Lectin-gated and glycan functionalized mesoporous silica nanocontainers for targeting cancer cells overexpressing Lewis X antigen.

Gated mesoporous silica nanoparticles can deliver payload upon the application of a predefined stimulus, and therefore are promising drug delivery systems. Despite their important role, relatively low emphasis has been placed on the design of gating systems that actively target carbohydrate tumor cell membrane receptors. We describe herein a new Lewis X (Lex) antigen-targeted delivery system comprising mesoporous silica nanoparticles (MSNs) loaded with ATTO 430LS dye, functionalized with a Lex derivative (1) and capped with a fucose-specific carbohydrate-binding protein (Aleuria aurantia lectin (AAL)). This design takes advantage of the affinity of AAL for Lex overexpressed receptors in certain cancer cells. In the proximity of the cells, AAL is detached from MSNs to bind Lex, and selectins in the cells bind Lex in the gated MSNs, thereby inducing cargo delivery. Gated MSNs are nontoxic to colon cancer DLD-1 cells, and ATTO 430LS dye delivered correlated with the amount of Lex antigen overexpressed at the DLD-1 cell surface. This is one of the few examples of MSNs using biologically relevant glycans for both capping (via interaction with AAL) and targeting (via interaction with overexpressed Lex at the cell membrane).

Blocking probe as a potential tool for detection of single nucleotide DNA mutations: design and performance.

Developing strategies to detect single nucleotide DNA mutations associated with treatment decisions in cancer patients from liquid biopsies is a rapidly emerging area of personalized medicine that requires high specificity. Here we report how to design an easy enzyme-free approach that could create a platform for detection of L858R mutation of EGFR that is a predictive biomarker of tyrosine kinase treatment in many cancers. This approach includes the addition of blocking probes with the antisense ssDNA at different blocking positions and different concentrations such as to avoid re-annealing with the respective sense ssDNA. The successful blocking strategy was corroborated by fluorescence spectroscopy in solution using two distinct FRET pairs and quartz crystal microbalance with dissipation (QCM-D) measurements under comparable experimental conditions, as the hybridization rate-limiting step in both methods is the nucleation process. The efficiency of hybridization of each blocking probe was strongly dependent on its position particularly when the analyte possesses a secondary hairpin-structure. We tested the performance of blocking probes in combination with gold nanoparticles; the obtained results were in agreement with those of QCM-D. These findings could facilitate the development of better biosensors, especially those using probes containing secondary structure.

Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation.

Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials for sensing and optical applications. NPs can spontaneously assemble at a liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening with the addition of electrolyte or pH adjustment. The in situ modulation of the nanoparticle position on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision.

Chemical solution approaches to YBa2Cu3O7_delta-Au nanocomposite superconducting thin films.

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.

Two-dimensional quasistatic stationary short range surface plasmons in flat nanoprisms.

We report on the nanometer scale spectral imaging of surface plasmons within individual silver triangular nanoprisms by electron energy loss spectroscopy and on related discrete dipole approximation simulations. A dependence of the energy and intensity of the three detected modes as function of the edge length is clearly identified both experimentally and with simulations. We show that for experimentally available prisms (edge lengths ca. 70 to 300 nm) the energies and intensities of the different modes show a monotonic dependence as function of the aspect ratio of the prisms. For shorter or longer prisms, deviations to this behavior are identified thanks to simulations. These modes have symmetric charge distribution and result from the strong coupling of the upper and lower triangular surfaces. They also form a standing wave in the in-plane direction and are identified as quasistatic short range surface plasmons of different orders as emphasized within a continuum dielectric model. This model explains in simple terms the measured and simulated energy and intensity changes as function of geometric parameters. By providing a unified vision of surface plasmons in platelets, such a model should be useful for engineering of the optical properties of metallic nanoplatelets.

Quantitative determination of the size dependence of surface plasmon resonance damping in single Ag@SiO(2) nanoparticles.

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

Field gradient imaging of nanoparticle systems: analysis of geometry and surface coating effects.

In this work we compare the standard imaging of various types of nanoparticles deposited on surfaces by atomic force microscopy (AFM) with a complementary analysis of the same samples by either electrostatic force microscopy (EFM) or magnetic force microscopy (MFM). Experiments were carried out on gold nanoparticles (decahedrons and stars) and two different iron oxide systems: goethite (alpha-FeOOH) and hematite (alpha-Fe(2)O(3)). Regardless of the particular geometry, the EFM signal appears to be stronger on edges or tips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out on iron oxide particles. Apart from the structural analysis, we analyzed the influence of a shell layer deposited on the gold and iron oxide particles, the shell being amorphous SiO(2). Although the silica layer was found to have an insulating effect around the particles, in all cases EFM/MFM measurements could still be performed by the proper choice of the scan lift height (with an eventual slight increase of the sample bias, where applicable).

Influence of silver nanoparticles concentration on the alpha- to beta-phase transformation and the physical properties of silver nanoparticles doped poly(vinylidene fluoride) nanocomposites.

This paper describes the processing of silver nanoparticle doped poly(vinylidene fluoride). The effect of the dopant concentration on the alpha- to beta-phase transformation of the polymer as well as in the morphological, thermal, optical and dielectric properties of the nanocomposites was investigated. Spherical silver nanoparticles were incorporated into the poly(vinylidene fluoride) polymeric matrix by the solvent casting method, with different Ag concentrations. Well-dispersed Ag nanoparticles act as nucleation centers, increasing the degree of crystallinity of the nanocomposites. Homogeneous dispersion of silver nanoparticles is demonstrated through the presence of surface plasmon resonance absorption in the nanocomposites. The alpha- to beta-phase transformation was achieved in the polymer matrix and a maximum of approximately equal to 70% of beta-PVDF was reached at 80 degrees C and a stretching ratio of 400%. The dielectric constant of the nanocomposites increases with increasing metal nanoparticle concentration, up to approximately equal to 26 at 0.020 wt% Ag content. The alpha- to beta-phase transformation affects both the dielectric response and the surface plasmon resonance.

Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging.

Using low-loss energy-filtering transmission electron microscopy (EFTEM) imaging, we map surface plasmon resonances (SPRs) at optical wavelengths on single triangular silver nanoprisms. We show that EFTEM imaging combining high spatial sampling and high energy resolution enables the detection and for the first time, to the best of our knowledge, mapping at the nanoscale of an extra multipolar SPR on these nanoparticles. As illustrated on a 276.5 nm long nanoprism, this eigenmode is found to be enhanced on the three edges where it exhibits a two-lobe distribution.

Studies on the attachment of DNA to silica-coated nanoparticles through a Diels-Alder reaction.

A new method has been investigated for the functionalization of gold nanoparticles with DNA. Silica-coated nanoparticles functionalized with a maleimide have been prepared. These particles are designed to react with modified DNA containing a diene functionality at one end of the molecule. The result would be the formation of a more stable attachment of the DNA to the particle through a Diels-Alder reaction. This covalent attachment would not be susceptible to ligand exchanges, which are known to occur in the conventional DNA functionalization of gold nanoparticles.

Photodegradation of SiO2-coated CdS nanoparticles within silica gels.

A comparative study of the photodegradation of CdS nanoparticles coated with silica shells dispersed in water and embedded in two silica gels with different pore size is presented. Although encapsulation of the quantum dots in a silica shell previously was proven to provide a basically permanent protection against light-induced surface oxidation (photodegradation), this protection is not always maintained when the coated particles are incorporated within different silica gels. Degradation of the CdS occurs when the coated particles are incorporated within silica gels with an open structure, which suggests that the shells somehow crack due to tension in the gel structure. This behavior is analyzed by absorption and luminescence spectroscopies, electron microscopy, and nitrogen sorption.