Dot Electrode Research Articles

Enhancing vertical assembly of Dot-LEDs for display application using metal chelate coordination chemical linkers

The chemical linker assembly technique for dot-LEDs described in this study offers practical solutions to critical challenges in micro-LED display production, such as high costs, low yield in mass transfer processes, and high cost of micro-LED chips. Dot-LEDs feature a cylindrical structure with a diameter ranging from 0.75 to 1.35 μm and an aspect ratio of 1.1∼1.2 for height to diameter. We introduce a viable approach using N-(carboxymethyl)-N-(11-mercaptoundecyl)glycine (gly-thiol) chemical linkers for the face-selective vertical assembly of dot-LEDs. The size scale of dot-LED enables solution assembly processes when manufacturing pixels. By bonding the Au surface of the p-GaN face to the bottom Au electrodes using the chelate bond of Au-gly-thiol-Zn2+-gly-thiol-Au, we intend to enhance the face-selective vertical assembly. The process involves forming two chelate coordination bonds of Zn2+ ion surrounded by a gly-thiol-treated dot and bottom electrodes, achieving over 60 % efficiency in face-selective vertical assembly. We achieved bright and uniform dot-LED electroluminescence devices, with a peak external quantum efficiency (EQE) of 8.1 % at 3.4 V and a luminance of 22,387 cd/m2 at 9.0 V. Our findings suggest substantial improvements in the assembly and efficiency of micro-nano-scale dot-LED displays, providing a display platform technology for their application in future display systems.

Wearable detection of tonic seizures in childhood epilepsy: an exploratory cohort study.

To investigate the performance of a multimodal wearable device for the offline detection of tonic seizures (TS) in a pediatric childhood epilepsy cohort, with a focus on patients with Lennox-Gastaut syndrome. Parallel with prolonged video-electroencephalography (EEG), the Plug 'n Patch system, a multimodal wearable device using the Sensor Dot and replaceable electrode adhesives, was used to detect TS. Multiple biosignals were recorded: behind-the-ear EEG, surface electromyography, electrocardiography, and accelerometer/gyroscope. Biosignals were annotated blindly by a neurologist. Seizure characteristics were described, and performance was assessed by sensitivity, positive predictive value (PPV), F1 score, and false alarm rate (FAR) per hour. Performance was compared to seizure diaries kept by the caretaker. Ninety-nine TS were detected in 13 patients. Seven patients (54%) had Lennox-Gastaut syndrome and six patients (46%) had other forms of (developmental) epileptic encephalopathies or drug-resistant epilepsy. All but one patient had intellectual disability. Overall sensitivity was 41%, with a PPV of 9%, an F1 score of 14%, and a median FAR per hour of 0.75. Performance increased to an F1 score of 66% for nightly seizures lasting at least 10 s (sensitivity 66%, PPV 66%) and 71% for nightly seizures lasting at least 20 s (sensitivity 62%, PPV 82%). For these seizures there were no false alarms in 10 of 13 patients. Sensitivity of seizure diaries reached a maximum of 52% for prolonged (≥20 s) nightly seizures, even though caretakers slept in the same room. We showed that it is feasible to use a multimodal wearable device with multiple adhesive sites in children with epilepsy and intellectual disability. For prolonged nightly seizures, offline manual detection of TS outperformed seizure diaries. The recognition of seizure-specific signatures using multiple modalities can help in the development of automated TS detection algorithms.

Hydro Electroactive Janus Micro/Nano Fiber Dressing with Exudate Management Ability for Wound Healing

Exudate management and bioelectric signals are critical to promoting wound healing. In this study, the thermoplastic polyurethane (TPU) nanofiber is directly electrospun on the cotton microfibers (Cotton) to prepare a Janus dressing (TPU/Cotton), which can unidirectionally drain the excess exudate. Then, Ag/Zn dot electrodes are deposited on the TPU layer, which can produce an electric field penetrating the wound when activated by wound exudate. The hydro‐activated Ag/Zn's electrical stimulation (ES) can promote the migration of fibroblast cells and shows excellent antibacterial activity against E. coli and S. aureus. Furthermore, in vivo experiments show that the exudate management coupled with ES accelerated wound healing at multiple stages by promoting re‐epithelization, collagen deposition, and vascularization. Moreover, the Ag/Zn@TPU/Cotton dressing shows excellent biocompatibility in the vitro cytotoxicity experiments. These findings may shed some light on developing the next generation of wound dressings with self‐activated electrical stimulation and exudate management.

Moist‐Electric Generator with Efficient Output and Scalable Integration Based on Carbonized Polymer Dot and Liquid Metal Active Electrode

AbstractMoisture‐enabled electricity generation (MEG) is highly promising in next‐generation energy conversion. However, the practical applications of existing MEG devices are limited due to their low current and voltage outputs, strong dependence on high moisture, and inflexible nature. Herein, an efficient MEG integrated with flexible, all‐weather, and scalable fabrication characteristics based on the rational combination of carbonized polymer dots (CPDs) and liquid metal (LM) active electrodes is developed for the first time. Remarkably, the fabricated MEG device can produce a stable voltage output of 800 mV and a record high current density of 1640 µA cm−2. Even at a low air humidity of 15%, the MEG device can provide a high voltage output of 0.65 V and a considerable current density of 12 µA cm−2. The prompted diffusion of hydrogen ions in CPDs and the additional metal ions ionized from the LM electrode contribute synergistically to the high electricity generation. Additionally, the device can be easily integrated on various flexible substrates and generate an ultrahigh voltage of 210 V to power commercial electronics, showing great potential in large‐scale fabrication and application.

Chip for dielectrophoretic microbial capture, separation and detection II: experimental study

In our previous paper we have modelled a dielectrophoretic force (DEP) and cell particle behavior in a microfluidic channel (Weber MU et al 2023 Chip for dielectrophoretic microbial capture, separation and detection I: theoretical basis of electrode design Nanotechnology this issue). Here we test and confirm the results of our modeling work by experimentally validating the theoretical design constraints of the ring electrode architecture. We have compared and tested the geometry and particle capture and separation performance of the two separate electrode designs (the ring and dot electrode structures) by investigating bacterial motion in response to the applied electric field. We have quantitatively evaluated the electroosmosis (EO) to positive DEP (PDEP) transition in both electrode designs and explained the differences in capture efficiency of the ring and dot electrode systems. The ring structure shows 99% efficiency of bacterial capture both for PDEP and for EO. Moreover, the ring structure shows an over 200 faster bacterial response to the electric field. We have also established that the ring electrode architecture, with appropriate structure periodicity and spacing, results in efficient capture and separation of microbial cells. We have identified several critical design constraints that are required to achieve high efficiency bacterial capture. We have established that the spacing between consecutive DEP traps smaller than the length of the depletion zone will ensure that the DEP force dominates bacterial motion over motility and Brownian motion.

Design and Analysis of Quartz Crystal Microbalance with a New Ring-Shaped Interdigital Electrode.

In this paper, a new type of ring-shaped interdigital electrode is proposed to improve the accuracy and repeatability of quartz crystal microbalance. The influence of different types of single finger, dot finger, dot double-finger electrodes on mass sensitivity distribution as well as the optimal proportion of finger and gap width are obtained through multi-physical coupling simulation. The results show that the design criteria of interdigital electrodes will not change with the increase in the number of fingers. The gap width should obey the decrease order from central to edge and be about twice the width of finger. The width of the outermost finger and the radius of the middle dot electrode should be maintained at about 0.4 and 0.2 times of the total electrode radius. An experiment was carried out to verify that the quartz wafer with a dot double-finger electrode has high quality factors and less modal coupling, which can satisfy the engineering application well. As a conclusion, this study provides a design idea for the electrode to maintain a uniform distribution of quartz crystal microbalance mass sensitivity.

A Portable Sweat Sensor Based on Carbon Quantum Dots for Multiplex Detection of Cardiovascular Health Biomarkers.

The future of personalized diagnostics and treatment of cardiovascular diseases lies in the use of portable sensors. Portable sensors can acquire biomarker information in biological fluids such as sweat, an approach that mitigates the shortcomings of conventional hospital-centered healthcare. Low sensitivity, selectivity, and specificity remain bottlenecks for the widespread use of portable sensors. Herein, we demonstrate a portable sensor that simultaneously detects Na+, ascorbic acid, and human neuropeptide Y in sweat, all useful biomarkers to index cardiovascular health. The portable sensor comprises a six-electrode system containing three working electrodes, two reference electrodes, and one counter electrode. The working electrodes were prepared by depositing sensing components on carbon quantum dot (CQD) electrodes. The sensing mechanisms were based on selective ion recognition, enzyme catalytic reaction, and immune response, which guarantees specificity to corresponding targets. The CQDs offer massive reactive sites and effectively reduce the interfacial impedance during the sensing reaction, thereby enhancing the three biomarkers' detection sensitivity. As evidence of portable sensor capability, we demonstrate herein its effective simultaneous detection of the three biomarkers in a real sweat from healthy volunteers during routine activities including exercise, extra ascorbic acid ingestion, and extra Na+ ingestion. As such, the sensor shows promise for real-time noninvasive personalized medical diagnostics and metabolic wellness management.

Rapid and selective electrochemical sensing of bacterial pneumonia in human sputum based on conductive polymer dot electrodes

A rapid wireless electrochemical biosensor that can discriminate between gram-negative and gram-positive bacteria is designed for the selective detection of pneumonia pathogens in human sputum. The selective binding with the bacterial cell wall of gram-negative and gram-positive bacteria is achieved by utilizing colistin- and vancomycin-conjugated polymer dot-coated electrodes (PD-Colis for gram-negative and PD-Vanco for gram-positive, respectively) and can be observed as changes in resistance (ΔR~12–15 kΩ for PD-Colis and ΔR~13–17 kΩ for PD-Vanco). The PD-Colis- and PD-Vanco-coated electrodes demonstrate high sensitivities determined by the low limit of detection (LOD) for both gram-negative (3.0 CFU/mL, R2=0.995) and gram-positive (3.1 CFU/mL, R2=0.994) bacteria. The electrodes can also be used to detect antibiotic-resistant bacteria, such as carbapenem-resistant K. pneumoniae (CRKP) and methicillin-resistant S. aureus (MRSA), as well as enabling selective detection in complex media such as human serum. Moreover, the sensors based on PD-Colis- and PD-Vanco-coated electrodes show excellent performance in real clinical samples such as human sputum. Finally, the integration of the sensor with a wireless sensing system provides in-line bacterial detection and allows monitoring via a smartphone. We anticipate that the bacterial sensor can be potentially used for the rapid and accurate diagnosis of bacterial infections in the clinic.

Development of an Electrodeposited Graphene Quantum Dot Electrode for the Electrochemical Detection of C‐Reactive Protein (CRP) Biomarker

AbstractC‐reactive protein (CRP) is a potential cardiac biomarker whose levels fluctuate in response to cardiac diseases. In particular, the severity of cardiovascular disease can be associated with the level of CRP, emphasizing the necessity for a highly sensitive biosensor capable of detecting CRP at ultralow levels in a short period of time. In this study, we used a facile pyrolysis method to synthesize graphene quantum dots (GQDs) with a diameter of 2.2 nm. Then, to fabricate the Au/GQDs/anti‐CRP electrode, GQDs were electrodeposited successfully on the surface of the bare Au electrode to provide a nano‐interfaced matrix platform for effective anti‐CRP immobilization. Cyclic voltammetry was used to investigate the contact between anti‐CRP and CRP in the Fe(CN)63−/4− as a mediator. The recorded current signal from differential pulse voltammetry measurements shows that the associative interaction between the anti‐CRP and CRP is efficiently induced. Furthermore, the Figureure of merits of the developed sensor, including the sensory response of <50 s with a high sensitivity of 58 μA ng−1 mL−1 cm−2 and a low detection capability of 0.104 ng mL−1 (n=3), suggests that it is a potential candidate for point‐of‐care testing. And the fabricated Au/GQDs/anti‐CRP biosensor were used to sense CRP in an artificial serum (ringer lactate) solution.

Rapid and Selective Electrochemical Sensing of Bacterial Pneumonia in Human Sputum Based on Conductive Polymer Dot Electrodes

Rapid and Selective Electrochemical Sensing of Bacterial Pneumonia in Human Sputum Based on Conductive Polymer Dot Electrodes

Uniformity characterization of SiC, GaN, and α-Ga2O3 Schottky contacts using scanning internal photoemission microscopy

Local variation within one dot electrode was characterized for Ni/SiC, Ni/GaN and Cu/Ti/α-Ga2O3 Schottky contacts by using scanning internal photoemission microscopy (SIPM). SIPM measurements were conducted for 200 μmϕ and 400 μmϕ dot electrodes with an energy resolution in determining Schottky barrier height (qϕ B) of less than 0.2 meV. All three kinds of Schottky contacts on the wide bandgap semiconductors exhibited good uniformity as small as less than 10 meV in a standard deviation of qϕ B. The Schottky barrier height and the standard deviation values are the basis for estimating device performances and designing large-area devices as a measurement-based physical value.

Effective strategy for optimizing the leakage current and ferroelectric polarization characteristics of BiFeO3_PVDF-TrFE nanocomposite films

BiFeO3 has been extensively studied as an important single-phase multiferroic material at room temperature in the application fields of energy storage, data storage, spintronics, and electro-magnetic sensors. However, the high leakage current caused by the presence of lattice defects such as vacancies constrains the further development of BiFeO3. In this paper, we presented a facile method to overcome the high leakage problem via blending BiFeO3 nanoparticles into the ferroelectric copolymer PVDF-TrFE matrix and introducing a barrier layer beneath the top Pt dot electrode. The leakage current and ferroelectric characteristics of BiFeO3_PVDF-TrFE nanocomposite films were discussed comprehensively. Consequently, compared with the composites without the barrier layer, the leakage current density of the BiFeO3_PVDF-TrFE composite films reduced two orders of magnitude after coating a pure copolymer layer. Moreover, the remnant ferroelectric polarization reached ~14 μC cm−2 for a moderate weight content (25 wt%) of BiFeO3 nanoparticle in the blends, with a remarkably smaller coercive electric field than that of pure PVDF-TrFE films. An electrical conduction blocking mechanism was established to elucidate the optimized electric and ferroelectric properties of nanocomposite films.

Electrocatalytic Oxidation of Glucose on Boron and Nitrogen Codoped Graphene Quantum Dot Electrodes in Alkali Media

A novel solvothermal technique has been developed in the presence of C/N/B precursor for synthesizing B-N-coped graphene quantum dots (GQDs) as non-metal electrocatalysts towards the catalytic glucose oxidation reaction (GOR). Both N-doped GQD and B-N-codoped GQD particles (~4.0 nm) possess a similar oxidation and amidation level. The B-N-codoped GQD contains a B/C ratio of 3.16 at.%, where the B dopants were formed through different bonding types (i.e., N‒B, C‒B, BC2O, and BCO2) inserted into or decorated on the GQDs. The cyclic voltammetry measurement revealed that the catalytic activity of B-N-codoped GQD catalyst is significantly higher compared to the N-doped GQDs (~20% increase). It was also shown that the GOR activity was substantially enhanced due to the synergistic effect of B and N dopants within the GQD catalysts. Based on the analysis of Tafel plots, the B-N-codoped-GQD catalyst electrode displays an ultra-high exchange current density along with a reduced Tafel slope. The application of B-N-codoped GQD electrodes significantly enhances the catalytic activity and results in facile reaction kinetics towards the glucose oxidation reaction. Accordingly, the novel design of GQD catalyst demonstrated in this work sets the stage for designing inexpensive GQD-based catalysts as an alternative for precious metal catalysts commonly used in bio-sensors, fuel cells, and other electrochemical devices.

Non-enzymatic electrochemical detection of hydrogen peroxide on highly amidized graphene quantum dot electrodes

An efficient infrared (IR)-assisted technique is developed to synthesize highly amidized graphene quantum dots (GQDs) as a metal-free catalyst for electrochemically detecting hydrogen peroxide. Through the IR-assisted pyrolysis of urea and citric acid at different chemical ratios, the GQDs with very high amidation level (N/C atomic ratio: 23–46 at.%) are synthesized, composed of pyrrolic/pyridinic N, graphitic N, and N-oxide functionalities. Through various electrochemical diagnostics, it is confirmed that highly amidized GQD electrodes enable high catalytic activity toward H2O2 reduction. The catalytic cycle includes the adsorption of H2O2 and two-stage charge transfer steps on highly amidized GQD catalyst, where the substitutional N atoms (i.e., pyridinic N) at the edge of carbon network provide additional electroactive sites for adsorbing H2O2. The amperometric investigation followed by a rigorous linear regression analysis confirms a high selectivity of 1.83 μA mM−1 cm−2 toward H2O2 detection within the concentration range of 0.5–40 mM. The major attributes of the GQD catalytic electrodes include high sensitivity, wide detection range, fast response time, and superior selectivity. Accordingly, the robust design of GQDs developed in this work paves the way for engineering highly selective catalyst as a robust electrochemical sensor for non-enzymatic H2O2 detection at ultra-low concentrations.

Electrochemical sensing of mercury ions in electrolyte solutions by nitrogen-doped graphene quantum dot electrodes at ultralow concentrations

Electrochemical detection of mercury ions in aqueous solution was investigated at indium tin oxide (ITO) conducting glass electrode modified by nitrogen-doped graphene quantum dots (N-doped GQDs). The N-doped GQDs with an average particle size of 4.5 nm were synthesized through an infrared-assisted pyrolysis of citric acid and urea at 250 °C. The GQD sample contains high oxidation and amidation level, i.e., O/C and N/C atomic ratios: 37.6% and 30.7%, respectively. The electrochemical sensing toward Hg2+ ions was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on the CV and EIS analyses, both the reductive and oxidative peak currents as well as the equivalent series resistance demonstrate a decreasing trend with increased Hg2+ concentration. The detection limit of N-doped GQD/ITO electrodes toward Hg2+ ions reached 10 ppb with the accumulation time of 32 s. The GQD/ITO electrodes also exhibit superior selectivity toward the target contaminant (i.e. Hg2+ ion). Accordingly, the functionalized GQDs pave the way for engineering the electrochemical sensors capable of detecting toxic Hg2+ ions with superb sensitivity and selectivity.

Multiplexed Readout of Enzymatic Reactions by Means of Laterally Resolved Illumination of Quantum Dot Electrodes.

Triggering electrochemical reactions with light provides a powerful tool for the control of complex reaction schemes on photoactive electrodes. Here, we report on the light-directed, multiplexed detection of enzymatic substrates using a nonstructured gold electrode modified with CdSe/ZnS quantum dots (QDs) and two enzymes, glucose oxidase (GOx) and sarcosine oxidase (SOx). While QDs introduce visible-light sensitivity into the electrode architecture, GOx and SOx allow for a selective conversion of glucose and sarcosine, respectively. For the QD immobilization to the gold electrode, a linker-assisted approach using trans-4,4'-stilbenedithiol has been used, resulting in the generation of a photocurrent. Subsequently, GOx and SOx have been immobilized in spatially separated spots onto the QD electrode. For the local readout of the QD electrode, a new measurement setup has been developed by moving a laser pointer across the surface to defined positions on the chip surface. The amplitudes of the photocurrents upon illumination of the GOx or SOx spot depend in a concentration-dependent manner on the presence of glucose and sarcosine, respectively. This measurement also allows for a selective detection in the presence of other substances. The setup demonstrates the feasibility of multiplexed measurements of enzymatic reactions using a focused light pointer, resulting in an illumination area with a diameter of 0.3 mm for analyzing spots of different enzymes. Moving the laser pointer in the x- and y-direction and simultaneously detecting the local photocurrent also allow a spatial imaging of enzyme immobilization. Here, not only the spot dimensions but also the activity of the enzyme can be verified.

Determination of electrophysiological properties of human monocytes and THP-1 cells by dielectrophoresis

Introduction: Dielectrophoresis (DEP) is based on polarization and bioparticle movement in applied electric fields. Each type of cells has its own electrical properties within the DEP spectra and undergoes significant changes in direction of frequency following an increase of an applied nonuniform alternating current (AC) electric field. Therefore, DEP can be an effective technique for characterization and separation of different cells. The goal of the current study was to determine the electrophysiological properties of human monocytes and a human monocytic cell line originated from an acute monocytic leukemia patient (THP-1), using a lab on a chip (LOC) device that utilised microarray dot electrodes.
 Methods: Ten microliters of human monocytes isolated from peripheral blood mononuclear cells and highly confluent THP-1 cells were diluted in DEP medium and added to the spacer of the LOC device. Subsequently, the AC signal in the range of 10 kHz to 2 MHz was supplied to the LOC device, and the dynamic behaviours of monocytes and THP-1 cells due to the DEP force were observed. Images were captured and analyzed using MATLAB software.
 Results: Microscopic visualization showed that THP-1 cells were physically larger than human monocytes. The dielectric parameters (radius, diameter, and conductivity and permittivity of the cytoplasm and membrane) were greater for THP-1 cells compared to monocytes. The cross-over frequencies for THP-1 cells and monocytes were respectively 66 kHz and 280 kHz.
 Conclusion: In conclusion, the DEP spectra reflected the morphological differences between monocytes and THP-1 cells. The dielectric properties for each type of cells can be used as the criteria in the development of DEP-based characterization assays.

Microfluidic device embedding electrodes for dielectrophoretic manipulation of cells-A review.

Microfluidic device embedding electrodes realizes cell manipulation with the help of dielectrophoresis. Cell manipulation is an important technology for cell sorting and cell population purification. Till now, the theory of dielectrophoresis has been greatly developed. Microfluidic devices with various arrangements of electrodes have been reported from the beginning of the single non-uniform electric field to the later multiple physical fields. This paper reviews the research status of microfluidic device embedding electrodes for cell manipulation based on dielectrophoresis. Firstly, the working principle of dielectrophoresis is explained. Next, cell manipulation approaches based on dielectrophoresis are introduced. Then, different types of electrode arrangements in the microfluidic device for cell manipulation are discussed, including planar, multilayered and microarray dot electrodes. Finally, the future development trend of the dielectrophoresis with the help of microfluidic devices is prospected. With the rapid development of microfluidic technology, in the near future, high precision, high throughput, high efficiency, multifunctional, portable, economical and practical microfluidic dielectrophoresis will be widely used in the fields of biology, medicine, agriculture and so on.

Interfacial Electron Transfer Involving Vanadium and Graphene Quantum Dots for Redox Flow Battery

ABSTRACTAmong energy storage devices, the redox flow batteries are important for variety of applications such as for grid storage. In this class of batteries a large number of redox couples have been examined in the past. The vanadium redox couple, although is attractive for this application, suffers from a) poor charge transfer characteristics b) electrode degradation and c) deteriorating performance. We wish to report here that all these deficiencies have been overcome by using a graphene quantum dot electrodes. This electrode has the advantage of large surface area, high electrical and thermal conductivity. The cell voltage of 1.5 V and power density of about 120 mW/cm2 and coulombic efficiency of 90% can be achieved as the redox couples, V(IV)/V(V) and V(III)/V(II) undergo fast electron transfer at the interface of the quantum dots and solution resulting in higher reversibility. The cyclic voltammetric experiments carried out with quantum dots in the solutions during the oxidation of V(IV) show enhanced currents, due to the movements of the dots which is conducive for power gain in the battery operation. The electrochemical degradation is absent with the quantum dot electrode. The charge/discharge cycles have been reproducible.

Retraction of “Composite of Zinc Using Graphene Quantum Dot Bath: A Prospective Material For Energy Storage”

The electrodeposition of a zinc–graphene composite has been achieved for the first time using a graphene quantum dot (GQD) electrode. At the GQD electrode, the electrochemical reduction of zinc ion is shifted to a lesser negative potential with the complementary anodic peak due to the oxidation of the composite shifted toward a positive potential as compared to zinc ion reduction in the GQD bath. The charge ratio of anodic to cathodic peaks is one that represents a gain of nearly ten percent over the conventional Zn/Zn2+ in the energy storage systems. In galvanostatic electrolysis, the deposition of zinc–graphene composite is carried out under neutral and acidic conditions. The X-ray diffraction of the electrolytically prepared composite shows distinct features of 2 theta reflection at 8° due to (001) plane of graphene, in addition to the characteristic reflections at 38.9°,43.2°, 54.3°, 70.1° and 90° arising from Zn at (002), (100), (101), (102) and (110). A large scale preparation of the zinc–graphene c...