Control of Meniscus Formation Using an Electrohydrodynamics Module in Roll-to-Roll Systems for the Stable Coating of Functional Layers.

In fabricating functional layers, including thin-film transistors and conductive electrodes, using roll-to-roll (R2R) processing on polymer-based PET film, the instability of the slot-die coating meniscus under a high-speed web impedes functional layer formation with the desired thickness and width. The thickness profiles of the functional layers significantly impact the performance of the final products. In this study, we introduce an electrohydrodynamic (EHD)-based voltage application module to a slot-die coater to ensure the uniformity of the cross-machine direction (CMD) thickness profile within the functional layer and enable a stable, high-speed R2R process. The module can effectively control the spreadability of the meniscus by utilizing variations in the surface tension of the ink. The effectiveness of the EHD module was experimentally verified by applying a high voltage to a slot-die coater while keeping other process variables constant. As the applied voltage increases, the CMD thickness deviation reduces by 64.5%, and the production rate significantly increases (up to 300%), owing to the formation of a stable coated layer. The introduction of the EHD-based application module to the slot-die coater effectively controlled the spreadability of the meniscus, producing large-area functional layers.

Room temperature roll-to-roll additive manufacturing of polydimethylsiloxane-based centrifugal microfluidic device for on-site isolation of ribonucleic acid from whole blood.

Polymer-based lab-on-a-disc (LoaD) devices for isolating ribonucleic acid (RNA) from whole blood samples have gained considerable attention for accurate biomedical analysis and point-of-care diagnostics. However, the mass production of these devices remains challenging in manufacturing cost and sustainability, primarily due to the utilization of a laser cutter or router computer numerical control (CNC) machine for engraving and cutting plastics in the conventional prototyping process. Herein, we reported the first energy-efficient room-temperature printing-imprinting integrated roll-to-roll manufacturing platform for mass production of a polydimethylsiloxane (PDMS)-based LoaD to on-site isolate ribonucleic acid (RNA) from undiluted blood samples. We significantly reduced energy consumption and eliminated thermal expansion variations between the mold, substrate, and resists by accelerating the PDMS curing time to less than 10 min at room temperature without using heat or ultraviolet radiation. The additive manufacturing technology was applied to fabricate a multi-depth flexible polymer mold that integrated macro (2 mm) and micro-sized (500 µm) features, which overcomes the economic and environmental challenges of conventional molding techniques. Our integrated R2R platform was enabled to print adhesion-promoting films at the first printing unit and continuously in-line imprint with a high replication accuracy (99%) for high-volume manufacturing of a new centrifugal microfluidic chip with an enhancement of mixing performance by integrating an efficient mixing chamber and serpentine micromixer. This research paved the way for scalable green manufacturing of large-volume polymer-based microfluidic devices, often required in real-world sample-driven analytical systems for clinical bioanalysis.

Mobile Efficient Diagnostics of Infectious Diseases via On-Chip RT-qPCR: MEDIC-PCR.

The COVID-19 outbreak has caused public and global health crises. However, the lack of on-site fast, reliable, sensitive, and low-cost reverse transcription polymerase chain reaction (RT-PCR) testing limits early detection, timely isolation, and epidemic prevention and control. Here, the authors report a rapid mobile efficient diagnostics of infectious diseases via on-chip -RT-quantitative PCR (RT-qPCR): MEDIC-PCR. First, the authors use a roll-to-roll printing process to accomplish low-cost carbon-black-based disposable PCR chips that enable rapid LED-induced photothermal PCR cycles. The MEDIC-PCR can perform RT (3 min), and PCR (9 min) steps. Further, the cohort of 89 COVID-19 and 103 non-COVID-19 patients testing is completed by the MEDIC-PCR to show excellent diagnostic accuracy of 97%, sensitivity of 94%, and specificity of 98%. This MEDIC-PCR can contribute to the preventive global health in the face of a future pandemic.

Tuning the charge carrier polarity of roll-to-roll gravure printed carbon nanotube-based thin film transistors by an atomic layer deposited alumina nanolayer.

Charge carrier polarity tuning in printed thin film transistors (TFTs) is a crucial step in order to obtain complementary printed devices. In this work, we studied the effect of an Al2O3 passivation layer on printed single-walled carbon nanotube (SWCNT) based TFTs to tune the charge carrier polarity. By varying the atomic layer deposition (ALD) temperature and Al2O3 layer thickness, we can tune the doping degree of Al2O3 to tailor the polarity of printed SWCNT-based TFTs (SWCNT-TFTs). The precise control of threshold voltage (Vth) and polarity from p-type to well-balanced ambipolar, and n-type SWCNT-TFTs is successfully demonstrated with high repeatability by optimizing the ALD temperature and Al2O3 layer thickness based on 20 printed samples per test. As a proof-of-concept, inverter logic circuits using the SWCNT-TFT with different polarity types are demonstrated. The ambipolar device-based inverter exhibits a voltage gain of 3.9 and the CMOS-based inverter exhibits a gain of approximately 4.3, which is comparable to the current roll-to-roll (R2R) printed inverter circuits. Different thicknesses of Al2O3 layer, coated by the ALD at different temperatures and thicknesses, provide a deep understanding of the device fabrication and control process to implement the tailored doping method to efficiently realize R2R printed SWCNT-TFT-based complementary electronic devices.

Towards Digital Twin Implementation in Roll-To-Roll Gravure Printed Electronics: Overlay Printing Registration Error Prediction Based on Printing Process Parameters.

Roll-to-roll gravure (R2Rg) has become highly affiliated with printed electronics in the past few years due to its high yield of printed thin-film transistor (TFT) in active matrix devices, and to its low cost. For printing TFTs with multilayer structures, achieving a high-precision in overlay printing registration accuracy (OPRA) is a key challenge to attain the high degree of TFT integration through R2Rg. To address this challenge efficiently, a digital twin paradigm was first introduced in the R2Rg system with an aim to optimize the OPRA by developing a predictive model based on typical input variables such as web tension, nip force, and printing speed in the R2Rg system. In our introductory-level digital twin, errors in the OPRA were collected with the variable parameters of web tensions, nip forces, and printing speeds from several R2Rg printing processes. Subsequently, statistical features were extracted from the input data followed by the training of a deep learning long-short term memory (LSTM) model for predicting machine directional error (MD) in the OPRA. As a result of training the LSTM model in our digital twin, its attained accuracy of prediction was 77%. Based on this result, we studied the relationship between the nip forces and printing speeds to predict the MD error in the OPRA. The results indicated a correlation between the MD error in the OPRA and the printing speed, as the MD error amplitude in the OPRA tended to decline at the higher printing speed.

Improving Stability of Roll-to-Roll (R2R) Gravure-Printed Carbon Nanotube-Based Thin Film Transistors via R2R Plasma-Enhanced Chemical Vapor-Deposited Silicon Nitride.

Single-walled carbon nanotubes (SWCNTs) have an advantage in printing thin film transistors (TFTs) due to their high carrier mobility, excellent chemical stability, mechanical flexibility, and compatibility with solution-based processing. Thus, the printed SWCNT-based TFTs (pSWCNT-TFTs) showed significant technological potential such as integrated circuits, conformable sensors, and display backplanes. However, the long-term environmental stability of the pSWCNT-TFTs hinders their commercialization. Thus, to extend the stability of the pSWCNT-TFTs, such devices should be passivated with low water and oxygen permeability. Herein, we introduced the silicon nitride (SiNx) passivation method on the pSWCNT-TFTs via a combination of roll-to-roll (R2R) gravure and the roll-to-roll plasma-enhanced vapor deposition (R2R-PECVD) process at low temperature (45 °C). We found that SiNx-passivated pSWCNT-TFTs showed ± 0.50 V of threshold voltage change at room temperature for 3 days and ±1.2 V of threshold voltage change for 3 h through a Temperature Humidity Test (85/85 test: Humidity 85%/Temperature 85 °C) for both p-type and n-type pSWCNT-TFTs. In addition, we found that the SiNx-passivated p-type and n-type pSWCNT-TFT-based CMOS-like ring oscillator, or 1-bit code generator, operated well after the 85/85 test for 24 h.

Rapid Uniformity Analysis of Fully Printed SWCNT-Based Thin Film Transistor Arrays via Roll-to-Roll Gravure Process.

The roll-to-roll (R2R) gravure process has the potential for manufacturing single-wall carbon nanotubes (SWCNT)-based thin film transistor (TFT) arrays on a flexible plastic substrate. A significant hurdle toward the commercialization of the R2R-printed SWCNT-TFT array is the lack of a suitable, simple, and rapid method for measuring the uniformity of printed products. We developed a probing instrument for characterizing R2R gravure printed TFT, named PICR2R-TFT, for rapidly characterizing R2R-printed SWCNT-TFT array that can present a geographical distribution profile to pinpoint the failed devices in an SWCNT-TFT array. Using the newly developed PICR2R-TFT instrument, the current-voltage characteristics of the fabricated SWCNT-TFT devices could be correlated to various R2R-printing process parameters, such as channel length, roll printing length, and printing speed. Thus, by introducing a characterization tool that is reliable and fast, one can quickly optimize the R2R gravure printing conditions to enhance product uniformity, thereby maximizing the yield of printed SWCNT-TFT arrays.

Vancomycin-conjugated polydopamine-coated magnetic nanoparticles for molecular diagnostics of Gram-positive bacteria in whole blood.

BACKGROUND: Sepsis is caused mainly by infection in the blood with a broad range of bacterial species. It can be diagnosed by molecular diagnostics once compounds in the blood that interfere with molecular diagnostics are removed. However, this removal relies on ultracentrifugation. Immunomagnetic separation (IMS), which typically uses antibody-conjugated silica-coated magnetic nanoparticles (Ab-SiO2-MNPs), has been widely applied to isolate specific pathogens in various types of samples, such as food and environmental samples. However, its direct use in blood samples containing bacteria is limited due to the aggregation of SiO2-MNPs in the blood and inability to isolate multiple species of bacteria causing sepsis. RESULTS: In this study, we report the synthesis of vancomycin-conjugated polydopamine-coated (van-PDA-MNPs) enabling preconcentration of multiple bacterial species from blood without aggregation. The presence of PDA and van on MNPs was verified using transmission electron microscopy, X-ray photoelectron spectroscopy, and energy disruptive spectroscopy. Unlike van-SiO2-MNPs, van-PDA-MNPs did not aggregate in the blood. Van-PDA-MNPs were able to preconcentrate several species of Gram-positive bacteria in the blood, lowering the limit of detection (LOD) to 10 colony forming units/mL by polymerase chain reaction (PCR) and quantitative PCR (qPCR). This is 10 times more sensitive than the LOD obtained by PCR and qPCR using van-SiO2-MNPs. CONCLUSION: These results suggest that PDA-MNPs can avoid aggregation in blood and be conjugated with receptors, thereby improving the sensitivity of molecular diagnostics of bacteria in blood samples.

Control of the Drying Patterns for Complex Colloidal Solutions and Their Applications.

The uneven deposition at the edges of an evaporating droplet, termed the coffee-ring effect, has been extensively studied during the past few decades to better understand the underlying cause, namely the flow dynamics, and the subsequent patterns formed after drying. The non-uniform evaporation rate across the colloidal droplet hampers the formation of a uniform and homogeneous film in printed electronics, rechargeable batteries, etc., and often causes device failures. This review aims to highlight the diverse range of techniques used to alleviate the coffee-ring effect, from classic methods such as adding chemical additives, applying external sources, and manipulating geometrical configurations to recently developed advancements, specifically using bubbles, humidity, confined systems, etc., which do not involve modification of surface, particle or liquid properties. Each of these methodologies mitigates the edge deposition via multi-body interactions, for example, particle-liquid, particle-particle, particle-solid interfaces and particle-flow interactions. The mechanisms behind each of these approaches help to find methods to inhibit the non-uniform film formation, and the corresponding applications have been discussed together with a critical comparison in detail. This review could pave the way for developing inks and processes to apply in functional coatings and printed electronic devices with improved efficiency and device yield.

Enhancing Mixing Performance in a Rotating Disk Mixing Chamber: A Quantitative Investigation of the Effect of Euler and Coriolis Forces.

Lab-on-a-CD (LOCD) is gaining importance as a diagnostic platform due to being low-cost, easy-to-use, and portable. During LOCD usage, mixing and reaction are two processes that play an essential role in biochemical applications such as point-of-care diagnosis. In this paper, we numerically and experimentally investigate the effects of the Coriolis and Euler forces in the mixing chamber during the acceleration and deceleration of a rotating disk. The mixing performance is investigated under various conditions that have not been reported, such as rotational condition, chamber aspect ratio at a constant volume, and obstacle arrangement in the chamber. During disk acceleration and deceleration, the Euler force difference in the radial direction causes rotating flows, while the Coriolis force induces perpendicular vortices. Increasing the maximum rotational velocity improves the maximum rotational displacement, resulting in better mixing performance. A longer rotational period increases the interfacial area between solutions and enhances mixing. Mixing performance also improves when there is a substantial difference between Euler forces at the inner and outer radii. Furthermore, adding obstacles in the angular direction also passively promotes or inhibits mixing by configuration. This quantitative investigation provides valuable information for designing and developing high throughput and multiplexed point-of-care LOCDs.

Strain Optimization of Tensioned Web through Computational Fluid Dynamics in the Roll-to-Roll Drying Process.

Unpredictable web temperature distributions in the dryer and strain deviations in the cross-machine (CMD) and machine (MD) directions could hamper the manufacture of smooth functional layers on polymer-based webs through the roll-to-roll (R2R) continuous process system. However, research on this topic is limited. In this study, we developed a structural analysis model using the temperature distribution of the web as a boundary condition to analyze the drying mechanism of the dryer used in an R2R system. Based on the results of this model, we then applied structural modifications to the flow channel and hole density of the aluminum plate of the dryer. The model successfully predicted the temperature and strain distributions of the web inside the dryer in the CMD and MD by forming a tension according to the speed difference of the driven rolls at both ends of the span. Our structural improvements significantly reduced the temperature deviation of the moving web inside the dryer by up to 74% and decreased the strain deviation by up to 46%. The findings can help prevent web unevenness during the drying process of the R2R system, which is essential to minimize the formation of defects on functional layers built over polymer-based webs.

Effect of Radial Stress on the Nanoparticle-Based Electrolyte Layer in a Center-Wound Roll with Roll-to-Roll Systems.

Recently, slot-die coating based on the roll-to-roll process has been actively used to fabricate nanoparticle-based electrolyte layers because it is advantageous for high-speed processes and mass production of uniformly thick electrolyte layers. In this process, the fabricated electrolyte layer is stored as a wound roll throughout the rewinding process. We analyzed the defects and geometric changes in an electrolyte layer, i.e., gadolinium-doped cerium oxide (GDC), due to the radial stress in the wound roll. We found that the thickness of the coated layer could be decreased by increasing the radial stress, i.e., cracks can be generated in the coated layer if excessively high radial stress is applied to the wound-coated layer. More thickness changes and crack defects were generated with time due to the residual stress in the wound roll. Finally, we analyzed the effects of taper tension profiles on the defects of the coated layer in the wound roll and determined the taper tension profile to minimize defects.

Impact of Sensor Data Characterization with Directional Nature of Fault and Statistical Feature Combination for Defect Detection on Roll-to-Roll Printed Electronics.

Gravure printing, which is a roll-to-roll printed electronics system suitable for high-speed patterning of functional layers have advantages of being applied to flexible webs in large areas. As each of the printing procedure from inking to doctoring followed by ink transferring and setting influences the quality of the pattern geometry, it is necessary to detect and diagnose factors causing the printing defects beforehand. Data acquisition with three triaxial acceleration sensors for fault diagnosis of four major defects such as doctor blade tilting fault was obtained. To improve the diagnosis performances, optimal sensor selection with Sensor Data Efficiency Evaluation, sensitivity evaluation for axis selection with Directional Nature of Fault and feature variable optimization with Feature Combination Matrix method was applied on the raw data to form a Smart Data. Each phase carried out on the raw data progressively enhanced the diagnosis results in contents of accuracy, positive predictive value, diagnosis processing time, and data capacity. In the case of doctor blade tilting fault, the diagnosis accuracy increased from 48% to 97% with decreasing processing time of 3640 s to 16 s and the data capacity of 100 Mb to 5 Mb depending on the input data between raw data and Smart Data.

Proving the robustness of a PEDOT:PSS-based thermistor via functionalized graphene oxide-poly(vinylidene fluoride) composite encapsulation for food logistics.

The instability of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) under a humid condition is the major limitation in the practical development of a flexible thermistor. Here, we introduced a functionalized graphene oxide-polyvinylidene fluoride (FGO-PVDF) composite as an encapsulation layer to prove the reliability of PEDOT:PSS thermistors under high-humidity conditions. The FGO-PVDF-encapsulated thermistor exhibited good linearity, a resolution of 1272.57 Ω per °C, a temperature coefficient of resistance equal to -3.95 × 10-3 per °C, stable performance, and an acceptable response time (∼40 s per °C) calibrated in the temperature range between -10 °C and 30 °C, resembling the temperature of a cold chain system. For applications in a food cold chain system, this thermistor was integrated into a roll-to-roll (R2R) gravure-printed NFC antenna, a microcontroller-embedded Si-chip transponder, and a printed battery to work as a smart label to wirelessly monitor the time-temperature history (TTH) of a food package. A proof-of-concept study was demonstrated by attaching an NFC-enabled hybrid TTH logger, a smart label, in a chicken package.

Roll-to-Roll Gravure Printed Electrochemical Sensors for Wearable and Medical Devices.

As recent developments in noninvasive biosensors spearhead the thrust toward personalized health and fitness monitoring, there is a need for high throughput, cost-effective fabrication of flexible sensing components. Toward this goal, we present roll-to-roll (R2R) gravure printed electrodes that are robust under a range of electrochemical sensing applications. We use inks and electrode morphologies designed for electrochemical and mechanical stability, achieving devices with uniform redox kinetics printed on 150 m flexible substrate rolls. We show that these electrodes can be functionalized into consistently high performing sensors for detecting ions, metabolites, heavy metals, and other small molecules in noninvasively accessed biofluids, including sensors for real-time, in situ perspiration monitoring during exercise. This development of robust and versatile R2R gravure printed electrodes represents a key translational step in enabling large-scale, low-cost fabrication of disposable wearable sensors for personalized health monitoring applications.

Methylxanthine Drug Monitoring with Wearable Sweat Sensors.

Drug monitoring plays crucial roles in doping control and precision medicine. It helps physicians tailor drug dosage for optimal benefits, track patients' compliance to prescriptions, and understand the complex pharmacokinetics of drugs. Conventional drug tests rely on invasive blood draws. While urine and sweat are attractive alternative biofluids, the state-of-the-art methods require separate sample collection and processing steps and fail to provide real-time information. Here, a wearable platform equipped with an electrochemical differential pulse voltammetry sensing module for drug monitoring is presented. A methylxanthine drug, caffeine, is selected to demonstrate the platform's functionalities. Sweat caffeine levels are monitored under various conditions, such as drug doses and measurement time after drug intake. Elevated sweat caffeine levels upon increasing dosage and confirmable caffeine physiological trends are observed. This work leverages a wearable sweat sensing platform toward noninvasive and continuous point-of-care drug monitoring and management.

Proving Scalability of an Organic Semiconductor To Print a TFT-Active Matrix Using a Roll-to-Roll Gravure.

Organic semiconductor-based thin-film transistors' (TFTs) charge-carrier mobility has been enhanced up to 25 cm2/V s through the improvement of fabrication methods and greater understanding of the microstructure charge-transport mechanism. To expand the practical feasibility of organic semiconductor-based TFTs, their electrical properties should be easily accessed from the fully printed devices through a scalable printing method, such as a roll-to-roll (R2R) gravure. In this study, four commercially available organic semiconductors were separately formulated into gravure inks. They were then employed in the R2R gravure system (silver ink for printing gate and drain-source electrodes and BaTiO3 ink for printing dielectric layers) for printing 20 × 20 TFT-active matrix with the resolution of 10 pixels per inch on poly(ethylene terephthalate) (PET) foils to attain electrical properties of organic semiconductors a practical printing method. Electrical characteristics (mobility, on-off current ratio, threshold voltage, and transconductance) of the R2R gravure-printed 20 × 20 TFT-active matrices fabricated with organic semiconducting ink were analyzed statistically, and the results showed more than 98% device yield and 50 % electrical variations in the R2R gravure TFT-active matrices along the PET web.

Fully gravure printed complementary carbon nanotube TFTs for a clock signal generator using an epoxy-imine based cross-linker as an n-dopant and encapsulant.

Printed p-type single walled carbon nanotube (SWCNT) based circuits exhibit high power dissipation owing to their thick printed dielectric layers (>2 µm) and long channels (>100 µm). In order to reduce the static power dissipation of printed SWCNT-base circuits while maintaining the same printing conditions and channel lengths, complementary metal-oxide-semiconductor (CMOS) based circuits are more ideal. These circuits, however, have not been successfully implemented in a scalable printing platform due to unstable threshold voltages of n-doped SWCNT based thin film transistors (TFTs). In this work, a thermally curable epoxy-imine-based n-doping ink is presented for achieving uniform doping and sealing of SWCNT layers by gravure printing. After printing the n-doping ink, the ink is cured to initiate a cross-linking reaction to seal the n-doped SWCNT-TFTs so that the threshold voltage of the n-doped SWCNT-TFTs is stabilized. Flexible CMOS ring oscillators using such n-doped SWCNT-TFTs combined with the intrinsically p-type SWCNT-TFTs can generate a 0.2 Hz clock signal with significantly lower power consumption compared to similarly printed p-type only TFT based ring oscillators. Moving forward, this CMOS flexible ring oscillator can be practically used to develop fully printed inexpensive wireless sensor tags.

Fully Printed and Encapsulated SWCNT-Based Thin Film Transistors via a Combination of R2R Gravure and Inkjet Printing.

Fully printed thin film transistors (TFT) based on poly(9,9-di-n-dodecylfluorene) (PFDD) wrapped semiconducting single walled carbon nanotube (SWCNT) channels are fabricated by a practical route that combines roll-to-roll (R2R) gravure and ink jet printing. SWCNT network density is easily controlled via ink formulation (concentration and polymer:CNT ratio) and jetting conditions (droplet size, drop spacing, and number of printed layers). Optimum inkjet printing conditions are established on Si/SiO2 in which an ink consisting of 6:1 PFDD:SWCNT ratio with 50 mg L-1 SWCNT concentration printed at a drop spacing of 20 µm results in TFTs with mobilities of ∼25 cm2 V-1 s-1 and on-/off-current ratios > 105. These conditions yield excellent network uniformity and are used in a fully additive process to fabricate fully printed TFTs on PET substrates with mobility values > 5 cm2 V-1 s-1 (R2R printed gate electrode and dielectric; inkjet printed channel and source/drain electrodes). An inkjet printed encapsulation layer completes the TFT process (fabricated in bottom gate, top contact TFT configuration) and provides mobilities > 1 cm2 V-1 s-1 with good operational stability, based on the performance of an inverter circuit. An array of 20 TFTs shows that most have less than 10% variability in terms of threshold voltage, transconductance, on-current, and subthreshold swing.

Structural Stability and Phase Transitions of Octanethiol Self-Assembled Monolayers on Au(111) in Ultrahigh Vacuum.

To understand the structural stability of as-prepared octanethiol (OT) self-assembled monolayers (SAMs) with a fully covered c(4 x 2) phase on Au(111) in ultrahigh vacuum (UHV) conditions of 3 x 10(-7) Pa at room temperature, we examined OT SAM samples obtained as a function of storage period using scanning tunneling microscopy (STM). STM imaging revealed that phase transition of OT SAMs after storage in UHV for 3 days occurs from the c(4 x 2) phase to the mixed phase containing ordered c(4 x 2) and disordered phases. It was also observed that the disordered phase was mainly located at around vacancy islands and near step edges of Au(111) terraces, implying that desorption of OT molecules chemisorbed on Au(111) in UHV occurs more quickly in these regions compared with in the closely packed and ordered domains. After a longer storage in UHV for 6 days, OT SAMs with the c(4 x 2) phase were changed to the disordered phase containing a partially ordered domain with a row structure. From this study, we clearly demonstrated that OT molecules in SAMs on Au(111) are desorbed spontaneously in UHV at room temperature, resulting in the formation of disordered and row phases.