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The development of amine-functionalized graphene quantum dots (GQDs) linked to mycolic acids (MAs) as a potential fluorescent biosensor to detect tuberculosis (TB) biomarkers is described. GQDs have attractive properties: high fluorescence, excellent biocompatibility, good water solubility, and low toxicity. MAs are lipids that are found in the cell wall of Mycobacterium tuberculosis that are antigenic, however, they are soluble only in chloroform and hexane. Chloroform-soluble MAs were covalently linked to synthesized water-soluble GQDs using an amide connection to create a potential fluorescent water-soluble TB biosensor: MA-GQDs. Fluorescence results showed that GQDs had a narrow emission spectrum with the highest emission at 440 nm, while MA-GQDs had a broader spectrum with the highest emission at 470 nm, after exciting at 360 nm. The appearance of the peptide bond (amide linkage) in the Fourier-transform infrared spectrum of MA-GQDs confirmed the successful linking of MAs to GQDs. Powder X-ray diffraction exhibited an increase in the number of peaks for MA-GQDs relative to GQDs, suggesting that linking MAs to GQDs changed the crystal structure thereof. The linked MA-GQDs showed good solubility in water, high fluorescence, and visual flow through a nitrocellulose membrane. These properties are promising for biomedical fluorescence sensing applications., (© 2022 John Wiley & Sons Ltd.)

This work explores the potential use of cadmium-based quantum dots (QDs) coupled to mycolic acids (MAs) as a fluorescent probe to detect anti-MA antibodies which are biomarkers for tuberculosis (TB). The use of free MAs as antigens for the serodiagnosis of TB is known but has not been developed into a point of care test. This study focuses on the synthesis, solubility, and lateral flow of QDs coupled to MAs. Water-soluble CdSe/ZnS QDs capped with l-cysteine were synthesised and covalently coupled to MAs via amide linkages to form a water-soluble fluorescent probe: MA-CdSe/ZnS QDs. The MA-CdSe/ZnS QDs showed broad absorption bands and coupling, confirmed by the presence of amide bonds in the Fourier-transform infrared (FTIR) spectrum, resulting in a blue shift in fluorescence. Powder X-ray diffraction (XRD) revealed a shift and increase in the number of peaks for MA-CdSe/ZnS QDs relative to the L-cys-CdSe/ZnS QDs, suggesting that coupling changed the crystal structure. The average particle size of MA-CdSe/ZnS QDs was ~3.0 nm. Visual paper-based lateral flow of MA-CdSe/ZnS QDs was achieved on strips of nitrocellulose membrane with both water and membrane blocking solution eluents. The highly fluorescent MA-CdSe/ZnS QDs showed good water solubility and lateral flow, which are important properties for fluorescence sensing applications., (© 2021 John Wiley & Sons Ltd.)