Exploring the Cation Regulation Mechanism for Interfacial Water Involved in the Hydrogen Evolution Reaction by In Situ Raman Spectroscopy.

Interfacial water molecules are the most important participants in the hydrogen evolution reaction (HER). Hence, understanding the behavior and role that interfacial water plays will ultimately reveal the HER mechanism. Unfortunately, investigating interfacial water is extremely challenging owing to the interference caused by bulk water molecules and complexity of the interfacial environment. Here, the behaviors of interfacial water in different cationic electrolytes on Pd surfaces were investigated by the electrochemistry, in situ core-shell nanostructure enhanced Raman spectroscopy and theoretical simulation techniques. Direct spectral evidence reveals a red shift in the frequency and a decrease in the intensity of interfacial water as the potential is shifted in the positively direction. When comparing the different cation electrolyte systems at a given potential, the frequency of the interfacial water peak increases in the specified order: Li+ < Na+ < K+ < Ca2+ < Sr2+. The structure of interfacial water was optimized by adjusting the radius, valence, and concentration of cation to form the two-H down structure. This unique interfacial water structure will improve the charge transfer efficiency between the water and electrode further enhancing the HER performance. Therefore, local cation tuning strategies can be used to improve the HER performance by optimizing the interfacial water structure.

Determination of heavy metals in water using an FTO electrode modified with CeO2/rGO nanoribbons prepared by an electrochemical method.

The rGO/CeO2/FTO nanocomposite modified electrode was prepared by an electrochemical method. A simple and highly sensitive electrochemical sensing platform for electrochemical rGO and modified CeO2 nanoribbons directly on FTO electrodes was developed. Simultaneous determination of Pb2+ and Cd2+ used the differential pulse anodic stripping voltammetry (DPASV) method. The method was simple to operate, and CeO2 nanobelts could be obtained simultaneously by electrodeposition and reduction of GO without further processing. This is an environmentally friendly electrochemical method to obtain modified electrodes under mild conditions. The experimental results showed that the linear calibration curves of Pb2+ and Cd2+ are 1-300 and 0.2-500 µg L-1, respectively. At the same time, no interference from other coexisting metal ions was found during the detection process, which proved that the modified electrode had good stability and repeatability.

Hollow Microneedles on a Paper Fabricated by Standard Photolithography for the Screening Test of Prediabetes.

Microneedle (MN) is a novel technique of the biomedical engineering field because of its ability to evaluate bioinformation via minimal invasion. One of the urgent requirements for ground-breaking health care monitoring is persistent monitoring. Hollow microneedles are extremely attractive to extract skin interstitial fluid (ISF) for analysis, which makes them perfect for sensing biomarkers and facilitating diagnosis. Nevertheless, its intricate fabrication process has hampered its extensive application. The present research demonstrates an easy one-step preparation approach for hollow MNs on the foundation of the refraction index variations of polyethylene glycol diacrylate (PEGDA) in the process of photopolymerization. The fabricated hollow microneedle exhibited ideal mechanical characteristics to penetrate the skin. Hydrodynamic simulations showed that the liquid was risen in a hollow microneedle by capillary force. Furthermore, a paper-based glucose sensor was integrated with the hollow microneedle. We also observed that the MN array smoothly extracted ISF in vitro and in vivo by capillary action. The outcomes displayed the applicability of the MN patch to persistent blood glucose (GLU) monitoring, diagnosis-related tests for patients and pre-diabetic individuals.

Digital Microfluidic Thermal Control Chip-Based Multichannel Immunosensor for Noninvasively Detecting Acute Myocardial Infarction.

Rapid and automated detection of acute myocardial infarction (AMI) at its developing stage is very important due to its high mortality rate. To quantitatively diagnose AMI, Myo, CK-MB, and cTnI are chosen as three biomarkers, which are usually detected through an immunosorbent assay, such as the enzyme-linked immunosorbent assay. However, the approach poses many drawbacks, such as long detection time, the cumbersome process, the need for professionals, and the difficulty of realizing automatic operation. Here, a multichannel digital microfluidic (DMF) thermal control chip integrated with a sandwich-based immunoassay strategy is proposed for the automated, rapid, and sensitive detection of AMI biomarkers. A miniaturized temperature control module is integrated on the back of the DMF chip, meeting the temperature requirement for the immunoassay. With this DMF thermal control chip, sample and reagent consumption are reduced to several microliters, significantly alleviating reagent consumption and sample dependence, and the automated and multichannel detection of biomarkers can be achieved. In this work, the simultaneously noninvasive detection of the human serum sample containing the three biomarkers of AMI is also achieved within 30 min, which improves the diagnostic accuracy of AMI. Due to the features of automation and miniaturization, the multichannel immunosensor can be used in community hospitals to increase the speed of diagnosis of patients with various acute diseases.

Optimization of twin parallel microstrips based nuclear magnetic resonance probe for measuring the kinetics in molecular assembly in ultra-small samples.

We present the design, fabrication, characterization, and optimization of a TPM (twin parallel microstrip)-based nuclear magnetic resonance (NMR) probe, produced by using a low-loss Teflon PTFE F4B high frequency circuit board. We use finite element analysis to optimize the radio frequency (RF) homogeneity and sensitivity of the TPM probe jointly for various sample volumes. The RF homogeneity of this TPM planar probe is superior to that of only a single microstrip probe. The optimized TPM probe properties such as RF homogeneity and field strength are characterized experimentally and discussed in detail. By combining this TPM based NMR probe with microfluidic technology, the sample amount required for kinetic study using NMR spectroscopy was minimized. This is important for studying costly samples. The TPM NMR probes provide high sensitivity to analysis of 5 µl samples with 2 mM concentrations within 10 min. The miniaturized microfluidic NMR probe plays an important role in realizing down to seconds timescale for kinetic monitoring.

3D-printed integrative probeheads for magnetic resonance.

Magnetic resonance (MR) technology has been widely employed in scientific research, clinical diagnosis and geological survey. However, the fabrication of MR radio frequency probeheads still face difficulties in integration, customization and miniaturization. Here, we utilized 3D printing and liquid metal filling techniques to fabricate integrative radio frequency probeheads for MR experiments. The 3D-printed probehead with micrometer precision generally consists of liquid metal coils, customized sample chambers and radio frequency circuit interfaces. We screened different 3D printing materials and optimized the liquid metals by incorporating metal microparticles. The 3D-printed probeheads are capable of performing both routine and nonconventional MR experiments, including in situ electrochemical analysis, in situ reaction monitoring with continues-flow paramagnetic particles and ions separation, and small-sample MR imaging. Due to the flexibility and accuracy of 3D printing techniques, we can accurately obtain complicated coil geometries at the micrometer scale, shortening the fabrication timescale and extending the application scenarios.

Flexible and Conductive Graphene-Poly (diallyldimethylammoniumchloride) Buckypaper.

This paper describes the fabrication and characterization of flexible, conductive reduced graphene oxide (rGO)-poly(diallyldimethylammoniumchloride) (PDDA) buckypaper (BP). PDDA acts as a reducing agent to prepare an rGO-PDDA nanosheet dispersion from graphite oxide. The incorporation of PDDA as a "glue" molecule successfully binds rGO nanosheets into BPs with strong interlayer binding. The resulting BPs were characterized by scanning electronic microscopy (SEM), Raman, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and resistivity measurements. The sp2 structure was greatly restored by the PDDA-induced reduction. Moreover, rGO was chemically doped from the adsorbed PDDA, which causes the Raman G band to shift from ~1585 to ~1610 cm(-1). This chemical doping substantially increased the density of the free charge carriers in rGO and thereby further enhanced the electrical conductivity of the rGO-BP. Good inter-layer connection in the rGO percolating network was obtained after thermal annealing at higher than ~250 °C. The resulting rGO-PDDA-BPs exhibited an isotropic sheet resistance as low as ~100 Ω/sq, which indicates a reduction by six orders of magnitude compared to the GO-BPs resistance before annealing. This PDDA-induced reduction with a low-temperature annealing process preserved the BPs' structural integrity and mechanical flexibility, thus overcoming the fragility problems with high-temperature annealing.

Electrostatically Gated Graphene-Zinc Oxide Nanowire Heterojunction.

This paper presents an electrostatically gated graphene-ZnO nanowire (NW) heterojunction for the purpose of device applications for the first time. A sub-nanometer-thick energy barrier width was formed between a monatomic graphene layer and electrochemically grown ZnO NWs. Because of the narrow energy barrier, electrons can tunnel through the barrier when a voltage is applied across the junction. A near-ohmic current-voltage (I-V) curve was obtained from the graphene-electrochemically grown ZnO NW heterojunction. This near-ohmic contact changed to asymmetric I-V Schottky contact when the samples were exposed to an oxygen environment. It is believed that the adsorbed oxygen atoms or molecules on the ZnO NW surface capture free electrons of the ZnO NWs, thereby creating a depletion region in the ZnO NWs. Consequentially, the electron concentration in the ZnO NWs is dramatically reduced, and the energy barrier width of the graphene-ZnO NW heterojunction increases greatly. This increased energy barrier width reduces the electron tunneling probability, resulting in a typical Schottky contact. By adjusting the back-gate voltage to control the graphene-ZnO NW Schottky energy barrier height, a large modulation on the junction current (on/off ratio of 10(3)) was achieved.

Electrochemistry at the edge of a single graphene layer in a nanopore.

We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and Al(2)O(3) dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to a unique edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 10(4) A/cm(2). The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many applications in sensitive chemical and biological sensing, and energy storage devices.

Wettability control of a transparent substrate using ZnO nanorods.

This paper presents a simple way of controlling the wettability of a structured surface with ZnO nanorods on a transparent substrate. A combination of ZnO nanostructures and stearic acid was used to create superhydrophobic surfaces with the potential properties of being self-cleaning, waterproof, and antifog. ZnO nanorods were uniformly covered on glass substrates through a simple hydrothermal method with varying growth time which affects the surface morphology. When a substrate is dipped into 10 mM stearic acid in ethanol for 24 h, chemisorption of the stearic acid takes place on the ZnO nanorod surface, after which the hydrophilic ZnO nanorod surfaces are modified into hydrophobic ones. The contact angle of a water droplet on this superhydrophobic ZnO nanorod surface increased from 110 degrees to 150 degrees depending on the growth time (from 3 to 6 h) with a high transparency of above 60%. In addition, the water contact angle can be made to as low as 27 degrees after exposing the substrate to 10-mW/cm2 UV for 1 h.

An electrochemical route to graphene oxide.

Large-scale graphene oxide (GO) with adjustable resistivity was synthesized from graphite via an electrochemical method using KCl solution as an effective electrolyte. During the exfoliation process, electrostatic force intercalates chloride ions between the expanded graphite layers on the anode. These chloride ions form small gas bubbles between the graphite layers in the electrochemical reaction. It is believed that the gas bubbles expand the gap between graphite sheets and produce a separating force between adjacent graphene layers. This separating force overcomes the Van der Waals force between adjacent sheets and exfoliates graphene layers from the starting graphite. Because the graphene is electrochemically oxidized by chorine during the exfoliation, the exfoliated GO sheets are hydrophilic and easily dispersed in the electrolyte solution. The GO solution prepared by the electrochemical exfoliation can be simply sprayed or spin-coated onto any substrate for device applications. The measured average thicknesses of a monolayer, bilayer, and trilayer exfoliated GO on SiO2 substrate were 1.9, 2.8, and 3.9 nm, respectively. It was observed that the measured resistance of the exfoliated GO sheets increases due to electrochemical oxidation in the solution. This electrochemical approach offers a low-cost and efficient route to the fabrication of graphene based devices.