![]() According to the latest literature data, there is no paper describing ZnO NCs synthesized by lactic acid bacteria (LAB) strain, naturally coated by organic deposit. obtained bio-AgNCs with the specific organic deposit connected with the silver core of nanoparticles. Moreover, the extracellular approach is also a more adequate choice to produce nanocomposites with organic deposits on their surfaces coming from microbial compounds of natural origin. As has been highlighted by literature data, the post-cultured method (extracellular synthesis) has its advantages, such as lower cost, simpler downstream processing (e.g., nanomaterial separation and purification processes) and possibility to reuse the bacterial cultures. Intracellular production involves bacteria biomass for the nanocomposite formation, while the extracellular approach, known also as the post-cultured method, excludes microbial cells and uses a supernatant rich in biologically active compounds (e.g., enzymes or metabolites). Among methods of microbial synthesis, two main types can be identified-intra- and extracellular methods. There is limited evidence of effective ZnO nanoparticle formation using plants, whereas the adoption of a microbiological approach for this purpose has still not been sufficiently described. Biosynthesis of zinc oxide can be carried out with various biological materials including bacteria, fungi and plant extracts. Therefore, synthesis of nano-ZnO using biological systems is attracting rising attention, mainly due to the lower consumption of hazardous reagents and lower cytotoxicity of the obtained nanomaterials (in comparison with traditional chemical and physical methods). Over the years, synthesis of nanomaterials has been of research interest but there is a growing need for development of more efficient, facile and environmentally friendly methods. The production of metal oxide nanomaterials such as zinc oxide nanocomposites (ZnO NCs) is an emerging and currently researched subject in nanotechnology. 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. 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). ![]() Despite ZnO NCs’ luminescent properties, they can also act as promising antiseptic agents against clinically relevant pathogens. Moreover, fluorescence data showed an increase in fluorescence signal in the presence of nanocomposites designed for potential use as, e.g., biosensors. In this context, mass spectrometry (MS) data confirmed the nano-ZnO formation mechanism. 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. The organic deposit on the nanoparticle surface was recorded by spectroscopic analysis in the infrared range (FT-IR). The ZnO nanocomposites (NCs) demonstrated thermal stability up to 130 ☌ based on the results of thermogravimetric TGA/DTG) analysis. ![]() 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. Results of spectroscopic and microscopic analysis confirmed the hexagonal crystalline structure of ZnO in the nanometer size. The obtained nanocomposites were subjected to comprehensive characterization by a broad spectrum of instrumental techniques. 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.
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