Chiung-Wen Hsieh

Aqueous self-assembly and surface-functionalized nanodots for live cell imaging and labeling

AbstractNanoparticles have enormous potential for bioimaging and biolabeling applications, in which conventional organically based fluorescent labels degrade and fail to provide long-term tracking. Thus, the development of approaches to make fluorescent probes water soluble and label cells efficient is desirable for most biological applications. Here, we report on the fabrication and characterization of self-assembled nanodots (SANDs) from 3-aminopropyltriethoxysilane (APTES) as a probe for protein labeling. We show that fluorescent SAND probes exhibit both bright photoluminescence and biocompatibility in an aqueous environment. Selective in vitro imaging using protein and carbohydrate labeling of hepatoma cell lines are demonstrated using biocompatible SANDs conjugated with avidin and galactose, respectively. Cytotoxicity tests show that conjugated SAND particles have negligible effects on cell proliferation. Unlike other synthetic systems that require multistep treatments to achieve robust surface functionalization and to develop flexible bioconjugation strategies, our results demonstrate the versatility of this one-step SAND fabrication method for creating multicolor fluorescent probes with the tailored functionalities, efficient emission, as well as excellent biocompatibility, required for broad biological use.

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.

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.

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.

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.

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.