Abstract
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.
Highlights
Photoluminescent nanomaterials have attracted much attention due to their excellent fluorescent properties and small size
Our results showed that while the commercially available FM4-64 dye was bleached after 30 s of irradiation, cells retained the polyethylene glycol6000 (PEG6000)/carbon nanodots (CDs) staining indicating that PEG6000/CD had better photostability and have potential role in cellular imagining (Figure 9)
We have developed a simple hydrothermal method to synthesize PEG6000/CD composites and have evaluated their function as bio-labels using four different bacteria
Summary
Photoluminescent nanomaterials have attracted much attention due to their excellent fluorescent properties and small size. Other advantages of CQDs, including water dispersibility, biocompatibility, lower toxicity, small size, amenable to modifications and low processing cost make them potential material for biomedical applications [5,13,14] Due to their similar size and photoelectrochemical properties, research on quantum dots has mostly focused on graphene quantum dots, CDs and polymer dots. The CQDs inherit the excellent optical characteristics of traditional semiconductor quantum dots and make up for the shortcomings of traditional materials in terms of cytotoxicity, environmental and biological hazards; they can be imparted multi-functionality when conjugated with other nanoparticles As a result, they have the potential in biomedical applications, such as drug delivery, photosensitizers and carriers for therapeutic and antimicrobial molecules. When compared with heavy metal-based semiconductor quantum dots, CQDs show better chemical and optical stability, excellent water dispersion, better biocompatibility and lower cytotoxicity, thereby making them optimal nanomaterial for developing effective nanoprobes in the field of biological imaging
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