage Devices. ECS Meeting s; 2019: IOP Publishing.Sundriyal P, Bhattacharya S. Textile-based supercapacitors for flexible and wearable electronic applications. Scientific reports. 2020;10(1):1-15.

Organic thin-film transistors with inkjet-printed electrodes on hydrophobic Teflon-AF gate dielectric with reversible surface properties

Printed organic thin-film transistors (OTFTs) are promising for flexible, low-cost electronics; however, a major challenge is that successive processing steps of multiple solution-processed layers can interfere with each other. In particular, hydrophobic fluoropolymers are a promising group of materials to fabricate gate dielectrics with low charge trap density and properties such as good thermal stability, chemical inertness, low dielectric constant, and water repellency. However, the main difficulty in incorporating hydrophobic fluoropolymers in printed electronic devices is their low surface energy. Plasma treatment is a common method for surface modification that renders these hydrophobic layers wettable to print subsequent layers. This plasma processing can also affect the interface with the organic semiconductor (OSC) and transistor performance, which is studied here for the first time. The morphological and surface chemical properties of Teflon amorphous fluoropolymer (Teflon-AF) films change after plasma treatment and gradually reverse after post-annealing of subsequent layers as demonstrated here. Here, we fabricate solution-processed OTFTs with Teflon-AF as the gate dielectric. We report OTFTs with inkjet-printed source and drain electrodes with a minimum channel length of 20 μm on Teflon-AF for the first time. We show that the annealing of the inkjet-printed electrodes changes the morphology and the surface chemistry of the Teflon-AF gate dielectric underneath, thus reversing the effect of the plasma. We show that this electrode post-annealing step can improve the transistor performance by improving the interface between the Teflon-AF gate dielectric and the OSC in terms of smoothness and hydrophobicity. The transistor parameters such as mobility, on/off current ratio, and threshold voltage all follow a trend explained here by the properties of the Teflon-AF films. Increasing the post-annealing temperature to just below complete surface reversibility decreases surface roughness and trap-sites created after plasma treatment leading to optimized device performance. We characterize the Teflon-AF surface with contact angle measurement, roughness measurement, Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS). This understanding of the reversibility of the Teflon-AF surface helps achieve optimal performance of devices and systems incorporating fluoropolymers. • The challenge of processing OTFT layers on hydrophobic dielectrics is addressed. • 20 μm channel OTFTs with inkjet-printed electrodes on hydrophobic dielectric are achieved. • Teflon-AF surface changes after plasma and reverses after post-annealing. • Electrode annealing changes the morphology and surface chemistry of the dielectric. • Electrode annealing can improve the gate dielectric/organic semiconductor interface.

Polymer Skulls With Integrated Transparent Electrode Arrays for Cortex-Wide Opto-Electrophysiological Recordings.

Electrophysiology and optical imaging provide complementary neural sensing capabilities - electrophysiological recordings have high temporal resolution, while optical imaging allows recording of genetically-defined populations at high spatial resolution. Combining these two modalities for simultaneous large-scale, multimodal sensing of neural activity across multiple brain regions can be very powerful. Here, transparent, inkjet-printed electrode arrays with outstanding optical and electrical properties are seamlessly integrated with morphologically conformant transparent polymer skulls. Implanted on transgenic mice expressing the Calcium (Ca2+ ) indicator GCaMP6f in excitatory neurons, these "eSee-Shells" provide a robust opto-electrophysiological interface for over 100 days. eSee-Shells enable simultaneous mesoscale Ca2+ imaging and electrocorticography (ECoG) acquisition from multiple brain regions covering 45 mm2 of cortex under anesthesia and in awake animals. The clarity and transparency of eSee-Shells allow recording single-cell Ca2+ signals directly below the electrodes and interconnects. Simultaneous multimodal measurement of cortical dynamics reveals changes in both ECoG and Ca2+ signals that depend on the behavioral state.