Pb2+ Responsive Cu-In-Zn-S Quantum Dots With Low Cytotoxicity

Green Synthesis of Carboxymethyl Chitosan-Based CuInS2 QDs with Luminescent Response toward Pb2+ Ion and Its Application in Bioimaging

Polysaccharide-based QDs have attracted great attention in the field of biological imaging and diagnostics. How to get rid of the high heavy metal toxicity resulting from conventional Cd- and Pb-based QDs is now the main challenge. Herein, we offer a simple and environmentally friendly approach for the "direct" interaction of thiol-ending carboxymethyl chitosan (CMC-SH) with metal salt precursors, resulting in CuInS2 QDs based on polysaccharides. A nucleation-growth mechanism based on the LaMer model can explain how CMC-CuInS2 QDs are formed. As-prepared water-soluble CMC-CuInS2 QDs exhibit monodisperse particles with sizes of 5.5-6.5 nm. CMC-CuInS2 QDs emit the bright-green fluorescence at 530 nm when excited at 466 nm with the highest quantum yield of ∼18.0%. Meanwhile, the fluorescence intensity of CMC-CuInS2 QD aqueous solution is quenched with the addition of Pb2+ and the minimal limit of detection is as little as 0.4 nM. Furthermore, due to its noncytotoxicity, great biocompatibility, and strong biorecognition ability, CMC-CuInS2 QDs can be exploited as a possible cell membrane imaging reagent. The imaging studies also demonstrate that CMC-CuInS2 QDs are suitable for Pb2+ detection in live cells and living organisms (zebrafish). Thus, this work offers such an efficient, green, and practical method for creating low-toxicity and water-soluble QD nanosensors for a sensitive and selective detection of toxic metal ion in live cells and organisms.

High Photoluminescence Polyindole/CuInS Quantum Dots for Pb Ions Sensor

Polyindole is considered an excellent conducting polymer with interested properties for different applications. A novel polyindole (PIn)/CuInS (CIS)/ZnS quantum dots (QDs) nanocomposite was synthesized via in situ polymerization of PIn in presence of CIS/ZnS QDs. By investigating the effect of CIS/ZnS QDs on optical properties of PIn, it was found that the optical band gaps of PIn, CIS/ZnS QDs, and PIn/CIS/ZnS QDs nanocomposite were 3.24 eV, 4.68 eV and 3.44 eV, respectively. From the luminance spectra, it was observed that emission peaks of PIn at 442 and 468 nm are independent of the excitation wavelength with the highest intensity at excitation wavelength of 380 nm. However, the luminance spectrum of PIn/CIS/ZnS QDs nanocomposite exhibited a quenching peak for CIS/ZnS QDs while the intensity of PIn peak was enhanced. High resolution of transmission electron microscope image of CIS/ZnS QDs revealed nanocrystals with a size of 3–4.5 nm and lattice space of 0.2 nm. PIn/CIS/ZnS QDs nanocomposite as the fluorescent probe was employed for sensing different concentrations of Pb2+ from 5 to 50 ppb. The reaction between PIn/CIS/ZnS QDs and Pb2+ was slightly quenched and fixed after 90 min. The emission peak was reduced gradually with increasing concentration of lead via photo-induced electron transfer or ion exchange mechanism. The value of correlation coefficient (R2) was 0.99, the sensitivity was 0.0041 ppb−1 and limit of detection value was 4.48 ppb.