Heteroatom modification represents one of the largest studied areas of research related to nanostructured carbon materials, with integrated applications stretching from energy production and storage to sustainability and medical uses. While a wide variety of dopants (boron, phosphorus, iodine, fluorine, etc.) have been studied, doping carbon structures with nitrogen ad-atoms has arguably experienced the greatest progress and brought the most attention over the last several years. Research in this field has conclusively demonstrated that nitrogen doping is an effective way to tailor the properties of carbon and tune the material for various applications of interest. This review provides a comprehensive overview of advances in the last half decade on state-of-the-art carbon modification with nitrogen heteroatoms. Improvements in well-established fabrication/modification processes are discussed as well as novel strategies. Additionally, recent theoretical and experimental findings related to the benefits and effects of nitrogen modification for specific applications in the energy and environmental fields are reviewed.

Recent progress on nitrogen/carbon structures designed for use in energy and sustainability applications

A review of recent advances in nonenzymatic glucose sensors.

Three-dimensional-networked Ni2P/Ni3S2 heteronanoflake arrays for highly enhanced electrochemical overall-water-splitting activity

Carbon materials on the nanoscale exhibit diverse outstanding properties, rendering them extremely suitable for the fabrication of electrochemical biosensors. Over the past two decades, advances in this area have continuously emerged. In this review, we attempt to survey the recent developments of electrochemical biosensors based on six types of carbon nanomaterials (CNs), i.e., graphene, carbon nanotubes, carbon dots, carbon nanofibers, nanodiamonds and buckminsterfullerene. For each material, representative samples are introduced to expound the different roles of the CNs in electrochemical bioanalytical strategies. In addition, remaining challenges and perspectives for future developments are also briefly discussed.

Carbon nanomaterial-based electrochemical biosensors: an overview

Self-assembled ultrathin NiCo2S4 nanoflakes grown on Ni foam as high-performance flexible electrodes for hydrogen evolution reaction in alkaline solution

Boron-doped diamond electrodes covered with a nanostructured Pt nanoparticle-polyaniline composite have been fabricated and employed as sensitive amperometric sensors with low detection limit. A highly conductive boron-doped diamond thin film (BDD) was prepared by chemical vapor deposition, and its morphology was characterized by scanning electron microscopy and transmission electron microscopy. The nanostructured composite layer was grown on the BDD electrode by electrochemical deposition of polyaniline and Pt nanoparticles. Glucose oxidase (GOx) was then adsorptively immobilized on the modified BDD electrode. The biosensor displays a large surface area, high catalytic activity of the Pt nanoparticles, efficient electron mediation through the conducting polymer, and low background current of the electrode. The biosensor exhibits an excellent response to glucose, with a broad linear range from 5.9 μM to 0.51 mM, a sensitivity of 5.5 μA·mM−1, a correlation coefficient (R) of 0.9947, and a detection limit of 0.10 μM. The apparent Michaelis-Menten constant (KMapp) and the maximum current density of the electrode are 4.1 mM and 0.021 mA, respectively. This suggests that the immobilized GOx possesses a higher affinity for glucose at the lower KMapp, and that the enzymatic reaction rate constitutes the rate-limiting step of the response.

Pt-polyaniline nanocomposite on boron-doped diamond electrode for amperometic biosensor with low detection limit

Non-Enzymatic Glucose Sensor Based on Cu Electrode Modified with CuO Nanoflowers

High-sensitivity non-enzymatic glucose biosensor based on Cu(OH)2 nanoflower electrode covered with boron-doped nanocrystalline diamond layer

A boron-doped diamond/carbon nanotube (BDD–CNT) hybrid material with a core-shell three-dimensional random network structure was fabricated using the electrostatic self-assembly of nanodiamond. In general, CNTs are easily etched out as hydrocarbons or transformed to graphitic clusters at defect sites in hydrogen-rich environments (that is, the typical conditions employed for diamond deposition). However, attaching a dense layer of nanodiamond particles to the outer wall of the CNTs suppressed CNT etching and promoted BDD growth. To attach the dispersed nanodiamond particles on the CNT surface, we used an electrostatic self-assembly technique in which the surface charges on the CNTs and the nanodiamond were controlled using cationic and anionic polymers. Following BDD deposition, the electrochemical properties of the BDD–CNT structures were examined by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the BDD–CNTs exhibited enhanced electron transport efficiency, large effective surface areas and high sensitivity, with a remarkably low detection limit. Researchers in South Korea have coated carbon nanotubes with nanodiamonds to form a highly sensitive glucose biosensor. The team, led by Dae-Soon Lim at Korea University, deposited a layer of boron-doped diamond nanoparticles onto the outer walls of multiwalled carbon nanotubes. They then confirmed the structure of the resultant nanowires using an electron microscope and measured their electrochemical properties. Next, the team demonstrated that the nanowires exhibit a higher sensitivity to glucose — as well as a significantly lower detection limit — than other existing electrodes. The new nanowires could potentially be used for the noninvasive detection of glucose in human body fluids containing lower concentrations of glucose than blood, such as saliva, tears or sweat. They could help to estimate the size of bacteria populations in sea water, as many bacteria use glucose as an energy source. 3D-networked boron-doped diamond/carbon nanotube (BDD–CNT) core-shell nanowires were fabricated using the electrostatic self-assembly of nanodiamond. Although CNTs are easily etched out at their defect sites in hydrogen-rich environments, densely attached nanodiamond particles suppressed the etching of the CNTs and promoted BDD growth. After BDD deposition, 3D-networked BDD–CNT nanowires were successfully developed. In comparison to other electrodes, the BDD–CNT electrode exhibited better electrochemical performances, that is, low electron transfer resistance, large effective surface area and high sensitivity with significantly low detection range (8.7 mA mM−1 in the range 0.65–83.75 nM). The improvement in the performances of the BDD–CNT electrode could be attributed to the geometry and electron pathways offered by CNTs as well as to the synergistic material properties of BDD and CNT. The BDD–CNT electrode shows promise for application in the noninvasive measurement of glucose in living beings as well as for environmental monitoring in sea water.

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Seung Koo Lee

Papers

Pt-polyaniline nanocomposite on boron-doped diamond electrode for amperometic biosensor with low detection limit

Non-Enzymatic Glucose Sensor Based on Cu Electrode Modified with CuO Nanoflowers

High-sensitivity non-enzymatic glucose biosensor based on Cu(OH)2 nanoflower electrode covered with boron-doped nanocrystalline diamond layer

3D-networked carbon nanotube/diamond core-shell nanowires for enhanced electrochemical performance

Electrochemical sensor based on Au nanoparticles decorated boron-doped diamond electrode using ferrocene-tagged aptamer for proton detection