1D ZnO-Au nanocomposites as label-free photoluminescence immunosensors for rapid detection of Listeria monocytogenes

In this study, we explore the potential of 1D ZnO-Au nanocomposites as innovative label-free photoluminescence (PL) immunosensors for rapidly detecting Listeria monocytogenes, a significant concern in food safety. We synthesized ZnO nanorods (ZnO_NR) and nanowires (ZnO_NW), followed by Au deposition to create ZnO_NR/Au and ZnO_NW/Au nanocomposites. Our analyses, including SEM, TEM, Raman spectroscopy, and photoluminescence (PL), revealed distinct structural and optical properties of these nanocomposites, especially noting the superior crystallinity and stability of ZnO_NR/Au. The biosensor performance was evaluated through PL sensitivity to Anti-Listeria antibodies, demonstrating that ZnO_NR with higher concentration of Au nanoparticles exhibited higher sensitivity and a lower limit of detection (LOD), attributed to a greater density of Listeria binding sites. The developed biosensor demonstrated a remarkable limit of detection (LOD) of 8.3 × 102 CFU/mL, rivaling or surpassing conventional culture-based methods and some molecular techniques. This research underscores the critical role of Au deposition duration in optimizing biosensor performance and presents a promising advancement in rapid and sensitive Listeria detection, with significant implications for enhancing food safety protocols.

Multifunctional ZnO:Gd@ZIF-8 hybrid nanocomposites with tunable luminescent-magnetic performance for potential bioapplication

Novel multifunctional ZnO:Gd@ZIF-8 hybrid inorganic-organic nanocomposites with tunable luminescent-magnetic performance were successfully fabricated using wet chemistry synthesis routes. Physico-chemical characterization including crystal structure, phase compositions, morphology, surface properties, as well as photoluminescent and magnetic characteristics was performed using powder X-ray diffraction (XRD), FT-IR analysis, transmission and scanning electron microscopies (TEM/SEM), N₂ adsorption/desorption, SQUID magnetometer, and photoluminescence spectroscopy. The biological studies of obtained materials, such as cytotoxicity profile and in vitro MRI imaging also investigated for potential use as contrast agents. Results showed that the doping with Gd³⁺ in a broad concentration range and the presence of ZIF-8 layer on ZnO affect the physico-chemical properties of the obtained composites. The obtained porous ZnO:Gd@ZIF-8 composites were highly crystalline with a large surface area. The XRD study indicated the formation of hexagonal wurtzite structure for ZnO and ZnO:Gd³⁺ (1-5 at.%). Luminescent studies showed, that ZnO is an ideal matrix for the incorporation of Gd³⁺ ions in a broad concentration range with efficient green luminescence. The PL intensity reached the maximum up to 5 at.% of Gd³⁺. The zeta potential values indicated the good stability of obtained nanoparticles. Proposed new materials with paramagnetic behavior and outstanding MR imaging capability could be used as potential contrast agents for magnetic resonance imaging.

Effect of Electrode Modification with Chitosan and Nafion® on the Efficiency of Real-Time Enzyme Glucose Biosensors Based on ZnO Tetrapods

Noninvasive, continuous glucose detection can provide some insights into daily fluctuations in blood glucose levels, which can help us balance diet, exercise, and medication. Since current commercially available glucose sensors can barely provide real-time glucose monitoring and usually imply different invasive sampling, there is an extraordinary need to develop new harmless methods for detecting glucose in non-invasive body fluids. Therefore, it is crucial to design (bio)sensors that can detect very low levels of glucose (down to tens of µM) normally found in sweat or tears. Apart from the selection of materials with high catalytic activity for glucose oxidation, it is also important to pay considerable attention to the electrode functionalization process, as it significantly contributes to the overall detection efficiency. In this study, the (ZnO tetrapods) ZnO TPs-based electrodes were functionalized with Nafion and chitosan polymers to compare their glucose detection efficiency. Cyclic voltammetry (CV) measurements have shown that chitosan-modified ZnO TPs require a lower applied potential for glucose oxidation, which may be due to the larger size of chitosan micelles (compared to Nafion micelles), and thus easier penetration of glucose through the chitosan membrane. However, despite this, both ZnO TPs modified with chitosan and Nafion membranes, provided quite similar glucose detection parameters (sensitivities, 7.5 µA mM⁻¹ cm⁻¹ and 19.2 µA mM⁻¹ cm⁻¹, and limits of detection, 24.4 µM and 22.2 µM, respectively). Our results show that both electrodes have a high potential for accurate real-time sweat/tears glucose detection.

ZnO size and shape effect on antibacterial activity and cytotoxicity profile

The aim of our work was the synthesis of ZnO nano- and microparticles and to study the effect of shapes and sizes on cytotoxicity towards normal and cancer cells and antibacterial activity toward two kinds of bacteria. We fabricated ZnO nano- and microparticles through facile chemical and physical routes. The crystal structure, morphology, textural properties, and photoluminescent properties were characterized by powder X-ray diffraction, electron microscopies, nitrogen adsorption/desorption measurements, and photoluminescence spectroscopy. The obtained ZnO structures were highly crystalline and monodispersed with intensive green emission. ZnO NPs and NRs showed the strongest antibacterial activity against Escherichia coli and Staphylococcus aureus compared to microparticles due to their high specific surface area. However, the ZnO HSs at higher concentrations also strongly inhibited bacterial growth. S. aureus strain was more sensitive to ZnO particles than the E. coli. ZnO NPs and NRs were more harmful to cancer cell lines than to normal ones at the same concentration.

Novel nanosystems to enhance biological activity of hydroxyapatite against dental caries

This work aimed to study for the first time to our knowledge the influence of the structure of the dental flosses (DF) coated by hydroxyapatite nanoparticles (HAP NPs) on the biological performance of saliva probiotic bacteria (S. salivarius), and human dermal and osteoblast-like cells. We used three types of HAP@DF composites (based on two unwaxed dental flosses - "fluffy" and "smooth", and one waxed "smooth") with different morphologies. Obtained composites were characterized from the point of view of their structure, morphological characteristics, elemental and chemical composition. We observed that HAP NPs coated "smooth" dental flosses led to an increase of viability and proliferation of oral cavity probiotic bacteria (Streptococcus salivarius) and human cells (dermal fibroblasts and osteoblast-like). In contrast, the highest viability loss of probiotic bacteria (S. salivarius), fibroblasts, and osteoblast-like cells were observed for "fluffy" unwaxed dental flosses due to high cytotoxicity. Our studies showed that HAP NPs significantly improved the biological properties of "fluffy" dental floss. Pristine "smooth" DFs (waxed and unwaxed), as well as all HAP-coated DFs, induced acceptable biocompatibility toward selected human cells.

Fabrication of Gelatin-ZnO Nanofibers for Antibacterial Applications

In this study, GNF@ZnO composites (gelatin nanofibers (GNF) with zinc oxide (ZnO) nanoparticles (NPs)) as a novel antibacterial agent were obtained using a wet chemistry approach. The physicochemical characterization of ZnO nanoparticles (NPs) and GNF@ZnO composites, as well as the evaluation of their antibacterial activity toward Gram-positive (Staphyloccocus aureus and Bacillus pumilus) and Gram-negative (Escherichia coli and Pseudomonas fluorescens) bacteria were performed. ZnO NPs were synthesized using a facile sol-gel approach. Gelatin nanofibers (GNF) were obtained by an electrospinning technique. GNF@ZnO composites were obtained by adding previously produced GNF into a Zn2+ methanol solution during ZnO NPs synthesis. Crystal structure, phase, and elemental compositions, morphology, as well as photoluminescent properties of pristine ZnO NPs, pristine GNF, and GNF@ZnO composites were characterized using powder X-ray diffraction (XRD), FTIR analysis, transmission and scanning electron microscopies (TEM/SEM), and photoluminescence spectroscopy. SEM, EDX, as well as FTIR analyses, confirmed the adsorption of ZnO NPs on the GNF surface. The pristine ZnO NPs were highly crystalline and monodispersed with a size of approximately 7 nm and had a high surface area (83 m2/g). The thickness of the pristine gelatin nanofiber was around 1 µm. The antibacterial properties of GNF@ZnO composites were investigated by a disk diffusion assay on agar plates. Results show that both pristine ZnO NPs and their GNF-based composites have the strongest antibacterial properties against Pseudomonas fluorescence and Staphylococcus aureus, with the zone of inhibition above 10 mm. Right behind them is Escherichia coli with slightly less inhibition of bacterial growth. These properties of GNF@ZnO composites suggest their suitability for a range of antimicrobial uses, such as in the food industry or in biomedical applications.

Synthesis, structure, EPR studies and up-conversion luminescence of ZnO:Er3+–Yb3+@Gd2O3 nanostructures

ZnO:Er³⁺–Yb³⁺@Gd₂O₃ nanostructures were obtained by “wet” chemistry methods – the sol–gel technique for the preparation of ZnO and ZnO:Er³⁺–Yb³⁺ nanoparticles (NPs), and the seed deposition method for obtaining Gd₂O₃.