Rapid and Sensitive SERS Detection of Bisphenol A Using Self-assembled Graphitic Substrates.

We have prepared and tested a new surface enhanced Raman scattering (SERS) substrate based on self-assembled graphitic sheets to detect bisphenol A (BPA) in plastic consumer goods. Transmission electron microscopy (TEM) and atomic-force microscopy (AFM) were used to characterize the structure of the graphitic sheets and showed a lattice spacing of 0.24 nm and layer height of 0.34 nm. These values were comparable to single monolayer graphene. The effective SERS detection limit of this method is 1 µM BPA, which is lower than the European Union specific migration limit for BPA of 0.6 mg/kg (2.6 µM). When used in salt solutions, graphitic sheets exhibited ultra-sensitivity toward BPA of 0.025 M to 2 M, which was broader than physiological ionic strength (0.14 M) and urinary NaCl (0.17 M). Our results demonstrated that this graphitic sheet based SERS detection platform can be used to determine BPA levels leached from commercial polycarbonate plastic products and for on-site rapid analysis with good results.

Nanoscale characterization illustrates the cisplatin-mediated biomechanical changes of B16-F10 melanoma cells.

Cells reorganize their membrane biomechanical dynamics in response to environmental stimuli or inhibitors associated with their physiological/pathological processes, and disease therapeutics. To validate the biophysical dynamics during cell exposure to anti-cancer drugs, we investigate the nanoscale biological characterization in melanoma cells undergoing cisplatin treatment. Using atomic force microscopy, we demonstrate that the cellular morphology and membrane ultrastructure are altered after exposure to cisplatin. In contrast to their normal spindle-like shape, cisplatin causes cell deformation rendering cells flat and enlarged, which increases the cell area by 3-4 fold. Additionally, cisplatin decreases the topography height values for both the cytoplasmic and nuclear regions (by 40-80% and 60%, respectively). Furthermore, cisplatin increases the cytoplasmic root mean square roughness by 110-240% in correlation with the drug concentration and attenuates the nuclear RMS by 60%. Moreover, the cellular adhesion force was enhanced, while the Young's modulus elasticity was attenuated by ∼2 and ∼2.3 fold, respectively. F-actin phalloidin staining revealed that cisplatin enlarges the cell size through enhanced stress fiber formation and promotes cytoskeletal reorganization. Immunoblot analyses further revealed that the activities of focal adhesion proteins, such as FAK and c-Src, are upregulated by cisplatin through phosphorylation at tyrosine 397 and 530, respectively. Collectively, these results show that cisplatin-treated melanoma cells not only exhibit the upregulation of FAK-mediated signaling to enhance the cytoskeleton mechanical stretch, but also promote the cytoskeletal rearrangement resulting in 43% decrease in the cell modulus. These mechanisms thus promote the malignancy and invasiveness of the melanoma cells.

Eco-friendly synthesis of shrimp egg-derived carbon dots for fluorescent bioimaging.

Developing synthetic methods to produce carbon dots (CDs) using natural biomass or other readily available carbon sources are currently being explored. We describe a simple and green synthetic method for preparing fluorescent CDs by water extraction from heat-treated shrimp eggs (SE-CDs). The SE-CDs appeared spherical with an average size of 3.25 ± 1.06 nm. Elemental analysis indicate that the SE-CDs have functional groups such as C-OH, C-O-C, CO, and C-H on the surface which give rise to a series of emissive traps between π-π* states. SE-CDs also showed a broad emission range with excellent quantum yield of 18.5 ± 2.6%. In addition, when compared with commonly used traditional CdSe and CdTe nanocrystals, SE-CDs were bio-tolerable to cell at high doses (200 µgml(-1)) in MTT assay. Thus, SE-CDs are very promising alternatives to semiconductor-based quantum dots for in vitro and in vivo bioimaging applications.

Porosity-controlled eggshell membrane as 3D SERS-active substrate.

We report on the fabrication of a surface-enhanced Raman scattering (SERS) platform, comprised of a three-dimensional (3D) porous eggshell membrane (ESM) scaffold decorated with Ag nanoparticles (NPs). Both native and treated ESM were used, where the treated ESM pore size and fiber crossing density was controlled by timed exposure to hydrogen peroxide (H2O2). Ag NPs were synthesized in situ by reduction of silver nitrate with ascorbic acid. Our results demonstrate that H2O2-treated Ag-ESM provides a more densely packed 3D network of active material, which leads to consistently higher SERS enhancement than untreated Ag-ESM substrates.

Effect of the surface chemistry of insulin fibrils on the aggregation rate.

Structure transition cascade: Insulin fibrils undergo a secondary structural transition-from the α-rich to the ß-rich form-upon progressively increasing the incubation time from 0.5 to ten hours. Atomic force microscopy measurements show that the fibril surface chemistry changes from hydrophilic to hydrophobic and the aggregation rate increases fivefold.

Label-free glucose detection using cantilever sensor technology based on gravimetric detection principles.

Efficient maintenance of glucose homeostasis is a major challenge in diabetes therapy, where accurate and reliable glucose level detection is required. Though several methods are currently used, these suffer from impaired response and often unpredictable drift, making them unsuitable for long-term therapeutic practice. In this study, we demonstrate a method that uses a functionalized atomic force microscope (AFM) cantilever as the sensor for reliable glucose detection with sufficient sensitivity and selectivity for clinical use. We first modified the AFM tip with aminopropylsilatrane (APS) and then adsorbed glucose-specific lectin concanavalin A (Con A) onto the surface. The Con A/APS-modified probes were then used to detect glucose by monitoring shifts in the cantilever resonance frequency. To confirm the molecule-specific interaction, AFM topographical images were acquired of identically treated silicon substrates which indicated a specific attachment for glucose-Con A and not for galactose-Con A. These results demonstrate that by monitoring the frequency shift of the AFM cantilever, this sensing system can detect the interaction between Con A and glucose, one of the biomolecule recognition processes, and may assist in the detection and mass quantification of glucose for clinical applications with very high sensitivity.

Hydrogen peroxide treatment of eggshell membrane to control porosity.

The eggshell membrane (ESM) is a naturally occurring biological polymer, which can be extracted from eggshells, and has been used for adsorption of dyes or heavy metals, as a semipermeable membrane to control particle transport, and as a natural biocompatible material for tissue replacement. In this study, we used hydrogen peroxide to control the pore size and fibre crossing density of the ESM. Structural and chemical properties were investigated using AFM, optical microscopy, contact angle, and FTIR. We show that the structure and permeability of the ESM can be controlled by timed exposure to H2O2 and we demonstrate this effect using red blood cells. This process provides a simple method for preparing biocompatible membranes, with controlled selectivity for biofiltration applications.

Substrate-free self-assembled SiOx-core nanodots from alkylalkoxysilane as a multicolor photoluminescence source for intravital imaging.

Intravital fluorescence imaging has great potential in biological and biomedical research, as it provides the ability to directly observe biological structures and processes in their natural state. Contrast agents for intravital imaging applications should exhibit good biocompatibility, multiphoton fluorescence, and long emission. Carbon nanodots and semiconductor nanocrystals meet these requirements in most cases, with the added benefit that their properties can be 'tuned' for specific applications by controlling the size and surface chemistry of the nanoparticles. Here, we report on a simple heat-assisted strategy to fabricate SiOx-core self-assembled nanodots using self-assembled monolayer (SAM) materials. Our results demonstrate that substrate-free self-assembled nanodots from alkylalkoxysilane exhibit controllable structural and chemical characteristics that are well suited for applications in biological, biomedical, and clinical research, and may find further use in optoelectronic and sensor devices.

A Spirobifluorene Derivative as a Single-Emitting Component for a Highly Efficient White Organic Electroluminescent Device.

We describe how the morphology, photoluminescence (PL), and electroluminescence properties of 2,2',7,7'-tetrakis(pyren-1-yl)-9,9'-spirobifluorene (TPSBF) are related to its film thickness and how, under optimized conditions, the three main PL emissions constitute a form of white light. We fabricated high-brightness, broad-spectrum, white-light organic light-emitting diodes, incorporating a single emission layer of the blue-light-emitting material TPSBF, which comprises four pyrene units linked to a spirobifluorene core. An organic light-emitting device with the configuration indium tin oxide (170 nm)/4,4',4''-tris[N-(2-naphthyl)-N-phenylamino]triphenylamine (15 nm)/4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (65 nm)/TPSBF (50 nm)/tris(8-hydroxyquinoline)aluminum (30 nm)/LiF (0.8 nm)/Al (200 nm) exhibited a broad-spectrum white emission with a maximum luminescence and current efficiency of 57 680 cd m-2 and 6.51 cd A-1 , respectively, and Commission International De l'Eclairage coordinates of (0.29,0.36).

Alignment of gold nanoparticles using insulin fibrils as a sacrificial biotemplate.

Insulin fibrils were used as a biotemplate for creating gold nanoparticle chains on glass substrates, and then subsequently removed by exposing the samples to a low-pressure plasma, leaving the gold nanoparticles on the glass surface in their template positions.

Molecular orientation and film structure of gramicidin on highly oriented pyrolitic graphite.

Gramicidin molecules were deposited on HOPG surfaces to characterize molecular orientation and film structure as a function of surface coverage and temperature. At low coverage (0.35 ML), the molecules adopted a flat-lying orientation and formed dendritic islands. At higher coverage (0.86 ML), molecules adopted an upright orientation and circular holes formed in the films. The upright film exhibited higher adhesion in force spectroscopy measurements, supporting our molecular orientation assignments. At elevated deposition temperatures (50 °C) on the higher coverage films, the holes were still present, but partially filled in. At 60 °C the film structure was quite different, forming tall irregular islands without the circular holes observed at lower temperatures. These results demonstrate that gramicidin molecular orientation and film structure on HOPG can be controlled by tuning the surface coverage and deposition temperature.

Ferritin protein imaging and detection by magnetic force microscopy.

Magnetic force microscopy was used to image and detect ferritin proteins and the strength of the magnetic signal is discussed, revealing a large workable lift height between the magnetic tip and the ferritin sample.

Constructions of silver nanowires and copper oxide microrings by a surface-formation technique.

We demonstrate a simple method to synthesize silver wires by thermal reduction of aqueous AgNO(3) droplet with catalytic anatase TiO(2) nanoparticles which were spin-coated on Si wafer. Structural characterization of the silver wires shows that the nanowires grow primarily along the [011] direction. SEM image of the silver wires clearly shows the catalytic TiO(2) nano-cluster attached to the end of the each silver wire. Since the process was surfactant-free, the silver nanowires prepared by our method retain the excellent electrical conductivity. The intrinsic resistivity calculated from the current-voltage curve for a wire with 12880.41 nm(2) cross-section area was 18.72 microohm cm, which is about 11.6 times higher than that of bulk silver (1.61 microohm cm). Our simple method can be also applied to generate CuO with ring-shaped microstructure by using ITO conducting glass as matrix. We have found that the size and reproducibility are well-controllable. A single phase of CuO ring-shaped microstructure with outer diameters ranging from approximately 13 to 17 microm and inner diameters ranging from approximately 1.4 to 3.3 microm was obtained. The composition of CuO microring was confirmed by thin-film XRD and XPS analyses.

Improved performance of aminopropylsilatrane over aminopropyltriethoxysilane as an adhesive film for anchoring gold nanoparticles on silicon surfaces.

Aminopropylsilatrane (AP-silatrane) was investigated as an adhesive layer for anchoring Au nanoparticles on silicon substrates. We compared the preparation procedure and film quality of the AP-silatrane films to those of 3-aminopropyltriethoxysilane (APTES), which is commonly used for nanoparticle attachment on silicon. The films were characterized by Fourier Transform infrared (FTIR) spectroscopy, contact angle measurements, and atomic force microscopy (AFM). The process for preparing the AP-silatrane films was much easier and resulted in more reproducibly high quality films due to its insensitivity to water. In surface roughness measurements, we observed a 39% increase (99 pm RMS) for the AP-silatrane film over that of a plasma-cleaned silicon sample (71 pm RMS). In contrast, we observed a 218% increase (226 pm RMS) for the APTES film. The much higher roughness observed for the APTES film was due to its sensitivity to water, which results in molecular aggregate formation and polymerization. Gold nanoparticles (7.5 nm) were deposited and firmly anchored to both types of film surfaces. The measured height of the particles on the films was less than the actual size of the particles, and plasma treatment was used to remove the organic layer, resulting in a corrected measurement of the particle size. AP-silatrane offers an easy preparation procedure that creates a smooth, aggregate-free adhesive layer for anchoring Au nanoparticles strongly to silicon substrates.