Isatin Detection Using a Boron-Doped Diamond 3-in-1 Sensing Platform

Challenges and strategies faced in the electrochemical biosensing analysis of neurochemicals in vivo: A review

Our brain is an intricate neuromodulatory network, and various neurochemicals, including neurotransmitters, neuromodulators, gases, ions, and energy metabolites, play important roles in regulating normal brain function. Abnormal release or imbalance of these substances will lead to various diseases such as Parkinson's and Alzheimer's diseases, therefore, in situ and real-time analysis of neurochemical interactions in pathophysiological conditions is beneficial to facilitate our understanding of brain function. Implantable electrochemical biosensors are capable of monitoring neurochemical signals in real time in extracellular fluid of specific brain regions because they can provide excellent temporal and spatial resolution. However, in vivo electrochemical biosensing analysis mainly faces the following challenges: First, foreign body reactions induced by microelectrode implantation, non-specific adsorption of proteins and redox products, and aggregation of glial cells, which will cause irreversible degradation of performance such as stability and sensitivity of the microsensor and eventually lead to signal loss; Second, various neurochemicals coexist in the complex brain environment, and electroactive substances with similar formal potentials interfere with each other. Therefore, it is a great challenge to design recognition molecules and tailor functional surfaces to develop in vivo electrochemical biosensors with high selectivity. Here, we take the above challenges as a starting point and detail the basic design principles for improving in vivo stability, selectivity and sensitivity of microsensors through some specific functionalized surface strategies as case studies. At the same time, we summarize surface modification strategies for in vivo electrochemical biosensing analysis of some important neurochemicals for researchers' reference. In addition, we also focus on the electrochemical detection of low basal concentrations of neurochemicals in vivo via amperometric waveform techniques, as well as the stability and biocompatibility of reference electrodes during long-term sensing, and provide an outlook on the future direction of in vivo electrochemical neurosensing.

Biocompatible reference electrodes to enhance chronic electrochemical signal fidelity in vivo

In vivo electrochemistry is a vital tool of neuroscience that allows for the detection, identification, and quantification of neurotransmitters, their metabolites, and other important analytes. One important goal of in vivo electrochemistry is a better understanding of progressive neurological disorders (e.g., Parkinson's disease). A complete understanding of such disorders can only be achieved through a combination of acute (i.e., minutes to hours) and chronic (i.e., days or longer) experimentation. Chronic studies are more challenging because they require prolonged implantation of electrodes, which elicits an immune response, leading to glial encapsulation of the electrodes and altered electrode performance (i.e., biofouling). Biofouling leads to increased electrode impedance and reference electrode polarization, both of which diminish the selectivity and sensitivity of in vivo electrochemical measurements. The increased impedance factor has been successfully mitigated previously with the use of a counter electrode, but the challenge of reference electrode polarization remains. The commonly used Ag/AgCl reference electrode lacks the long-term potential stability in vivo required for chronic measurements. In addition, the cytotoxicity of Ag/AgCl adversely affects animal experimentation and prohibits implantation in humans, hindering translational research progress. Thus, a move toward biocompatible reference electrodes with superior chronic potential stability is necessary. Two qualifying materials, iridium oxide and boron-doped diamond, are introduced and discussed in terms of their electrochemical properties, biocompatibilities, fabrication methods, and applications. In vivo electrochemistry continues to advance toward more chronic experimentation in both animal models and humans, necessitating the utilization of biocompatible reference electrodes that should provide superior potential stability and allow for unprecedented chronic signal fidelity when used with a counter electrode for impedance mitigation.

Boron doped diamond thin films for the electrochemical detection of SARS-CoV-2 S1 protein

Amidst a global pandemic, a precise and widely accessible rapid detection method is needed for accurate diagnosis and contact tracing. The lack of this technology was exposed through the outbreak of SARS-CoV-2 beginning in 2019. This study sets the foundation for the development of a boron doped diamond (BDD)-based impedimetric sensor. While specifically developed for use in the detection of SARS-CoV-2, this technology uses principles that could be adapted to detect other viruses in the future. Boron doped polycrystalline diamond electrodes were functionalized with a biotin-streptavidin linker complex and biotinylated anti-SARS-CoV-2 S1 antibodies. Electrodes were then incubated with the S1 subunit of the SARS-CoV-2 spike surface protein, and an electrical response was recorded using the changes to the electrode's charge transfer resistance (R_ct), measured through electrochemical impedance spectroscopy (EIS). Detectable changes in the R_ct were observed after 5-min incubation periods with S1 subunit concentrations as low as 1 fg/mL. Incubation with Influenza-B Hemagglutinin protein resulted in minimal change to the R_ct, indicating specificity of the BDD electrode for the S1 subunit of SARS-CoV-2. Detection of the S1 subunit in a complex (cell culture) medium was also demonstrated by modifying the EIS protocol to minimize the effects of sample matrix binding. BDD films of varying surface morphologies were investigated, and material characterization was used to give insight into the microstructure-performance relationship of the BDD sensing surface.

Sodium Dodecyl Sulfate Modified Carbon Nano Tube Paste Electrode for Sensitive Cyclic Voltammetry Determination of Isatin

Purpose: Isatin (IS) is a synthetically significant heterocyclic moiety with an influential pharmacodynamic indole nucleus and hence the electrocatalytic property of has been investigated.

Methods: The electrochemical analysis was demonstrated by cyclic voltammetry (CV) in the potential window of 0.2 V to 1.4 V using sodium dodecyl sulfate (SDS) modified carbon nano tube paste electrode (SDSMCNTPE) over a pH range of 6 to 8.5 in 0.2 M phosphate buffer solution (PBS). Surface morphology was studied by using Field emission-scanning electron microscopy (FESEM).

Results: The CV study discloses that under ideal condition oxidation of IS arises at a potential of 0.970 V accompanied with an exceptional stability, selectivity and sensitivity for the resultant SDSMCNTPE contrasting to bare carbon nano tube paste electrode (BCNTPE). Individual parameters like electrode surface area, effect of surfactant, detection limit, simultaneous detection of IS and resorcinol (RC) were studied at a scan rate of 0.1 V/s. Scan rate study uncovers the process is diffusion controlled. The oxidation peak current amplified linearly with the surge in concentration of IS under ideal condition. Detection limit (LOD) and limit of quantification (LOQ) in the solution of optimum pH (7.5) at a scan rate of 0.100V/s is 2.4×10^-7 M and 8.2 × 10^-7 M respectively.

Conclusion: The proposed electrode portrays excellent repeatability, reproducibility and reliability to resistant electrode fouling.

Polychlorinated Biphenyl Electrochemical Aptasensor Based on a Diamond-Gold Nanocomposite to Realize a Sub-Femtomolar Detection Limit

Polychlorinated biphenyls (PCBs) with high toxicity, low lethal dose, and bioaccumulation have been inhibited for application in wide fields, and a highly efficient trace detection is thus greatly desirable. In this study, we produce dense Au-nanoparticles by twice sputtering and twice annealing (T-Au-NPs) on boron-doped diamond (BDD). The successful formation of T-Au-NPs/BDD nanocomposites was confirmed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. Based on T-Au-NPs/BDD, an electronic biosensor with aptamers is fabricated to detect trace polychlorinated biphenyl-77 (PCB-77) by electrochemical impedance. A good linear relationship in the range of femtomolar to micromolar and significantly low detection limit of sub-femtomolar level (0.32 fM) are realized based on the biosensor. The emphasis of this research lies in the key role of the diamond substrate in the biosensor. It is demonstrated that the biosensor has excellent sensitivity, specificity, stability, and recyclability, which are favorable for detecting the trace PCB-77 molecule. It is attributed to the important effect presented by the BDD substrate and the synergistic influence of T-Au-NPs combined with aptamers.

Synthesis, crystal structures, antiproliferative activities and reverse docking studies of eight novel Schiff bases derived from benzil

Eight novel Schiff bases derived from benzil dihydrazone (BDH) or benzil monohydrazone (BMH) and four fused-ring carbonyl compounds (3-formylindole, FI; 3-acetylindole, AI; 3-formyl-1-methylindole, MFI; 1-formylnaphthalene, FN) were synthesized and characterized by elemental analysis, ESI-QTOF-MS, ¹H and ¹³C NMR spectroscopy, as well as single-crystal X-ray diffraction. They are (1Z,2Z)-1,2-bis{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFI), C₃₂H₂₄N₆, (1Z,2Z)-1,2-bis{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethane (BDHAI), C₃₄H₂₈N₆, (1Z,2Z)-1,2-bis{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BMHMFI) acetonitrile hemisolvate, C₃₄H₂₈N₆·0.5CH₃CN, (1Z,2Z)-1,2-bis{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFN), C₃₆H₂₆N₄, (Z)-2-{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFI), C₂₃H₁₇N₃O, (Z)-2-{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethanone (BMHAI), C₂₄H₁₉N₃O, (Z)-2-{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHMFI), C₂₄H₁₉N₃O, and (Z)-2-{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFN) C₂₅H₁₈N₂O. Moreover, the in vitro cytotoxicity of the eight title compounds was evaluated against two tumour cell lines (A549 human lung cancer and 4T₁ mouse breast cancer) and two normal cell lines (MRC-5 normal lung cells and NIH 3T3 fibroblasts) by MTT assay. The results indicate that four (BDHMFI, BDHFN, BMHMFI and BMHFN) are inactive and the other four (BDHFI, BDHAI, BMHFI and BMHAI) show severe toxicities against human A549 and mouse 4T₁ cells, similar to the standard cisplatin. All the compounds exhibited weaker cytotoxicity against normal cells than cancer cells. The Swiss Target Prediction web server was applied for the prediction of protein targets. After analyzing the differences in frequency hits between these active and inactive Schiff bases, 18 probable targets were selected for reverse docking with the Surflex-dock function in SYBYL-X 2.0 software. Three target proteins, i.e. human ether-á-go-go-related (hERG) potassium channel, the inhibitor of apoptosis protein 3 and serine/threonine-protein kinase PIM1, were chosen as the targets. Finally, the ligand-based structure-activity relationships were analyzed based on the putative protein target (hERG) docking results, which will be used to design and synthesize novel hERG ion channel inhibitors.

Conductive diamond: synthesis, properties, and electrochemical applications

This review summarizes systematically the growth, properties, and electrochemical applications of conductive diamond.

Oxidation of hydroxide ions in weak basic solutions using boron-doped diamond electrodes: effect of the buffer capacity

The electrochemical oxidation of hydroxide ions using boron-doped diamond (BDD) electrodes in weak basic solutions was examined.