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This review summarizes progress in electroanalysis of organic compounds and biomacromolecules by means of bare BDD-based electrodes for the period of 2009-2018. New trends, which have emerged in the reported decade and which have improved their performance in batch voltammetric and amperometric methods and electrochemical detection in liquid flow techniques are commented. Importance of BDD surface termination, effect of boron doping level, and utilization of adsorption of analytes on BDD surfaces enabling development of adsorptive voltammetric techniques are addressed. Further, possibilities of simultaneous determination of analytes by means of voltammetric techniques utilizing computational approaches and multiple-pulse amperometric detection are discussed. Strategies leading to enhancement of sensitivity such as nanostructuring of the BDD surface, fabrication of BDD-based composite materials or new approaches in construction of microelectrodes and microelectrode arrays for biosensing represent another area of interest. Attention is paid to possibilities in detection of amino acids, peptides and proteins, nucleobases, nucleos(t)ides and DNA/RNA.

Determination of cholesterol in food matrices is essential for quality control concerning the health of consumers. Herein, a simple electrochemical approach for cholesterol quantitation in dairy products is evaluated. The newly developed differential pulse voltammetric method using acetonitrile-perchloric acid mixture as a supporting electrolyte is statistically compared to GC-MS and HPLC-UV. Oxidation signals of cholesterol at +1.5 V and +1.4 V (vs. Ag/AgNO

The electrochemical behaviour of two main catecholamine metabolites serving as diagnostic tumour biomarkers, homovanillic acid (HVA) and vanillylmandelic acid (VMA), on anodically oxidized boron doped diamond (BDD) electrodes, non-modified glassy carbon electrodes (GCE), and GCE modified by polymers, namely by Nafion (Nafion/GCE) and by poly(neutral red) (PNR/GCE), was investigated. The voltammetric responses of both biomarkers are strongly dependent on pH of the aqueous buffer solution and electrode material used. BDD electrodes exhibit more positive oxidation potentials and lower current densities for oxidation of both analytes, depending also on the surface termination. Concentration dependences were measured in 0.1 mol L−1 phosphate buffer pH 3.0, as optimal supporting electrolyte for differential pulse voltammetric determination. Achieved detection limits were 0.6, 0.9, 0.8, and 1.2 μmol L−1 for HVA and 0.4, 1.5, 2.4, and 1.1 μmol L−1 for VMA at BDD electrodes, non-modified GCE, Nafion/GCE, and PNR/GCE, respectively. The limits of quantification for both organic compounds on all tested electrode materials are sufficiently low for their determination in urine. Verification of the possibility of simultaneous voltammetric determination of the studied biomarkers in the mixture was also carried out.

Electrochemical properties of 4-nitrophenyl triazole labeled 2′-deoxycytidine (dCTRNO2) and 7-deazaadenosine (dATRNO2) were studied using alumina-polished boron doped diamond (BDD) electrode in acetate buffer pH 5.0. Cyclic voltammetry revealed peak-shaped signals for reduction of the nitro group at the potentials of ca − 0.6 V (vs. AgƖAgClƖ3 mol L− 1 KCl reference electrode) and for the hydroxylamine/nitroso pair exhibiting quasireversible electron transfer at potentials comparable with redox processes of other nitro aromatic compounds at BDD electrodes. All electrochemical processes are directed by adsorption. Moreover, ex situ adsorption of dATRNO2 and transfer to supporting electrolyte enables its quantitation using square wave voltammetry in small (several microliter) sample volumes after optimization of parameters for the hydroxylamine/nitroso redox couple. Competitive adsorption/desorption at the BDD surface was further studied by cyclic voltammetry with dATRNO2 in the presence of electrochemically inactive phenyl triazole 7-deazaadenosine conjugate (dATR), revealing mutual displacement of both compounds at BDD surface. Further, the redox processes of simpler aromatic nitro compounds (4-nitrophenyl acetylene and 2-nitronaphthalene) are strongly affected when the BDD surface is covered by dATR.

Bile acids and sterols in general have long been considered practically inactive for direct redox processes. Herein, a novel way of electrochemical oxidation of primary bile acids is reported, involving an initial acid-induced dehydration step, as confirmed by capillary electrophoresis–mass spectrometry, thereby extending the electrochemical activity of the steroid core. Oxidation potentials were found to be ca +1.2 V vs. Ag/AgNO3 in acetonitrile on boron doped diamond, glassy carbon, and platinum electrodes in a mixed acetonitrile–aqueous medium employing perchloric acid as a chemical reagent, and as a supporting electrolyte for the voltammetric measurements. The chemical step proved to be effective only for primary bile acids, possessing an axial 7α-hydroxyl group, which is a prerequisite for providing a well-developed voltammetric signal. Preliminary results show that other steroids, e.g., cholesterol, can also be oxidized by employing a similar approach. Keywords: Bile acids, Steroid dehydration, Electrochemical oxidation, Bare electrode, Voltammetry

Novel porous boron-doped diamond (BDDporous)-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 BDDporous 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 BDDporous 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 BDDporous 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 BDDporous electrodes.

The effect of boron content in nanocrystalline anodically polarized boron doped diamond (BDD) thin films deposited at B/C ratio 500 ppm – 8000 ppm on their morphology, quality, and electrochemical and spectral properties was investigated using scanning electron and atomic force microscopies and Raman spectroscopy, where the shift of maximum Lorentzian component of diamond phonon at ∼1332 cm−1 was used as the function of boron concentration. Cyclic voltammetry with the outer- and inner sphere redox markers ([Ru(NH3)6]3+/2+ and [Fe(CN)6]3−/4−) enables to differentiate among the semiconductive films (500 ppm and 1000 ppm) and films with metallic conductivity (2000 ppm – 8000 ppm). Nevertheless, only the inner sphere character of [Fe(CN)6]3−/4− redox marker enables to visualize the differences between individual boron content for metallic films. Further, reversible behavior with ΔEp of 59.8 ± 0.9 mV (n = 5) and Ipa/Ipc ratio 1.00 at the scan rate of 100 mV s−1 was achieved for this redox marker at 2000 ppm film; this film just above the semiconductive/metallic threshold exhibited also favorable spectral (e.g., roughness surface factor) and electrochemical characteristics. The width of the potential window in aqueous media of different pH values and in wide variety of supporting electrolytes decreases with increasing boron content, with independence of anodic potential limit for 2000 ppm – 8000 ppm electrodes and more pronounced dependence of cathodic potential limit on boron content for all tested BDD films. Further, well-defined and highly reproducible anodic DP voltammetric peak of 2-aminobiphenyl with peak current increasing with boron content were obtained at ca +0.7 V (vs. Ag/AgCl/3 mol L−1 KCl) at all BDD films tested.

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. Graphic abstract

Producción Científica, Terconazole belongs to synthetic triazole antifungal agents, inhibiting biosynthesis of ergosterol or other sterols and thus disrupting cell wall synthesis in fungi. In this study, electrochemical behavior of terconazole was studied for the first time using cyclic voltammetry and differential pulse voltammetry on boron doped diamond electrode (BDD) with different surface treatments leading to O-terminated, H-terminated and polished surfaces, as well as on glassy carbon (GCE) and basal-plane pyrolytic graphite electrodes (PGE). Terconazole is not reducible within the potential window on these electrode materials. It is oxidizable in aqueous solutions in pH range from 2.0 to 12.0 in two steps due to the presence of piperazine ring in its molecule, possessing two redox centers at the tertiary nitrogen atoms, by an ECE mechanism. Optimal conditions were found for determination of terconazole in 0.1 mol L−1 phosphate buffer pH 7.2. Using differential pulse voltammetry, the lowest detection limit of 0.40 μmol L−1 and excellent repeatability (RSD 1.1%) were achieved on O-terminated BDD when in-situ anodic activation was used prior to each scan. This is beneficial in comparison with GCE and PGE; their necessity of ex-situ polishing worsens the signal repeatability (RSD ~ 4%) and detection limits reaching 0.50 μmol L−1 and 1.23 μmol L−1, respectively., Czech Science Foundation (project 18-01710S) and carried out within the framework of Specific University Research (SVV 260440), Junta de Castilla y León y EU-FEDER (CLU 2017-09)

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.

Triazole pesticides act as sterol synthesis inhibitors and have been considered as redox-inactive with a variety of electrode materials. In this study, electrochemical oxidation of the fungicide difenoconazole (DFC) was studied in aqueous solutions on oxygen terminated boron doped diamond electrode. It provided a pH-independent irreversible anodic peak at a very positive potential of ca +1.75 V (vs. Ag/AgCl) in acidic media, which could be used for its quantitation in batch voltammetry and flow injection analysis with amperometric detection. The attained detection limits for the determination of DFC in 0.1 mol L−1 HNO3 / phosphate buffer pH 2.0 were 0.049 μmol L−1 for differential pulse voltammetry and 1.58 μmol L−1 for FIA-ED. The former method did not suffer from any significant matrix interferences or interferences of other fungicides and yielded acceptable percentage recovery values (ranging from 96% to 107%) for DFC determination in model river water samples. Similar results comparing both methods at a 95% confidence level were obtained for DFC determination in pesticide preparations. Further, an oxidation mechanism leading to hydroxylated derivative of DFC and subsequent formation of a quinone was suggested. Results were supported with HOMO spatial distribution calculations and atomic charges calculations for arising radical cations.

In this work, we employed multiple linear regression analyses to satisfactorily determine cold symptoms treatment drugs paracetamol, phenylephrine hydrochloride, and loratadine in pharmaceutical formulations with combined dosage and spiked human urine sample. All the drugs are irreversibly oxidized on the boron-doped diamond electrode (BDDE) in diffusion-controlled oxidation processes with well-separated potentials in acidic media. A square-wave voltammetric (SWV) method was developed for their simultaneous determination in 0.1 mol L–1 H2SO4 and simple and multiple linear regression analyses were compared as calibration methods for SWV data. Precision and selectivity were also studied. The high concentration ratio between paracetamol and the other two drugs being minor components in the formulated dosage forms caused interference in their voltammetric responses. An assay based on multiple linear regression equations considering these multiple effects revealed statistically the same results as those obtained by a comparative HPLC-UV method at a 95% confidence level. We demonstrated that multiple linear regression provided adequate recovery for the determination of PAR, PHE, and LOR in spiked human urine sample. The developed SWV method is a very fast, low-cost, and environmentally friendly alternative to the routine simultaneous analysis of PAR, PHE, and LOR performed by HPLC-UV.

Highlights • An integrated electrochemical platform was manufactured by bi-material 3D printing. • It was applied to investigate the reaction between hydrazine and carbon dioxide. • Experimental results were supported by finite-element method numerical simulations., The combination of computer assisted design and 3D printing has recently enabled fast and inexpensive manufacture of customized ‘reactionware’ for broad range of electrochemical applications. In this work bi-material fused deposition modeling 3D printing is utilized to construct an integrated platform based on a polyamide electrochemical cell and electrodes manufactured from a polylactic acid-carbon nanotube conductive composite. The cell contains separated compartments for the reference and counter electrode and enables reactants to be introduced and inspected under oxygen-free conditions. The developed platform was employed in a study investigating the electrochemical oxidation of aqueous hydrazine coupled to its bulk reaction with carbon dioxide. The analysis of cyclic voltammograms obtained in reaction mixtures with systematically varied composition confirmed that the reaction between hydrazine and carbon dioxide follows 1/1 stoichiometry and the corresponding equilibrium constant amounts to (2.8 ± 0.6) × 103. Experimental characteristics were verified by results of numerical simulations based on the finite-element-method., Graphical abstract Image, graphical abstract

An innovative voltammetric approach to the detection of cholic and chenodeoxycholic acids is presented. These two primary bile acids are important biomarkers of liver function in humans and are involved in many physiological processes in the human body. Herein we describe a way to reproducibly convert the hard-to-detect bile acid molecule into an easily detectable derivative in situ using 0.1 M HClO4 in acetonitrile (water content 0.55%). Under these conditions the bile acids are dehydrated and the resulting alkenes can be subsequently oxidized electrochemically on polished boron-doped diamond electrode under unchanged conditions at approximately +1.2 V vs. Ag/AgNO3 in acetonitrile. After optimization, differential pulse voltammetry provides competitive limits of detection of 0.5 µM and 1.0 µM for cholic and chenodeoxycholic acid, respectively, with a linear course of calibration dependency to the minimum of 80 µM. The method was applied for detection of cholic and chenodeoxycholic acids in artificial and human serum samples using single solid phase extraction on C-18 cartridge for preliminary separation of the analytes. High recoveries of 80–90% were consistently obtained by the proposed voltammetric method and reference HPLC with fluorescence detection for human serum samples, confirming good selectivity for real-life samples.

The voltammetric signal of 5-nitroquinoline with reducible nitro and quinoline moieties largely depends on the pH of the indifferent electrolyte, electrode pretreatment, activation between individual scans, and boron concentration of the BDD film electrode. Anodic pretreatment at +2.4 V for 5 min in 0.5 mol dm−3 H2SO4 and 20 s stirring between individual scans assured repeatable signals of nitro group in the whole pH range 2.0–12.0; in acetate buffer pH 5.0 limit of detection is 2 × 10−7 mol dm−3 for differential pulse voltammetry. The reduction of quinoline skeleton is visible in the pH range of 6.0–11.0. Presence of oxygen in the measured solutions led to slight increase of peak heights and acceptable increase of its relative standard deviation. BDD films with metallic type of conductivity deposited at B/C ratio 2000–8000 ppm exhibit faster electron transfer at lower potential for nitro group reduction than semiconductive films 500 and 1000 ppm.

The electroanalytical performance of bare glassy carbon electrodes (GCE) for the determination of 1-aminonaphthalene (1-AN) and 2-aminonaphthalene (2-AN) was compared with GCE modified by a Nafion permselective membrane or multiwalled carbon nanotubes and with other types of carbon-based materials, carbon film and boron doped diamond. Nafion-modified GCE gave the highest sensitivity and lowest detection limit (0.4 µmol L−1) for differential pulse voltammetric determination of 1-AN. Electrochemical impedance spectroscopy gave information about the processes at the electrode surface. Simultaneous determination of 1-AN and 2-AN in a mixture at GCE and their determination in model samples of river water is presented.

The goal of this study was to determine benzophenone-3 at the boron-doped diamond electrode and in the presence of cetyltrimethylammonium bromide by adsorptive stripping voltammetry. The oxidation of benzophenone-3 was irreversible by differential pulse voltammetry. The peak height increased with boron concentration in the electrode film deposited as 500–8000 parts per million boron/carbon. Limits of detection of 1.5, 1.9, and 0.8 micromoles per liter were obtained for 2000, 4000, and 8000 parts per million films in Britton-Robinson buffer at pH 12.0. Positive effect of cetyltrimethylammonium bromide on the determination of benzophenone-3 includes higher sensitivity, a shift of the peak potential to less positive values, and an improved limit of detection by an order of magnitude to 0.1 micromole per liter.

High performance liquid chromatography with electrochemical detection using a wall-jet arrangement with a working boron-doped diamond film electrode was used for the determination of 2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol using reduction and oxidation modes. The optimal conditions for separation at a C18 reverse phase column (125 × 4 millimeters, 5 micrometers) and amperometric detection of these nitrophenols were determined. Acetate buffer (0.05 mole per liter pH 4.7/methanol 58/42, v/v) was chosen as the mobile phase for cathodic detection at the potential of −1.2 volts. The linear dynamic range was 2 × 10−6 to 1 × 10−4 mole per liter and the limits of detection were from 0.7 to 1.2 micromole per liter. For anodic detection, the mobile phase was 0.05 mole per liter phosphate buffer pH 6.75/methanol (65/35, v/v) at a detection potential of +1.3 volts. The linear dynamic range was from 2 × 10−6 to 1 × 10−4 mole per liter with limits of detection from 0.6 to 1.5 micromoles per liter. T...

A method for localizing double bonds in triacylglycerols using high-performance liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization (APCI) was developed. The technique was based on collision-induced dissociation or pulsed Q collision-induced dissociation of the C3H5N(+•) adducts ([M + 55](+•)) formed in the presence of acetonitrile in the APCI source. The spectra were investigated using a large series of standards obtained from commercial sources and prepared by randomization. The fragmentation spectra made it possible to determine (i) the total number of carbons and double bonds in the molecule, (ii) the number of carbons and double bonds in acyls, (iii) the acyl in the sn-2 position on the glycerol backbone, and (iv) the double-bond positions in acyls. The double-bond positions were determined based on two types of fragments (alpha and omega ions) formed by cleavages of C-C bonds vinylic to the original double bond. The composition of the acyls and their positions on glycerol were established from the masses and intensities of the ions formed by the elimination of fatty acids from the [M + 55](+•) precursor. The method was applied for the analysis of triacylglycerols in olive oil and vernix caseosa.

Voltammetric method for the determination of a pyridine herbicide triclopyr (3,5,6-trichloro-2-pyridyloxyacetic acid) is presented for the first time using bare boron-doped diamond electrode. Triclopyr provides one well-developed, pH-independent oxidation signal at ca. +1.9 V (vs. Ag∣AgCl∣KCl (sat.)) contrary to structurally related clopyralid, which is not oxidizable at the working electrode. Britton–Robinson buffer (pH 2.0) was chosen as optimal electrolyte for determination of triclopyr using square wave and differential pulse voltammetry. The latter method provided slightly better detection limit of 0.82 μmol L −1 and linearity in the concentration range 1.0–108.8 μmol L −1 . Applicability of the proposed method was verified by analysis of pesticide preparation, spiked water and urine with excellent results.

Complex characterization of as-deposited conventional planar and newly available porous boron doped diamond (BDD) films with various boron doping levels (B/C ratio in the gas phase: 500 ppm, 1000 ppm, 2000 ppm, 4000 ppm, and 8000 ppm) was carried out by scanning electron microscopy, Raman spectroscopy and electrochemistry by performing cyclic voltammetric (CV) experiments with outer- and inner-sphere redox probes [Ru(NH3)6]3+/2+, [Fe(CN)6]3−/4−, and dopamine. The double layer capacitance was estimated from CV and electrochemical impedance spectroscopic measurements. For planar BDD films, a roughly 80% increase in the double layer capacitance, a 100 mV narrower potential window and a 51 mV negative shift of the peak potential of dopamine were observed when the boron doping level increased from 500 ppm to 8000 ppm. Conversely, higher sp2 carbon content confirmed by Raman spectra affects the electrochemical performance of porous samples more significantly than the doping level. For the set of porous BDD electrodes, the double layer capacitance decreased by ca 95% with increasing boron content, peak-to-peak separation values of the studied inorganic redox markers were lower than 59 mV, suggesting their partial adsorption in the bulk of the material, and lower potentials for dopamine oxidation approaching values obtained for other sp2 carbon-based materials were recorded, but no dependency of potential values on boron concentration was revealed. Enhanced electron transfer rate on porous BDD materials resulted in increased sensitivity for dopamine detection using square-wave voltammetry in contrast to the planar set of electrodes. The lowest detection limit of 2 × 10−7 mol L−1 was estimated in a medium of 0.1 mol L−1 phosphate buffer pH 7.4 on B/C 4000 ppm porous electrodes with increased BDD growth time, without any activation applied between the individual scans. Moreover, for selected porous electrodes, improved selectivity for dopamine sensing in excess of common interfering compounds such as uric acid, ascorbic acid and paracetamol was achieved.