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

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.

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.

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 quantum dot molecularly imprinted polymer sensor for fluorescence detection of atrazine.

Atrazine is a common agricultural pesticide which has been reported to occur widely in surface drinking water, making it an environmental pollutant of concern. In the quest for developing sensitive detection methods for pesticides, the use of quantum dots (QDs) as sensitive fluorescence probes has gained momentum in recent years. QDs have attractive and unique optical properties whilst coupling of QDs to molecularly imprinted polymers (MIPs) has been shown to offer excellent selectivity. Thus, the development of QD@MIPs based fluorescence sensors could provide an alternative for monitoring herbicides like atrazine in water. In this work, highly fluorescent CdSeTe/ZnS QDs were fabricated using the conventional organometallic synthesis approach and were then encapsulated with MIPs. The CdSeTe/ZnS@MIP sensor was characterized and applied for selective detection of atrazine. The sensor showed a fast response time (5 min) upon interaction with atrazine and the fluorescence intensity was linearly quenched within the 2-20 mol L-1 atrazine range. The detection limit of 0.80 × 10-7  mol L-1 is comparable to reported environmental levels. Lastly, the sensor was applied in real water samples and showed satisfactory recoveries (92-118%) in spiked samples, hence it is a promising candidate for use in water monitoring.

Validation of the AGDISP model for predicting airborne atrazine spray drift: A South African ground application case study.

Air dispersion software models for evaluating pesticide spray drift during application have been developed that can potentially serve as a cheaper convenient alternative to field monitoring campaigns. Such models require validation against field monitoring data in order for them to be employed with confidence, especially when they are used to implement regulatory measures or to evaluate potential human exposure levels. In this case study, off-target pesticide drift was monitored during ground application of a pesticide mixture to a sorghum field in South Africa. Atrazine was used as a drift tracer. High volume air sampling onto polyurethane foam (PUF) was conducted at six downwind locations and at four heights at each sampling point. Additional data, including meteorological information, required to simulate the spray drift with the AGDISP® air dispersion model was collected. The PUF plugs were extracted by a plunger method utilizing a hexane:acetone mixture with analysis by GC-NPD (94.5% recovery, 3.3% RSD, and LOD 8.7 pg). Atrazine concentrations ranged from 4.55 ng L(-1) adjacent to the field to 186 pg L(-1) at 400 m downwind. These results compared favourably with modeled output data, resulting in the validation of the model up to 400 m from the application site for the first time. Sensitivity studies showed the importance of droplet size distribution on spray drift, which highlighted the need for good nozzle maintenance. Results of this case study indicate that the model may provide meaningful input into environmental and human health risk assessment studies in South Africa and other developing countries.