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Titanium–Gadolinium Quantum Dot Staining Agent Specific to Bacterial Cells

To overcome the antibiotic resistance and absolute necessity of finding an alternative to existing antibiotics with negligible toxicity, proper biocompatibility, and fulfil the needs of clinical research, novel antibacterial agents like nanoparticles, peptides, metabolites, oligonucleotides, and other biogenic or chemical compounds have been introduced.

Nanaoparticles with few modifications help in site specific drug delivery by reducing target toxicity. Quantum dots (QDs) are a type of nanoparticles with the ability to fluoresce, which is helping in the development of new detection and imaging techniques. A few novel QDs have been reported to have antibacterial and anticancer properties, which elevates their value even more in the field of biomedicine with some drawbacks like toxicity, inflammation, and stability.

In this study, we used titanium and gadolinium together to synthesize a titanium–gadolinium quantum dot (TGQG), the first of its kind, and its characterization was undertaken using dynamic light scattering, spectrophotometry, X-ray fluorescence, scanning electrochemical microscope (SECM), and scanning electron microscope (SEM). Thereafter, TGQD was used as a stain in the detection of VRSA using a fluorescence microscope. Furthermore, the antibacterial activity was tested against the pathogenic strains of vancomycin resistant S. aureus (VRSA), methicillin resistant S. aureus (MRSA), and the mechanism of action was also investigated.

The limitations of fluorescence dye (SYTO9) to stain specific bacteria were overcome by TGQD because there is no bacteria specific stain that can stain only bacteria and no other cells, but SYTO9 stains both bacteria and human cells. The TGQD stained the VRSA cells to emit bluish white fluorescence without staining the PNT1A cells, but SYTO9 stained both types of cells emitting green fluorescence. Furthermore, the TGQD inhibits by interacting with the bacterial cells causing cell leakage, and ultimately the release of the inner components.

The antibacterial activities of the TGQD against S. aureus and its resistant strains showed strong inhibitory activities, which were validated by microscopic evidence. The mode of action was cell disruption and leakage of cytoplasmic content, which led to the precipitation and accumulation of bacterial cells with the amount of oxygen demand decreasing. However, it was also observed that the presence of any bacteria live or dead was detected by TGQD through fluorescence microscopic analysis. Finally, the cytotoxicity test of the TGQD showed no toxicity and proved the TGQD was biocompatible for normal human cells in vitro.

The examined TGQD with biocompatibility and non-toxicity can be used as potential theranostics to detect and inhibit the presence of bacteria in different types of co-cultures or mixed samples with significant antibacterial activity. To the best of our knowledge, there is no such staining agent present that can stain only bacterial cells. In various research purposes like host pathogen interaction, study requires a specific staining agent. Thus, TGQD can be very useful for host pathogen interaction study.

A Novel Biocompatible Titanium–Gadolinium Quantum Dot as a Bacterial Detecting Agent with High Antibacterial Activity. Nanomaterials. Published 17 April 2020.

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