Interaction of Folic Acid with Mn2+ Doped CdTe/ZnS Quantum Dots: In Situ Detection of Folic Acid.

To utilize the nanomaterials as an effective carrier for the drug delivery applications, it is important to study the interaction between nanomaterials and drug or biomolecules. In this study GSH functionalized Mn2+-doped CdTe/ZnS QDs has been utilized as a model nanomaterial due to its high luminescence property. Folic acid (FA) gradually quenches the FL of GSH functionalized Mn2+ - doped CdTe/ZnS QDs. The Stern-Volmer quenching constant (Ksv), binding constant (Ks) and effective quenching constant (Ka) for the FA-QDs system is calculated to be 1.32 × 105 M-1, 1.92 × 105 and 0.27 × 105 M-1, respectively under optimized condition (Temp. 300 K, pH 8.0, incubation time 40 min.). The effects of temperature, pH, and incubation time on FA-QDs system have also been studied. Statistical analysis of the quenched FL intensity versus FA concentration revealed a linear range from 1 × 10-7 to 5.0 × 10-5 for FA detection. The LOD of the current nano-sensor for FA was calculated to be 0.2 µM. The effect of common interfering metal ions and other relevant biomolecules on the detection of FA (12.0 µM) have also been investigated. L-cysteine and glutathione displayed moderate effect on FA detection. Similarly, the common metal ions (Na+, K+, Ca2+ and Mg2+) produced minute interference while Zn2+ Cu2+ and Fe3+ exert moderate interference. Toxic metal ions (Hg2+ and Pb2+) produced severe interferences in FA detection.Graphical abstract GSH-Mn2+ CdTe/ZnS QDs based Fluorescence Nanosensor for Folic acid.

CdTe QD-based inhibition and reactivation assay of acetylcholinesterase for the detection of organophosphorus pesticides.

An enzyme immobilized glutathione (GSH)-capped CdTe quantum dot (QD)-based fluorescence assay has been developed for monitoring organophosphate pesticides. In principle, GSH-capped CdTe QDs exhibit higher sensitivity towards H2O2 produced from the active enzymatic reaction of acetylcholinesterase (AChE) and choline oxidase (CHOx), which results in the fluorescence (FL) "turn-off" of the GSH-capped CdTe QDs. A "turn-on" FL of the CdTe QDs at 520 nm was recovered in the presence of organophosphate (OP). The FL changes of the GSH-capped CdTe QD/AChE/CHOx biosensor reasonably correspond to the amount of OP pesticides. The detection limit of the CdTe/AChE/CHOx biosensor towards paraoxon, dichlorvos, malathion and triazophos was 1.62 × 10-15 M, 75.3 × 10-15 M, 0.23 × 10-9 M and 10.6 × 10-12 M, respectively. The GSH-capped CdTe QDs/AChE/CHOx biosensor was applied as a FL nanoprobe for assaying the enzymatic activity of AChE. The inhibited AChE was reactivated up to 94% using pyridine oximate (2-PyOx-), and functionalized pyridinium oximates (4-C12PyOx- and 4-C18PyOx-) of varying chain lengths. It was found that the reactivation potency of the tested oximes varied with the chain length of the oximes. This biosensing system offers the promising benefit for the determination of the OP pesticides in food, water and environmental samples.