Photoluminescent nanomaterials have immense potential for use in biological systems due to their excellent fluorescent properties and small size. Traditional semiconductor quantum dots are heavy-metal-based and can be highly toxic to living organisms, besides their poor photostability and low biocompatibility. Nano-sized carbon quantum dots and their surface-modified counterparts have shown improved characteristics for imaging purposes. We used 1,3, 6-trinitropyrene (TNP) and polyethylene glycol₆₀₀₀ (PEG₆₀₀₀) in a hydrothermal method to prepare functional polyethylene glycol₆₀₀₀/carbon nanodots (PEG₆₀₀₀/CDs) and analyzed their potential in fluorescent staining of different types of bacteria. Our results demonstrated that PEG₆₀₀₀/CDs stained the cell pole and septa of gram-positive bacteria B. Subtilis and B. thuringiensis but not those of gram-negative bacteria. The optimal concentration of these composite nanodots was approximately 100 ppm and exposure times varied across different bacteria. The PEG₆₀₀₀/CD composite had better photostability and higher resistance to photobleaching than the commercially available FM4-64. They could emit two wavelengths (red and green) when exposed to two different wavelengths. Therefore, they may be applicable as bioimaging molecules. They can also be used for differentiating different types of bacteria owing to their ability to differentially stain gram-positive and gram-negative bacteria.

Stenotrophomonas sp. CD02 was isolated from a site that previously had been contaminated with high concentrations of the heavy metals cadmium (3 mg kg⁻¹) and chromium (115 mg kg⁻¹). This strain was able to grow on complex (Luria Bertani) medium containing high concentrations of cadmium ion (up to 4 mM). Additionally, it could remove up to 80% of the dissolved ions but only after reaching stationary growth phase. Strain CD02 also tolerated high concentrations of other heavy metals such as chromium, zinc, copper, nickel, and lead at levels more than 2 mM. Although strain CD02 can tolerate much higher cadmium concentrations than the three Stenotrophomonas maltophilia strains tested, they all possess resistance to the same range of antibiotics. This suggests that strain CD02 possesses a mechanism that allows it to tolerate and remove cadmium differently from those conferring resistance to antibiotics. Strain CD02 can be a suitable candidate for heavy metal bioremediation in contaminated environment because it is able to tolerate high concentration of heavy metals and remove cadmium aerobically.