Fluorescent Nanocomposites Research Articles

Synthesis of Fe3O4/CdSe/CdS magnetic fluorescent nanocomposites by a stepwise heterocoagulation approach

In this thesis, Fe3O4/CdSe/CdS magnetic fluorescent nanocomposites (MFNC) were synthesized by an approach of stepwise heterocoagulation. Fe3O4 magnetic nanoparticles were prepared by hydro-thermal coprecipitation of ferric and ferrous ions. The as-prepared nanoparticles were modified by oleic acid, and then formed the anionic water based ferrofluids (FFs) by utilizing a nonionic surfactant of polyoxyethylene nonylphenol to create a colloidal suspension. CdSe/CdS quantum dots (QDs) were synthesized using mercaptoacetic acid as stabilizer. At last, Fe3O4/CdSe/CdS magnetic/luminescent bifunctional nanocomposites were prepared successfully using cationic polyethyleneimine (PEI) as a crosslinker. The as-synthesized nanocomposites possessed structure with an average diameter of 70–80nm. They retained the strong photoluminescence effect of CdSe/CdS QDs and also exhibited a typical superparamagnetic behavior of Fe3O4 nanoparticles.

Inclusion of thiol DAB dendrimer/CdSe quantum dots based in a membrane structure: Surface and bulk membrane modification

The behavior of a fluorescent nanocomposite, obtained by means of a thiol polypropylenimine dendrimer of third generation coated with CdSe quantum dots, and embedded in a hydrophilic cellulosic membrane as support is electrochemically studied in order to evaluate its applicability as a sensor in liquid media. The characterization of the nanocomposite by TEM and EDAX shows uniform nano morphology (size comprised in the range 60–90nm) and composition, respectively. The analysis of the engineered hybrid cellulose-dendrimer quantum dots material by confocal fluorescence microscopy indicates almost mono-dispersion distribution of the nanocomposite when irradiated under UV light, while its presence on the film surface was determined by X-ray photoelectron spectroscopy. Impedance spectroscopy measurements performed with dry membrane samples show a decrease in the conductivity and dielectric constant of the modified membrane in comparison with the raw support. Electrical changes in the modified film associated to the presence of Cd(II) uptakes from a Cl2Cd solution were also obtained. These results support the possible application of this nanocomposite material as heavy metal sensor in liquid media.

Highly Selective and Sensitive Fluorescent Paper Sensor for Nitroaromatic Explosive Detection

Rapid, sensitive, and selective detection of explosives such as 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP), especially using a facile paper sensor, is in high demand for homeland security and public safety. Although many strategies have been successfully developed for the detection of TNT, it is not easy to differentiate the influence from TNP. Also, few methods were demonstrated for the selective detection of TNP. In this work, via a facile and versatile method, 8-hydroxyquinoline aluminum (Alq(3))-based bluish green fluorescent composite nanospheres were successfully synthesized through self-assembly under vigorous stirring and ultrasonic treatment. These polymer-coated nanocomposites are not only water-stable but also highly luminescent. Based on the dramatic and selective fluorescence quenching of the nanocomposites via adding TNP into the aqueous solution, a sensitive and robust platform was developed for visual detection of TNP in the mixture of nitroaromatics including TNT, 2,4-dinitrotoluene (DNT), and nitrobenzene (NB). Meanwhile, the fluorescence intensity is proportional to the concentration of TNP in the range of 0.05-7.0 μg/mL with the 3σ limit of detection of 32.3 ng/mL. By handwriting or finger printing with TNP solution as ink on the filter paper soaked with the fluorescent nanocomposites, the bluish green fluorescence was instantly and dramatically quenched and the dark patterns were left on the paper. Therefore, a convenient and rapid paper sensor for TNP-selective detection was fabricated.

Thiolated DAB dendrimer/ZnSe nanoparticles for C-reactive protein recognition in human serum

A nanocomposite obtained by a thiol DAB-dendrimer (generation 5), coated with fluorescent ZnSe quantum dots, was successfully synthesized for the selective recognition of C-reactive protein. The procedure presented was carried out by a novel, cheap and non-toxic bottom up synthesis. The nanocomposite showed an excitation at 180nm, with two emission bands at 411 and 465nm, with a full-width at half-maximum of 336nm. The Stokes shift was influenced by the presence of coating molecules and the intensity was dependent on pH due to the presence of a charge transfer process. The transmission electron microscopy images demonstrated that the spherical nanoparticles obtained displayed a regular shape of 30nm size. The fluorescence intensity was markedly quenched by the presence of C-reactive protein, with a dynamic Stern–Volmer constant of 0.036M−1. The quenching profile shows that about 51% of the ZnSe QDs are located in the external layer of the thiol dendrimer accessible to the quencher. The precision of the method obtained as relative standard deviation was 3.76% (4mgL−1, n=3). This water soluble fluorescent nanocomposite showed a set of favorable properties to be used as a sensor for the C-reactive protein in serum samples, at concentrations of risk levels.

Plasmonic Fluorescent Nanocomposites of Cyanines Self-assembled upon Gold Nanoparticle Scaffolds

Plasmonic fluorescent nanocomposites are difficult to prepare due to strong quenching effects on fluorophores in the vicinity of noble metal nanoparticles such as gold (AuNPs). We successfully prepared plasmonic fluorescent nanocomposites of two cyanines (1 and 2) aggregating upon 2 - 40 nm AuNPs or streptavidin-conjugated 10 nm AuNPs. We used high throughput screening (HTS) for the first time to characterize the spectral properties, aggregation kinetics, aggregation density and photostability of the nanocomposites. Fluorescence from nanocomposites declined inversely with AuNPs size: 40 nm ≥ 20 nm > 10 nm > 5 nm > 2 nm. Sensitivity (limit of detection, LOD, 10(5) - 10(11) AuNPs/mL), brightness of the nanocomposites and surface coverage of AuNPs by cyanine aggregates were all influenced by five factors: 1) AuNPs size; 2) cyanine type (1 or 2); 3) aggregate density; 4) distance between aggregates and AuNPs surface; and 5) streptavidin protein conjugation to AuNPs. We propose a model for plasmonic fluorescent nanocomposites based on these observations. Our plasmonic fluorescent nanocomposites have applications in chemical and biological assays.

PHOTOPHYSICAL BEHAVIOR OF FLUORESCENT NANOCOMPOSITES OF PHTHALOCYANINE LINKED TO QUANTUM DOTS AND MAGNETIC NANOPARTICLES

Fluorescent nanocomposite that consists of 3-aminopropyltriethoxysilane coated magnetic iron nanoparticles (MN), mercaptopropionic acid capped CdTe quantum dots (QD) and octacarboxy metallophthalocyanine (MOCPc) with either aluminium ((OH)AlOCPc) or zinc ( ZnOCPc ) as central metals have been prepared with (linked MOCPc-QD-MN) and without (mixed MOCPc-QD-MN) linking agents. The results presented give evidence of linkage within the components of the linked MOCPc-QD-MN. A red shift in the emission peak of QD within the linked nanocomposite compared to emission peak of QD alone was observed. Photoexcitation of both linked and mixed MOCPc-QD-MN at the excitation wavelength of the QD resulted in energy transfer from QD to the respective MOCPc while at the excitation wavelength of the MOCPc, a shift in emission peak of the linked MOCPc-QD-MN was observed resulting in large Stokes' shifts. The linked and mixed MOCPc-QD-MN were found to exhibit high triplet state quantum yields compared to the MOCPcs alone.

Preparation of a novel fluorescent nanocomposite: CeO2 / ANS by a simple method

For the first time, a novel fluorescent material, composed of CeO2/ANS nanocomposites was successfully synthesized by a simple ultrasonic method, using CeO2 nanoparticles and 8-anilino-1-naphthalenesulfonic acid (ANS) as the raw materials. The samples were characterized by scanning electron microscope (SEM), photoluminescence spectroscopy and Fourier transformation infrared spectroscopy (FTIR). The results showed that the PL intensity of the CeO2/ANS nanocomposites was higher than that of both CeO2 nanoparticles and ANS powders, and the peak wavelength was also different from the peak wavelength typical of each of the used materials, which suggests that the chemical reaction occurs between CeO2 nanoparticles and ANS molecules. In addition, the effect of the ANS concentrations on the photoluminescence of the nanocomposites was also investigated.

Fluorescent Nanocomposite Based on PVA Polymer Dots

Fluorescent Nanocomposite Based on PVA Polymer Dots

Quick and simple estimation of bacteria using a fluorescent paracetamol dimer–Au nanoparticle composite

Rapid, simple and sensitive detection of bacterial contamination is critical for safeguarding public health and the environment. Herein, we report an easy method of detection as well as enumeration of the bacterial cell number on the basis of fluorescence quenching of a non-antibacterial fluorescent nanocomposite, consisting of paracetamol dimer (PD) and Au nanoparticles (NPs), in the presence of bacteria. The composite was synthesized by reaction of paracetamol (p-hydroxyacetanilide) with HAuCl(4). The Au NPs of the composite were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction and selected area electron diffraction analysis. The paracetamol dimer in the composite showed emission peak at 435 nm when excited at 320 nm. The method successfully detected six bacterial strains with a sensitivity of 100 CFU mL(-1). The gram-positive and gram-negative bacteria quenched the fluorescence of the composite differently, making it possible to distinguish between the two. The TEM analysis showed interaction of the composite with bacteria without any apparent damage to the bacteria. The chi-square test established the accuracy of the method. Quick, non-specific and highly sensitive detection of bacteria over a broad range of logarithmic dilutions within a short span of time demonstrates the potential of this method as an alternative to conventional methods.

High-throughput Screening of Transglutaminase Activity Using Plasmonic Fluorescent Nanocomposites

We describe a high-throughput screening (HTS) assay for transglutaminase (TG) enzyme activity using plasmonic fluorescent nanocomposites. We used TG to covalently crosslink 500 μM solution of 5'-biotinamidopentylamine (BP) to N,N'-dimethylcasein (DMC) which was adsorbed onto 384-well microplates. We then bound 0.2 - 2.0 × 10(11)/mL of 10 nm gold nanoparticles-streptavidin conjugate (10 nm AuNPs-SA) to BP via biotin-streptavidin interactions. Finally, J-aggregation of cyanine 1 (25 μM) or 2 (10 μM) upon the 10 nm AuNPs elicited absorption and fluorescence signaling of TG catalysis. The cyanines could be added sequentially to elicit green (590 nm) and red (700 nm) spectral responses from the same set of reactions. Catalysis was linear (r(2) > 0.98) up to 10 min within a linear dynamic range (LDR) of 0.1 - 5 μg/mL enzyme. The multi-wavelength interrogation offered fast results (< 5 min), sensitivity (limit of detection, LOD of 5 ng or 64 fmol TG) and intermediate precision (relative standard deviation, RSD of < 20% over 42 days). Plasmonic fluorescent nanocomposites offer new ways of interrogating biomolecules in HTS format.

Preparation of fluorescent nanocomposites with CdSe/CdS quantum dots by dispersion polymerization in supercritical carbon dioxide

A new method for preparing fluorescent polymer nanocomposites based on dispersion copolymerization of methyl methacrylate and styrene in the presence of CdSe/CdS quantum dots in supercritical carbon dioxide medium is proposed. A one-step scheme of the formation of fine poly(methyl methacrylate)/polystyrene/CdSe/CdS nanocomposites is realized, and the factors influencing their photoluminescent characteristics and photochemical stability under prolonged exposure to natural conditions (sunlight) and intense UV irradiation in air are examined.

Thiolated DAB dendrimers and CdSe quantum dots nanocomposites for Cd(II) or Pb(II) sensing

Four different generation of thiol-DAB dendrimers were synthesized, S-DAB-Gx (x=1, 2, 3 and 5), and coupled with CdSe quantum dots, to obtain fluorescent nanocomposites as metal ions sensing. Cd(II) and Pb(II) showed the higher enhancement and quenching effects respectively towards the fluorescence of S-DAB-G5-CdSe nanocomposite. The fluorescence enhancement provoked by Cd(II) can be linearized using a Henderson–Hasselbalch type equation and the quenching provoked by Pb(II) can be linearized by a Stern–Volmer equation. The sensor responds to Cd(II) ion in the 0.05–0.7μM concentration range and to Pb(II) ion in the 0.01–0.15mM concentration range with a LOD of 0.06mM. The sensor has selectivity limitations but its dendrimer configuration has analytical advantages.

Synthesis and luminescence properties for europium oxide nanotubes

Abstract A novel high temperature sensitive fluorescent nanocomposite has been successfully synthesized by an economic hydrothermal method using carbon nanotubes (CNTs), europium oxide, and sodium dodecyl benzene sulfonate (SDBS). To our great interest, the nanocomposites show high temperature sensitivity after calcinations at various temperatures, suggesting a synergetic effect of CNTs and europium oxide which leads to ultrahigh fluorescence intensity of europium oxide nanotubes. When the novel high temperature sensitive fluorescent nanocomposites were calcined beyond 620 °C for 4 h, the obtained nanocomposites have a strong emission peak at around 540 and 580 nm, due to the 5D0 → 7Fj (j = 0, 1) forced electric dipole transition of Eu3+ ions. In turn, the emission spectra showed a slight blue shift. The intensity of this photoluminescence (PL) band is remarkably temperature-dependent and promotes strongly beyond 620 °C. This novel feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu3+ energy levels. The novel high temperature sensitive fluorescent nanocomposite has potential applications in high temperature warning materials, sensors and field emission displays. It is also interesting to discover that CNTs have the effect of fluorescence quenching.

Porphyrin-magnetite nanoconjugates for biological imaging

BackgroundThe use of silica coated magnetic nanoparticles as contrast agents has resulted in the production of highly stable, non-toxic solutions that can be manipulated via an external magnetic field. As a result, the interaction of these nanocomposites with cells is of vital importance in understanding their behaviour and biocompatibility. Here we report the preparation, characterisation and potential application of new "two-in-one" magnetic fluorescent nanocomposites composed of silica-coated magnetite nanoparticles covalently linked to a porphyrin moiety.MethodThe experiments were performed by administering porphyrin functionalised silica-coated magnetite nanoparticles to THP-1 cells, a human acute monocytic leukaemia cell line. Cells were cultured in RPMI 1640 medium with 25 mM HEPES supplemented with heat-inactivated foetal bovine serum (FBS).ResultsWe have synthesised, characterised and analysed in vitro, a new multimodal (magnetic and fluorescent) porphyrin magnetic nanoparticle composite (PMNC). Initial co-incubation experiments performed with THP-1 macrophage cells were promising; however the PMNC photobleached under confocal microscopy study. β-mercaptoethanol (β-ME) was employed to counteract this problem and resulted not only in enhanced fluorescence emission, but also allowed for elongated imaging and increased exposure times of the PMNC in a cellular environment.ConclusionOur experiments have demonstrated that β-ME visibly enhances the emission intensity. No deleterious effects to the cells were witnessed upon co-incubation with β-ME alone and no increases in background fluorescence were recorded. These results should present an interest for further development of in vitro biological imaging techniques.

Label-Free Biosensing Based on Multilayer Fluorescent Nanocomposites and a Cationic Polymeric Transducer

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Fabrication of fine powder fluorescent polymer nanocomposites based on CdSe quantum dots using supercritical carbon dioxide

A method of diffusion introduction of CdSe quantum dots (QDs) into polymer microparticles in supercritical carbon dioxide was proposed, implemented, and studied. Photoluminescence (PL) spectra of fine nanocomposite powders based on polymethyl methacrylate/polystyrene and CdSe QDs were measured and analyzed. Produced samples are characterized by a pronounced PL band with a general maximum at 620 nm. It was found that QD introduction into polymer microparticles by impregnation in a supercritical carbon dioxide medium efficiently stabilizes them in space and significantly increases photochemical stability of their luminescence characteristics.

Fabrication of rare-earth/quantum-dot nanocomposites for color-tunable sensing applications

We developed a new fluorescent nanocomposite by using a layer-by-layer approach to link NaYF4:Ce,Tb rare-earth (RE) nanocrystals and CdSe/ZnSe semiconductor quantum dots (QDs) with opposite charges. Under ultraviolet light excitation, the nanocomposites exhibited both the green Tb emission centered at 550 nm, and the red QD emission at 650 nm. Sensing applications showed that the red QD emission was quenched by trace amount of Cu2+ (or Ag+) ions due to the ion displacement mechanism, while the green RE emission kept constant. Thus, the nanocomposites with the decreased QD/RE emission intensity ratio and changed fluorescence output color provided a visible “indicator” to detect metal ions quantificationally. In comparison with single emission materials, the dual emission nanocomposites can be a more reliable probe for various sensing applications.

Preparation of γ-Al2O3 porous nanosolid/fluorescein fluorescent nanocomposites by a simple method

Abstract γ-Al2O3 porous nanosolid has been successfully prepared by a hydrothermal hot-press method, using γ-Al2O3 nanoparticles as the raw material. Furthermore, an orange-red compound, C20H12O5, that exhibits intense fluorescence in alkaline solution, fluorescein was assembled into the pores of γ-Al2O3 porous nanosolids by a simple method, thus a γ-Al2O3/fluorescein nanocomposite was obtained. Because of the interaction between fluorescein molecules and the surface atoms of pores of γ-Al2O3 porous nanosolid, a photoluminescent enhancement was observed in γ-Al2O3/fluorescein nanocomposite by comparing with that of fluorescein. In addition, the effect of the fluorescein concentrations on the photoluminescence of the nanocomposites was also investigated.

Deposition and Characterization of CdSe Nanoparticles in Polymeric Materials

Cadmium selenide nanoparticles coated with zinc sulphide CdSe/ZnS were prepared using dual source method. The composites were fabricated by stabilizing chemically synthesized semiconductor CdSe/ZnS into Laurylmethacrylate (LMA) and ethyleneglycol dimethacrylate (EGDMA) matrices in the presence of tri-n-octylphosphine (TOP). CdSe/ZnS were dispersed in toluene as a compatible medium for the polymerization and cross-linking of poly Laurylmethacrylate (LMA) networks. Transparent, fluorescent and flexible nano composites (NCs) materials resulted. The nano size particles and polymer composites were characterized by XRD, TG-DTA, IR, TEM and SEM.

Preparation and Application of Fluorescein Isothiocyanate Fluorophore Nano-composites

Nano-composite fluorescence with silica shell was prepared by improving Stöber route. The precursor was obtained via chemical reaction of fluorescein isothiocyanate (FITC) and 3-aminopropyltriethoxysilane (APTEOS). The controlled hydrolysis and condensation of tetraethylorthosilicate (TEOS) leaded to the formation of organic-inorganic nano-composites fluorescent. The image of transmission electron microscope (TEM) showed that the nano-composites with a diameter of approximately 70 nm were uniform, spherical and monodispersed. The nano-composites fluorescence significantly reduced dye leaching and had strong fluorescence when they were washed by water for several times. Green fluorescence was observed by laser scanning confocal microscope (LSCM) from the bovine scrum albumin (BSA) labeled with fluorescent nano-composites.