A ratiometric fluorometric method is described for the determination of arsenate via its inhibitory effect on the activity of the enzyme acid phosphatase. A nanoprobe was designed that consists of CdSe/ZnS quantum dots (QDs) coated with the terbium(III) complex of guanosine monophosphate (Tb-GMP). The nanoprobe was synthesized from carboxylated QDs, Tb(III) and GMP via binding of Tb(III) by both the carboxy and the phosphate groups. The nanoprobe, under single-wavelength excitation (at 280 nm), displays dual (red and green) emission, with peaks at around 652 nm from the QDs, and at 547 nm from the Tb-GMP coordination polymers. It is shown to be a viable nanoprobe for fluorometric determination of As(V) detection through it inhibitory action on the activity of acid phosphatase (ACP). The enzyme destroys the Tb-GMP structure via hydrolysis of GMP, and hence the fluorescence of the Tb-GMP complex is quenched. In contrast, the fluorescence of the CdSe/ZnS QDs remains inert to ACP. It therefore can serve as an internal reference signal. In the presence of arsenate (an analog of phosphate), the activity of ACP is inhibited due to competitive binding. Thus, hydrolysis of GMP is prevented. These findings were used to design a ratiometric fluorometric method for the quantification of As(V). The ratio of fluorescences at 547 and 652 nm increases linearly in the 0.5 to 200 ppb As(V) concentation range, and the limit of detection is 0.39 ppb. Under a UV lamp, the probe shows distinguishable color from green to red on increasing the concentration of As(V).
Schematic illustration of CdSe/ZnS quantum dot coated with carboxy-PEG and modified with the terbium(III)-GMP complex as a fluorescent nanoprobe for ratiometric determination of arsenate via its inhibition of ACP activity.
Mingrui Liu,Guangmin Li,Shunsheng Wei,Hongfei Liu,Gaoling Yang
Chiral semiconductor nanocrystals (NCs) represent a promising class of materials for various applications, including biological sensing, photonics, and spin-polarized devices. However, the comprehension of the mechanisms underlying ligand-induced chiroptical effects in NCs has been limited by the constraints of current theoretical and experimental models, particularly those involving simple spherical NCs. In this study, we examined the relationship between optical activity and band structures in core–shell dot-in-rod NCs, specifically CdSe@CdS, ZnSe/CdS@CdS, and ZnSeTe/CdS@CdS dot-in-rod NCs, which were functionalized with chiral ligands. By manipulating the wave function distribution of electrons and holes within the dot-in-rod NCs, we demonstrated through circular dichroism (CD) measurements that a reduction in the number of holes within the synthesized dot-in-rod NCs correlates with a decrease in the g factor. This conclusion was corroborated by theoretical calculations. Furthermore, the fabrication of chiral CdS-Au heterojunctions and the application of electron quenchers revealed that the reduction of the g factor also suggests the significant role of electrons in the generation of chirality. Our findings not only enhance the understanding of the fundamental origins of induced chirality effects in semiconductor NCs but also provide a clear methodology for the design of optimal optically active chiral NCs, thereby paving the way for future applications utilizing chiroptical materials.
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