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α-MnO2 nanofibers combined with nitrogen and sulfur co-doped reduced graphene oxide (α-MnO2/N&S-rGO) were prepared through simple hydrothermal and ball milling processes. Structural characterization results by X-ray diffraction, X-ray photoemission spectroscopy, electron microscopy and Raman spectroscopy demonstrated that α-MnO2 nanofibers with the average diameter of ~40 nm were well dispersed on N&S-rGO nanoflakes. The synthesized material was incorporated into supercapacitor (SC) electrodes and assembled with the quasi-solid-state electrolyte comprising N,N-Diethyl-N-methyl-N-(2-methoxy-ethyl)ammonium bis (trifluoromethyl-sulfonyl)amide [DEME][TFSA]/polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) to produce coin-cell SCs. Electrochemical performances of SCs were measured by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. From the electrochemical data, SC using α-MnO2/N&S-rGO exhibited a good specific capacitance of 165F g−1 at 0.25 A g−1 with a wide potential window of 0–4.5 V, corresponding to a high energy density of 110 Wh kg−1 and a power density of 550 W kg−1. In addition, it exhibited good electrochemical stability with a capacitance retention of 75% after 10,000 cycles at 1 A g−1 and a low self-discharge loss. The attained energy-storage performances indicated that the α-MnO2/N&S-rGO composite could be highly promising for high-performance ionic liquid-based quasi solid-state supercapacitors.

In this paper, a low-cost and disposable electrowetting-on-dielectric (EWOD) digital microfluidic chip with an integrated electrochemical detector was fabricated based on a screen printing process. T-junction EWOD electrodes for merging buffer and analyte droplets were formed by screen-printing of silver paste before covering with spin-coated polydimethylsiloxane dielectric and Teflon AF hydrophobic layers, respectively. The electrochemical detector comprising three electrodes, including carbon working, carbon counter, and silver/silver chloride reference electrodes, was subsequently deposited on the dielectric layer by two additional screen-printing steps. The system was tested for rapid electrochemical analyses of nicotinamide adenine dinucleotide and L-ascorbic acid. The analyte and buffer droplets were blended under the EWOD actuation with varying concentrations and detected at the electrochemical detector using cyclic voltammetry. The results showed good detection performances with medium sensitivity, moderate detection limits, and short total analysis times of less than 14 s. Therefore, the screen-printed EWOD chip with integrated screen-printed carbon electrodes could be a promising alternative for low-cost automated chemical analyses.

In this work, a screen-printed electrochemical detector was fabricated on a digital electrowetting-on- dielectric (EWOD) microfluidic chip for the first time and employed for rapid chemical analysis. The digital microfluidic system consisted of a T-junction EWOD platform for merging buffer and analyte droplets and an electrochemical detector at the end of T-junction. The detector comprised three electrodes including carbon working, carbon counter and silver/silver chloride reference electrodes. The system was successfully fabricated by microfabrication and screen-printing processes and tested for electrochemical analyses of potassium hexacyanoferrate and hydrogen peroxide. The analyte and buffer droplets were controlled to mix with different concentrations and detected at the electrochemical detector using cyclic voltammetry. The results showed good detection performances with medium sensitivity, moderate detection limits, high stability and good reproducibility. In addition, the total analysis time including droplet mixing and CV measurement was shorter than 14 s. Therefore, the EWOD chip with integrated screen-printed carbon electrodes was a promising candidate for rapid automated chemical analysis.

α-MnO

In this work, a screen-printed carbon paste electrode (SPCE) combined with multi-walled carbon nanotubes (MCNT) and graphene (GP) in different mixing ratios was fabricated. Electrode materials were characterized by scanning electron microscopy as well as Raman spectroscopy and their performance as electrochemical sensors was evaluated by cyclic voltammetry. Results showed that SPCEs composited with 1 w% MCNT and 1 w% graphene achieved the most promising sensing performance for K4FeCN6 with a sensitivity of 0.0054 µA µM−1 and limit of detection (LOD) (3S/N) at 3.1 µM. The so-prepared electrode was then employed to detect H2O2 and nicotinamide adenine dinucleotide (NAD+/NADH) achieving sensitivity and LOD of 0.0027 µA µM−1 and 7.1 µM for H2O2, and 0.0075 µA µM−1 and 3.6 µM for NADH, respectively. Therefore, it was found that the addition of MCNT and graphene to commercial carbon paste for screen printable electrochemical sensor is feasible for fabrication of sensing electrodes for electrochemical detection.

Vibrio parahaemolyticus is one of the most important foodborne pathogens that cause various life-threatening diseases in human and animals. Here, we present a rapid detection platform for V. parahaemolyticus by combining loop-mediated isothermal amplification (LAMP) and disposable electrochemical sensors based on screen-printed graphene electrodes (SPGEs). The LAMP reactions using primers targeting V. parahaemolyticus toxR gene were optimized at an isothermal temperature of 65 °C, providing specific detection of V. parahaemolyticus within 45 min at the detection limit of 0.3 CFU per 25 g of raw seafood. The LAMP amplicons can be effectively detected using unmodified SPGEs, redox active molecules namely Hoechst-33258 and a portable potentiostat. Therefore, the proposed system is particularly suitable as a point-of-care device for on-site detection of foodborne pathogens.

In this research, graphene digital microfluidics microchip was designed and fabricated by screen printing. The microchip was designed with electrowetting on dielectric as digital microfluidic microchip combine with electrochemical detector on single plate substrate. For the design, the chip consist of T-junction EWOD digital microfluidics microchip for merging buffer reagent and analyze droplets and an electrochemical detector at the end of T-junction EWOD. Both parts were fabricated by screen printed technique. The EWOD microchip consists of silver paste for electrodes layers and PDMS for dielectric and Teflon® AF hydrophobic layers. Three electrodes of electrochemical detector consists of a graphene-carbon paste working electrode and a graphene-carbon paste counter electrode, and silver/silver chloride paste reference electrode for rapid analysis with minimal reagent consumption. In experiment, the electrochemical detector combine with EWOD microchip was tested for electrochemical analysis with concentration of the reagent that were varied with 10, 50, 100, 250, and 500 μM with cyclic voltammograms. The results showed that the system was successfully tested for rapid analysis with minimal reagent consumption of ferri/ferrocyanide (Fe(CN) 6 3−/4−) and hydrogen peroxide (H 2 O 2 ) with time was less than 20 seconds.

In this work, a screen-printed electrochemical detector with electrowetting on dielectric (EWOD) digital microfluidics lab on a chip was designed, fabricated, and experimental studied for biological, biomedical, and chemical analysis. For the design, the electrochemical EWOD digital microfluidics system consists of T-junction EWOD microchip for merging buffer reagent and analyte droplets and three screen-printed electrochemical detectors at the end of T-junction. The detectors consist of three electrodes: carbon working electrode, carbon counter electrode and silver/silver chloride reference electrode with minimal reagent consumption and rapid analysis. The systems has been successfully fabricated and tested for rapid analysis. In experiment, the electrochemical detector with EWOD microchip was fabricated and tested to control moving (merging and transporting) droplet on the microchip to analyte at three electrochemical detector. For analysis, the electrochemical detectors was demonstrated for minimal reagent consumption which were potassium ferricyanide and L-ascorbic. The concentration of the reagent were varied from 1, 2, 3, 5, 7 and 10 mM for analysis. Microdroplets of buffer reagent and analyte droplet solution was mixed and detected by cyclic voltammetry. The total analysis time including droplet mixing and measurement was less than 20 seconds.