Synthesis and characterisation of quantum dots coupled to mycolic acids as a water‐soluble fluorescent probe for potential lateral flow detection of antibodies and diagnosis of tuberculosis

Abstract 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.