Blue emission from cysteine ester passivated cadmium sulfide nanoclusters

Development of luminescent atacamite nanoclusters for bioimaging and photothermal applications

Fluorescent atacamite nanoclusters (FANCs) have been developed and modified with silica for Drosophila salivary gland tissue imaging and photothermally induced cell death of osteosarcoma MG-63 cells. FANCs were synthesized with Moringa oleifera leaf extract without using any hazardous reducing and external capping agents. FANC was further used to evaluate light absorption, fluorescence emission, band gap, and magnetic properties as the first report on such nanoclusters. Upon excitation with a 350 nm light source, FANCs exhibited fluorescence at 460 nm, with a relative quantum yield of 0.3%. Besides, silica-encapsulated fluorescent atacamite nanoclusters (SEFANC) manifested remarkable improvement in emission, quantum yield (1.7%), shelf-life (15 d), biocompatibility, and photostability. Concomitantly, it has also increased the absorption in the near-infrared region and demonstrated high heat generation potential (42 °C → 50 °C). The above results suggest that FANC can be a potential candidate in the area of nanomedicine for a number of applications such as bioimaging, photothermal therapy, etc.

Alkaline post-treatment of Cd(II)-glutathione coordination polymers: toward green synthesis of water-soluble and cytocompatible CdS quantum dots with tunable optical properties

In this study, we demonstrate a facile and environmentally friendly method for the synthesis of glutathione (GSH)-capped water-soluble CdS quantum dots (QDs) with a high cytocompatibility and a tunable optical property based on alkaline post-treatment of Cd-GSH coordination polymers (CPs). Cd-GSH CPs are synthesized with the coordination reaction of Cd(2+) with GSH at different pH values, and the CdS QDs are then formed by adding NaOH to the aqueous dispersion of the Cd-GSH CPs to break the coordination interaction between Cd(2+) and GSH with the release of sulfur. The particle size and optical property of the as-formed CdS QDs are found to be easily tailored by simply adjusting the starting pH values of GSH solutions used for the formation of Cd-GSH CPs, in which the wavelengths of trap-state emission of the QDs red-shift with an increase in the sizes of the QDs that is caused by an increase in the starting pH values of GSH solutions. In addition, the use of GSH as the capping reagent eventually endows the as-formed CdS QDs with enhanced water solubility and good cytocompatibility, as demonstrated with HeLa cells. The method demonstrated here is advantageous in that the cadmium precursor and the sulfur source are nontoxic and easily available, and the size, optical properties, water solubility, and cytocompatibilty of the as-formed CdS QDs are simply achieved and experimentally regulated. This study offers a new and green synthetic route to water-soluble and cytocompatible CdS QDs with tunable optical properties.

Structural phase behavior and vibrational spectroscopic studies of biofunctionalized CdS nanoparticles

Biomodified CdS nanoparticles were synthesized using l-cysteine as a capping agent in the colloidal state as a function of pH. The role of pH on the size and structure of CdS nanoparticles was investigated in detail. At pH 7.4 and 9.1, X-ray diffraction spectra of as prepared samples showed the presence of a mixture of cubic and hexagonal phases while cubic phase was formed at pH 11.2. A gradual transition to the hexagonal phase was observed for refluxed samples at pH 9.1 and 11.2. Whereas, at pH 7.4, the sample remains in a mixture of cubic and hexagonal phase even after refluxing. The particle size of as prepared samples was about 2 nm, and for refluxed samples the size increased up to 10 nm. The binding of cadmium through thiol group is evidenced by infrared spectra. An intense band due to C-C-N vibration was observed after 24 h of reflux. The formation of a specific molecular cluster determines the growth of a particular phase. Transmission electron microscopy (TEM) studies support the X-ray diffraction (XRD) studies and exhibit well separated spherical particles while refluxed samples show clustering.

Surface modification of CdS quantum dots using thiols-structural and photophysical studies

This study is aimed at identifying a suitable organic thiol for CdS by studying its structural, thermal and photophysical characteristics. Quantum dots of the II-VI semiconductor CdS, in the size regime of 2.0-3.3 nm, were prepared in the cubic phase by a wet chemical method. Five organic thiols were used for capping: (i) 1,4-dithiothreitol (DTT), (ii) 2-mercaptoethanol (ME), (iii) cysteine (Cys), (iv) methionine (Meth), and (v) glutathione (GSH). Structural studies were carried out by x-ray diffraction (XRD) and transmission electron microscopy (TEM), which revealed the cubic phase of CdS. Optical properties were studied by FT-IR, UV-visible and fluorescence spectroscopic techniques, and a comparison was made between uncapped and capped CdS. FT-IR studies suggested two different bonding mechanisms of the capping agents with the CdS. GSH and DTT capped CdS showed significant decrease in absorption wavelengths. An increase in band gap was observed in two cases: when (i) capped and (ii) decreased in size. The band gap was increased from 2.50 eV for the uncapped to 2.77 eV for the DTT capped CdS. DTT was found to be the best capping agent for CdS among these five organic thiols in two aspects: (i) yielding lower grain size in cubic phase, and (ii) good fluorescence properties with efficient quenching of the surface traps.

One-pot synthesis of highly luminescent CdTe/CdS core/shell nanocrystals in aqueous phase

Surface passivation of nanocrystals with suitable organic or inorganic materials is key to improving the photoluminescence (PL) efficiency and stability of nanocrystals. Although the hot-injection organometallic approach is a powerful tool to achieve different kinds of core/shell structures, direct synthesis of such structures in aqueous phase, which bears many advantages such as biocompatibility, water-solubility, environment-friendliness, and cheapness, is less often reported. Herein we present a facile approach for the one-pot preparation of a water-soluble core/shell structure with CdTe cores packed in a CdS shell in aqueous phase. In comparison with plain CdTe nanocrystals, the PL efficiency of the obtained CdTe/CdS core/shell structure can approach about 75%. The stability of the core/shell structure to UV irradiation and oxidation is also improved.

Temperature-induced aggregation of poly(N-isopropylacrylamide)-stabilized CdS quantum dots in water

Water-soluble nanosized semiconductor CdS particles (quantum dots, QDs) were synthesized with a protective layer of covalently grafting linear thermally sensitive poly(N-isopropylacrylamide) chains. Reversible association and dissociation of these CdS particles can be induced via an alteration of the solution temperature. The formation and fragmentation of the QD aggregates of the CdS particles were systematically investigated by laser light scattering (LLS) and confirmed by transmission electron microscopy (TEM). There exists a hysteresis during one heating-and-cooling cycle. The CdS particles stabilized with shorter PNIPAM chains (Mn=15,000 g/mol) can associate to form larger and denser spherical aggregates with a much higher aggregation number than those grafted with longer PNIPAM chains (Mn=31,000 g/mol) in the heating process. The dissociation (fragmentation) in the cooling process has two stages: initially, the aggregates dissociate as the temperature decreases, and then, the fragmentation stops over a wider temperature range before complete dissociation. We attribute such a two-stage fragmentation to a balanced effect of inter- and intrachain hydrogen bonding as well as the hydrophobic interaction between PNIPAM chains and CdS particles.

In situ synthesis and photoluminescence of QD-CdS on silk fibroin fibers at room temperature

A convenient room-temperature bioinspired technique has been developed to synthesize hybrid nanocomposites consisting of well-dispersed CdS quantum dots (QD) and the substrate silk fibroin fibers (SFF). The biomaterial SFF provides both a supporting substrate and functional sites for the in situ generation of QD-CdS, which is supported by FTIR and PL measurements. The solid QD-CdS/SFF nanocomposites could be useful in photocatalyst, novel luminescence and photoelectron transfer devices. The QD-CdS/silk fibroin (SF) colloid, in which SF acts as both an inherent biocompatibilizer and an efficient passivator of trap sites on the QD-CdS surface, is also available for some potential applications in the biological fields. The bioinspired method and relevant ideas could extend to fabricating other functional hybrid materials.

Preparation of a novel composite particles and its application in the fluorescent detection of proteins

A new fluorescence method for the detection of proteins with novel composite nanoparticles (CdS/PPA) has been developed. The composite nanoparticles have been prepared through an in-situ polymerization method under ultrasonic irradiation. The surface of the composite nanoparticles was covered with functional groups (-COOH). These groups may play a major role in the improving the water solubility and biocompatibility of the nanoparticles. The composite particles is combined with proteins in NaAc-HCl buffer solution (pH=1.99), which can result in strong fluorescence, and the response is linearly proportional to the concentration of proteins. In lambdaem/lambdaex=650 nm/365 nm place (the stoke' shift is 285 nm), its fluorescent strength reaches the maximum. Under the optimum conditions, the linear range is 0.10-20.0 microg.ml(-1) with the detection limit of 41 ng.ml(-1) for HSA, and 0.10-15.0 microg.ml(-1) with the detection limit of 35 ng.ml(-1) for Human gamma-IgG . The method has been applied to the determination of the total protein in human serum samples collected from the hospital and the results are satisfactory.

Size tunable synthesis of cysteine-capped CdS nanoparticles by γ-irradiation

Highly water soluble and biocompatible L-cysteine-capped CdS nanoparticles having narrow size distribution were synthesized for the first time by gamma-irradiation technique without using any additional stabilizer. FTIR study shows that CdS nanoparticles are capped through mercapto-group of cysteine amino acid while its free amino and carboxylate groups make it amenable to bio-conjugation. Size and luminescence of the nanoparticles can be well controlled by varying the parameters like radiation dose, pH and concentration of cysteine. The observed results suggest that pH 7 can be optimum for the synthesis of L-cysteine-capped CdS nanoparticles. CdS nanoparticles synthesized with molar ratio of Cd(2+):cysteine, 1:60 at pH 7 were found to be most luminescent. All nanoparticles formed lie in the size quantization regime and exhibit good crystallinity. Remarkable improvement in stability and luminescence was achieved on changing pH of as-prepared nanoparticles from 7 to 11.

Glyconanoparticles: types, synthesis and applications in glycoscience, biomedicine and material science

Nanoparticles are the subject of numerous papers and reports and are full of promises for electronic, optical, magnetic and biomedical applications. Although metallic nanoparticles have been functionalized with peptides, proteins and DNA during the last 20 years, carbohydrates have not been used with this purpose until 2001. Since the first synthesis of gold nanoparticles functionalized with carbohydrates (glyconanoparticles) was reported, the number of published articles has considerably increased. This article reviews progress in the development of nanoparticles functionalized with biological relevant oligosaccharides. The glyconanoparticles constitute a good bio-mimetic model of carbohydrate presentation at the cell surface, and maybe, excellent tools for Glycobiology, Biomedicine and Material Science investigations.

Nucleotide passivated cadmium sulfide quantum dots

Semiconductor quantum dots are finding numerous applications in biological systems; in this paper, we report the simple in situ preparation of nucleotide capped cadmium sulfide (CdS) nanoparticles and investigate the interaction of the capping agent with the nanoparticle surface.

One-Step Synthesis and Structural Features of CdS/Montmorillonite Nanocomposites

A novel synthesis method was introduced for the nanocomposites of cadmium sulfide and montmorillonite. This method features the combination of an ion exchange process and an in situ hydrothermal decomposition process of a complex precursor, which is simple in contrast to the conventional synthesis methods that comprise two separate steps for similar nanocomposite materials. Cadmium sulfide species in the composites exist in the forms of pillars and nanoparticles, the crystallized sulfide particles are in the hexagonal phase, and the sizes change when the amount of the complex for the synthesis is varied. Structural features of the nanocomposites are similar to those of the clay host but changed because of the introduction of the sulfide into the clay.