Introduction

Accurately detecting bacterial endotoxin levels is essential for effective pharmaceutical quality control. Endotoxins refers to lipopolysaccharides that are present in the outer membrane of Gram-negative bacteria. They elicit a robust inflammatory response upon exposure. Gold nanoclusters (AuNCs) show potential as fluorescent nanotags due to their ease of synthesis, wide Stokes shift, and exceptional photostability. This study introduces fluorescent AuNCs for endotoxin detection for the first time.

Methods

Glutathione-stabilized gold nanoclusters (GSH-AuNCs) were synthesized and characterized. Lipopolysaccharide extraction from Pseudomonas putida bacterial biofilms was carried out. The relationship between the change in fluorescence intensity of GSH-AuNCs and the concentration of P. putida endotoxin was established. The micelle characterization of the endotoxin was conducted using dynamic light scattering (DLS).

Results

Orange-emitting 1.5 nm GSH-AuNCs were produced. Upon interacting with endotoxin micelles, the fluorescence signal increased and the emission peak shifted by 7-10 nm towards the blue end of the spectrum. This was attributed to the phenomenon of aggregation-induced emission (AIE). The detection limit for the endotoxin in aqueous solutions was determined to be 400 ng/ml. The size of the endotoxin micelles was measured to be 62 ± 15 nm.

Conclusions

We have developed a nanosensor based on fluorescent AuNCs for endotoxin detection without requiring extra recognition molecules. The detection principle relies on the modulation of the fluorescence properties of GSH-AuNCs in the presence of endotoxin micelles. This nanosensor holds potential for endotoxin detection in pharmaceutical preparations and buffer solutions.

Acknowledgements

This research was supported by the Russian Science Foundation, grant number № 23-24-00246 (https://rscf.ru/project/23-24-00246/).