Polyimide Sheets Research Articles

Electrochemical sensor for rapid detection of fentanyl using laser-induced porous carbon-electrodes.

The growing pervasiveness of opioid-based drugs such as fentanyl and its analogs represent a foremost hazard to the civilian population and burden on the first responders and clinicians. Thus, to enable a rapid and low-cost surveillance system to detect fentanyl in a non-ideal environment, we demonstrate the use of laser-induced nano-porous carbon structures directly onto commercially available polyimide sheets for rapid and cost-effective manufacturing of electrochemical sensors for fentanyl detection. The porous carbon surface instigated by various laser energy densities was analyzed towards morphological, vibrational, and fentanyl sensing properties. The results showed that laser carbonized electrode (LCE) prepared with 31J/cm2 laser energy densities showed the highest level of porosity, surface roughness, and thereby enhanced sensitivity towards fentanyl detection by square-wave voltammetry (SWV) with a 1µM limit of detection. This new disposable sensor strip offers an information-rich electrochemical fingerprint of fentanyl oxidation at + 0.526V (vs Ag/AgCl) on the surface of laser carbonized electrodes with high linear (R2 = 0.99) sensitivity (0.025 µA⋅µM-1⋅cm-2) and reproducibility (RSD = 5%), within the clinically relevant working range of 20-200µM with similar performance in both PBS and serum samples. The laser carbonized electrode surface was further found to be selective towards fentanyl concentrations in the presence of various cutting agents. This technology could provide a new route towards scalable manufacturing of cost-effective sensors for rapid detection of opioid misuse and potentially save the lives from systemic side effects.

Carbon Cloth-Based Electrochemical Device for Specific and Sensitive Detection of Ascorbic Acid and Tryptophan

Herein, a novel, flexible and inexpensive carbon-cloth based electrochemical device (CCED) is proposed with polyimide (PI) sheet as a base substrate. CC, embedded with numerous microfibers, was used as a sensing substrate. A CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser was employed for laser cutting three CC electrodes with desired dimensions, which were bonded on the PI sheet using a double-sided tape. Unmodified CC was used as working and counter electrodes, whereas Ag/AgCl ink modified CC was a reference electrode. For creating a hydrophobic region and insulating the electrodes, lamination process was used. Further ascorbic acid (AA) and tryptophan (Tr) were used as analytes for sensing with natural and unmodified CCED surface. The electrochemical response was analyzed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimized conditions, the CCED was observed to be capable of determining AA and Tr in a neutral pH (phosphate buffer solution) at 0.4 V and 0.6 V in a linear range of 30 - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8000 ~\mu \text{M}$ </tex-math></inline-formula> and 20 – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6000 ~\mu \text{M}$ </tex-math></inline-formula> , with LOD of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$21.76 ~\mu \text{M}$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11.84 ~\mu \text{M}$ </tex-math></inline-formula> respectively at (S/N=3). Additionally, it was thoroughly investigated for common interfering species including Xanthine (Xn), Hypoxanthine (Hx), Uric acid (UA), Cysteine (Cy), Glucose (G) and Folic Acid (FA). The sensing platform was successfully applied for determination of AA and Tr in human real serum sample with appreciable recoveries.

Electrochemical Biosensor Based on Laser-Induced Graphene for COVID-19 Diagnosing: Rapid and Low-Cost Detection of SARS-CoV-2 Biomarker Antibodies

The severe acute respiratory syndrome originated by the new coronavirus (SARS-CoV-2) that emerged in late 2019, known to be a highly transmissible and pathogenic disease, has caused the COVID-19 global pandemic outbreak. Thus, diagnostic devices that help epidemiological public safety measures to reduce undetected cases and isolation of infected patients, in addition to significantly help to control the population’s immune response to vaccine, are required. To address the negative issues of clinical research, we developed a Diagnostic on a Chip platform based on a disposable electrochemical biosensor containing laser-induced graphene and a protein (SARS-CoV-2 specific antigen) for the detection of SARS-CoV-2 antibodies. The biosensors were produced via direct laser writing using a CO2 infrared laser cutting machine on commercial polyimide sheets. The presence of specific antibodies reacting with the protein and the K3[Fe(CN)6] redox indicator produced characteristic and concentration-dependent electrochemical signals, with mean current values of 9.6757 and 8.1812 µA for reactive and non-reactive samples, respectively, proving the effectiveness of testing in clinical samples of serum from patients. Thus, the platform is being expanded to be measured in a portable microcontrolled potentiostat to be applied as a fast and reliable monitoring and mapping tool, aiming to assess the vaccinal immune response of the population.

Albedo‐Enabled Enhanced Energy Harvesting via GaAs Bifacial Thin‐Film Solar Cells

In addition to direct solar illumination to the photovoltaic cell, the albedo effect provides a unique opportunity to enhance energy harvesting. However, conventional solar cells are inefficient albedo energy harvesters because the rear side of the cell is usually blocked by a thick substrate or metal contact. In this study, structurally thin active layers of GaAs thin‐film solar cells covered with transparent Ag nanowires that enable bifacial solar cell operations are fabricated. The GaAs bifacial thin‐film solar cell is fabricated by bonding the active regions of the solar cell on colorless polyimide sheets with highly transparent epoxy adhesives. The fabricated bifacial solar cells without any anti‐reflection coatings demonstrated power conversion efficiencies of 8.54 and 6.78% at the front and rear sides, respectively, under AM 1.5 G irradiance conditions. The increase in energy harvesting by the GaAs bifacial thin‐film solar cells was estimated, which showed approximately a 72% increase in short‐circuit current density (JSC) when the solar cells operated on a high‐reflection‐coated ground. Positioning the solar cells on snow or sand (deserts and beaches) increasedJSCby ≈44 and 31%, respectively, compared to monofacial solar cells.

Sub‐Zero Temperature Sensor Based on Laser‐Written Carbon

AbstractSub‐zero temperature sensors (SZTSs) have potential applications in safely storing COVID‐19 vaccines. Herein, an SZTS based on laser‐induced carbonization (LIC) achieved by a nanosecond infrared laser with a wavelength of 1064 nm is reported. Direct laser writing is adopted for laser‐induced carbon in Kapton polyimide sheets with a thickness of 125 µm. The sensor exhibits a good linear change in resistance to sub‐zero temperatures ranging from 0 to −150 °C, where the coefficient of determination adjusted R‐square (R2) value is 0.99238, which indicates a good linear fit. The sensor exhibits a stable static response at all temperatures over time. The dynamic responses by controlling the liquid nitrogen gas and placing an ice cube on the sensor are also measured to validate the sensor. Notably, the electrical performance of the sensor remains stable even after 15 h. The sensor response of the LIC sample validates the 3D variable range‐hopping charge transport mechanism, governed by the Mott equation with a good linear fit, which is mainly owing to disorder in its structure. LIC‐based SZTSs can enable sensors that are ultra‐fast to fabricate, roll‐to‐roll processable, economical, and more significantly, can be interfaced with flexible printed circuit boards without any additional interfacing.

Development of an Efficient Voltammetric Sensor for the Monitoring of 4-Aminophenol Based on Flexible Laser Induced Graphene Electrodes Modified with MWCNT-PANI.

Sensitive electrodes are of a great importance for the realization of highly performant electrochemical sensors for field application. In the present work, a laser-induced carbon (LIC) electrode is proposed for 4-Aminophenol (4-AP) electrochemical sensors. The electrode is patterned on a commercial low-cost polyimide (Kapton) sheet and functionalized with a multi-walled carbon nanotubes polyaniline (MWCNT-PANI) composite, realized by an in-situ-polymerization in an acidic medium. The LIC electrode modified with MWCNT-PAPNI nanocomposite was investigated by SEM, AFM, and electrochemically in the presence of ferri-ferrocyanide [Fe(CN)6]3−/4− by cyclic voltammetry and impedance spectroscopy. The results show a significant improvement of the electron transfer rate after the electrode functionalization in the presence of the redox mediators [Fe(CN)6]3−/4−, related directly to the active surface, which itself increased by about 18.13% compared with the bare LIG. The novel electrode shows a good reproducibility and a stability for 20 cycles and more. It has a significantly enhanced electro-catalytic activity towards electrooxidation reaction of 4-AP inferring positive synergistic effects between carbon nanotubes and polyaniline PANI. The presented electrode combination LIC/MWCNT-PANI exhibits a detection limit of 0.006 μM for the determination of 4-AP at concentrations ranging from 0.1 μM to 55 μM and was successfully applied for the monitoring in real samples with good recoveries.

Joining of Magnesium Alloy with Hard Laminates by Shot Peening

Magnesium alloys are increasingly being used in the field of transportation equipment, such as automobiles and aircraft, where energy saving is being promoted. However, the problem with magnesium alloys is that they have lower corrosion and wear resistance than steel materials. Therefore, a lot of research on alloy development and surface modification has been attempted. In the present study, to improve the corrosion resistance and wear resistance of magnesium alloys, dissimilar materials were joined using shot peening. Using a cast steel projection material having a diameter of 1 mm, the projection was performed at a projection speed of 60 m / s and a processing temperature of 300 ° C. The base alloys are AZ31, AZ61, AZX611, and AZ91D. The dissimilar material was an aluminum laminated material containing ceramic powders and a heat-resistant resin sheet. The ceramic powders were alumina and zirconia, with a particle size of 0.1 to 0.3 mm. Resin was a sheet of polyimide, with a thickness of 0.025 mm. The joinability was determined by microstructure observation and bending test. The three-point bending test destroyed the joint surface, but did not cause peeling of dissimilar materials from the substrate. It was also found that wear resistance was improved by joining hard dissimilar materials.

In situ growth of laser-induced graphene micro-patterns on arbitrary substrates.

In this article we report a new laser processing method, combining the in situ graphitization of polyimide with simultaneous transfer of the graphene patterns to arbitrary substrates. The synthesis conditions are similar to those normally used for the well-known laser-induced graphene method. The approach is based on the enclosure of polyimide sheets between microscope glass slides. Graphene patterns have been successfully generated on glass and on PDMS, as well as graphene decorated with metals and oxides. In order to illustrate the usefulness of the proposed approach, the method was applied to the fabrication of hybrid supercapacitors, which exhibited very good electrochemical performance.

Laser-Induced Graphene, Fused Filament Fabrication, and Aerosol Jet Printing for Realizing Conductive Elements of UHF RFID Antennas

In this work, three promising Additive Manufacturing (AM)/3D-printing technologies, able to realize conductive elements, are adopted in the realization of antennas. The selected techniques are Fused Filament Fabrication (FFF), Aerosol Jet Printing (AJP), and Laser-Induced Graphene (LIG), which have been compared by measuring the performance of an ultrahigh (UHF) radiofrequency identification (RFID) tag, specifically designed, and realized for the scope. Results have also been analyzed against to data obtained by a reference sample realized in Aluminum. The FFF tag has been manufactured by extruding the Electrifi conductive filament over an ABS printed substrate, used also for the AJP-made antenna. Conversely, the LIG tag has been produced by laser-burning a Kapton polyimide sheet. All the tested technologies, each one with its pros and cons, allowed to realize working prototypes, even if, as expected, with performance lower than the comparison sample. An electroplating process has been also adopted to increase conductivity, with improvements in the FFF prototype. The obtained results are quite satisfactory. Those related to LIG technology do not yet guarantee performance comparable to the other techniques. Nevertheless, the prospect of creating “green” and cost-effective antennas pushes towards further studies, already underway, which include the study of antenna shapes more suitable for the specific technique as well as process optimizations to increase conductivity.

Flexible Low-Temperature Ammonia Gas Sensor Based on Reduced Graphene Oxide and Molybdenum Disulfide

Owing to harsh working environments and complex industrial requirements, traditional gas sensors are prone to deformation damage, possess a limited detection range, require a high working temperature, and display low reliability, thereby necessitating the development of flexible and low-temperature gas sensors. In this study, we developed a low-temperature polyimide (PI)-based flexible gas sensor comprising a reduced graphene oxide (rGO)/MoS2 composite. The micro-electro-mechanical system technology was used to fabricate Au electrodes on a flexible PI sheet to form a “sandwiched” sensor structure. The rGO/MoS2 composites were synthesized via a one-step hydrothermal method. The gas-sensing response was the highest for the composite comprising 10% rGO. The structure of this material was characterized, and a PI-based flexible gas sensor comprising rGO/MoS2 was fabricated. The optimal working temperature of the sensor was 141 °C, and its response-recovery time was significantly short upon exposure to 50–1500 ppm NH3. Thus, this sensor exhibited high selectivity and a wide NH3 detection range. Furthermore, it possessed the advantages of low power consumption, a short response-recovery time, a low working temperature, flexibility, and variability. Our findings provide a new framework for the development of pollutant sensors that can be utilized in an industrial environment.

Multifunctional Metal‐oxide Integrated Monolayer Graphene Heterostructures for Planar, Flexible, and Skin‐mountable Device Applications

The adoption of nanostructured metal-oxides integrated graphene monolayers-based heterostructures appears to be a promising approach for enhancing the performance of various devices. However, precisely controlled growth of such unique heterostructures without disturbing the monolayer graphene characteristics remains a challenging task especially over a large area with good uniformity. Herein, ultrathin metal-oxide (p-Co 3 O 4 and n-ZnO) nanostructures (MONSs) integrated graphene monolayer (GML) heterostructures are carefully developed by fascinating the graphene native defects while nucleation and growth of MONSs. Metal-oxides integrated graphene monolayers with lower material densities (≤ 30 μg/cm 2 ) significantly enhanced the quality (2D/G ~5–9) and reduced the electrical resistance (11–17 Ω/sq.) of graphene layers, whereas the heterostructures developed with higher densities possess predominant water-oxidation characteristics than that of their individual components. Further, the Co 3 O 4 /GML heterostructures-based micro-supercapacitors, fabricated over 25 µm polyimide sheets, showed excellent mechanical stability and flexibility with a volumetric and specific capacitance of 7.76 F/cm 3 and 1.27 F/g, respectively. The ZnO/GML heterostructures designed over micron thick parylene film displayed exciting photoresistor characteristics with photosensitivity of ~1.54 and superb flexibility and skin-mountability. Synergistic multifunctional characteristics of these ultrathin heterostructures offer the possibility to realize various eco-friendly ultrathin as well as skin-mountable energy and health monitoring devices. Ultrathin metal-oxide(s) precisely integrated single-layer graphene heterostructures, developed by low-temperature methods, exhibit high conductivity and multifunctional characteristics. As a catalyst, the heterostructures show excellent electrocatalytic performance, and whereas, the active electrodes defined over flexible and skin-mountable surfaces exhibit significant energy storage and photoresistive characteristics. • Ultrathin metal-oxides nanostructures integrated graphene monolayers developed. • The heterostructures grown under optimum conditions possess high conductivity. • These heterostructures exhibited synergistic OER electrocatalytic performance. • Supercapacitors on flexible sheets showed good mechanical stability and durability. • The structures developed on ultrathin sheets are skin-mountable and integratable.

High-Performance Washable PM2.5 Filter Fabricated with Laser-Induced Graphene.

This study demonstrates a novel application of laser-induced graphene (LIG) as a reusable conductive particulate matter (PM) filter. Four types of LIG-based filters were fabricated based on the laser-induced pyrolysis of thin polyimide (PI) sheets, each pyrolyzed on either a single side or both sides, with or without densification. The LIG filters exhibited a high removal efficiency while maintaining minimal pressure drop compared to a commercial fiberglass filter. The densified LIG (dLIG) filters displayed a higher PM2.5 removal efficiency (>99.86%) than regular LIG filters. The dLIG filters also exhibited excellent durability when tested for washability by ultrasonication in tap water. After being cleaned and left to dry, the structures of the dLIG filters were well-maintained; their filtration efficiencies were also well-maintained (less than a 7% change in PM2.5 removal efficiency), and their resistances only marginally increased (less than a 7% increase after five uses). These results demonstrate the robustness and reusability of the dLIG filters and the accessibility of their cleaning (not requiring aggressive cleaning agents). These promising features will enable the application of LIG in economical, scalable, and high-performance air cleaning.

Soft, Bistable Actuators for Reconfigurable 3D Electronics.

Existing strategies for reconfigurable three-dimensional (3D) electronics are greatly constrained by either the complicated driven mechanisms or harsh demands for conductive materials. Developing a simple and robust strategy for 3D electronics reconstruction and function extension remains a challenge. Here, we propose a solvent-driven bistable actuator, which acts as a substrate to reconstruct the combined 3D electronic device. Extraction of silicon oil from a hybrid poly(dimethylsiloxane) (PDMS) circle sheet buckles the dish to a bistable structure. The ultraviolet (UV)/ozone treatment on one surface of the PDMS structure introduces an oxidized layer, yielding a bilayered, solvent-driven bistable smart actuator. The snap-back stimulus to the oxidized layer differs from the snap-through stimulus. Experimental and numerical studies reveal the fundamental regulations for buckling configurations and the bistable behavior of the actuator. The prepared bistable actuator drives the bonded kirigami polyimide (PI) sheets to diverse 3D structures from the original bending configuration, reversibly. A frequency-reconfigurable electrically small monopole antenna is presented as a demonstration, which paves a way for the applications of this actuator in the field of reconfigurable 3D electronics.

Surface Modification of Space Exposed Materials Induced by Low Energetic Proton Irradiation

The aim of this paper is to verify if commonly occurring space debris materials change their reflectivity and morphology after being exposed to low energy protons. Therefore, a set of six different materials frequently used in spacecraft engineering was irradiated with low energy (100 keV) protons to simulate the aging of their surfaces due to space radiation in low Earth orbit (LEO). A microscopic and spectroscopic analysis of the irradiated samples reveals that the tested materials containing organic polymers (Polytetrafluoroethylene (PTFE) and carbon fiber reinforced plastic (CFRP)) show changes in surface morphology. Metallic surfaces did not show surface modifications but we found changes in the reflectivity of coated polyimide sheets, like used in Multi Layer Insulation blankets, during and after proton irradiation. Our results show that space materials exhibit significant changes after irradiation equivalent to the dose accumulated after 100 years in LEO. This knowledge is highly relevant for the interpretation of optical data related to the observation of space debris as well as to studies about laser-matter interaction for laser-based debris removal.

Laser-scribed graphene sensor based on gold nanostructures and molecularly imprinted polymers: Application for Her-2 cancer biomarker detection

Laser scribed graphene (LSG) has shown great potential as a sensing platform due to its high sensitivity, simplicity, porosity, and flexibility. In this context, we report a novel biosensing platform that utilizes LSG electrodes modified with nanostructured gold and molecularly imprinted polymer (MIP) to enhance its sensitivity and selectivity. This biomimetic sensing platform is used to detect the human epidermal growth factor receptor 2 (Her-2) protein, a significant breast cancer biomarker. Hence, a simple and accurate biomimetic sensor is developed in this study. To the best of our knowledge, this is the first report on nanostructured gold modified MIP-based LSG sensor for Her-2. LSG electrodes are fabricated by irradiation of a polyimide sheet using a CO2 laser. Nanostructured gold is electrodeposited onto the LSG to enhance its sensitivity and facilitate better Her-2 immobilization on the sensor surface. For MIP preparation, 3, 4-ethylenedioxythiophene (EDOT) was electropolymerized after pre-adsorption of Her-2 on the electrode surface for 20 min. The MIP deposition, removal, and adsorption parameters were investigated and optimized. The developed sensing strategy showed an excellent ability to detect Her-2 in the concentration range from 1 to 200 ng/mL with a LOD of 0.43 ng/mL. The biomimetic sensor showed high selectivity towards the detection of Her-2 in the presence of other interfering molecules and appreciable recovery values of Her-2 in the spiked undiluted human serum samples. Finally, to show the potential application of the developed LSG-AuNS-MIP sensor as a point-of-care device, the sensor is integrated with a homemade open-source electrochemical analyzer KAUSTat to detect Her-2.

Laboratory diffracted x-ray blinking to monitor picometer motions of protein molecules and application to crystalline materials.

In recent years, real-time observations of molecules have been required to understand their behavior and function. To date, we have reported two different time-resolved observation methods: diffracted x-ray tracking and diffracted x-ray blinking (DXB). The former monitors the motion of diffracted spots derived from nanocrystals labeled onto target molecules, and the latter measures the fluctuation of the diffraction intensity that is highly correlated with the target molecular motion. However, these reports use a synchrotron x-ray source because of its high average flux, resulting in a high time resolution. Here, we used a laboratory x-ray source and DXB to measure the internal molecular dynamics of three different systems. The samples studied were bovine serum albumin (BSA) pinned onto a substrate, antifreeze protein (AFP) crystallized as a single crystal, and poly{2-(perfluorooctyl)ethyl acrylate} (PC8FA) polymer between polyimide sheets. It was found that not only BSA but also AFP and PC8FA molecules move in the systems. In addition, the molecular motion of AFP molecules was observed to increase with decreasing temperature. The rotational diffusion coefficients (DR) of BSA, AFP, and PC8FA were estimated to be 0.73 pm2/s, 0.65 pm2/s, and 3.29 pm2/s, respectively. Surprisingly, the DR of the PC8FA polymer was found to be the highest among the three samples. This is the first report that measures the molecular motion of a single protein crystal and polymer by using DXB with a laboratory x-ray source. This technique can be applied to any kind of crystal and crystalline polymer and provides atomic-order molecular information.

Simultaneous detection of Vitamin B12 and Vitamin C from real samples using miniaturized laser-induced graphene based electrochemiluminescence device with closed bipolar electrode

Herein, a two and three-channel laser-induced graphene (LIG) based closed bipolar Electrochemiluminescence (LIG-C-BPE-ECL) system was developed for sensing various analytes. Polyimide sheet was extensively used to fabricate two and three-channel LIG-C-BPE-ECL device as it has the ability to produce graphitized zones in a single step. CO2 infrared laser, with optimized parameters, was effectively used to fabricate closed bipolar (C-BPE) and driving electrodes (DEs). A miniaturized portable 3D printed system was developed to hold the device and place the smartphone to create a standalone ECL sensing platform. The smartphone not only captured the ECL signal but also powered the ECL device through DC to DC buck-boost converter. Two and three-channel LIG-C-BPE-ECL device was fabricated for the sensing of both individual and two analytes at the same time. The performance of the two-channel LIG-C-BPE-ECL device was validated by doing individual sensing of Hydrogen peroxide (H2O2), Vitamin B12 and Vitamin C for the linear range of 0.5–100 μM, 0.5–1000 nM and 1–1000 μM with a limit of detection (LOD) 0.303 μM, 0.109 nM and 0.96 μM respectively. Subsequently, three-channel LIG-C-BPE-ECL device was fabricated and simultaneous detection of Vitamin B12 and Vitamin C was accomplished. Finally, real sample analysis has been performed by doing concurrent sensing of vitamin B12 and vitamin C using three-channel LIG-C-BPE-ECL device with a good recovery rate. Such a miniaturized portable LIG-C-BPE-ECL system has great potential to be used in various applications including point of care testing.

A Field‐Deployable, Wearable Leaf Sensor for Continuous Monitoring of Vapor‐Pressure Deficit

AbstractThis work presents a wearable sensor for real‐time on‐leaf monitoring of relative humidity (RH), temperature, and vapor‐pressure deficit (VPD) of plants in both controlled environments and under field conditions. This sensor is flexible and conformable to the leaf surface. By integrating a graphene‐based RH sensing element and a gold‐based thin‐film thermistor on a polyimide sheet, the sensor allows accurate and continuous determination of VPD at the leaf surface, thereby providing information on plant transpiration. A greenhouse experiment validates the ability of the sensor to continuously and simultaneously monitor both the leaf RH and temperature of maize plants over more than 2 weeks. The sensor output also demonstrates the influences of light and irrigation on maize transpiration. Uniquely, by attaching multiple sensors onto different locations of a plant, it is possible to estimate the time required for water to be transported from the roots to each of the measured leaves along the stalk, as well as longitudinally from one position on a leaf toward the leaf tip. Sensors are also deployed in crop production fields where they demonstrate the ability to detect difference in transpiration between fertilized and unfertilized maize plants.

IR and UV Laser‐Induced Graphene: Application as Dopamine Electrochemical Sensors

AbstractLaser‐induced graphene (LIG) is inexpensive, fast, and easy to produce when compared to many other forms of graphene. Within the biosensing field, LIG electrodes are most often produced via infrared (IR) laser irradiation of polyimide sheets. Nevertheless, the usage of ultraviolet (UV) laser to produce LIG provides advantages in terms of sensor miniaturization because of its inherently higher scribing resolution. Yet, studies on the electrochemical performance of UV LIG, its relation with morphological and structural aspects as well as its comparison with IR LIG are still lacking. This work shows that both LIGs present swift electron transfer kinetics constituting excellent electrodes for electroanalysis. Extreme sensitivities of 93 and 58 µA µm−1 cm−2 at physiologically relevant dopamine (DA) concentrations are found for IR and UV LIG, respectively. Such sensitivities and good selectivity are achieved in the presence of physiologically relevant concentrations of ascorbic and uric acids, contrasting to the related literature employing IR LIG where such interferents are below the physiological range. Despite providing lower sensitivity, UV LIG is still an excellent material for DA biosensors, with the above‐mentioned advantages in terms of miniaturization. To our knowledge, these are among the highest sensitivities reported for voltammetric measurement of DA using carbon‐based materials.

Laser-Induced Graphene Printed Wearable Flexible Antenna-Based Strain Sensor for Wireless Human Motion Monitoring

Leveraging laser-induced graphene (LIG) in various flexible polymer electronics applications is becoming tremendously popular. LIG is porous multilayer graphene generated by a single-step process using infrared CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser onto the carbon-based polymers. In this article, a direct LIG printed microstrip patch antenna operating at the 5.8-GHz unlicensed band is presented. Based on simulations, the proposed design exhibited the desired unidirectional radiation characteristics with a measured gain of 1.82 dBi at the resonant frequency. The LIG-based rectangular patch was printed using the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser by selective reduction of polyimide (PI) sheet. The chemical properties of LIG were examined using various structural and morphological characterization techniques, which confirmed the formation of multilayer graphene. The sensitivity of the patch antenna was analyzed for measuring strain and its effect on LIG. By harnessing LIG on flexible material such as PI sheet, the antenna exhibited a threshold increase in sensitivity. The proposed sensor shows a sensitivity of 14.08 and 11.34 for compressive and tensile strain, respectively. Inspired by the significant sensitivity, the fabricated device has been examined for human motion monitoring by attaching it to the human hand for practical usage in real-time applications. The proposed antenna-based sensor reduces the number of components by eliminating external wiring and onboard battery. Moreover, it serves as both the sensing and wireless data transmitting element. Overall, this work demonstrates designing a compact, easy-to-fabricate, sensitive, and flexible antenna-based Internet of Things (IoT) sensor for motion detection, structural health monitoring, and industrial strain sensing applications.