Silica-coated nanocomposites of magnetic nanoparticles and quantum dots

Quantum dots (QDs) and magnetic nanoparticles (MPs) are of interest for biological imaging, drug targeting, and bioconjugation because of their unique optoelectronic and magnetic properties, respectively. To provide for water solubility and biocompatibility, QDs and MPs were encapsulated within a silica shell using a reverse microemulsion synthesis. The resulting SiO2/MP-QD nanocomposite particles present a unique combination of magnetic and optical properties. Their nonporous silica shell allows them to be surface modified for bioconjugation in various biomedical applications.     

Fluorescence detection of Escherichia coli on mannose modified ZnTe quantum dots

Rapid detection and identification of Escherichia coli(E.coli) is essential to prevent its quickly spread.In this study,a novel fluorescence probe based on ZnTe quantum dots(QDs) modified by mannose(MAN)had been prepared for the determination of E.coli.The results showed that the obtained QDs showed excellent selectivity toward E.coli,and presented a good linearity in range of 1.0×10⁵～1.0×10⁸ CFU/mL.The optimum fluorescence intensity for detecting E. coli was found to be at...     

Surface modification of quantum dots and magnetic nanoparticles with PEG-conjugated chitosan derivatives for biological applications

In this paper, amphiphilic chitosan derivatives (N-octyl-N-mPEG-chitosan, mPEG = poly(ethylene glycol) monomethyl ether; OPEGC) were successfully synthesised via the Schiff base reduction reaction of chitosan and mPEG-aldehyde, or octanal, with chitosan acting as the backbone of the grafted copolymers, and mPEG-aldehyde providing the hydrophilic chain or octanal providing the hydrophobic alkyl chain. The synthesis was confirmed by characterisation employing Fourier transform infrared spectroscopy (FTIR) and ¹H NMR. In the subsequent procedure, water-soluble quantum dots (QDs) and iron(II,III) oxide (IO) nanoparticles, widely used as nanoprobes in medical applications, were produced by the incorporation of QDs or IO inside the polymeric micelle core. Finally, the optical properties of QDs incorporated into OPEGC (OPEGC@QDs) were characterised by UV-VIS spectroscopy, fluorescence spectroscopy, cell viability was obtained through MTT, and the morphology of their assembly formed in water were observed by atomic force microscope (AFM) and transmission electron microscope (TEM) and the QDs content of OPEGC@QDs was calculated following thermo gravimetric analysis (TGA). In addition, the properties of IO incorporated into OPEGC (OPEGC@IO) were characterised by vibrating sample magnetometry (VSM), FT-IR, MTT, TGA, AFM, and TEM. The results indicated that the OPEGC composite nanoparticles with size narrowly distributed, good water solubility, and low cytotoxicity were prepared here, which represented a high quantum yield or good super-paramagnetism.     

Study of the bioeffects of CdTe quantum dots on Escherichia coli cells

Quantum dots (QDs) hold great potential for applications in nanomedicine, however, only a few studies investigate their toxic- and bio-effects. Using Escherichia coli (E. coli) cells as model, we found that CdTe QDs exhibited a dose-dependent inhibitory effect on cell growth by microcalorimetric technique and optical density (OD(600)). The growth rate constants (k) were determined, which showed that they were related to the concentration of QDs. The mechanism of cytotoxicity of QDs was also studied through the attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra, fluorescence (FL) polarization, and scanning electron microscopy (SEM). It was clear that the cell out membrane was changed or damaged by the addition of QDs. Taken together, the results indicated that CdTe QDs have cytotoxic effects on E. coli cells, and this effects might attribute to the damaged structure of the cell out membrane, thus QDs and by-products (free radicals, reactive oxygen species (ROS), and free Cd(2+)) which might enter the cells.     

Synthesis of carbohydrate-conjugated nanoparticles and quantum dots

Nanoparticle-based probes are emerging as alternatives to molecular probes due to their various advantages, such as bright and tunable optical property, enhanced chemical and photochemical stability, and ease of introduction of multifunctionality. This work presents a simple and general approach for functionalizing various nanoparticle systems for use as glycobiological probes. Silica-coated nanoparticles of Ag, Fe3O4, and ZnS-CdSe were synthesized and functionalized with dextran. The resulting 10-40-nm-sized particles were robust, water-soluble, colloidally stable, and biochemically active.     

SERS-based sandwich immunoassay using antibody coated magnetic nanoparticles for Escherichia coli enumeration

A method combining immunomagnetic separation (IMS) and surface-enhanced Raman scattering (SERS) was developed to enumerate Escherichia coli (E. coli). Gold-coated magnetic spherical nanoparticles were prepared by immobilizing biotin-labeled anti-E. coli antibodies onto avidin-coated magnetic nanoparticles and used in the separation and concentration of the E. coli cells. Raman labels have been constructed using rod shaped gold nanoparticles coated with 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. Then DTNB-labeled gold nanorods were interacted with gold-coated magnetic spherical nanoparticle-antibody-E. coli complex. The capture efficiency and calibration graphs were obtained and examined in different E. coli concentrations (10(1)-10(7) cfu mL(-1)). The correlation between the concentration of bacteria and SERS signal was found to be linear within the range of 10(1)-10(4) cfu mL(-1) (R(2) = 0.992). The limit of detection (LOD) and limit of quantification (LOQ) values of the developed method were found to be 8 and 24 cfu mL(-1), respectively. The selectivity of the developed immunoassay was examined with Enterobacter aerogenes, Enterobacter dissolvens, and Salmonella enteriditis which did not produce any significant response. The ability of the immunoassay to detect E. coli in real water samples was also investigated and the results were compared with the experimental results from plate-counting methods. There was no significant difference between the methods that were compared (p > 0.05). This method is rapid and sensitive to target organisms with a total analysis time of less than 70 min.     

A perspective on bioconjugated nanoparticles and quantum dots

Bioconjugated nanoparticles and quantum dots are among the most exciting nanomaterials with promising application potentials in nanomedicine field. These applications include biosensing, bioimaging, bioassay, targeted drug delivery and new therapeutic agents or method development. Although most of these applications are based on the optical properties of nanoparticle materials such as surface plasmon resonance, surface enhanced Raman scattering and strong photoluminescence, other aspects of nanoparticles such as the catalytic effect and amplification effect associated with the nanoscale dimension have also been explored. This review presents a narrative summary on the use of bioconjugated nanoparticles and quantum dots for biological applications, along with a discussion on some critical challenges existing in the field and possible solutions that have been or are being developed to overcome these challenges.     

水溶性CdSe量子点的合成及其作为荧光探针对大肠杆菌的快速检测

采用水相法以谷胱甘肽为稳定剂合成高稳定性的CdSe量子点,利用化学偶联剂的作用使得量子点表面基团与菌体之间的成功结合,对偶联的条件进行了优化.基于荧光分析法建立了一种快速简便的大肠杆菌检测定量分析方法.研究结果表明:合成的量子点具有稳定、荧光性能良好等突出优点.通过偶联剂量子点能与大肠杆菌结合,其荧光强度与大肠杆菌浓度...     

Ultrafine biocompatible chitosan nanoparticles encapsulating multi-coloured quantum dots for bioapplications

Owing to their excellent optical properties, luminescent semi-conductor quantum dots (QDs) have proven themselves to be an attractive choice in biological labeling. However, there exists the concern of cytotoxicity in using these heavy metal-based nanoparticles as molecular probes. In order to improve their general biocompatibility, CdSe/ZnS QDS are encapsulated in the natural biopolymer chitosan, forming monodisperse chitosan nanoparticles in the range of 60 nm in 1 single step. This straight forward method also allows for the synthesis of chitosan nanoparticles encapsulating multi-coloured QDs. In vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests on primary myoblast cells suggest that the cytotoxicity of the QDs is greatly reduced after chitosan encapsulation. At the same time, fluorescence confocal microscopy studies also prove that nanoparticles are small enough to be internalized into the myoblast cells. Our results show the ease of synthesizing biocompatible, nanometer-sized chitosan nanoparticles encapsulating QDs and their promise in biological applications such as ultra-sensitive bio-detection and labeling of biomolecules.     

Synthesis and electronic properties of semiconductor nanoparticles/quantum dots

This review examines recent work on the synthesis, characterisation and potential applications of semiconductor nanoparticles (quantum dots). Recent advances in single quatum dot spectroscopy is also reviewed.     

Electrochemical charge transfer mediated by metal nanoparticles and quantum dots

Electron transfer processes mediated by nanostructured materials assembled at electrode surfaces underpin fundamental processes in novel electrochemical sensors, light energy conversion systems and molecular electronics. Functionalisation of electrode surfaces with hierarchical architectures incorporating self-assembling molecular systems and materials, such as metal nanostructures, quantum dots, carbon nanotubes, graphene or biomolecules have been intensively studied over the last 20 years. Important steps have been made towards the rationalisation of the charge transfer dynamics from redox species in solution across molecular self-assembling systems to electrode surfaces. For instance, a unified picture has emerged describing the factors which determine the rate constant for electron transfer processes across rigid self-assembling molecular barriers. An increasing bulk of evidence has recently shown that the incorporation of nanomaterials into self-assembling monolayers leads to an entirely different electrochemical behaviour. This perspective rationalises some of the key observations associated with nanoparticle mediated charge transfer, such as the apparent distance independent charge transfer resistance observed for redox species in solution. This behaviour only manifests itself clearly in the case where the probability of direct charge transfer from the redox probe to the electrode is strongly attenuated by self-assembling molecular barriers. Here we will highlight specific issues concerning self-assembled monolayers as blocking barriers prior to discussing the effect of nanoparticles on the electrochemical response of the system. Selected examples will provide conclusive evidence that the extent of charge transfer mediation is determined by the overlap between the density of states of the nanostructures and the energy levels of redox species in solution. Only in the case where a strong overlap exists between the energy levels of the two components, the nanostructures behave as "electron launchers", allowing efficient charge transfer across insulating molecular layers.     

A comparative physicochemical study of unsymmetrical indium phthalocyanines in the presence of magnetic nanoparticles or quantum dots

Asymmetric indium phthalocyanine (3, containing an NH₂ group) was conjugated (via an amide bond) to magnetic nanoparticle (MNP) functionalized with carboxylic acid or glutathione-capped CdTe/ZnSe/ZnO quantum dots to form 3-MNPs or 3-QDs. Techniques such as time-resolved fluorescence measurements, transmission electron microscopy, XPS, elemental analysis, FTIR, NMR (¹H, ¹³C, and cozy), electronic spectroscopy, as well as mass spectroscopy were employed to characterize 3 and its nanoconjugates. The phthalocyanine conjugated to quantum dot (3-QDs) possesses the lowest Ф_pd higher Ф_? and Ф_T as well as longer triplet lifetimes compares to 3-MNPs and free phthalocyanine.     

Selective binding of mannose-encapsulated gold nanoparticles to type 1 pili in Escherichia coli

The synthesis, characterization and biological application of mannose encapsulated gold nanoparticles (m-AuNP) are reported. m-AuNP is well dispersed and very stable without aggregation in the media of broad ion strength and pH ranges. The selective binding of m-AuNP to the mannose adhesin FimH of bacterial type 1 pili is demonstrated using transmission electron microscopy. The competition assay with free mannose suggests that m-AuNP binds FimH better than free mannose does. This work demonstrates that carbohydrate attached nanoparticles can be used as an efficient affinity label and a multi-ligand carrier in a biological system.     

Chemically fabricated magnetic quantum dots of InP:Mn

Quantum dots of InP:Mn are chemically prepared by following hot colloidal nanochemistry with starting precursors that obviate the need for external surfactant. These quantum dots are uniform spheres with 3-nm diameters; they are crystalline, photoluminescent, and magnetic. The crystallographic and optical properties are similar to those of undoped InP nanocrystallites, while the magnetism is consistent with the ferromagnetic response observed in a class of diluted magnetic semiconductors. Because of the ultrafine sizes, the sample shows superparamagnetic behavior, whereas ferromagnetic hysteresis loops are clearly seen below the blocking temperature. Structural characterization and analysis confirm that the magnetism in these quantum dots is not due to segregated binary MnP or MnO phases and that they truly represent a homogeneous dilute magnetic semiconductor.     

Selective fluorescence sensor based on ion-imprinted polymer-modified quantum dots for trace detection of Cr(VI) in aqueous solution

Analytical and Bioanalytical Chemistry - A new fluorescence sensor (QDs-IIP), based on ion-imprinted polymers (IIP) as recognition element and Mn-doped ZnS quantum dots (QDs) as fluorophore, was...     

Phosphonate-anchored monolayers for antibody binding to magnetic nanoparticles

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody.     

Multifunctional compact zwitterionic ligands for preparing robust biocompatible semiconductor quantum dots and gold nanoparticles

We describe the synthesis of a series of four different ligands which are used to prepare hydrophilic, biocompatible luminescent quantum dots (QDs) and gold nanoparticles (AuNPs). Overall, the ligands are designed to be compact while still imparting a zwitterionic character to the NPs. Ligands are synthesized appended to a bidentate dihydrolipoic acid- (DHLA) anchor group, allowing for high-affinity NP attachment, and simultaneously incorporate tertiary amines along with carboxyl and/or hydroxyl groups. These are placed in close proximity within the ligand structure and their capacity for joint ionization imparts the requisite zwitterionic nature to the nanocrystal. QDs functionalized with the four different compact ligands were subjected to extensive physical characterization including surface charge, wettability, hydrodynamic size, and tolerance to a wide pH range or high salt concentration over time. The utility of the compact ligand coated QDs was further examined by testing of direct conjugation to polyhistidine-appended protein and peptides, aqueous covalent-coupling chemistry, and the ability to engage in F?rster resonance energy transfer (FRET). Conjugating cell penetrating peptides to the compact ligand coated QD series facilitated their rapid and efficient cellular uptake, while subsequent cytotoxicity tests showed no apparent decreases in cell viability. In vivo biocompatibility was also demonstrated by microinjecting the compact ligand coated QDs into cells and monitoring their stability over time. Inherent benefits of the ligand design could be extended beyond QDs as AuNPs functionalized with the same compact ligand series showed similar colloidal properties. The strong potential of these ligands to expand NP capabilities in many biological applications is highlighted.