Carbon quantum dots (CQDs) are novel nanocarbon materials and widely used nanoparticles. They have gradually gained popularity in various fields due to their abundance, inexpensive cost, small size, ease of engineering, and distinct properties. To determine the antibacterial activity of metal-doped CQDs (metal-CQDs) containing Fe, Zn, Mn, Ni, and Co, we chose Staphylococcus aureus as a representative Gram-positive strain and Escherichia coli as a representative Gram-negative bacterial strain. Paper disc diffusion tests were conducted for the qualitative results, and a cell growth curve was drawn for quantitative results. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and IC50 were measured from cell growth curves. As a result, all of the metal-CQDs showed toxicity against both Gram-positive and Gram-negative bacteria. Furthermore, Gram-negative bacteria was vulnerable to metal-CQDs than Gram-positive bacteria. The toxicity differed concerning the type of metal-CQDs; Mn-CQDs exhibited the highest efficacy. Hence, this study suggested that CQDs can be used as new nanoparticles for antibiotics.

The world is transitioning towards sustainable agriculture, which includes reducing chemical fertilizers and increasing the adoption of eco-friendly materials. Red clay, known for its colloidal properties, adsorption, and ion exchange capabilities, has become eco-friendly due to its non-toxic nature. However, when red clay is applied in its insoluble powdered form, its absorption by plants is limited. Processed red clay (PRC) was developed to overcome these limitations, and microbial formulations containing Lactobacillus fermentum (MFcL) were applied alongside it. Chlorophyll content and fluorescence values decreased over time after cucumber transplantation. However, co-application of PRC and MFcL resulted in higher chlorophyll content than PRC alone, suggesting that this combination could alleviate plant growth reduction caused by stress. Although the total yield of cucumbers was highest in the NF group, yield per plant increased by more than 10% in the PRC treatment compared to NF. Additionally, yield was higher when PRC was applied alongside MFcL than with MFcL alone. While the proportion of marketable fruits decreased over time in the NF treatment, it increased in the PRC treatment. Soil analysis revealed that PRC application increased soil pH by 3% and available silicon content by 7.6% compared to NF, while available phosphate levels decreased by 13%. Analysis of microbial density in the soil showed that bacteria levels significantly increased by 2-fold in PRC+MFcL compared to NF, while actinomycetes decreased by 1.5-fold. In conclusion, PRC treatment positively influenced cucumber growth, and co-application with microbial fertilizers demonstrated a synergistic effect.