Fluorescence Invigoration in Carbon-Incorporated Zinc Oxide Nanowires from Passage of Field Emission Electrons

Zinc Oxide Nanocomposites-Extracellular Synthesis, Physicochemical Characterization and Antibacterial Potential

This research presents, for the first time, the potential of the Lactobacillus paracasei LC20 isolated from sweet whey as a novel, effective and accessible source for post-cultured ZnO nanocomposites synthesis. The obtained nanocomposites were subjected to comprehensive characterization by a broad spectrum of instrumental techniques. Results of spectroscopic and microscopic analysis confirmed the hexagonal crystalline structure of ZnO in the nanometer size. The dispersion stability of the obtained nanocomposites was determined based on the zeta potential (ZP) measurements-the average ZP value was found to be -29.15 ± 1.05 mV in the 7-9 pH range. The ZnO nanocomposites (NCs) demonstrated thermal stability up to 130 °C based on the results of thermogravimetric TGA/DTG) analysis. The organic deposit on the nanoparticle surface was recorded by spectroscopic analysis in the infrared range (FT-IR). Results of the spectrometric study exhibited nanostructure-assisted laser desorption/ionization effects and also pointed out the presence of organic deposits and, what is more, allowed us to identify the specific amino acids and peptides present on the ZnO NCs surfaces. In this context, mass spectrometry (MS) data confirmed the nano-ZnO formation mechanism. Moreover, fluorescence data showed an increase in fluorescence signal in the presence of nanocomposites designed for potential use as, e.g., biosensors. Despite ZnO NCs' luminescent properties, they can also act as promising antiseptic agents against clinically relevant pathogens. Therefore, a pilot study on the antibacterial activity of biologically synthesized ZnO NCs was carried out against four strains (Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa) by using MIC (minimal inhibitory concentration). Additionally, the colony forming units (CFU) assay was performed and quantified for all bacterial cells as the percentage of viable cells in comparison to a control sample (untreated culture) The nanocomposites were effective among three pathogens with MIC values in the range of 86.25-172.5 μg/mL and showed potential as a new type of, e.g., medical path or ointment formulation.

Electrically Tailored Metachrosis in ZnO-C Nanowires

Carbon incorporated zinc oxide (ZnO:C) nanowires (NWs) are found to be remarkable morphing NWs. We show that the physical properties of ZnO:C NWs are engineered via the passage of electric current to produce fluorescence differences and negative differential resistance as well as electroluminescence. When a ZnO:C NW is subjected to an applied voltage bias and under ultraviolet (UV) excitation, electron-hole separation due to the voltage biasing suppresses their fluorescence at low voltages. At medium voltages, the NW exhibits metastable chemical changes that translates to tunable and reversible optical alterations akin to metachrosis found in chameleons. Concurrently, the NW displays electrical alterations with negative differential resistance behaviors. At higher voltages, these NWs are permanently modified with distinct heterogeneous chemical stoichiometry, fluorescence, and electronic properties. Such heterogeneity within the NW allows for emergence of junctions capable of electroluminescence.