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

Inkjet Printing-Manufactured Boron-Doped Diamond Chip Electrodes for Electrochemical Sensing Purposes

Fabrication of patterned boron-doped diamond (BDD) in an inexpensive and straightforward way is required for a variety of practical applications, including the development of BDD-based electrochemical sensors. This work describes a simplified and novel bottom-up fabrication approach for BDD-based three-electrode sensor chips utilizing direct inkjet printing of diamond nanoparticles on silicon-based substrates. The whole seeding process, accomplished by a commercial research inkjet printer with piezo-driven drop-on-demand printheads, was systematically examined. Optimized and continuous inkjet-printed features were obtained with glycerol-based diamond ink (0.4% vol/wt), silicon substrates pretreated by exposure to oxygen plasma and subsequently to air, and applying a dot density of 750 drops (volume 9 pL) per inch. Next, the dried micropatterned substrate was subjected to a chemical vapor deposition step to grow uniform thin-film BDD, which satisfied the function of both working and counter electrodes. Silver was inkjet-printed to complete the sensor chip with a reference electrode. Scanning electron micrographs showed a closed BDD layer with a typical polycrystalline structure and sharp and well-defined edges. Very good homogeneity in diamond layer composition and a high boron content (∼2 × 1021 atoms cm-3) was confirmed by Raman spectroscopy. Important electrochemical characteristics, including the width of the potential window (2.5 V) and double-layer capacitance (27 μF cm-2), were evaluated by cyclic voltammetry. Fast electron transfer kinetics was recognized for the [Ru(NH3)6]3+/2+ redox marker due to the high doping level, while somewhat hindered kinetics was observed for the surface-sensitive [Fe(CN)6]3-/4- probe. Furthermore, the ability to electrochemically detect organic compounds of different structural motifs, such as glucose, ascorbic acid, uric acid, tyrosine, and dopamine, was successfully verified and compared with commercially available screen-printed BDD electrodes. The newly developed chip-based manufacture method enables the rapid prototyping of different small-scale electrode designs and BDD microstructures, which can lead to enhanced sensor performance with capability of repeated use.

Core-shell copper-gold nanoparticles modified at the boron-doped diamond electrode for oxygen sensors

Bimetallic copper-gold (Cu@Au) nanoparticles were synthesized and utilised to modify boron-doped diamond (BDD) electrodes. Nanorod particles with a diameter size of around 10 nm and a length of around 20 nm were successfully synthesized. These nanoparticles were then attached to the BDD surface by using allylamine as the bridge. Comparison among the BDD modified with Cu@Au and individual gold nanoparticles showed that Cu@Au nanoparticles created around 3 times higher gold coverage on the BDD surface than normal gold nanoparticles. It was also found that the use of allylamine as the bridge can attach more gold than copper nanoparticles. Moreover, around two times higher current responses of oxygen reduction reaction were observed at Cu@Au-modified BDD. Good linearity in a concentration range from 2 to 9 ppm could be achieved with a sensitivity of 0.0138 mA ppm^-1 and limit detection of 1.98 ppm. An application of the modified BDD for a biochemical oxygen demand (BOD) sensor using Rhodotorula mucilaginosa UICC Y-181 as the biosensing agent was also demonstrated with glucose solutions as the solution model. Sensitivity equivalent to 17.4 μA mM^-1 BOD could be achieved. The system showed good stability with an RSD of 3.45% in 10 measurements.

Experimental insights into anodic oxidation of hexafluoropropylene oxide dimer acid (GenX) on boron-doped diamond anodes

GenX is the trade name of the ammonium salt of hexafluoropropylene oxide dimer acid (HFPO-DA) and is used as a replacement for the banned perfluorooctanoic acid (PFOA). However, recent studies have found GenX to be more toxic than PFOA. This work deals with the electrochemical degradation of HFPO-DA using boron-doped diamond anodes. For the first time, an experimental study was conducted to investigate the influence of sulfate concentration and other operating parameters on HFPO-DA degradation. Results demonstrated that sulfate radicals were ineffective in HFPO-DA degradation due to steric hindrance by -CF₃ branch. Direct electron transfer was found as the rate-determining step. By comparing degradation of HFPO-DA with that of PFOA, it was observed that the steric hindrance by -CF₃ branch in HFPO-DA decreased the rate of electron transfer from the carboxyl head group even though its defluorination rate was faster. Conclusively, a degradation pathway is proposed in which HFPO-DA mineralizes to CO₂ and F- via formation of three intermediates.