Graphene Oxide Quantum Dots as a Sensing Platform for the Detection of Pathogenic Bacteria

Graphene oxide quantum dots (GQDs) are a zero-dimensional (0D) nanomaterial of the carbon family that has attracted much attention in biomedical applications. Top-down and bottom-up approaches are used to synthesize GQDs. Exfoliation of carbon precursors from GQDs is a top-down strategy that includes chemical exfoliation, electrochemical exfoliation, hydrothermal/solvothermal exfoliation, and microwave/ultrasound-assisted exfoliation, whereas pyrolysis is a bottom-up strategy that includes heating of carbon precursors at higher temperatures above the melting point.   

The quantum confinement effect, stable photoluminescence (PL), and good biocompatibility of GQDs make them promising candidates for use in a variety of fields, including bioimaging devices, drug delivery, electrochemical biosensors, detecting pathogenic bacteria, and live-cell imaging. The hydroxyl and epoxy groups on Graphene oxide (GO) provide a stable adsorption substrate for biomolecules like proteins and nucleic acids(DNA). Quantum dots (QDs), on the other hand, are a type of fluorescence probe with photoelectronic properties. In GQDs, the proximity of QDs and GO causes FRET (Förster or fluorescence resonance energy transfer) and quenches the fluorescent signal. The quenching signal is recovered in a concentration-dependent manner in the presence of the target gene/DNA. This principle is employed as a sensing platform for detecting vital genes in pathogenic bacteria.

For the identification of the invA gene of Salmonella sps., a novel and rapid GQD-FRET assay was utilized, with a LOD of 4nM and a quenching efficiency of 52% and better specificity. The invA gene was also detected by the sensing system in the contaminated food samples. Furthermore, tetracycline antibiotic resistance genes (ARGs) in methicillin-resistant Staphylococcus aureus were quantified using FRET-based Zinc finger proteins (ZFP) and GQD technology, with detection limits as low as 1nM and quenching efficiency of 42%. GQDs, in comparison to conventional techniques such as PCR analysis, which require more time and technical sample preparation, provide rapid and sensitive detection of pathogen bacteria (target gene/DNA).

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