Paweł Niedziałkowski

Coordination compounds with transition metals, especially of molybdenum, are promising cytoprotective agents. In this work, we analyzed the changes in HT-22 cell viability under the influence of molybdenum(VI) Schiff base complexes per se or in cellular injury induced by hydrogen peroxide (annexin V and propidium iodine staining assay). The results allowed to identify the most active compound with dioxidomolybdenum(VI) ion coordinated to Schiff base derived from 1S,2S-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol and 5-methoxysalicylaldehyde, protecting the cells and possessing low cytotoxicity. We addressed a range of active concentrations (statistically significant effect from 5 µM to 50 µM) and the temporal characteristics of the effect (which is evident in 1-h preincubation regimen or adding the compound 1 h after hydrogen peroxide). Importantly, the effect was present at different levels of glucose in the medium and in cellular injury induced by glutamate. Less pronounced protective effect was seen in SH-SY5Y cells on the model of hydrogen peroxide-induced (but not in glutamate-induced) cytotoxicity. Among the possible mechanisms of cytoprotective activity, there is a direct interaction with hydrogen peroxide (measured by cyclic voltammetry), decrease in reactive oxygen species generation (DCFH-DA assay in HT-22 cells) and maintenance of catalase activity (assessed in lysates of HT-22 cells on the model of hydrogen peroxide-induced injury).

This study presents the first integration of nanodiamonds (NDs) with a microcavity in-line Mach-Zehnder interferometer (μIMZI) fabricated by femtosecond laser micromachining in the side surface of an optical fiber. NDs of different sizes form a structured and functional layer for receptor immobilization. Numerical analyses were performed to investigate how the ND particle size influences the optical field distribution in the cavity. The sensor's spectral response and refractive index sensitivity have been investigated experimentally. The results have shown that the ND layer enhanced light-surface interaction and increased the available area for binding, improving surface sensitivity and enhancing receptor loading. Among the tested configurations, the μIMZI modified with a 250 nm-thick ND layer exhibited the most favorable characteristics, achieving RI sensitivity of approximately 15,300 nm/RIU, and was therefore employed for specific, label-free detection of a model low-molecular-weight protein, green fluorescent protein (eGFP). The modified sensor demonstrated monotonic change and reproducible spectral response down to a protein concentration of 0.35 μg/mL, while the limit of detection was equal to 0.14 μg/mL, with a response time of about 30 minutes, which can be further optimized. In contrast, a non-modified reference μIMZI showed no response to comparable concentrations. Besides label-free detection, the multifunctional nature of NDs was further explored by exciting nitrogen-vacancy centers in the diamond structure, aiming for fluorescence-based sensing. These experiments confirmed that, in this configuration, the centers could be optically excited by a light guided through the fiber core, which is partially exposed within the microcavity and can interact directly with the ND-coated surface. The resulting fluorescence was detected from the microcavity region, demonstrating excitation and readout capabilities. Altogether, this work demonstrates that ND-based surface modification can simultaneously enhance sensitivity and expand the functional capabilities of these highly compact optical fiber biosensors.

In this article, the binding interactions of lysozyme with hexacyanoferrate(III)/(II), i.e., [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ ions, have been characterised using steady-state fluorescence spectroscopy (SF), isothermal titration calorimetry (ITC), circular dichroism spectroscopy (CD), cyclic voltammetry (CV), and molecular-dynamics-based computational approaches. Studies have shown that under experimental conditions (10 mM cacodylate buffer, pH 7, 298.15 K), complexes with a 1:1 stoichiometry are formed. Four distinct regions on the lysozyme surface patches with the potential to bind hexacyanoferrate(III)/(II) were identified and described. Thermodynamic parameters revealed that the interactions are predominantly governed by electrostatic and van der Waals forces. These interactions enhance the electron transfer kinetics of the [Fe(CN)₆]^3−/4− system. The secondary structure of the protein is not affected by these interactions. Enzyme activity studies demonstrated that the affinity of lysozyme for the substrate remained unchanged regardless of whether free lysozyme or the lysozyme-[Fe(CN)₆]^3−/4− complex was present in the test sample. Finally, biological tests performed on both Gram-positive (B. subtilis, S. aureus) and Gram-negative (E. coli, P. aeruginosa) bacteria confirmed the results of the biochemical analysis, indicating that [Fe(CN)₆]^3−/4− ions do not block the active site of the enzyme and do not interfere with its activity.

This study presents the fabrication of a novel biosensor platform based on semitransparent titania nanotubes (TiO2NTs) decorated with thermally treated gold layers. The platform is designed for multimodal opto-impedimetric monitoring, exploring the impact of gold coverage and morphology on physicochemical properties and electrochemical activity. When annealed, the gold layer of different thicknesses results in various nanoarchitectures, modulating charge transfer kinetics, plasmonic effects, and steric hindrance within the receptor layer. The proof-of-concept aptamer-based platform for biomolecular recognition is also discussed. Furthermore, the investigation explores electric field modulation through voltammetry to identify efficient analyte-to-receptor binding, verified by singular value decomposition (SVD) for rapid diagnostics. A non-trivial, electrostatic-driven behaviour of DNA conformation at the electrode surface was identified and discussed. A surface-enhanced fluorescence effect was achieved for the smallest gold layer thickness of 5 nm, where DNA hybridisation is most effective due to the highest surface curvature. This approach leverages both biosensor surface nanostructurization and multiparametric impedance discriminant analysis (MIDA)-aided signal processing to enhance biosensor performance. Our platform offers a promising route for developing advanced biosensors with dual-mode capabilities, integrating optical and electrochemical tools. Moreover, the methods employed for fabricating this novel platform, namely magnetron sputtering and anodisation, are scalable and cost-effective while offering high uniformity and precise control over nanostructure dimensions, making them ideal for various applications.

Electrochemical analysis, materials chemistry, and transparent conductive oxide (TCO) electrodes are explored in this study within the context of surface modification and sensing. High electrical conductivity and optical transparency make TCO electrodes essential for electrochemical sensing and surface modification, surpassing optoelectronics. These systems can be used for new sensing platforms since optical detection complements electrochemical measurements. Biosensors, environmental monitoring, and clinical diagnosis use TCO electrodes because of their surface changes, which make them selective, sensitive, and stable. Attaching organic chemicals, functional molecules, or polymers to TCO electrodes makes them more adaptable and functional. These enhancements enable customized chemical sensors and electrocatalytic systems for electrochemical reactions and improve electrocatalysis. With cyclic voltammetry (CV), this comprehensive study examines the complex interactions between fluorine-doped tin oxide (FTO) electrode surface and electrochemical processes with ferri/ferrocyanide [Fe(CN)6]3-/4- and hydroquinone/quinone (H2Q/Q) redox couple, organic modifiers, and variable pH conditions from 2 to 9.2. We are especially interested in how surface modifications and the presence of organic, electroactive compounds in the modified layer affect the electrochemical properties of the electrode. The FTO electrode was treated with (3-aminopropyl)trimethoxysilane (APTMS) to enhance its reversibility and current values. The incorporation of anthraquinone and rhodamine derivatives to the FTO/APTMS electrode altered the redox reactions, leading to hindered transportation of redox ions due to steric hindrance. The electrode processes were considerably influenced by the pH of the solution. APTMS-modified electrodes showed improved reversibility in acidic conditions. The results improve materials chemistry knowledge and enable cutting-edge sensing platforms with many technological and scientific applications.

3D-printable composites have become an attractive option used for the design and manufacture of electrochemical sensors. However, to ensure proper charge-transfer kinetics at the electrode/electrolyte interface, activation is often required, with this step consisting of polymer removal to reveal the conductive nanofiller. In this work, we present a novel effective method for the activation of composites consisting of poly(lactic acid) filled with carbon black (CB-PLA) using microwave radiation. A microwave synthesizer used in chemical laboratories (CEM, Matthews, NC, USA) was used for this purpose, establishing that the appropriate activation time for CB-PLA electrodes is 15 min at 70 °C with a microwave power of 100 W. However, the usefulness of an 80 W kitchen microwave oven is also presented for the first time and discussed as a more sustainable approach to CB-PLA electrode activation. It has been established that 10 min in a kitchen microwave oven is adequate to activate the electrode. The electrochemical properties of the microwave-activated electrodes were determined by electrochemical techniques, and their topography was characterized using scanning electron microscopy (SEM), Raman spectroscopy, and contact-angle measurements. This study confirms that during microwave activation, PLAs decompose to uncover the conductive carbon-black filler. We deliver a proof-of-concept of the utility of kitchen microwave-oven activation of a 3D-printed, free-standing electrochemical cell (FSEC) in paracetamol electroanalysis in aqueous electrolyte solution. We established satisfactory limits of linearity for paracetamol detection using voltammetry, ranging from 1.9 μM to 1 mM, with a detection limit (LOD) of 1.31 μM.