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.

Development of a mycolic acid‐graphene quantum dot probe as a potential tuberculosis biosensor

“…It can be deduced that the MA‐GQDs were more dispersible in water as compared to the coupled material prepared with semiconductor quantum dots reported in our previous work. [ 22 ] As can be seen in the inset shown in Figure 10, all the sample at the spotting point eluted up the strip, while for the semiconductor based MA‐QDs, some spotted sample remained at the initial spotting point. Good solubility in water and low toxicity thus makes MA‐GQDs the preferred material to potentially detect anti‐MA antibodies and diagnosis of TB using the nitrocellulose membrane flow technique.…”

“…The fluorescence quantum yield of the GQDs and MA-GQDs is somewhat lower than the fluorescence quantum yield of semiconductor-based quantum dots and the corresponding MA-QDs reported in our previous work. [22] 3.4 | FTIR analysis of MA, GQDs and MA-GQDs…”

“…In this study, we present for the first time the linking of chloroform-soluble MAs to water-soluble GQDs to form MA-GQDs and show that this enhances the solubility of MAs, and enables their lateral flow, whilst also reducing the toxicity of the sensor material as compared to semiconductor-based quantum dots, which we have reported on previously. [22] F I G U R E 1 Schematic of the hydrothermal synthesis of GQDs from citric acid and ethylenediamine as sources of carbon and nitrogen respectively.…”