Biofouling and performance of boron-doped diamond electrodes for detection of dopamine and serotonin in neuron cultivation media.

Boron doped diamond has been considered as a fouling-resistive electrode material for in vitro and in vivo detection of neurotransmitters. In this study, its performance in electrochemical detection of dopamine and serotonin in neuron cultivation media Neurobasal™ before and after cultivation of rat neurons was investigated. For differential pulse voltammetry the limits of detection in neat Neurobasal™ medium of 2 µM and 0.2 µM for dopamine and serotonin, respectively, were achieved on the polished surface, which is comparable with physiological values. On oxidized surface twofold higher values, but increased repeatabilities of the signals were obtained. However, in Neurobasal™ media with peptides-containing supplements necessary for cell cultivation, the voltammograms were notably worse shaped due to biofouling, especially in the medium isolated after neuron growth. In these complex media, the amperometric detection mode at +0.75 V (vs. Ag/AgCl) allowed to detect portion-wise additions of dopamine and serotonin (as low as 1-2 µM), mimicking neurotransmitter release from vesicles despite the lower sensitivity in comparison with neat NeurobasalTM. The results indicate substantial differences in detection on boron doped diamond electrode in the presence and absence of proteins, and the necessity of studies in real media for successful implementation to neuron-electrode interfaces.

The Biomimetic Synthesis of Polyarylated Fluorenes, Relevant to Selaginellaceae Polyphenols, Leading to the Spontaneous Formation of Stable Radicals.

This work reports a biomimetic synthesis of polyarylated fluorene derivatives. The molecules are formed via intramolecular electrophilic aromatic substitution, resembling a cyclization leading towards the natural selaginpulvilins from selaginellins. The scope of the reaction was investigated, and the products were obtained in 60-95 % yields. Some of the compounds decompose to a stable radical. We investigated the nature and the origin of the radical using experimental methods, including EPR or electrochemical measurements, as well as theoretical methods, such as DFT calculations. Based on our observations, we hypothesize, that phenoxy radicals are formed in the first instance, which however undergo internal rearrangement to thermodynamically more stable carbon-centered radicals. The preliminary data also show the cytotoxic properties of some of the molecules.

Non-enzymatic electrochemical determination of cholesterol in dairy products on boron-doped diamond electrode.

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/AgNO3 in acetonitrile) provide detection limits of 4.9 µM and 6.1 µM on boron-doped diamond and glassy carbon electrodes, respectively. A simple liquid-liquid extraction procedure from dairy products into hexane resulted in a recovery rate of (74.8 ± 3.8)%. The method provides results in close agreement (at a 95% confidence level) with GC-MS, while HPLC-UV resulted in a significant difference in estimated cholesterol concentrations for all samples. This newly developed method is a simpler, faster and cheaper alternative to instrumentally demanding MS-based methods and clearly outperforms HPLC-UV.

Structural Characterization of Unusual Fatty Acid Methyl Esters with Double and Triple Bonds Using HPLC/APCI-MS2 with Acetonitrile In-Source Derivatization.

Double and triple bonds have significant effects on the biological activities of lipids. Determining multiple bond positions in their molecules by mass spectrometry usually requires chemical derivatization. This work presents an HPLC/MS method for pinpointing the double and triple bonds in fatty acids. Fatty acid methyl esters were separated by reversed-phase HPLC with an acetonitrile mobile phase. In the APCI source, acetonitrile formed reactive species, which added to double and triple bonds to form [M + C3H5N]+• ions. Their collisional activation in an ion trap provided fragments helpful in localizing the multiple bond positions. This approach was applied to fatty acids with isolated, cumulated, and conjugated double bonds and triple bonds. The fatty acids were isolated from the fat body of early-nesting bumblebee Bombus pratorum and seeds or seed oils of Punicum granatum, Marrubium vulgare, and Santalum album. Using the method, the presence of the known fatty acids was confirmed, and new ones were discovered.

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

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.

Voltammetry of 7-dehydrocholesterol as a new and useful tool for Smith-Lemli-Opitz syndrome diagnosis.

7-Dehydrocholesterol is an essential biomarker of Smith-Lemli-Opitz syndrome, a congenital autosomal recessive disorder. This study shows for the first time that electrochemical oxidation of 7-dehydrocholesterol can be used for its voltammetric determination. Two classes of supporting electrolytes in acetonitrile and a mixture of acetonitrile-water were used: inorganic acids known to promote structural changes of steroids and indifferent electrolytes. Oxidation of 7-dehydrocholesterol at ca +0.8 V (vs. Ag/AgNO3 in acetonitrile) in 0.1 mol L-1 NaClO4 in acetonitrile is useful for its voltammetric detection using common bare electrode materials. Detection limits for 7-dehydrocholesterol lie in the low micromolar range for all the working electrodes, including boron-doped diamond (0.4 µmol L-1) and disposable thin-film platinum electrodes (0.5 µmol L-1), which are advantageous because of the low volumes of studied solutions. After Bligh-Dyer extraction, quantification of 7-dehydrocholesterol concentration (boron-doped diamond) or concentration range (thin-film platinum) is easily attainable in artificial serum. The mere knowledge of the concentration range provides clinically valuable information, as 7-dehydrocholesterol levels are employed for SLOS diagnosis as a binary criterion (elevated, tens to hundreds µmol L-1 in symptomatic/non-elevated, typically bellow 1 µmol L-1 in healthy individuals in plasma). Moreover, it is shown that 7-dehydrocholesterol (provitamin D3) and cholecalciferol (vitamin D3) can be oxidized in 0.1 mol L-1 HClO4 in acetonitrile. Under these conditions, their voltammetric response changes dramatically, and their oxidation potential difference transiently increases from 0.08 V to 0.25 V, which should facilitate their simultaneous voltammetric determination. This work constitutes a foundation for a reliable and straightforward method for Smith-Lemli-Opitz syndrome diagnosis and monitoring 7-dehydrocholesterol's biotransformation to cholecalciferol.

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.

The development of a fully integrated 3D printed electrochemical platform and its application to investigate the chemical reaction between carbon dioxide and hydrazine.

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.

A novel voltammetric approach to the detection of primary bile acids in serum samples.

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.

Recent progress in the applications of boron doped diamond electrodes in electroanalysis of organic compounds and biomolecules - A review.

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.

Twinned Growth of Metal-Free, Triazine-Based Photocatalyst Films as Mixed-Dimensional (2D/3D) van der Waals Heterostructures.

Design and synthesis of ordered, metal-free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed-dimensional (2D/3D) metal-free van der Waals (vdW) heterostructures based on triazine (C3 N3 ) linkers grow as large area, transparent yellow-orange membranes on copper surfaces from solution. The membranes have an indirect band gap (Eg,opt = 1.91 eV, Eg,elec = 1.84 eV) and are moderately porous (124 m2 g-1 ). The material consists of a crystalline 2D phase that is fully sp2 hybridized and provides structural stability, and an amorphous, porous phase with mixed sp2 -sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one-pot reaction mixture: unprecedented for metal-free frameworks and a direct consequence of on-catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal-free, light-induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h-1 g-1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of "wet" chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.

Non-Enzymatic Electrochemistry in Characterization and Analysis of Steroid Compounds.

This review summarizes achievements in electrochemistry-related research of steroid-based compounds in clinical, pharmaceutical, and environmental analysis. Special attention is paid to compounds possessing none or only isolated double bonds at the steroid core. Their direct redox activity is limited to far positive/negative potentials under variety of conditions and electrode materials and relies on the functional groups attached to the steroid skeleton, or as the case may be its double bond or moieties present at the side chain. The possibilities of electroanalytical methods in sterol characterization and analysis are demonstrated in a table with 31 references devoted to direct voltammetric and amperometric methods of oxidation of cholesterol, phytosterols, oxysterols, and related compounds at carbon-based and metal-based nanoparticles modified electrodes, and the reduction of bile acids and their conjugates at mercury-based electrodes, and modified glassy carbon electrodes. Furthermore, methods based on the indirect oxidation of cholesterol using bromine species as a mediator at platinum electrode and non-enzymatic cholesterol biosensors are reviewed. Their drawbacks and benefits are discussed with respect to the challenging task of identification and quantitation of these compounds in biological matrices, otherwise mostly performed using expensive mass spectrometric techniques preceded by a chromatographic separation step.

Localization of double bonds in triacylglycerols using high-performance liquid chromatography/atmospheric pressure chemical ionization ion-trap mass spectrometry.

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.

New MALDI matrices based on lithium salts for the analysis of hydrocarbons and wax esters.

Lithium salts of organic aromatic acids (lithium benzoate, lithium salicylate, lithium vanillate, lithium 2,5-dimethoxybenzoate, lithium 2,5-dihydroxyterephthalate, lithium α-cyano-4-hydroxycinnamate and lithium sinapate) were synthesized and tested as potential matrices for the matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry analysis of hydrocarbons and wax esters. The analytes were desorbed using nitrogen laser (337.1 nm) and ionized via the attachment of a lithium cation, yielding [M + Li](+) adducts. The sample preparation and the experimental conditions were optimized for each matrix using stearyl behenate and n-triacontane standards. The performance of the new matrices in terms of signal intensity and reproducibility, the mass range occupied by matrix ions and the laser power threshold were studied and compared with a previously recommended lithium 2,5-dihydroxybenzoate matrix (LiDHB) (Cvacka and Svatos, Rapid Commun. Mass Spectrom. 2003, 17, 2203). Several of the new matrices performed better than LiDHB. Lithium vanillate offered a 2-3 times and 7-9 times higher signal for wax esters and hydrocarbons, respectively. Also, the signal reproducibility improved substantially, making this matrix a suitable candidate for imaging applications. In addition, the diffuse reflectance spectra and solubility of the synthesized compounds were investigated and discussed with respect to the compound's ability to serve as MALDI matrices. The applicability of selected matrices was tested on natural samples of wax esters and hydrocarbons.

The use of silver solid amalgam electrodes for voltammetric and amperometric determination of nitrated polyaromatic compounds used as markers of incomplete combustion.

Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs) are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs) with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds) have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE), which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10(-7) mol L(-1) concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L(-1) phosphate buffer, pH 7.0 : methanol (15 : 85, v/v) mobile phase, and C(18) reversed stationary phase. Limits of detection of around 1 · 10(-5) mol L(-1) were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10(-6) mol L(-1).

Localization of double bonds in wax esters by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry utilizing the fragmentation of acetonitrile-related adducts.

Unsaturated wax esters (WEs) provided molecular adducts with C(3)H(5)N ([M + 55](+•)) in APCI sources in the presence of acetonitrile. CID MS/MS of [M + 55](+•) yielded fragments allowing the localization of double bond(s) in the hydrocarbon chains of the WEs. These fragments were formed by a cleavage on each side of the double bond. In methylene-interrupted polyunsaturated WEs, diagnostic fragments related to each double bond were detected; the most abundant were those corresponding to the cleavage of the C-C bond next to the first and the last double bond. To differentiate between those fragments differing in their structure or origin, a simple nomenclature based on α and ω ions has been introduced. Fragmentation of the α-type ions (fragments containing an ester bond) provided information on the occurrence of a double bond in the acid or alcohol part of the WEs. While no significant differences between the spectra of the WEs differing by cis/trans isomerism were found, the isomers were separated chromatographically. A data-dependent HPLC/APCI-MS(2) method for the comprehensive characterization of WEs in their complex mixtures has been developed and applied to natural mixtures of WEs isolated from jojoba oil and beeswax. More than 50 WE molecular species were completely identified, including the information on the acid and alcohol chain length and the position of the double bonds.

Voltammetric determination of aminobiphenyls at a boron-doped nanocrystalline diamond film electrode.

Voltammetric behavior of 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl at a boron-doped nanocrystalline diamond film electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Optimum conditions have been found for the determination of those genotoxic substances by differential pulse voltammetry at the above given electrode in the concentration range of 2 x 10(-7) to 1 x 10(-5) mol/L.

Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene.

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2 x 10(-6) - 1 x 10(-4), 2 x 10(-7) - 1 x 10(-4), 1 x 10(-8) - 1 x 10(-4) and 2 x 10(-9) - 1 x 10(-8) M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid-liquid and solid-phase extraction with limits of determination of 3 x 10(-10) M (drinking water) and 3 x 10(-9) M (river water).