Porous boron doped diamond for dopamine sensing: Effect of boron doping level on morphology and electrochemical performance

Smart and emerging point of care electrochemical sensors based on nanomaterials for SARS-CoV-2 virus detection: Towards designing a future rapid diagnostic tool

In the recent years, researchers from all over the world have become interested in the fabrication of advanced and innovative electrochemical and/or biosensors for respiratory virus detection with the use of nanotechnology. These fabricated sensors demonstrated a number of benefits, including precision, affordability, accessibility, and miniaturization which makes them a promising test method for point-of-care (PoC) screening for SARS-CoV-2 viral infection. In order to comprehend the principles of electrochemical sensing and the role of various types of sensing interfaces, we comprehensively explored the underlying principles of electroanalytical methods and terminologies related to it in this review. In addition, it is addressed how to fabricate electrochemical sensing devices incorporating nanomaterials as graphene, metal/metal oxides, metal organic frameworks (MOFs), MXenes, quantum dots, and polymers. We took an effort to carefully compile current developments, advantages, drawbacks, possible solutions in nanomaterials based electrochemical sensors.

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.

Electrochemical Evaluation of Cd, Cu, and Fe in Different Brands of Craft Beers from Quito, Ecuador

The presence of heavy metals in craft beers can endanger human health if the total metal content exceeds the exposure limits recommended by sanitary standards; in addition, they can cause damage to the quality of the beer. In this work, the concentration of Cd(II), Cu(II), and Fe(III) was determined in 13 brands of craft beer with the highest consumption in Quito, Ecuador, by differential pulse anodic stripping voltammetry (DPASV), using as boron-doped diamond (BDD) working electrode. The BDD electrode used has favorable morphological and electrochemical properties for the detection of metals such as Cd(II), Cu(II), and Fe(III). A granular morphology with microcrystals with an average size between 300 and 2000 nm could be verified for the BDD electrode using a scanning electron microscope. Double layer capacitance of the BDD electrode was 0.01412 μF cm^-2, a relatively low value; Ip_ox/Ip_red ratios were 0.99 for the potassium ferro-ferricyanide system in BDD, demonstrating that the redox process is quasi-reversible. The figures of merit for Cd(II), Cu(II), and Fe(III) were; DL of 6.31, 1.76, and 1.72 μg L^-1; QL of 21.04, 5.87, and 5.72 μg L^-1, repeatability of 1.06, 2.43, and 1.34%, reproducibility of 1.61, 2.94, and 1.83% and percentage of recovery of 98.18, 91.68, and 91.68%, respectively. It is concluded that the DPASV method on BDD has acceptable precision and accuracy for the quantification of Cd(II), Cu(II), and Fe(III), and it was verified that some beers did not comply with the permissible limits of food standards.

Improved procedure for square-wave voltammetric sensing of fenhexamid residues on blueberries peel surface at the anodically pretreated boron-doped diamond electrode

BACKGROUND

Fungicide fenhexamid (FH) has a high residual concentration on fruits and vegetables, thus, it is of high importance to monitor the level of FH residues on foodstuff samples. So far, the assay of FH residues in selected foodstuff samples has been conducted by electroanalytical methods on sp² carbon-based electrodes that are well-known to be susceptible to severe fouling of the electrodes surfaces during electrochemical measurements. As an alternative, sp³ carbon-based electrode such as boron-doped diamond (BDD) can be used in the analysis of FH residues retained on the peel surface of foodstuff (blueberries) sample.

RESULTS

In situ anodic pretreatment of the BDDE surface was found to be the most successful strategy to remediate the passivated BDDE surface by FH oxidation (by)products, and the best validation parameters, i.e., the widest linear range (3.0-100.0 μmol L^-1), the highest sensitivity (0.0265 μA L μmol^-1) and the lowest limit of detection (0.821 μmol L^-1), were achieved on the anodically pretreated BDDE (APT-BDDE) in a Britton-Robinson buffer, pH 2.0, using square-wave voltammetry (SWV). The assay of FH residues retained on blueberries peel surface was performed on the APT-BDDE using SWV, and the obtained concentration of FH residues of 6.152 μmol L^-1 (1.859 mg kg^-1) was found to be below the maximum residue value fixed for blueberries by the European Union regulations (20 mg kg^-1).

SIGNIFICANCE AND NOVELTY

In this work, a protocol based on a very easy and fast foodstuff sample preparation procedure combined with the straightforward pretreatment approach of the BDDE surface was elaborated for the first time for the monitoring of the level of FH residues retained on the peel surface of blueberries samples. The presented reliable, cost-effective, and easy-to-use protocol could find its application as a rapid screening method for the control of food safety.

Microporous poly- and monocrystalline diamond films produced from chemical vapor deposited diamond-germanium composites

We report on a novel method for porous diamond fabrication, which is based on the synthesis of diamond-germanium composite films followed by etching of the Ge component. The composites were grown by microwave plasma assisted CVD in CH₄-H₂-GeH₄ mixtures on (100) silicon, and microcrystalline- and single-crystal diamond substrates. The structure and the phase composition of the films before and after etching were analyzed with scanning electron microscopy and Raman spectroscopy. The films revealed a bright emission of GeV color centers due to diamond doping with Ge, as evidenced by photoluminescence spectroscopy. The possible applications of the porous diamond films include thermal management, surfaces with superhydrophobic properties, chromatography, supercapacitors, etc.

Highly porous seeding-free boron-doped ultrananocrystalline diamond used as high-performance anode for electrochemical removal of carbaryl from water

Boron-doped diamond (BDD) electrodes are regarded as the most promising catalytic materials that are highly efficient and suitable for application in advanced electrochemical oxidation processes targeted at the removal of recalcitrant contaminants in different water matrices. Improving the synthesis of these electrodes through the enhancement of their morphology, structure and stability has become the goal of the material scientists. The present work reports the use of an ultranano-diamond electrode with a highly porous structure (B-UNCD_WS/TDNT/Ti) for the treatment of water containing carbaryl. The application of the proposed electrode at current density of 75 mA cm^-2 led to the complete removal of the pollutant (carbaryl) from the synthetic medium in 30 min of electrolysis with an electric energy per order of 4.01 kWh m^-3 order^-1. The results obtained from the time-course analysis of the carboxylic acids and nitrogen-based ions present in the solution showed that the concentrations of nitrogen-based ions were within the established maximum levels for human consumption. Under optimal operating conditions, the proposed electrode was successfully employed for the complete removal of carbaryl in real water. Thus, the findings of this study show that the unique, easy-to-prepare BDD-based electrode proposed in this study is a highly efficient tool which has excellent application potential for the removal of recalcitrant pollutants in water.

Bottom-Up Evolution of Diamond-Graphite Hybrid Two-Dimensional Nanostructure: Underlying Picture and Electrochemical Activity

The diamond-graphite hybrid thin film with low-dimensional nanostructure (e.g., nitrogen-included ultrananocrystalline diamond (N-UNCD) or the alike), has been employed in many impactful breakthrough applications. However, the detailed picture behind the bottom-up evolution of such intriguing carbon nanostructure is far from clarified yet. Here, the authors clarify it, through the concerted efforts of microscopic, physical, and electrochemical analyses for a series of samples synthesized by hot-filament chemical vapor deposition using methane-hydrogen precursor gas, based on the hydrogen-dependent surface reconstruction of nanodiamond and on the substrate-temperature-dependent variation of the growth species (atomic hydrogen and methyl radical) concentration near substrate. The clarified picture provides insights for a drastic enhancement in the electrochemical activities of the hybrid thin film, concerning the detection of important biomolecule, that is, ascorbic acid, uric acid, and dopamine: their limits of detections are 490, 35, and 25 nm, respectively, which are among the best of the all-carbon thin film electrodes in the literature. This work also enables a simple and effective way of strongly enhancing AA detection.

Enhancing electroanalytical performance of porous boron-doped diamond electrodes by increasing thickness for dopamine detection

Novel porous boron-doped diamond (BDD_porous)-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD_porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO₂ nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10²¹ atoms cm^-3 and increased content of non-diamond (sp²) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm^-2 to 1060 μF cm^-2), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm² to 7.72 mm²), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol^-1 L was achieved on a BDD_porous electrode with five layers and dropped to 35.9 μA μmol^-1 L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L^-1 was obtained on a BDD_porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD_porous electrodes.

Conductive Nanodiamond-Based Detection of Neurotransmitters: One Decade, Few Sensors

Nanodiamond (ND) is a class of carbon nanomaterial with covalently connected sp³ carbon atoms in its core and an sp² carbon adorned surface via edge defects or doping. Endogenous chemicals that provoke physiological responses in the human system called neurotransmitters (NTs) have been detected with several sensors with carbon-based nanomaterials. Nanodiamonds (NDs), another class of carbon nanomaterial, have shown the requisite surface area and electrocatalytic activity toward NTs in the past decade. Surprisingly, only a few electrochemical ND based NT sensors are available. This work briefly looked into the performance of the available sensors, NT and ND interactions, and the possible reason for data paucity on the subject matter.

Double-side effect of B/C ratio on BDD electrode detection for heavy metal ion in water

BDD (Boron-doped Diamond) electrode may hold a promising application to detect heavy metal ions for actual water monitoring and early warning, but a poor understanding of influence mechanism of B/C ratio on detection performance is in the way of its fabrication and application. This work is intended to reveal the double-side effect of B/C ratio on detection performance of BDD electrode so as to facilitate its actual application. SBDD (Self-supported Boron-doped Diamond) electrode is introduced for the first time to get rid of the interference factors such as substrate. A systematic investigation is conducted for the influence of B/C ratio on microstructure and electrochemical behavior of SBDD electrodes. With the increase of B/C ratio, the grain size continuously increases, and the preferred orientation gradually changes from plane (220) to (111). The gradual increasing of impurity phase content indicates a deterioration of diamond phase quality. In addition, the electrode electrochemical behavior initially gets better then worse. SBDD electrode with a B/C ratio of 1/500 has the largest active surface area of 2.1 cm², the smallest diffusion resistance and the highest signal response. Under optimal parameter set, the SBDD electrode enjoys a sensitivity of 0.42 μA L μg^-1 cm^-2 and a detection limit of 1.12 μg L^-1 in a wide linear range of 5-120 ppb. The phase quality and grain morphology jointly contribute to the double-side effect. A suitable B-sp³-C content, preferred orientation of (111) and small particle size may make the performance improvement of BDD electrode available.

Next-Generation Diamond Electrodes for Neurochemical Sensing: Challenges and Opportunities

Carbon-based electrodes combined with fast-scan cyclic voltammetry (FSCV) enable neurochemical sensing with high spatiotemporal resolution and sensitivity. While their attractive electrochemical and conductive properties have established a long history of use in the detection of neurotransmitters both in vitro and in vivo, carbon fiber microelectrodes (CFMEs) also have limitations in their fabrication, flexibility, and chronic stability. Diamond is a form of carbon with a more rigid bonding structure (sp3-hybridized) which can become conductive when boron-doped. Boron-doped diamond (BDD) is characterized by an extremely wide potential window, low background current, and good biocompatibility. Additionally, methods for processing and patterning diamond allow for high-throughput batch fabrication and customization of electrode arrays with unique architectures. While tradeoffs in sensitivity can undermine the advantages of BDD as a neurochemical sensor, there are numerous untapped opportunities to further improve performance, including anodic pretreatment, or optimization of the FSCV waveform, instrumentation, sp2/sp3 character, doping, surface characteristics, and signal processing. Here, we review the state-of-the-art in diamond electrodes for neurochemical sensing and discuss potential opportunities for future advancements of the technology. We highlight our team's progress with the development of an all-diamond fiber ultramicroelectrode as a novel approach to advance the performance and applications of diamond-based neurochemical sensors.

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp² content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

Comparison of electrochemical performance of various boron-doped diamond electrodes: Dopamine sensing in biomimicking media used for cell cultivation

Chemically inert and biocompatible boron-doped diamond (BDD) has been successfully used in neuroscience for sensitive neurochemicals sensing and/or as a growth substrate for neurons. In this study, several types of BDD differing in (i) fabrication route, i.e. conventional microwave plasma enhanced chemical vapour deposition (MW-PECVD) reactor vs. MW-PECVD with linear antenna delivery system, (ii) morphology, i.e. planar vs. porous BDD, and (iii) surface treatment, i.e. H-terminated (H-BDDs) vs. O-terminated (O-BDDs), were characterized from a morphological, structural, and electrochemical point of view. Further, planar and porous BDD-based electrodes were tested for sensing of dopamine in common biomimicking environments of pH 7.4, namely phosphate buffer (PB) and HEPES buffered saline (HBS). In HBS, potential windows are narrowed due to electrooxidation of its buffering component (i.e. HEPES), however, dopamine sensing in HBS is possible. H-BDDs (both planar and porous) outperformed O-BDDs as they provided clearer dopamine signals with higher peak currents. As expected, due to its enlarged surface area and increased sp² content, the highest sensitivity and lowest detection limits of 8 × 10^-8 mol L^-1 and 6 × 10^-8 mol L^-1 in PB and HBS media, respectively, were achieved by square-wave voltammetry on porous H-BDD.

A cost-efficient approach for simultaneous scanning electrochemical microscopy and scanning ion conductance microscopy

A novel and cost-efficient probe fabrication method yielding probes for performing simultaneous scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) is presented. Coupling both techniques allows distinguishing topographical and electrochemical activity information obtained by SECM. Probes were prepared by deposition of photoresist onto platinum-coated, pulled fused silica capillaries, which resulted in a pipette probe with an integrated ring ultramicroelectrode. The fabricated probes were characterized by means of cyclic voltammetry and scanning electron microscopy. The applicability of probes was demonstrated by measuring and distinguishing topography and electrochemical activity of a model substrate. In addition, porous boron-doped diamond samples were investigated via simultaneously performed SECM and SICM.

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Application of spike sorting algorithm to neuronal signals originated from boron doped diamond micro-electrode arrays

In this work we report on the implementation of methods for data processing signals from microelectrode arrays (MEA) and the application of these methods for signals originated from two types of MEAs to detect putative neurons and sort them into subpopulations. We recorded electrical signals from firing neurons using titanium nitride (TiN) and boron doped diamond (BDD) MEAs. In previous research, we have shown that these methods have the capacity to detect neurons using commercially-available TiN-MEAs. We have managed to cultivate and record hippocampal neurons for the first time using a newly developed custom-made multichannel BDD-MEA with 20 recording sites. We have analysed the signals with the algorithms developed and employed them to inspect firing bursts and enable spike sorting. We did not observe any significant difference between BDD- and TiN-MEAs over the parameters, which estimated spike shape variability per each detected neuron. This result supports the hypothesis that we have detected real neurons, rather than noise, in the BDD-MEA signal. BDD materials with suitable mechanical, electrical and biocompatibility properties have a large potential in novel therapies for treatments of neural pathologies, such as deep brain stimulation in Parkinson's disease.

Electrostatic repulsion strategy for high-sensitive and selective determination of dopamine in the presence of uric acid and ascorbic acid

In this work, poly(sodium 4-styrenesulfonate)-functionalized three-dimensional graphene (PFSG) composites were realized via a facile and green strategy. The nanocomposite was characterized by scanning electron microscopy, ultraviolet and visible spectroscopy, X-ray photoelectron spectroscopy, and electrochemical method. An electroanalytical sensor of dopamine (DA) with high sensitivity and selectivity was fabricated based on PFSG modified glassy carbon electrode (GCE). Under the optimum conditions, the negatively charged PFSG composites exhibit strong electrostatic attraction for DA and electrostatic repulsion to the negatively charged ascorbic acid (AA) and uric acid (UA) molecules. Such electrostatic interaction hindered the enrichment of AA and UA on the surface of PSFG/GCE, which make a higher selectivity for the DA even in the presence of 120-fold AA and UA. Owing to the enhanced electron transfer rate and the stronger surface attraction, the current signal of DA on PFSG/GCE was about 160 times enhanced compared with the bare electrode. There was a good linear relationship between the reduction peak current of DA and concentration across the range of 0.002-2.0 μmol L^-1 and 2.0-10.0 μmol L^-1 with the limit of 0.8 nmol L^-1. Further, the PFSG/GCE was applied to the detection of DA in human serum samples. This biosensor is simple, sensitive, selective and highly stable, which provided a new design strategy and a valuable tool to detect DA in complex samples.