Synthesis and characterization of quantum dot-polymer composites

The bioengineered and multifunctional nanoparticles in pancreatic cancer therapy: Bioresponisive nanostructures, phototherapy and targeted drug delivery

The multidisciplinary approaches in treatment of cancer appear to be essential in term of bringing benefits of several disciplines and their coordination in tumor elimination. Because of the biological and malignant features of cancer cells, they have ability of developing resistance to conventional therapies such as chemo- and radio-therapy. Pancreatic cancer (PC) is a malignant disease of gastrointestinal tract in which chemotherapy and radiotherapy are main tools in its treatment, and recently, nanocarriers have been emerged as promising structures in its therapy. The bioresponsive nanocarriers are able to respond to pH and redox, among others, in targeted delivery of cargo for specific treatment of PC. The loading drugs on the nanoparticles that can be synthetic or natural compounds, can help in more reduction in progression of PC through enhancing their intracellular accumulation in cancer cells. The encapsulation of genes in the nanoparticles can protect against degradation and promotes intracellular accumulation in tumor suppression. A new kind of therapy for cancer is phototherapy in which nanoparticles can stimulate both photothermal therapy and photodynamic therapy through hyperthermia and ROS overgeneration to trigger cell death in PC. Therefore, synergistic therapy of phototherapy with chemotherapy is performed in accelerating tumor suppression. One of the important functions of nanotechnology is selective targeting of PC cells in reducing side effects on normal cells. The nanostructures are capable of being surface functionalized with aptamers, proteins and antibodies to specifically target PC cells in suppressing their progression. Therefore, a specific therapy for PC is provided and future implications for diagnosis of PC is suggested.

Revolutionizing Food Safety with Quantum Dot-Polymer Nanocomposites: From Monitoring to Sensing Applications

The present review article investigates the prospective utilisation of quantum dot-polymer nanocomposites in the context of ensuring food safety. The text pertains to the advancement of nanocomposites, encompassing their distinctive optical and electrical characteristics, and their prospective to transform the detection and perception of food safety risks. The article explores diverse methodologies for producing nanocomposites and underscores their potential utility in identifying impurities, microorganisms, and harmful substances in food. The article provides an overview of the challenges and limitations associated with the utilisation of nanocomposites in food safety applications, encompassing concerns regarding toxicity and the necessity for standardised protocols. The review article presents a comprehensive examination of the present research status in this area and underscores the potential of quantum dots-polymer nanocomposites in transforming food safety monitoring and sensing.

Biocompatible chitin-encapsulated CdS quantum dots: Fabrication and antibacterial screening

Chitin-encapsulated cadmium sulfide quantum dots (CdS@CTN QDs) were successfully synthesized from chitin and Cd(NO₃)₂ precursor using the colloidal chemistry method, toward the development of biocompatible and biodegradable QDs for biomedical applications. CdS@CTN QDs exhibited the nanocrystalline cubic CdS encapsulated by α-chitin. The average particle size of CdS@CTN QDs was estimated using empirical Henglein model to be 3.9 nm, while their crystallite size was predicted using Scherrer equation to be 4.3 nm, slightly larger compared to 3-mercaptopropionic acid-capped CdS QDs (3.2 and 3.6 nm, respectively). The mechanism of formation was interpreted based on the spectroscopic data and X-ray crystal structures of CdS@CTN QDs fabricated at different pH values and mass ratios of chitin to Cd(NO₃)₂ precursor. As an important step to explore potential biomolecular and biological applications of CdS@CTN QDs, their antibacterial activities were tested against four different bacterial strains; i.e. Escherichia coli, Bacillus subtillus, Staphylococcus aureus and Pseudomonas aeruginosa.

Fluorescent dynamics of CsPbBr3 nanocrystals in polar solvents: a potential sensor for polarity

During synthesis, device processes, and applications of perovskite nanocrystals (NCs), there are usually inevitable interactions between perovskite NCs and polar solvents. To elaborately control the properties of perovskite NCs, investigating the effects of solvent polarity on perovskite NCs is thus highly important. Herein, fluorescent variations induced by different solvents into CsPbBr₃ NCs solution are systematically studied. In this report, it is found that when CsPbBr₃ NCs are treated with polar solvents, the fluorescence intensity decreases with a general redshift of fluorescence peak position. Moreover, the fluorescence quenching and peak position shift amplitude monotonously increase with the solvent polarity. Absorption spectra and fluorescent lifetime suggest that, with addition of polar solvents, the surface of NCs are destroyed and defect states are generated, leading to the fluorescent variations. Besides, dielectric constant of the solvent also increases with polarity, which may weaken the quantum confinement effect and decrease the exciton binding energy. We find the fluorescence may slightly blue shift if the emission of free carrier is strong enough with certain solvents, such as dimethylsulfoxide (DMSO). We also find the fluorescence intensity generally deceases to a stable state in 2 min, indicating quick interactions between CsPbBr₃ NCs and solvents. However, water continuously quenches the fluorescence of CsPbBr₃ NCs up to 72 h due to the poor miscibility between water and n-hexane. This work not only provides a comprehensive understanding on the fluorescent dynamics of CsPbBr₃ NCs in polar solvents but also affords a potential fluorescent indicator for solvent polarity.

Quantum Dot-Acrylic Acrylate Oligomer Hybrid Films for Stable White Light-Emitting Diodes

White light-emitting diodes (LEDs) have been achieved using photopolymerization. Red and green CdSe/ZnS core-shell quantum dots (QDs) are dispersed in photopolymerized aliphatic acrylic acrylate resins, cured by using 36 W UV light for 1.5 min producing QD-acrylate nanocomposites, and then a hybrid LED device is achieved using the QD-acrylate nanocomposite with two emission wavelengths excited by using a blue InGaN LED chip. The cured QD-acrylate nanocomposite films are characterized by using ultraviolet-visible, fluorescence, scanning electron microscopy, atomic force microscopy, and thermogravimetric analysis measurements. Photopolymerization is conveniently employed to adjust several parameters of the CIE-1931 coordinate (x, y), color temperature, and color rending index (CRI). Good white balance of the red-green hybrid device achieves a luminance of 7976 lm/m² at a 30 mA working current. The light emission efficiency, CRI, and color temperature of 14%, 47, and 11 204 K, respectively, are attained at this working current.

Structural and Optical Characteristics of PVA:C-Dot Composites: Tuning the Absorption of Ultra Violet (UV) Region

: In this work the influence of carbon nano-dots (CNDs) on absorption of ultra violet (UV) spectra in hybrid PVA based composites was studied. The FTIR results reveal the complex formation between PVA and CNDs. The shifting was observed in XRD spectrum of PVA:CNDs composites compared to pure PVA. The Debye-Scherrer formula was used to calculate the crystallite size of CNDs and crystalline phases of pure PVA and PVA:CNDs composites. The FESEM images emphasized the presence and dispersion of C-dots on the surface of the composite samples. From the images, a strong and clear absorption was noticed in the spectra. The strong absorption that appeared peaks at 280 nm and 430 nm can be ascribed to the n-π* and π-π* transitions, respectively. The absorption edge shifted to lower photon energy sides with increasing CNDs. The luminescence behavior of PVA:CNDs composite was confirmed using digital and photo luminescence (PL) measurements. The optical dielectric constant which is related to the density of states was studied and the optical band gap was characterized accurately using optical dielectric loss parameter. The Taucs model was used to determine the type of electronic transition in the samples.

A small heterobifunctional ligand provides stable and water dispersible core-shell CdSe/ZnS quantum dots (QDs)

We describe a simple method to prepare water dispersible core-shell CdSe/ZnS quantum dots (QDs) 1 by capping QDs with a new thiol-containing heterobifunctional dicarboxylic ligand 4 (DHLA-EDADA). This ligand, obtained on a gram scale through a few synthetic steps, provides a compact layer on the QDs, whose hydrodynamic size in H2O is 15 nm ± 3 nm. The colloidal stability is dramatically enhanced with respect to the well-known (±) α-lipoic acid (DHLA). The ligand affinity towards QDs and the water dispersibility of nanocrystals 1 are addressed by the dithiol groups of DHLA, which chelate the zinc of the shell, and by the dicarboxylic groups of the ethylenediamine-N,N-diacetic acid (EDADA) residue, respectively. The effects of pH, buffer solutions, and biological medium on the stability of QDs 1 were assessed by monitoring the photoluminescence (PL) and hydrodynamic size over time. Highly fluorescent QD dispersions, stable over extended periods of time and over broad pH ranges and buffer types, were obtained. Furthermore, we show that the DHLA-EDADA ligand 4 also endows QDs with functional groups suitable for further conjugation and for metal ion detection. As a case study to illustrate the potential of our approach, we report the preparation and characterization of a highly luminescent orange light emitting polymer-QD 1 composite film.

Synthesis of highly stable quantum-dot silicone nanocomposites via in situ zinc-terminated polysiloxane passivation

Quantum dot (QD) silicone nanocomposites are promising luminescent materials for developing high performance light-emitting diodes (LEDs). However, their practical application still faces a critical issue of strong fluorescence quenching in commercial silicone, which is normally induced by the agglomeration of QDs and the impurities such as a Pt-catalyst and oxygen in the silicone matrices. This article reports the development of zinc-terminated polydimethylsiloxane (Zn-PDMS) to passivate CdSe/CdS/ZnS QDs via an in situ approach. The Zn-PDMS passivation protects the QDs from reacting with impurities and provides the mono-dispersion of QDs in silicone resin, leading to over 80% quantum efficiency as well as effective anti-quenching properties for the QD-silicone nanocomposite under an ambient atmosphere. A high performance warm-white LED prototype with direct on-chip packaging using the as-prepared QDs is developed.

Broadband optical transparency in plasmonic nanocomposite polymer films via exciton-plasmon energy transfer

Inherent absorptive losses affect the performance of all plasmonic devices, limiting their fascinating applications in the visible range. Here, we report on the enhanced optical transparency obtained as a result of the broadband mitigation of optical losses in nanocomposite polymeric films, embedding core-shell quantum dots (CdSe@ZnS QDs) and gold nanoparticles (Au-NPs). Exciton-plasmon coupling enables non-radiative energy transfer processes from QDs to metal NPs, resulting in gain induced transparency of the hybrid flexible systems. Experimental evidences, such as fluorescence quenching and modifications of fluorescence lifetimes confirm the presence of this strong coupling between plexcitonic elements. Measures performed by means of an ultra-fast broadband pump-probe setup demonstrate loss compensation of gold NPs dispersed in plastic network in presence of gain. Furthermore, we compare two films containing different concentrations of gold NPs and same amount of QDs, to investigate the role of acceptor concentration (Au-NPs) in order to promote an effective and efficient energy transfer mechanism. Gain induced transparency in bulk systems represents a promising path towards the realization of loss compensated plasmonic devices.

CdSe/ZnS quantum dots induce photodynamic effects and cytotoxicity in pancreatic cancer cells

AIM: To investigate the photodynamic effect of CdSe/ZnS quantum dots (QDs) on pancreatic cancer cells and elucidate the probable mechanisms.

METHODS: The pancreatic cancer cell line SW1990 was treated with different concentrations of CdSe/ZnS QDs (0, 0.5, 1.0, 1.5, 2.0, 2.5 μmol/L), with or without illumination. The viability of SW1990 cells was tested using the Cell Counting Kit-8 (CCK-8) assay. The ultrastructural changes of SW1990 cells were observed by transmission electron microscopy. Apoptosis was detected by nuclear staining and flow cytometry (FCM). Reactive oxygen species (ROS) were measured by dichlorofluorescein diacetate via fluorescence microscopy. Expression of Bax, Bcl-2 and caspase-3 was measured by real-time polymerase chain reaction (PCR) and protein immunoblotting 24 h after SW1990 cells were treated with CdSe/ZnS QDs and illuminated.

RESULTS: The CCK-8 assay results showed that both CdSe/ZnS QDs with and without illumination suppressed SW1990 cell proliferation. Cell viability was significantly lower when illuminated or with a longer incubation time and a higher light dose. CdSe/ZnS QDs with illumination caused ultrastructural changes in SW1990 cells, such as organelle degeneration and chromatin condensation and aggregation at the periphery of the nucleus. Fluorescence microscopy and FCM showed that CdSe/ZnS QDs (1.5 μmol/L) with illumination increased SW1990 cell apoptosis (53.2%) and ROS generation compared with no illumination. Real-time PCR showed that expression of Bax and caspase-3 was upregulated and Bcl-2 was downregulated. Immunoblotting results were consistent with real-time PCR results. Inhibition of ROS and apoptosis both attenuated QD-photodynamic-therapy-induced cell death.

CONCLUSION: CdSe/ZnS QDs can be used as a photosensitizer to inhibit SW1990 cell proliferation through ROS generation and apoptotic protein expression regulation.

White lighting device from composite films embedded with hydrophilic Cu(In, Ga)S2/ZnS and hydrophobic InP/ZnS quantum dots

Two types of non-Cd quantum dots (QDs)-In/Ga ratio-varied, green-to-greenish-yellow fluorescence-tuned Cu-In-Ga-S (CIGS) alloy ones, and red-emitting InP ones-are synthesized for use as down-converters in conjunction with a blue light-emitting diode (LED). Among a series of Ga-rich CI1-xGxS/ZnS core/shell QDs (x = 0.7, 0.8, and 0.9), CI0.2G0.8S/ZnS QD is chosen for the hydrophobic-to-hydrophilic surface modification via an in-situ ligand exchange and then embedded in a water-soluble polyvinyl alcohol (PVA). This free-standing composite film is utilized as a down-converter for the fabrication of a remote-type white QD-LED, but the resulting bi-colored device exhibits a cool white light with a limited color rendering index property. To improve white light qualities, another QD-polymer film of hydrophobic red InP/ZnS QD-embedding polyvinylpyrrolidone is sequentially stacked onto the CI0.2G0.8S/ZnS QD-PVA film, producing a unique dual color-emitting, flexible and transparent bilayered composite film. Tri-colored white QD-LED integrated with the bilayered QD film possesses an exceptional color rendering property through reinforcing a red spectral component and balancing a white spectral distribution.

Recent advances in quantum dot surface chemistry

Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, this review addresses three main issues: (i) how surface chemistry affects the optical properties of QDs, (ii) how it influences the excited state dynamics, and (iii) how one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles, and in self-assembled QD monolayers.

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x(CuInS2)1-x/ZnS (core-shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose-quantum dot hybrid aerogels have apparent densities of 37.9-57.2 mg cm-3. Their BET surface areas range from 296 to 686 m2 g-1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)2 route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO2 drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.

Plasmon mediated super-absorber flexible nanocomposites for metamaterials

A flexible host has been selected to achieve, for the first time, functional nanocomposites based on CdSe@ZnS core-shell type quantum dots (QDs) and Au nanoparticles (NPs), simultaneously dispersed in a polymer matrix. Coherent interactions between QDs and plasmonic Au NPs embedded in PDMS films have been demonstrated to lead to a relevant enhancement of the absorption cross-section of the QDs, remarkably modifying the optical response of the entire system. Optical and time resolved spectroscopy studies revealed an active gain-plasmon feedback behind the super-absorbing overall effect.

Synthesis and characterization of the hole-conducting silica/polymer nanocomposites and application in solid-state dye-sensitized solar cell

Hole-conducting silica/polymer nanocomposites exhibit interesting physical and chemical properties with important applications in the field of energy storage and hybrid solar cells. Although the conventional strategy of grafting hole-conducting polymer onto the surface of silica nanoparticles is to use in situ oxidative polymerization, a promising alternative of using surface-initiated controlled living radical polymerization has arisen to anchor the polymer on the silica. The resulting silica/polymer nanocomposites from the latter method are more chemically and thermally stable because of the strong covalent bonding compared to the electrostatic interaction from in situ polymerization. The use of these nanocomposites mixed with spiro-MeOTAD (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene) as a new hole conductor in the application of solid-state dye-sensitized solar cell (ss-DSSC) is reported here. The power conversion efficiency of this ss-DSSC is higher than the full spiro-MeOTAD ss-DSSC. Notably, the short circuit current improves by 26%. It is explained by large size silica/polymer nanocomposites forming an additional light scattering layer on the top of photoanode. This is the first time a conductive light scattering layer is introduced into ss-DSSC to enhance cell performance.

Investigating photoinduced charge transfer in carbon nanotube-perylene-quantum dot hybrid nanocomposites

In this study, we investigate photophysical and photoinduced current responses of a nanocomposite which consists of multiwalled carbon nanotubes (CNTs), thiol derivative perylene compound (ETPTCDI), and cadmium selenide quantum dots (QDs). These QDs as well as the ETPTCDI harvest photons and transfer their excited electrons or holes to CNTs to complete the circuit. Both QDs and ETPTCDI contribute charges to the carbon nanotubes, which increased the overall photon harvest efficiency of the nanocomposite. Herein, we investigate through a series of photophysical photoluminescence quenching studies the charge transfer between donors (QDs and ETPTCDI) and acceptor (CNTs). The incorporation of ETPTCDI into the nanocomposite significantly increases the adhesion between QDs and CNTs through bonding between QDs and thiol groups on ETPTCDI and π-π interactions between ETPTCDI and CNTs. Thus, ETPTCDI acted as a molecular linker between QDs and CNTs. Furthermore, a significant increase (>5 times) in the Stern-Volmer constant, K(sv), for QD emission after addition of ETPTCDI-tagged CNTs clearly indicates a large enhancement in the adhesion between CNTs and QDs. The nanocomposite shows a ∼2-4-fold increase in the photoconductivity when exposed to AM1.5 solar-simulated light. The damage to the nanocomposite from the intensity of the solar-simulated light is also investigated. The proposed nanocomposite has the potential for photovoltaic applications such as being the active component in a hybrid bulk heterojunction solar cell.