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.

Green synthesis of glyco-CuInS2 QDs with visible/NIR dual emission for 3D multicellular tumor spheroid and in vivo imaging.

Glyco-quantum dots (glyco-QDs) have attracted significant interest in bioimaging applications, notably in cancer imaging, because they effectively combine the glycocluster effect with the exceptional optical properties of QDs. The key challenge now lies in how to eliminate the high heavy metal toxicity originating from traditional toxic Cd-based QDs for in vivo bioimaging. Herein, we report an eco-friendly pathway to prepare nontoxic Cd-free glyco-QDs in water by the "direct" reaction of thiol-ending monosaccharides with metal salts precursors. The formation of glyco-CuInS2 QDs could be explained by a nucleation-growth mechanism following the LaMer model. As-prepared four glyco-CuInS2 QDs were water-soluble, monodispersed, spherical in shape and exhibited size range of 3.0-4.0 nm. They exhibited well-separated dual emission in the visible region (500-590 nm) and near-infrared range (~ 827 nm), which may be attributable to visible excitonic emission and near-infrared surface defect emission. Meanwhile, the cell imaging displayed the reversibly distinct dual-color (green and red) fluorescence in tumor cells (HeLa, A549, MKN-45) and excellent membrane-targeting properties of glyco-CuInS2 QDs based on their good biorecognition ability. Importantly, these QDs succeed in penetrating uniformly into the interior (the necrotic zone) of 3D multicellular tumor spheroids (MCTS) due to their high negative charge (zeta potential values ranging from - 23.9 to - 30.1 mV), which overcame the problem of poor penetration depth of existing QDs in in vitro spheroid models. So, confocal analysis confirmed their excellent ability to penetrate and label tumors. Thus, the successful application in in vivo bioimaging of these glyco-QDs verified that this design strategy is an effective, low cost and simple procedure for developing green nanoparticles as cheap and promising fluorescent bioprobes.

Nonconjugated fluorescent polymer nanoparticles by self-assembly of PIMA-g-ß-CD for live-cell long-term tracking.

Fluorescent non-conjugated nanoparticles without any π-aromatic building blocks are of great interest in biological applications due to their low cytotoxicity and biocompatibility. Herein, the non-conjugated AIE-active polymer nanoparticles bearing ß-cyclodextrin (ß-CD-PNs) were obtained through self-assembly of amphiphilic poly(isobutylene-alt-maleic anhydride)-g-ß-CD (PIMA-g-ß-CD). Unexpectedly, ß-CD-PNs without conventional AIE fluorophores showed strong fluorescence emission in the aggregated state, excellent photostability and water-solubility. More interestingly, ß-CD-PNs showed excellent biocompatibility and low biotoxicity after being co-incubated with HeLa cells and passaged several times. As a result, the strong blue fluorescence signals could still be detected in HeLa cells after up to 15 generations of passages and showed complete cell morphology. Furthermore, ß-CD-PNs could also be used in zebrafish for bioimaging. The results indicated that ß-CD-PNs was a good choice as a tracer for long-term cell tracking and in vivo imaging agent. Our research provided an effective strategy for developing low-toxicity bioprobes based on ß-CD.

Determination of silver ion with cadmium sulfide quantum dots modified by bismuthiol II as fluorescence probe.

CdS quantum dots (QDs) modified with bismuthiol II potassium salt is prepared in one step. Based on the characteristic fluorescence enhancement of CdS QDs at 480 nm by silver ions, simultaneously, a red shift of fluorescence emission bands of CdS QDs from 460 to 480 nm is observed. A simple, rapid, sensitive and specific detection method for silver ion is proposed. Under optimum conditions, the fluorescence intensity of CdS QDs was linearly proportional to silver ion concentration from 0.01 to 5.0 micromol L(-1) with a detection limit of 1.6 nmol L(-1). In comparison with single organic fluorophores, functionalized CdS quantum dots are brighter, more stable against photobleaching and do not suffer from blinking. Furthermore, the proposed method shows higher sensitivity and selectivity. A possible fluorescence enhancement mechanism is also studied.

Efficient Detection of Trace Hg²âº in Water Based on the Fluorescence Quenching of Environment-friendly Thiol-functionalized Poly(vinyl alcohol) Capped CdS Quantum Dots Nanocomposite.

Using environment-friendly materials for sensing toxic metal ions has drawn significant attention in recent research. Herein, we present an aqueous synthesis of stable CdS quantum dots (QDs) using thiol-functionalized poly(vinyl alcohol) (PVA) as the unique capping ligand for the detection of trace Hg(2+) in environmental water samples. The CdS QDs with an average size of 3.3 nm had good water-solubility and favorable fluorescence with a quantum yield of 32.8% and a longer luminescence lifetime of 31.9 ns. The fluorescence intensity of QDs aqueous solution in the 520 nm wavelength was quenched upon the addition of Hg(2+). Under the optimal conditions, the ratio of the blank fluorescence intensity to the quenched fluorescence intensity was linearly proportional to the Hg(2+) concentration from 2 to 4000 nM with a detection limit of 1 nM. Also, many co-existing metal ions were not interfered with the detection of Hg(2+). This nanomaterial was successfully applied to the measurement of Hg(2+) in water samples.

Synthesis and efficiency of a chelating fiber for preconcentration and separation of trace Au(III) and Pd(IV) from solution samples.

A novel poly(acryl-benzoylamidrazone-acryl-benzoylhydrazine) chelating fiber was synthesized simply from nitrilon (polyacrylonitrile fiber). The structure of the chelating fiber was verified with the help of FT-IR spectrum. The parameters influencing the efficiency of the fiber for concentrating trace amounts of Au(III) and Pd(IV) were investigated in detail. Trace Au(III) and Pd(IV) were enriched and separated from real sample solutions and detected using inductively coupled plasma atomic emission spectrometry (ICP-AES) with satisfactory results. The experiments show that the method is rapid, precise, simple and convenient to use.

Interaction among cadmium sulfide nanoparticles, acridine orange, and deoxyribonucleic acid in fluorescence spectra and a method for deoxyribonucleic acid determination.

Some studies on quantum dots (QD) as donors that enhance the fluorescence of a dye as an acceptor through fluorescence resonance energy transfer (FRET) have been reported. However, in the present work we discovered that CdS quantum dots sharply quenched the fluorescence of acridine orange (AO). Also, DNA enhanced the fluorescent signals of AO quenched by CdS. The extents of enhancement were in good proportion to the DNA concentrations. Based on this, a sensitive method was employed to determine DNA with both good selectivity and sensitivity. The calibration curve was linear over 60-4,000 ng mL(-1) and the determination limit (3sigma) was 4.39 ng mL(-1).