Role of sp² carbon in non-enzymatic electrochemical sensing of glucose using boron-doped diamond electrodes

Boron-doped diamond (BDD) is of increasing interest for applications in electrochemical sensing. It is well known that the sp2 carbon content in BDD influences its electrochemical properties as electrode material. In this work, evidence is provided that the surface sp2 carbon content plays a crucial role in the electrochemical sensitivity of BDD towards glucose. Single-crystal BDD, freestanding polycrystalline BDD and glassy carbon (sp2 carbon reference material) were examined by voltammetry. Neither single-crystal BDD, which is free of sp2 carbon, nor pure sp2 glassy carbon could detect glucose in the range of 0.2–1.0 V. On the other hand, glucose oxidation was observed on polycrystalline BDD, and with increasing intensity with increase of sp2 carbon content. Thus, an optimum amount of (B-doped) sp2 carbon in the BDD electrode is needed for best sensing performance. Understanding this, and being able to control the composition of BDD, are not only important to glucose detection but to any electrochemical sensing application involving BDD.Micro and Nano Engineerin

Inkjet-printed high-Q nanocrystalline diamond resonators

Diamond is a highly desirable material for state-of-the-art micro-electromechanical (MEMS) devices, radio-frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si-based components remain costly and complex. In this work, a lithography-free, low-cost method is introduced to fabricate diamond-based micro-resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ∅50–60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9–30 MHz, with Q-factors exceeding 104, and (f0 × Q) figure of merit up to ≈2.5 × 1011 Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q-factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet-printed diamond resonators yield mass responsivities up to 981 Hz fg−1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top-down, lithography-based techniques. In summary, this work demonstrates the fabrication of functional high-performance diamond-based micro-sensors by direct inkjet printing.</p

Inkjet-printed high-Q nanocrystalline diamond resonators

Diamond is a highly desirable material for state-of-the-art micro-electromechanical (MEMS) devices, radio-frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si-based components remain costly and complex. In this work, a lithography-free, low-cost method is introduced to fabricate diamond-based micro-resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ∅50–60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9–30 MHz, with Q-factors exceeding 104, and (f0 × Q) figure of merit up to ≈2.5 × 1011 Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q-factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet-printed diamond resonators yield mass responsivities up to 981 Hz fg−1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top-down, lithography-based techniques. In summary, this work demonstrates the fabrication of functional high-performance diamond-based micro-sensors by direct inkjet printing.Micro and Nano EngineeringDynamics of Micro and Nano SystemsQN/Steeneken La

Template-assisted bottom-up growth of nanocrystalline diamond micropillar arrays

Micro-patterned diamond has been investigated for numerous applications, such as biomimetic surfaces, electrodes for cell stimulation and energy storage, photonic structures, imprint lithography, and others. Controlled patterning of diamond substrates and moulds typically requires lithography-based top-down processing, which is costly and complex. In this work, we introduce an alternative, cleanroom-free approach consisting of the bottom-up growth of nanocrystalline diamond (NCD) micropillar arrays by chemical vapour deposition (CVD) using a commercial porous Si membrane as a template. Conformal pillars of ~4.7 μm in height and ~2.2 μm in width were achieved after a maximum growth time of 9 h by hot-filament CVD (2% CH 4 in H 2 , 725 °C at 10 mbar). In order to demonstrate one of many possible applications, micropillar arrays grown for 6 h, with ~2 μm in height, were evaluated as moulds for imprint lithography by replication onto hard cyclic olefin copolymer (COC) and onto soft polydimethylsiloxane (PDMS) elastomer. The results showed preserved mechanical integrity of the diamond moulds after replication, as well as full pattern transfer onto the two polymers, with matching dimensions between the grown pillars and the replicated holes. Prior surface treatment of the diamond mould was not required for releasing the PDMS replica, whereas the functionalisation of the diamond surface with a perfluorododecyltrichlorosilane (FDDTS) anti-stiction layer was necessary for the successful release of the COC replica from the mould. In summary, this paper presents an alternative and facile route for the fabrication of diamond micropillar arrays and functional micro-textured surfaces. Micro and Nano Engineerin

Heavily boron-doped diamond grown on scalable heteroepitaxial quasi-substrates: A promising single crystal material for electrochemical sensing applications

In this work, three distinct heteroepitaxial single-crystal boron-doped diamond (SC-BDD) electrodes were fabricated and subjected to detailed surface analysis and electrochemical characterization. Specifically, the heteroepitaxy approach allowed to synthesize large-area (1 cm2) and heavily-doped (100)-oriented SC-BDD electrodes. Their single-crystal nature and crystal orientation were confirmed by X-ray diffraction, while scanning electron and atomic force microscopies revealed marked variations in surface morphology resulting from their growth on respective on-axis and off-axis substrates. Further, absence of sp2 impurities along with heavy boron doping (&gt;1021 cm−3) was demonstrated by Raman spectroscopy and Mott-Schottky analysis, respectively. Cyclic voltammetry (CV) in a 0.1 M KNO3 solution revealed wide potential windows (∼3.3 V) and low double-layer capacitance (&lt;4 μF cm−2) of the SC-BDD electrodes. Their highly conductive, ‘metal-like’ nature was confirmed by CV with [Ru(NH3)6]3+/2+ probe manifesting near-reversible redox response with ΔEp approaching 0.059 V. The same probe was used to record scanning electrochemical micrographs, which clearly demonstrated homogeneously distributed electrochemical activity of the heteroepitaxial SC-BDD electrodes. Minor differences in their electrochemical performance, presumably resulting from the somewhat different morphological features, were only unveiled during CV with surface sensitive compounds [Fe(CN)6]3−/4− and dopamine. The latter was also used to show the possibility of applying herein developed heteroepitaxial SC-BDD electrodes for electrochemical sensing, whereas experiments with anthraquinone-2,6-disulfonate revealed their enhanced resistance to fouling. All in all, heteroepitaxial SC-BDD represents a highly attractive electrode material which can, owing to the fabrication strategy, easily overcome size limitation, currently preventing broader use of single crystal diamond electrodes in electrochemical applications.Micro and Nano EngineeringTeam Arjan MolTeam Yaiza Gonzalez Garci

Laser-induced Periodic Surface Structures (LIPSS) on heavily boron-doped diamond for electrode applications

Diamond is known as a promising electrode material in the fields of cell stimulation, energy storage (e.g., supercapacitors), (bio)sensing, catalysis, etc. However, engineering its surface and electrochemical properties often requires costly and complex procedures with addition of foreign material (e.g., carbon nanotube or polymer) scaffolds or cleanroom processing. In this work, we demonstrate a novel approach using laser-induced periodic surface structuring (LIPSS) as a scalable, versatile, and cost-effective technique to nanostructure the surface and tune the electrochemical properties of boron-doped diamond (BDD). We study the effect of LIPSS on heavily doped BDD and investigate its application as electrodes for cell stimulation and energy storage. We show that quasi-periodic ripple structures formed on diamond electrodes laser-textured with a laser accumulated fluence of 0.325 kJ/cm2 (800 nm wavelength) displayed a much higher double-layer capacitance of 660 μF/cm2 than the as-grown BDD (20 μF/cm2) and that an increased charge-storage capacity of 1.6 mC/cm2 (&gt;6-fold increase after laser texturing) and a low impedance of 2.74 ω cm2 turn out to be appreciable properties for cell stimulation. Additional morphological and structural characterization revealed that ripple formation on heavily boron-doped diamond (2.8 atom % [B]) occurs at much lower accumulated fluences than the 2 kJ/cm2 typically reported for lower doping levels and that the process involves stronger graphitization of the BDD surface. Finally, we show that the exposed interface between sp2 and sp3 carbon layers (i.e. the laser-ablated diamond surface) revealed faster kinetics than the untreated BDD in both ferrocyanide and RuHex mediators, which can be used for electrochemical (bio)sensing. Overall, our work demonstrates that LIPSS is a powerful single-step tool for the fabrication of surface-engineered diamond electrodes with tunable material, electrochemical, and charge-storage properties.Micro and Nano Engineerin